**Meet the editor**

Alicia Esther Ares has been a headline professor of Materials Science at the Chemical Engineering Department, School of Sciences (FCEQyN), National University of Misiones (UNaM), Posadas, Misiones, Argentina, since December 2013. She has also been an independent researcher at the National Scientific and Technical Research Council (CONICET), Argentina since January 2015. Previously a

research associate at CONICET (2008–2014) and associate professor at UNaM (2007–2013), she has also been an assistant professor at UNaM (1989–2007). She graduated at the University of Misiones in 1992 and completed a PhD degree in Materials Science at the Institute of Technology "Jorge Sabato," UNSAM-CNEA, Buenos Aires, Argentina. Later, she undertook postdoctoral stays at the following institutions: Faculdade de Engenharía Mecânica, Departamento de Engenharía de Materiais, Universidade Estadual de Campinas, Campinas, São Paulo, Brasil (2001 and 2005-2006); Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States (2002-2003); and the Faculty of Sciences, National University of Misiones, Posadas-Misiones, Argentina (2003–2004).

She has 30 years of teaching experience both at the undergraduate and graduate levels. Her articles are published in well-established international journals.

Contents

**Preface VII**

**Ni41Co9Mn31.5Ga18.5 1**

**Memory Alloys 17**

**Polymers 75**

**Interactions 95**

Hiroyuki Nojiri and Yoshiya Adachi

Minciună and Manuela-Cristina Perju

Meddour Belkacem and Brek Samir

Velaphi Msomi and Graeme Oliver

Chapter 6 **Shape Memory Hydrogels Based on Noncovalent**

Gutiérrez-Zorrilla and José Luis Vilas

Chapter 3 **Modeling of the Two-Way Shape Memory Effect 43**

Chapter 4 **Linear Shape Memory Alloy Thermomechanical Actuators 57**

Chapter 5 **Experiments and Models of Thermo-Induced Shape Memory**

Qianhua Kan, Jian Li, Guozheng Kang and Zebin Zhang

Leire Ruiz-Rubio, Leyre Pérez-Álvarez, Beñat Artetxe, Juan M.

Chapter 1 **Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy**

Chapter 2 **Aspects Regarding Thermal-Mechanical Fatigue of Shape**

Takuo Sakon, Naoki Fujimoto, Sho Saruki, Takeshi Kanomata,

Petrică Vizureanu, Dragoș-Cristian Achiței, Mirabela-Georgiana

## Contents

**Preface XI**


Preface

desired forms.

SMPs.

**Ni41Co9Mn31.5Ga18.5**

times without deteriorating.

appropriate field, the problem would be solved.

for the future of SMMs are presented in this book.

in the second state is different, but the neighbors do not change.

Shape-memory materials (SMMs) are materials that react under physical or chemical changes, variations of magnetic or electric fields, and that when returning to the initial con‐ ditions recover their original form, capable of repeating this process an infinite number of

Shape-memory materials are materials with shape-memory, capable of self-diagnosis and repair, thanks to their capacity for change. These materials are assigned an initial shape, and after being subjected to the physical field or corresponding chemical reaction, their shape is adjusted, so that, in the presence of said field or reaction, the materials vary between the two

This kind of material has an infinite number of applications, for example, replacing the valves in motors or bearings, since one could take advantage of the capacity of self-regener‐ ation so as not to have to change them if they are degraded, but by submitting them to the

Shape-memory alloys have two types of special behaviors, which are actually two expres‐ sions of the same phenomenon: shape-memory and super elasticity. In both cases, the be‐ havior is the product of a transformation of phases without diffusion, of martensitic type, in which the order to first neighbors is not lost. Strictly speaking, order is lost, but what is not lost are neighboring atoms. If in a state, an atom has a group of first neighbors, its position

Fitting the material properties of polymers is much easier compared with that of metals/ alloys. In addition, the cost (both material cost and processing cost) of polymers is traditional‐ ly much lower. SMP composites have remarkably widened the potential applications of

This book, "Shape-Memory Materials," logically develops through careful presentation of relevant theories and models occurring in a variety of materials. Conclusions and outlooks

**Section I: Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy**

The authors investigate the magnetic functionality of polycrystalline metamagnetic Heusler alloy Ni41Co9Mn31.5Ga18.5 and performed magnetic field-induced strain (MFIS) measure‐ ments. The investigation of time response of the MFIS was performed by means of sweep water-cooled electric magnet, zero magnetic field to 1.66 T in 8.0 seconds at 354 K. 2.210-4

## Preface

Shape-memory materials (SMMs) are materials that react under physical or chemical changes, variations of magnetic or electric fields, and that when returning to the initial con‐ ditions recover their original form, capable of repeating this process an infinite number of times without deteriorating.

Shape-memory materials are materials with shape-memory, capable of self-diagnosis and repair, thanks to their capacity for change. These materials are assigned an initial shape, and after being subjected to the physical field or corresponding chemical reaction, their shape is adjusted, so that, in the presence of said field or reaction, the materials vary between the two desired forms.

This kind of material has an infinite number of applications, for example, replacing the valves in motors or bearings, since one could take advantage of the capacity of self-regener‐ ation so as not to have to change them if they are degraded, but by submitting them to the appropriate field, the problem would be solved.

Shape-memory alloys have two types of special behaviors, which are actually two expres‐ sions of the same phenomenon: shape-memory and super elasticity. In both cases, the be‐ havior is the product of a transformation of phases without diffusion, of martensitic type, in which the order to first neighbors is not lost. Strictly speaking, order is lost, but what is not lost are neighboring atoms. If in a state, an atom has a group of first neighbors, its position in the second state is different, but the neighbors do not change.

Fitting the material properties of polymers is much easier compared with that of metals/ alloys. In addition, the cost (both material cost and processing cost) of polymers is traditional‐ ly much lower. SMP composites have remarkably widened the potential applications of SMPs.

This book, "Shape-Memory Materials," logically develops through careful presentation of relevant theories and models occurring in a variety of materials. Conclusions and outlooks for the future of SMMs are presented in this book.

## **Section I: Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5**

The authors investigate the magnetic functionality of polycrystalline metamagnetic Heusler alloy Ni41Co9Mn31.5Ga18.5 and performed magnetic field-induced strain (MFIS) measure‐ ments. The investigation of time response of the MFIS was performed by means of sweep water-cooled electric magnet, zero magnetic field to 1.66 T in 8.0 seconds at 354 K. 2.210-4 MFIS was observed, which was 80% of the MFIS in 60 seconds mode. This indicates that high-speed transition has occurred with the application of magnetic fields.

## **Section II: Aspects Regarding Thermal-Mechanical Fatigue of Shape-Memory Alloys**

The authors present advanced research about the use of metallic alloys with shape-memory properties in construction and exploitation of parts subjected to combined stress by thermal and mechanical fatigue during their functioning. The research and results presented in this chapter make useful data on design principles available to scientists.

## **Section III: Modeling of the Two-Way Shape Memory Effect**

The authors developed a 3D constitutive model using the principles of thermodynamics and a simple formalism. These principles have permitted the authors to write criteria of trans‐ formation. This macroscopic model is developed by simple formalism and assumptions. This model can be used in applications for engineering problems, in order to simulate the pseudoelastic effect of shape-memory alloys.

### **Section IV: Linear Shape-Memory Alloy Thermomechanical Actuators**

The authors developed a finite element analysis based on the proposed SMA model. The finite element analysis was performed on the 1D setup, which was oriented on the 2D space. The c++ code was developed in order to perform the 2D numerical analysis. The experiment was per‐ formed in order to obtain the parameters to input in the developed code and also to validate the numerical results. The maximum deflection obtained numerically matches that which was measured experimentally. It was verified through the results that the developed SMA model has the ability to capture all the temperature range and not only the intended range.

## **Section V: Experiments and Models of Thermo-Induced Shape-Memory Polymers**

The authors studied some important viscoelastic and viscoplastic features, such as rate-de‐ pendent and temperature-dependent stress-strain curves and nonuniform temperature dis‐ tribution. The results were experimentally investigated and discussed regarding the interaction between the mechanical deformation and the internal heat generation. The influ‐ ences of loading rate and peak strain on the shape-memory effect (SME) and shape-memory degeneration of TSMPs were revealed under monotonic and cyclic thermo-mechanical load‐ ings, respectively.

#### **Section VI: Shape-Memory Hydrogels Based on Noncovalent Interactions**

Shape-memory polymers (SMPs) are polymeric materials that are capable of fixing tempora‐ ry shape and recovering the permanent shape in response to external stimuli. The authors described shape memory hydrogels based on noncovalent interactions.

> **Alicia Esther Ares** Chemical Engineering Department School of Sciences (FCEQyN) National University of Misiones (UNaM) Posadas, Misiones, Argentina

**Chapter 1**

**Provisional chapter**

**Magnetic Field-Induced Strain of Metamagnetic**

**Magnetic Field-Induced Strain of Metamagnetic** 

DOI: 10.5772/intechopen.76291

Mn31.5Ga18.5 is a re-entrant and metamagnetic Heusler alloy. In order to investigate

strain (MFIS) measurements were performed. A 0.12% MFIS was observed at 340 K and 10 T. Strict MFISs between 330 and 370 K were observed. These magneto-structural variances acted in concert with the metamagnetic property observed by the magnetization measurements and magneto-caloric property observed by the caloric measurements in applied magnetic fields. The MFISs were proportional to the fourth power of the magnetization, and this result is in agreement with Takahashi's spin fluctuation theory of itinerant electron magnetism. The investigation of time response of the MFIS was performed by means of water-cooled electric magnet, zero magnetic field to 1.66 T in 8.0 s at 354 K. A 2.2×10−4 MFIS was observed, which was 80% of the MFIS in a 60-s mode. This indicates

Mn31.5Ga18.5, magnetic field-induced

MnGa is the most famous alloy

3*m*), and ferromagnetic

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

**Heusler Alloy Ni41Co9Mn31.5Ga18.5**

**Heusler Alloy Ni41Co9Mn31.5Ga18.5**

Takuo Sakon, Naoki Fujimoto, Sho Saruki, Takeshi Kanomata, Hiroyuki Nojiri and

Takuo Sakon, Naoki Fujimoto, Sho Saruki, Takeshi Kanomata, Hiroyuki Nojiri and

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

the magnetic functionality of polycrystalline Ni41Co9

date of the functional materials widely. Among FSMA, Ni2

that a high-speed transition has occurred on applying magnetic fields.

**Keywords:** magnetostriction, Heusler alloys, shape memory alloys, metamagnetic

In recent years, the ferromagnetic shape memory alloy (FSMA) was investigated as a candi-

Heusler structure (space group of *Fm*¯

http://dx.doi.org/10.5772/intechopen.76291

transition, itinerant magnetism

Yoshiya Adachi

**Abstract**

Ni41Co9

**1. Introduction**

[1]. The alloy has a cubic *L2*<sup>1</sup>

Yoshiya Adachi

#### **Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5 Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5**

DOI: 10.5772/intechopen.76291

Takuo Sakon, Naoki Fujimoto, Sho Saruki, Takeshi Kanomata, Hiroyuki Nojiri and Yoshiya Adachi Takuo Sakon, Naoki Fujimoto, Sho Saruki, Takeshi Kanomata, Hiroyuki Nojiri and Yoshiya Adachi

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.76291

#### **Abstract**

MFIS was observed, which was 80% of the MFIS in 60 seconds mode. This indicates that

The authors present advanced research about the use of metallic alloys with shape-memory properties in construction and exploitation of parts subjected to combined stress by thermal and mechanical fatigue during their functioning. The research and results presented in this

The authors developed a 3D constitutive model using the principles of thermodynamics and a simple formalism. These principles have permitted the authors to write criteria of trans‐ formation. This macroscopic model is developed by simple formalism and assumptions. This model can be used in applications for engineering problems, in order to simulate the

The authors developed a finite element analysis based on the proposed SMA model. The finite element analysis was performed on the 1D setup, which was oriented on the 2D space. The c++ code was developed in order to perform the 2D numerical analysis. The experiment was per‐ formed in order to obtain the parameters to input in the developed code and also to validate the numerical results. The maximum deflection obtained numerically matches that which was measured experimentally. It was verified through the results that the developed SMA model

The authors studied some important viscoelastic and viscoplastic features, such as rate-de‐ pendent and temperature-dependent stress-strain curves and nonuniform temperature dis‐ tribution. The results were experimentally investigated and discussed regarding the interaction between the mechanical deformation and the internal heat generation. The influ‐ ences of loading rate and peak strain on the shape-memory effect (SME) and shape-memory degeneration of TSMPs were revealed under monotonic and cyclic thermo-mechanical load‐

Shape-memory polymers (SMPs) are polymeric materials that are capable of fixing tempora‐ ry shape and recovering the permanent shape in response to external stimuli. The authors

**Alicia Esther Ares**

Chemical Engineering Department School of Sciences (FCEQyN)

Posadas, Misiones, Argentina

National University of Misiones (UNaM)

has the ability to capture all the temperature range and not only the intended range. **Section V: Experiments and Models of Thermo-Induced Shape-Memory Polymers**

**Section VI: Shape-Memory Hydrogels Based on Noncovalent Interactions**

described shape memory hydrogels based on noncovalent interactions.

**Section II: Aspects Regarding Thermal-Mechanical Fatigue of Shape-Memory Alloys**

high-speed transition has occurred with the application of magnetic fields.

chapter make useful data on design principles available to scientists.

**Section IV: Linear Shape-Memory Alloy Thermomechanical Actuators**

**Section III: Modeling of the Two-Way Shape Memory Effect**

pseudoelastic effect of shape-memory alloys.

ings, respectively.

VIII Preface

Ni41Co9 Mn31.5Ga18.5 is a re-entrant and metamagnetic Heusler alloy. In order to investigate the magnetic functionality of polycrystalline Ni41Co9 Mn31.5Ga18.5, magnetic field-induced strain (MFIS) measurements were performed. A 0.12% MFIS was observed at 340 K and 10 T. Strict MFISs between 330 and 370 K were observed. These magneto-structural variances acted in concert with the metamagnetic property observed by the magnetization measurements and magneto-caloric property observed by the caloric measurements in applied magnetic fields. The MFISs were proportional to the fourth power of the magnetization, and this result is in agreement with Takahashi's spin fluctuation theory of itinerant electron magnetism. The investigation of time response of the MFIS was performed by means of water-cooled electric magnet, zero magnetic field to 1.66 T in 8.0 s at 354 K. A 2.2×10−4 MFIS was observed, which was 80% of the MFIS in a 60-s mode. This indicates that a high-speed transition has occurred on applying magnetic fields.

**Keywords:** magnetostriction, Heusler alloys, shape memory alloys, metamagnetic transition, itinerant magnetism

## **1. Introduction**

In recent years, the ferromagnetic shape memory alloy (FSMA) was investigated as a candidate of the functional materials widely. Among FSMA, Ni2 MnGa is the most famous alloy [1]. The alloy has a cubic *L2*<sup>1</sup> Heusler structure (space group of *Fm*¯*m* 3), and ferromagnetic

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

transition realized [2, 3]. Cooling from room temperature, a martensite transition occurred at the martensitic transition temperature, *T*M. Below *T*M, a superstructure state occurred as a result of lattice deformation [4-6].

of the free energy. By Eq. (6.101) of [27], the magnetostriction is proportional to the fourth

ferromagnet MnSi was performed by Matsunaga et al. [29]. They plotted the magnetostriction

linearity. Takahashi mentioned that the linearity was confirmed by plotting the magnetostric-

In this chapter, we preformed MFIS measurements by means of a 10-T helium-free superconducting magnet and a 1.7-T water-cooled electric magnet. We compared the results of the strain and calorimetric differential scanning colorimetry (DSC) measurements and discussed the irreversibility of the MFIS and the reverse martensitic and metamagnetic transition. We investigated the correlations between magneto-structural variance and the magneto-caloric property observed by the caloric measurements in applied magnetic fields. It is interesting with the investigation of time response of the MFIS for the purpose of industrial use [30]. The time response of the MFIS performed by means of a 1.6-T watercooled electric magnet and under atmospheric pressure, *P* = 0.1 MPa, was investigated. We also investigated the relation between the magnetostriction and the magnetization accord-

ing to Takahashi's spin fluctuation theory of the itinerant ferromagnet for Ni<sup>2</sup>

ration of polycrystalline alloy was shown in our former article [23]. The nominal concentrations of the elements were Ni 41.0, Co 9.0, Mn 31.5, and Ga 18.5 at.%. The concentrations of the elements after thermal treatment are shown in **Table 1**. The ratio was almost the same as that of the nominal state. When cooling from 500 K, a ferromagnetic transition in the austen-

the magnetization decreased drastically. The reverse martensitic transition temperature *T*<sup>R</sup> was 380 K. The re-entrant magnetism, ferromagnetic-paramagnetic state, should be interacted with the crystal structures. The hysteresis of temperature, *T*R - *T*M was 65 K, which is much

MFIS measurements were performed with bulk samples with the size of 0.8 × 3.0 × 4.0 mm3

Strain gauges were used (KFH-02-120-C1–16, size: sensor grid 0.2 mm length × 1.0 mm width, film base 2.5 mm length × 2.2 mm width, Kyowa Dengyo Co., Ltd., Yamagata, Japan). Strain

gauge was fixed parallel to the long distance direction (4.0 mm) of the sample.

**Ni Co Mn Ga** 40.8 9.0 31.5 18.7

**Table 1.** The concentrations of elements by means of EDS spectrometry (at. %).

at *T* = 29 K around *T*C.

**2. Sample properties and experimental details**

. Around the Curie temperature, *T*<sup>C</sup> = 30 K, the plot considerably deviated from the

. The experimental magnetostriction study of weak itinerant

http://dx.doi.org/10.5772/intechopen.76291

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

Mn31.5Ga18.5 is tetragonal *DO*22 structure, and the sample prepa-

<sup>A</sup> = 465 K. At the martensitic transition temperature, *T*<sup>M</sup> = 315 K,

MnGa-type alloys. This is due to the large motive force in order

MnGa and

3

.

power of the magnetization, *M*<sup>4</sup>

against *M*<sup>2</sup>

Ni41Co9

Mn31.5Ga18.5.

The crystal structure of Ni41Co9

ite phase was realized at *T*<sup>C</sup>

larger than that of other Ni2

for a martensitic transition to occur [24].

tion data against *M*<sup>4</sup>

New alloys in the FMSAs of NiMnIn-, NiMnSn-, and NiMnSb-type Heusler alloys have been studied [7, 8]. In these alloys, a metamagnetic transition from paramagnetic martensite phase to ferromagnetic austenite phase occurred, and reverse martensitic transition, which was induced by magnetic fields, occurred under high magnetic fields [9, 10]. These alloys are hopeful as a metamagnetic shape memory alloys with a magnetic field-induced shape memory effect (MSIF) and as magnetocaloric materials which can be cooled down or heated up on applying external magnetic fields. It is noticeable that 3% MFIS has been observed for Ni45Co5 Mn36.7In13.3 single crystal in compressive stress–strain measurements [11].

The Co-doped NiCoMnGa-type alloys turned the magnetic order of the parent phase from antiferromagnetic or paramagnetic phase, due to a large magnetization change across the transformation. As a result, it strengthens magnetic field driving force dramatically [12-24]. As for Ni50-*<sup>x</sup>* Co*<sup>x</sup>* Mn31.5Ga18.5, the determined phases are a paramagnetic austenite (Para-A) phase, ferromagnetic austenite phase (Ferro-A), paramagnetic martensite phase (Para-M), and ferromagnetic martensite (Ferro-M) phase, with cooling from a higher temperature than *T*C, which indicates re-entrant ferromagnetism [23].

Albertini et al. performed the experimental studies regarding the composition dependence of the structural and magnetic properties of the Ni-Mn-Ga ferromagnetic shape memory alloys substituting Co for Ni atoms around the composition of Ni50Mn30Ga20 [12, 20]. The magnetic and structural properties indicated remarkable discontinuities around the martensitic transition. A metamagnetic transition appeared in the magnetic field around 400 K. The field dependence of the reverse martensitic transition temperature *dT*R*/μ*<sup>0</sup> *dH* was −2.8 K/T and that of the thermal strain was reported. The most characteristic alloy is Ni41Co9 Mn32Ga18. The magnetic susceptibility indicates a re-entrant magnetism property. We studied the magnetic properties of polycrystalline Ni41Co9 Mn31.5Ga18.5. Magnetization results indicated the metamagnetic transition between 330 and 370 K for 0–10 T. Moreover, a 0.1% magnetic field-induced strain (MFIS) was observed at the temperature of 340 K [23].

In our former article [25], we determined the magnetic field dependence of the magnetization of Ni41Co9 Mn31.5Ga18.5 around the Curie temperature in the martensite phase in order to investigate the properties of the itinerant electron magnetism according to Takahashi's spin fluctuation theory of itinerant electron magnetism [26, 27]. The *M*<sup>4</sup> versus *H/M* plot was crossed across the coordinate axis at the Curie temperature in the martensite phase, *T*CM = 263 K, and indicates a good linear relation behavior around *T*CM. The results were in agreement with the Takahashi's theory concerning itinerant electron magnetism [26, 27]. Moreover, the spin fluctuation temperature *T*A can be obtained from the *M*<sup>4</sup> versus *H/M* plot. The obtained *T*A was 703 K. This value was much smaller than Ni (1.76 × 10<sup>4</sup> K). The value was comparable to that of UGe2 (493 K), which is famous for the strongly correlated heavy fermion ferromagnet [27, 28].

Takahashi suggested that the anomalous behavior for the magnetostriction can be observed under the influence of the itinerant spin fluctuations around the critical temperature [27]. It is mentioned that the reason is that the magnetostriction is given by the volume derivative of the free energy. By Eq. (6.101) of [27], the magnetostriction is proportional to the fourth power of the magnetization, *M*<sup>4</sup> . The experimental magnetostriction study of weak itinerant ferromagnet MnSi was performed by Matsunaga et al. [29]. They plotted the magnetostriction against *M*<sup>2</sup> . Around the Curie temperature, *T*<sup>C</sup> = 30 K, the plot considerably deviated from the linearity. Takahashi mentioned that the linearity was confirmed by plotting the magnetostriction data against *M*<sup>4</sup> at *T* = 29 K around *T*C.

In this chapter, we preformed MFIS measurements by means of a 10-T helium-free superconducting magnet and a 1.7-T water-cooled electric magnet. We compared the results of the strain and calorimetric differential scanning colorimetry (DSC) measurements and discussed the irreversibility of the MFIS and the reverse martensitic and metamagnetic transition. We investigated the correlations between magneto-structural variance and the magneto-caloric property observed by the caloric measurements in applied magnetic fields. It is interesting with the investigation of time response of the MFIS for the purpose of industrial use [30]. The time response of the MFIS performed by means of a 1.6-T watercooled electric magnet and under atmospheric pressure, *P* = 0.1 MPa, was investigated. We also investigated the relation between the magnetostriction and the magnetization according to Takahashi's spin fluctuation theory of the itinerant ferromagnet for Ni<sup>2</sup> MnGa and Ni41Co9 Mn31.5Ga18.5.

## **2. Sample properties and experimental details**

transition realized [2, 3]. Cooling from room temperature, a martensite transition occurred at the martensitic transition temperature, *T*M. Below *T*M, a superstructure state occurred as a

New alloys in the FMSAs of NiMnIn-, NiMnSn-, and NiMnSb-type Heusler alloys have been studied [7, 8]. In these alloys, a metamagnetic transition from paramagnetic martensite phase to ferromagnetic austenite phase occurred, and reverse martensitic transition, which was induced by magnetic fields, occurred under high magnetic fields [9, 10]. These alloys are hopeful as a metamagnetic shape memory alloys with a magnetic field-induced shape memory effect (MSIF) and as magnetocaloric materials which can be cooled down or heated up on applying external magnetic fields. It is noticeable that 3% MFIS has been observed for

Mn36.7In13.3 single crystal in compressive stress–strain measurements [11].

The Co-doped NiCoMnGa-type alloys turned the magnetic order of the parent phase from antiferromagnetic or paramagnetic phase, due to a large magnetization change across the transformation. As a result, it strengthens magnetic field driving force dramatically [12-24].

phase, ferromagnetic austenite phase (Ferro-A), paramagnetic martensite phase (Para-M), and ferromagnetic martensite (Ferro-M) phase, with cooling from a higher temperature than

Albertini et al. performed the experimental studies regarding the composition dependence of the structural and magnetic properties of the Ni-Mn-Ga ferromagnetic shape memory alloys substituting Co for Ni atoms around the composition of Ni50Mn30Ga20 [12, 20]. The magnetic and structural properties indicated remarkable discontinuities around the martensitic transition. A metamagnetic transition appeared in the magnetic field around 400 K. The field

netic susceptibility indicates a re-entrant magnetism property. We studied the magnetic prop-

transition between 330 and 370 K for 0–10 T. Moreover, a 0.1% magnetic field-induced strain

In our former article [25], we determined the magnetic field dependence of the magnetization

tigate the properties of the itinerant electron magnetism according to Takahashi's spin fluc-

across the coordinate axis at the Curie temperature in the martensite phase, *T*CM = 263 K, and indicates a good linear relation behavior around *T*CM. The results were in agreement with the Takahashi's theory concerning itinerant electron magnetism [26, 27]. Moreover, the spin

703 K. This value was much smaller than Ni (1.76 × 10<sup>4</sup> K). The value was comparable to that of

Takahashi suggested that the anomalous behavior for the magnetostriction can be observed under the influence of the itinerant spin fluctuations around the critical temperature [27]. It is mentioned that the reason is that the magnetostriction is given by the volume derivative

(493 K), which is famous for the strongly correlated heavy fermion ferromagnet [27, 28].

Mn31.5Ga18.5 around the Curie temperature in the martensite phase in order to inves-

Mn31.5Ga18.5, the determined phases are a paramagnetic austenite (Para-A)

Mn31.5Ga18.5. Magnetization results indicated the metamagnetic

*dH* was −2.8 K/T and that

versus *H/M* plot was crossed

versus *H/M* plot. The obtained *T*A was

Mn32Ga18. The mag-

result of lattice deformation [4-6].

2 Shape-Memory Materials

Ni45Co5

As for Ni50-*<sup>x</sup>*

of Ni41Co9

UGe2

Co*<sup>x</sup>*

erties of polycrystalline Ni41Co9

*T*C, which indicates re-entrant ferromagnetism [23].

(MFIS) was observed at the temperature of 340 K [23].

fluctuation temperature *T*A can be obtained from the *M*<sup>4</sup>

tuation theory of itinerant electron magnetism [26, 27]. The *M*<sup>4</sup>

dependence of the reverse martensitic transition temperature *dT*R*/μ*<sup>0</sup>

of the thermal strain was reported. The most characteristic alloy is Ni41Co9

The crystal structure of Ni41Co9 Mn31.5Ga18.5 is tetragonal *DO*22 structure, and the sample preparation of polycrystalline alloy was shown in our former article [23]. The nominal concentrations of the elements were Ni 41.0, Co 9.0, Mn 31.5, and Ga 18.5 at.%. The concentrations of the elements after thermal treatment are shown in **Table 1**. The ratio was almost the same as that of the nominal state. When cooling from 500 K, a ferromagnetic transition in the austenite phase was realized at *T*<sup>C</sup> <sup>A</sup> = 465 K. At the martensitic transition temperature, *T*<sup>M</sup> = 315 K, the magnetization decreased drastically. The reverse martensitic transition temperature *T*<sup>R</sup> was 380 K. The re-entrant magnetism, ferromagnetic-paramagnetic state, should be interacted with the crystal structures. The hysteresis of temperature, *T*R - *T*M was 65 K, which is much larger than that of other Ni2 MnGa-type alloys. This is due to the large motive force in order for a martensitic transition to occur [24].

MFIS measurements were performed with bulk samples with the size of 0.8 × 3.0 × 4.0 mm3 . Strain gauges were used (KFH-02-120-C1–16, size: sensor grid 0.2 mm length × 1.0 mm width, film base 2.5 mm length × 2.2 mm width, Kyowa Dengyo Co., Ltd., Yamagata, Japan). Strain gauge was fixed parallel to the long distance direction (4.0 mm) of the sample.


**Table 1.** The concentrations of elements by means of EDS spectrometry (at. %).

External magnetic field was applied parallel to the long distance direction of the sample, and elongation of the sample was measured in applied magnetic fields and in atmospheric pressure. Measurements were performed by means of a 10-T helium-free magnet (10 T-CSM) at High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. We also performed MFIS measurements by means of a 1.7-T water-cooled electric magnet at Ryukoku University in order to investigate time response of MFIS. The magnetization measurements were performed by using a pulsed-field magnet with the time constant of 6.3 ms. The absolute value was calibrated against a sample of pure Ni.

## **3. Results and discussion**

#### **3.1. Relation between the magnetic field-induced strain and the magnetic entropy of Ni41Co9 Mn31.5Ga18.5**

In this section, we compared the results of the strain and calorimetric DSC measurements of Ni41Co9 Mn31.5Ga18.5. We considered the correlation between the magnetic field-induced strain and the magnetic entropy.

**Figure 1** shows the MFIS under steady field by means of the helium-free superconducting magnet. The MFIS measurements in this study were performed under atmospheric pressure and without the compression to make a pre-strain. The point zero of MFIS at each temperature is moved by 1 × 10−4 below 315 K and by 5 × 10−4 above 330 K. The thermal condition was the same as that for the magnetization measurement [23]. When increasing the magnetic field, distinct MFIS was observed. The maximum MFIS was 0.12%, which was approximately the same value as that of the thermal strain for the reverse martensitic transition. The shape of MFIS is similar to that of polycrystalline Ni41Co9 Mn32Ga16In2 , where the alloy is also a reentrant metamagnetic Heusler alloy, and 0.30% MFIS was observed [12]. The field dependence of the reverse martensitic transition temperature, *dT*R*/μ*<sup>0</sup> *dH,* are −7.9, −6.8, and − 4.8 K/T for Ni41Co9 Mn31.5Ga18.5 [23], Ni41Co9 Mn32Ga16In2 [12], and Ni45Co5 Mn36.7In13.3, respectively [11]. The field dependence of the reverse martensitic transition temperature of the ferromagnetic and non-metamagnetic Ni2 MnGa type alloys is between 0.2 and 1.0 K/T [2, 31, 32]. As for metamagnetic Heusler alloys, *dT*R*/μ*<sup>0</sup> *dH* is much larger than that of non-metamagnetic Heusler alloys. Therefore, the MFIS occurs at a wide temperature range. The strain curves shown in **Figure 1** and the thermal strain in Ref. [23] suggest that the magneto-structural transition of Ni41Co9 Mn31.5Ga18.5 alloy is very sensitive to magnetic fields. Below 330 K, the MFIS value returned to zero when a magnetic field became zero. By contrast, the MFIS value remained at the limit value without returning zero.

that the magneto-structural coupling is large. The 0.12% (1200 ppm) MFIS is larger than the magnetostriction of TbDyFe single crystal under atmospheric pressure [33]. In this study,

crystalline sample by means of the differential scanning calorimetry (DSC) measurements [25].

polycrystalline ferromagnetic shape memory alloy (FSMA) were performed across the *T*R, at atmospheric pressure. When the sample was warmed from the martensite phase, a gradual increase in the thermal expansion due to the reverse martensitic transition at *T*R was observed by the thermal expansion experimental study. These transition temperatures decreased steeply with an increasing magnetic field. The field dependence of the reverse martensitic

the value of the latent heat was obtained as 2.6 kJ/kg in zero fields. The maximum value of

*dH*, is −7.9 K/T near zero fields. From the DSC measurements,

In the former article, we studied the magneto-caloric properties of Ni41Co9

Magneto-calorimetric measurements and magnetization measurements of Ni41Co9

Mn38.5Ga18.5 is a polycrystalline sample; then, it is easier to process and handle the sample than single crystals. **Table 2** indicates the thermal linear striction *ΔL/L*(t), saturated magnetostriction *ΔL/L*(m), and relative volume discontinuity at the martensitic transition, *ΔV/V*.

Mn31.5Ga18.5 in static magnetic fields. The point zero at each temperature is moved by 1 × 10−4

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

http://dx.doi.org/10.5772/intechopen.76291

5

Mn31.5Ga18.5 poly-

Mn31.5Ga18.5

Ni41Co9

**Figure 1.** MFIS of Ni41Co9

below 315 K and by 5 × 10−4 above 330 K.

transition temperature, *dTR/μ*<sup>0</sup>

The MFIS of 2, 4, 6, and 8 T is shown in **Figure 2**. Between 340 and 370 K, large MFIS was observed. Metamagnetic S-shape like *M*-*H* curve was observed for the magnetization around 360 K [23]. The decreasing field process shows ferromagnetic behavior. Magnetization process indicates that the paramagnetic to ferromagnetic transition occurred. Considering the magnetization, MFIS indicates that the structural transformation from the paramagnetic martensite phase to the austenite ferromagnetic phase occurred. The MFIS and metamagnetism indicate Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5 http://dx.doi.org/10.5772/intechopen.76291 5

External magnetic field was applied parallel to the long distance direction of the sample, and elongation of the sample was measured in applied magnetic fields and in atmospheric pressure. Measurements were performed by means of a 10-T helium-free magnet (10 T-CSM) at High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. We also performed MFIS measurements by means of a 1.7-T water-cooled electric magnet at Ryukoku University in order to investigate time response of MFIS. The magnetization measurements were performed by using a pulsed-field magnet with the time

constant of 6.3 ms. The absolute value was calibrated against a sample of pure Ni.

**3.1. Relation between the magnetic field-induced strain and the magnetic entropy of** 

In this section, we compared the results of the strain and calorimetric DSC measurements of

**Figure 1** shows the MFIS under steady field by means of the helium-free superconducting magnet. The MFIS measurements in this study were performed under atmospheric pressure and without the compression to make a pre-strain. The point zero of MFIS at each temperature is moved by 1 × 10−4 below 315 K and by 5 × 10−4 above 330 K. The thermal condition was the same as that for the magnetization measurement [23]. When increasing the magnetic field, distinct MFIS was observed. The maximum MFIS was 0.12%, which was approximately the same value as that of the thermal strain for the reverse martensitic transition. The shape

entrant metamagnetic Heusler alloy, and 0.30% MFIS was observed [12]. The field dependence

field dependence of the reverse martensitic transition temperature of the ferromagnetic and

alloys. Therefore, the MFIS occurs at a wide temperature range. The strain curves shown in **Figure 1** and the thermal strain in Ref. [23] suggest that the magneto-structural transition

returned to zero when a magnetic field became zero. By contrast, the MFIS value remained at

The MFIS of 2, 4, 6, and 8 T is shown in **Figure 2**. Between 340 and 370 K, large MFIS was observed. Metamagnetic S-shape like *M*-*H* curve was observed for the magnetization around 360 K [23]. The decreasing field process shows ferromagnetic behavior. Magnetization process indicates that the paramagnetic to ferromagnetic transition occurred. Considering the magnetization, MFIS indicates that the structural transformation from the paramagnetic martensite phase to the austenite ferromagnetic phase occurred. The MFIS and metamagnetism indicate

[12], and Ni45Co5

Mn31.5Ga18.5 alloy is very sensitive to magnetic fields. Below 330 K, the MFIS value

Mn31.5Ga18.5. We considered the correlation between the magnetic field-induced strain

Mn32Ga16In2

MnGa type alloys is between 0.2 and 1.0 K/T [2, 31, 32]. As for meta-

*dH* is much larger than that of non-metamagnetic Heusler

, where the alloy is also a re-

*dH,* are −7.9, −6.8, and − 4.8 K/T for

Mn36.7In13.3, respectively [11]. The

**3. Results and discussion**

**Mn31.5Ga18.5**

and the magnetic entropy.

of MFIS is similar to that of polycrystalline Ni41Co9

Mn31.5Ga18.5 [23], Ni41Co9

the limit value without returning zero.

magnetic Heusler alloys, *dT*R*/μ*<sup>0</sup>

of the reverse martensitic transition temperature, *dT*R*/μ*<sup>0</sup>

Mn32Ga16In2

**Ni41Co9**

4 Shape-Memory Materials

Ni41Co9

Ni41Co9

of Ni41Co9

non-metamagnetic Ni2

**Figure 1.** MFIS of Ni41Co9 Mn31.5Ga18.5 in static magnetic fields. The point zero at each temperature is moved by 1 × 10−4 below 315 K and by 5 × 10−4 above 330 K.

that the magneto-structural coupling is large. The 0.12% (1200 ppm) MFIS is larger than the magnetostriction of TbDyFe single crystal under atmospheric pressure [33]. In this study, Ni41Co9 Mn38.5Ga18.5 is a polycrystalline sample; then, it is easier to process and handle the sample than single crystals. **Table 2** indicates the thermal linear striction *ΔL/L*(t), saturated magnetostriction *ΔL/L*(m), and relative volume discontinuity at the martensitic transition, *ΔV/V*.

In the former article, we studied the magneto-caloric properties of Ni41Co9 Mn31.5Ga18.5 polycrystalline sample by means of the differential scanning calorimetry (DSC) measurements [25]. Magneto-calorimetric measurements and magnetization measurements of Ni41Co9 Mn31.5Ga18.5 polycrystalline ferromagnetic shape memory alloy (FSMA) were performed across the *T*R, at atmospheric pressure. When the sample was warmed from the martensite phase, a gradual increase in the thermal expansion due to the reverse martensitic transition at *T*R was observed by the thermal expansion experimental study. These transition temperatures decreased steeply with an increasing magnetic field. The field dependence of the reverse martensitic transition temperature, *dTR/μ*<sup>0</sup> *dH*, is −7.9 K/T near zero fields. From the DSC measurements, the value of the latent heat was obtained as 2.6 kJ/kg in zero fields. The maximum value of

**Figure 2.** Field dependences of the MFIS of Ni41Co9 Mn31.5Ga18.5. The values of MFIS at 350 K were quoted from our former result [23].


**Table 2.** The thermal linear striction *ΔL/L*(t), saturated magnetostriction *ΔL/L*(m), and the relative volume discontinuity at the martensitic transition, *ΔV/V*.

**3.2. Forced magnetostriction around the critical temperatures**

In this study, we measured the magnetostriction of Ni2

presents the magnetostriction *ΔL/L* versus *M*<sup>4</sup>

the *M*<sup>4</sup>

∝ *M<sup>δ</sup>*

[35]. As for Ni2

around 7.5 J/kgK.

tism. Nishihara et al. studied the magnetic field dependences of Ni and Ni<sup>2</sup>

In this section, we offer a topic of forced magnetostriction around the Curie temperature or magneto-structural transition temperature. The spin fluctuation theory of itinerant electron magnetism suggests that the critical index *δ* is defined by the critical magnetic isotherm function, *H* ∝ *M<sup>δ</sup>*

**Figure 3.** Temperature dependence of the MFIS at 6 T. Entropy change obtained from DSC results *ΔS* [29] between zero field and 6 T is also shown. Thin dotted lines indicate the area for *ΔS* > 0. Bold dotted lines indicate the area for *ΔS*

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

http://dx.doi.org/10.5772/intechopen.76291

where *δ* is around 5 [27]. Some scientists studied this relation concerning itinerant ferromagne-

, at the Curie temperature was 4.70 ± 0.5 [34]. We measured the magnetization of Ni2

the magnetization is 4.70 and confirms the result of the former magnetization experiment.

the Takahashi's spin fluctuation theory. The magnetization analysis of Ni41Co9

the Curie temperature, *T*<sup>C</sup> = 375 K. **Figure 4** presents the *M<sup>δ</sup>*−1 versus *H/M* plot. This figure indicates good linearity. These results indicate that the critical index *δ* of the magnetic field dependence of

order to investigate the magnetization dependence of the forced magnetostriction. **Figure 5**

order to guide the eyes. The result shows good linearity. It is considered that this result orders

around the Curie temperature in the martensite phase according to the Takahashi's spin fluctuation theory was performed in the former article, as mentioned in Section 1 [25].

 versus *H/M* plot shows the reasonable linear relation at the Curie temperature. The critical temperature of the spin fluctuation temperature, *T*A, was obtained as 1.76 × 10<sup>4</sup> K. This value is comparable with the value of 1.26 × 10<sup>4</sup> K, which was obtained by neutron diffraction experiments

MnGa, the critical index *δ* of the magnetic field dependence of the magnetization, *H*

,

7

MnGa at

Mn31.5Ga18.5

MnGa [34]. As for Ni,

MnGa at the Curie temperature in

plot. The dotted line indicates a linear plot in

the entropy change *ΔS* was 7.0 J/kgK in zero fields, and with increasing magnetic fields, *ΔS* was gradually increased. The relative cooling power (RCP) is obtained by integration *ΔS* with the temperature. The RCP was 104 J/kg at 2.0 T, which was almost as same as the value with In-doped Ni41Co9 Mn32Ga16In2 alloy [12].

Now, we compare the results of the strain and calorimetric DSC measurements. **Figure 3** shows the temperature dependence of the MFIS and entropy change. The entropy change *ΔS* = *S*(6 T) - *S*(0 T) was obtained from magnetization results and DSC results between zero field and 6 T, from the DSC results *ΔS* in steady fields [25].

*ΔS* shows a finite value above 330 K. On the contrary, the MFIS shows almost zero below 330 K. The reversible MFIS (magnetostriction) was observed below 330 K. Above 330 K, irreversible MFIS and S-shape like *M-H* curve were observed. Considering these results, in the irreversible region *T≥* 330 K, metamagnetic and reverse martensitic transition occurred between the paramagnetic martensite and ferromagnetic parent austenite phases. Around *T*R, large latent heat was observed by DSC measurement. The irreversible MFIS, S-shape like *M-H* curve, and the observation of latent heat indicates that this transition is first-order transition. Therefore, in the finite *ΔS* value region (330 K≤T*≤* 390 K), irreversible and large MFIS can be observed. This result indicates the strong influence of magnetic fields for magneto-structural transformation.

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5 http://dx.doi.org/10.5772/intechopen.76291 7

**Figure 3.** Temperature dependence of the MFIS at 6 T. Entropy change obtained from DSC results *ΔS* [29] between zero field and 6 T is also shown. Thin dotted lines indicate the area for *ΔS* > 0. Bold dotted lines indicate the area for *ΔS* around 7.5 J/kgK.

#### **3.2. Forced magnetostriction around the critical temperatures**

the entropy change *ΔS* was 7.0 J/kgK in zero fields, and with increasing magnetic fields, *ΔS* was gradually increased. The relative cooling power (RCP) is obtained by integration *ΔS* with the temperature. The RCP was 104 J/kg at 2.0 T, which was almost as same as the value with

**Table 2.** The thermal linear striction *ΔL/L*(t), saturated magnetostriction *ΔL/L*(m), and the relative volume discontinuity

**Alloys** *ΔL/L***(t)** *ΔL/L***(m)** *ΔV/V* **(%) Reference**

Mn32Ga16In2 3.5 × 10−3 3.0 × 10−3 ~0.9 [12]

Mn31.5Ga18.5 1.1 × 10−3 1.2 × 10−3 ~0.33 This work

Mn31.5Ga18.5. The values of MFIS at 350 K were quoted from our former

Now, we compare the results of the strain and calorimetric DSC measurements. **Figure 3** shows the temperature dependence of the MFIS and entropy change. The entropy change *ΔS* = *S*(6 T) - *S*(0 T) was obtained from magnetization results and DSC results between zero

*ΔS* shows a finite value above 330 K. On the contrary, the MFIS shows almost zero below 330 K. The reversible MFIS (magnetostriction) was observed below 330 K. Above 330 K, irreversible MFIS and S-shape like *M-H* curve were observed. Considering these results, in the irreversible region *T≥* 330 K, metamagnetic and reverse martensitic transition occurred between the paramagnetic martensite and ferromagnetic parent austenite phases. Around *T*R, large latent heat was observed by DSC measurement. The irreversible MFIS, S-shape like *M-H* curve, and the observation of latent heat indicates that this transition is first-order transition. Therefore, in the finite *ΔS* value region (330 K≤T*≤* 390 K), irreversible and large MFIS can be observed. This result indicates the strong influence of magnetic fields for magneto-structural transformation.

In-doped Ni41Co9

at the martensitic transition, *ΔV/V*.

result [23].

6 Shape-Memory Materials

Ni41Co9

Ni41Co9

Mn32Ga16In2

**Figure 2.** Field dependences of the MFIS of Ni41Co9

alloy [12].

field and 6 T, from the DSC results *ΔS* in steady fields [25].

In this section, we offer a topic of forced magnetostriction around the Curie temperature or magneto-structural transition temperature. The spin fluctuation theory of itinerant electron magnetism suggests that the critical index *δ* is defined by the critical magnetic isotherm function, *H* ∝ *M<sup>δ</sup>* , where *δ* is around 5 [27]. Some scientists studied this relation concerning itinerant ferromagnetism. Nishihara et al. studied the magnetic field dependences of Ni and Ni<sup>2</sup> MnGa [34]. As for Ni, the *M*<sup>4</sup> versus *H/M* plot shows the reasonable linear relation at the Curie temperature. The critical temperature of the spin fluctuation temperature, *T*A, was obtained as 1.76 × 10<sup>4</sup> K. This value is comparable with the value of 1.26 × 10<sup>4</sup> K, which was obtained by neutron diffraction experiments [35]. As for Ni2 MnGa, the critical index *δ* of the magnetic field dependence of the magnetization, *H* ∝ *M<sup>δ</sup>* , at the Curie temperature was 4.70 ± 0.5 [34]. We measured the magnetization of Ni2 MnGa at the Curie temperature, *T*<sup>C</sup> = 375 K. **Figure 4** presents the *M<sup>δ</sup>*−1 versus *H/M* plot. This figure indicates good linearity. These results indicate that the critical index *δ* of the magnetic field dependence of the magnetization is 4.70 and confirms the result of the former magnetization experiment.

In this study, we measured the magnetostriction of Ni2 MnGa at the Curie temperature in order to investigate the magnetization dependence of the forced magnetostriction. **Figure 5** presents the magnetostriction *ΔL/L* versus *M*<sup>4</sup> plot. The dotted line indicates a linear plot in order to guide the eyes. The result shows good linearity. It is considered that this result orders the Takahashi's spin fluctuation theory. The magnetization analysis of Ni41Co9 Mn31.5Ga18.5 around the Curie temperature in the martensite phase according to the Takahashi's spin fluctuation theory was performed in the former article, as mentioned in Section 1 [25].

**Figure 4.** The *M*3.7 versus *H/M* plot of Ni2 MnGa. The dotted line is a fitted linear line.

**Figure 5.** The magnetostriction *ΔL/L* versus *M*<sup>4</sup> plot of Ni2 MnGa. The dotted line is a fitted linear line.

We studied the magnetostriction at the Curie temperature in the martensite phase, *T*<sup>C</sup> <sup>M</sup> = 263K.At this temperature, no structural phase transition occurred. Therefore, the striction under magnetic fields was decided as the magnetostriction. **Figure 6** shows the plot of the magnetostriction against *M*<sup>2</sup> at 263 K for Ni41Co9 Mn31.5Ga18.5. The magnetostriction was not proportional to *M*<sup>2</sup> . The plot was rounded. The plot of the numerically estimated magnetostriction at *T*C was also rounded against *M*<sup>2</sup> [27]. **Figure 7** shows the plot of the magnetostriction against *M*<sup>4</sup> at 263 K. The dotted lines are linearly fitted lines. The fitted line passed the origin and shows good linearity, as that of Ni2 MnGa. It is conceivable that these results indicate that the magnetostriction is proportional to the fourth power of the magnetization, *M*<sup>4</sup> .

Further, we investigated the MFIS around the reverse martensitic transition temperature. **Figures 8** and **9** show the magnetic field dependences of the magnetization and the MFIS at 330 and 340 K, respectively. These temperatures are around the reverse martensitic transition start temperature. The gradient of the magnetization and magnetostriction has tendencies toward increasing with the magnetic field increases for each temperature. However, the degree of the rate of increase of the magnetostriction is larger than that of the magnetization. From these figures, a correlation between the magnetostriction and magnetization could

at 263 K for Ni41Co9

at 263 K for Ni41Co9

Mn31.5Ga18.5.

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

http://dx.doi.org/10.5772/intechopen.76291

9

Mn31.5Ga18.5 is an itinerant ferromagnet.

Mn31.5Ga18.5. The dotted line is a fitted linear line.

at the Curie temperature in the martensite phase.

not be identified. As mentioned in Section 1, Ni41Co9

The magnetostriction is proportional to *M*<sup>4</sup>

**Figure 7.** The plot of the magnetostriction against *M*<sup>4</sup>

**Figure 6.** The plot of the magnetostriction against *M*<sup>2</sup>

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5 http://dx.doi.org/10.5772/intechopen.76291 9

**Figure 6.** The plot of the magnetostriction against *M*<sup>2</sup> at 263 K for Ni41Co9 Mn31.5Ga18.5.

We studied the magnetostriction at the Curie temperature in the martensite phase, *T*<sup>C</sup>

plot of Ni2

at 263 K for Ni41Co9

tion is proportional to the fourth power of the magnetization, *M*<sup>4</sup>

tion against *M*<sup>2</sup>

also rounded against *M*<sup>2</sup>

**Figure 5.** The magnetostriction *ΔL/L* versus *M*<sup>4</sup>

**Figure 4.** The *M*3.7 versus *H/M* plot of Ni2

8 Shape-Memory Materials

linearity, as that of Ni2

*M*<sup>2</sup>

this temperature, no structural phase transition occurred. Therefore, the striction under magnetic fields was decided as the magnetostriction. **Figure 6** shows the plot of the magnetostric-

MnGa. The dotted line is a fitted linear line.

. The plot was rounded. The plot of the numerically estimated magnetostriction at *T*C was

263 K. The dotted lines are linearly fitted lines. The fitted line passed the origin and shows good

Mn31.5Ga18.5. The magnetostriction was not proportional to

MnGa. The dotted line is a fitted linear line.

.

[27]. **Figure 7** shows the plot of the magnetostriction against *M*<sup>4</sup>

MnGa. It is conceivable that these results indicate that the magnetostric-

<sup>M</sup> = 263K.At

at

**Figure 7.** The plot of the magnetostriction against *M*<sup>4</sup> at 263 K for Ni41Co9 Mn31.5Ga18.5. The dotted line is a fitted linear line.

Further, we investigated the MFIS around the reverse martensitic transition temperature. **Figures 8** and **9** show the magnetic field dependences of the magnetization and the MFIS at 330 and 340 K, respectively. These temperatures are around the reverse martensitic transition start temperature. The gradient of the magnetization and magnetostriction has tendencies toward increasing with the magnetic field increases for each temperature. However, the degree of the rate of increase of the magnetostriction is larger than that of the magnetization. From these figures, a correlation between the magnetostriction and magnetization could not be identified. As mentioned in Section 1, Ni41Co9 Mn31.5Ga18.5 is an itinerant ferromagnet. The magnetostriction is proportional to *M*<sup>4</sup> at the Curie temperature in the martensite phase.

**Figure 8.** The magnetic field dependences of the magnetization and the MFIS at 330 K for Ni41Co9 Mn31.5Ga18.5.

**Figure 9.** The magnetic field dependences of the magnetization and the MFIS at 340 K for Ni41Co9 Mn31.5Ga18.5.

Therefore, it is presumed that the MFIS is also conformed to the power law suggested by Takahashi's theory.

**3.3. The time response of the magnetic field-induced strain of Ni**

magnetic fields.

**Figure 10.** The plot of MFIS against *M*<sup>2</sup>

**Figure 11.** The plot of MFIS against *M*<sup>4</sup>

In order to investigate time response of the MFIS, fast speed sweeping of the magnetic fields was performed at 354 K, as shown in **Figure 12**. The applied magnetic field increased from the zero magnetic field to 1.66 T in 8.0 s and under atmospheric pressure. **Figure 13** shows the MFIS, in which the applied magnetic field increased from the zero magnetic field to 1.66 T in 60 s. As for an 8.0-s mode, 2.2 × 10−4 MFIS was observed, which was 80% of the MFIS in a 60-s mode. This indicates that a high-speed transition has occurred on applying

at 330 and 340 K for Ni41Co9

at 330 and 340 K for Ni41Co9

Mn31.5Ga18.5.

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

http://dx.doi.org/10.5772/intechopen.76291

11

Mn31.5Ga18.5.

**<sup>41</sup>Co9**

**Mn31.5Ga18.5**

**Figure 10** shows the plot of MFIS against *M*<sup>2</sup> at 330 and 340 K. The dotted lines are linearly fitted lines. These fitted lines did not pass the origin, and the plot was rounded. **Figure 11** shows the plot of MFIS against *M*<sup>4</sup> at 330 and 340 K. The dotted lines are linearly fitted lines. These fitted lines passed the origin. It is conceivable that these results indicate that the MFIS is proportional to the fourth power of the magnetization, *M*<sup>4</sup> , which was suggested by Takahashi's theory [27]. It is interesting that the *M*<sup>4</sup> behavior matures until 7 T at 330 K.At this temperature, magneto-structural transition (reverse martensitic and metamagnetic transition) occurred.

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5 http://dx.doi.org/10.5772/intechopen.76291 11

**Figure 10.** The plot of MFIS against *M*<sup>2</sup> at 330 and 340 K for Ni41Co9 Mn31.5Ga18.5.

**Figure 11.** The plot of MFIS against *M*<sup>4</sup> at 330 and 340 K for Ni41Co9 Mn31.5Ga18.5.

Therefore, it is presumed that the MFIS is also conformed to the power law suggested by

**Figure 9.** The magnetic field dependences of the magnetization and the MFIS at 340 K for Ni41Co9

**Figure 8.** The magnetic field dependences of the magnetization and the MFIS at 330 K for Ni41Co9

ted lines. These fitted lines did not pass the origin, and the plot was rounded. **Figure 11** shows

fitted lines passed the origin. It is conceivable that these results indicate that the MFIS is pro-

magneto-structural transition (reverse martensitic and metamagnetic transition) occurred.

at 330 and 340 K. The dotted lines are linearly fit-

behavior matures until 7 T at 330 K.At this temperature,

, which was suggested by Takahashi's

Mn31.5Ga18.5.

Mn31.5Ga18.5.

at 330 and 340 K. The dotted lines are linearly fitted lines. These

Takahashi's theory.

10 Shape-Memory Materials

the plot of MFIS against *M*<sup>4</sup>

**Figure 10** shows the plot of MFIS against *M*<sup>2</sup>

theory [27]. It is interesting that the *M*<sup>4</sup>

portional to the fourth power of the magnetization, *M*<sup>4</sup>

#### **3.3. The time response of the magnetic field-induced strain of Ni 41Co9 Mn31.5Ga18.5**

In order to investigate time response of the MFIS, fast speed sweeping of the magnetic fields was performed at 354 K, as shown in **Figure 12**. The applied magnetic field increased from the zero magnetic field to 1.66 T in 8.0 s and under atmospheric pressure. **Figure 13** shows the MFIS, in which the applied magnetic field increased from the zero magnetic field to 1.66 T in 60 s. As for an 8.0-s mode, 2.2 × 10−4 MFIS was observed, which was 80% of the MFIS in a 60-s mode. This indicates that a high-speed transition has occurred on applying magnetic fields.

performed. Strain gauge was fixed parallel to the long distance direction (4.0 mm) of the sample. The external magnetic field was applied parallel to the long distance direction of the sample, and the elongation of the sample was measured. A 0.12% MFIS was observed at 340 K and 10 T. Strict MFISs between 300 and 370 K were observed. These magnetostructural variances acted in concert with the metamagnetic property observed by the magnetization measurements and magneto-caloric property observed by the caloric measurements in the applied magnetic fields. The MFISs were proportional to the fourth power of the magnetization, and this result is in agreement with Takahashi's spin fluctuation theory of itinerant electron magnetism. The investigation of time response of the MFIS was performed by means of a sweep water-cooled electric magnet, and zero magnetic field to 1.66 T in 8.0 s at 354 K. 2.2 × 10−4 MFIS was observed, which was 80% of the MFIS in a 60-s mode. This indicates that a high-speed transition has occurred on applying

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

http://dx.doi.org/10.5772/intechopen.76291

13

The authors thank Mr. M. Okamoto for helping prepare equipment for MFIS measuring system. This experimental study was partly performed at High Field Laboratory for

, Takeshi Kanomata2

, Hiroyuki Nojiri3

and

Superconducting Materials, Institute for Materials Research, Tohoku University.

, Sho Saruki1

3 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan

1 Department of Mechanical and System Engineering, Faculty of Science and Technology,

2 Research Institute for Engineering and Technology, Tohoku Gakuin University, Tagajo,

4 Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata,

magnetic fields.

**Acknowledgements**

**Conflicts of interest**

**Author details**

Takuo Sakon1

Miyagi, Japan

Japan

Yoshiya Adachi<sup>4</sup>

The authors declare no conflict of interest.

\*, Naoki Fujimoto1

Ryukoku University, Otsu, Shiga, Japan

\*Address all correspondence to: sakon@rins.ryukoku.ac.jp

**Figure 12.** Time dependence of MFIS of Ni41Co9 Mn31.5Ga18.5 at 354 K in increasing magnetic fields by means of a watercooled magnet. The applied magnetic field increased from the zero magnetic field to 1.66 T in 8.0 s.

**Figure 13.** MFIS of Ni41Co9 Mn31.5Ga18.5 at 354 K by means of a water-cooled magnet. The applied magnetic field increased from the zero magnetic field to 1.66 T in 60 s.

The MFIS effect occurs at the temperature between room temperature and 370 K; therefore, it is useful for magnetic sensors, or actuators in the high temperature region, *ex.* the engine room in the motor vehicles.

#### **4. Conclusions**

In order to investigate the magnetic functionality of polycrystalline metamagnetic Heusler alloy Ni41Co9 Mn31.5Ga18.5, magnetic field-induced strain (MFIS) measurements were performed. Strain gauge was fixed parallel to the long distance direction (4.0 mm) of the sample. The external magnetic field was applied parallel to the long distance direction of the sample, and the elongation of the sample was measured. A 0.12% MFIS was observed at 340 K and 10 T. Strict MFISs between 300 and 370 K were observed. These magnetostructural variances acted in concert with the metamagnetic property observed by the magnetization measurements and magneto-caloric property observed by the caloric measurements in the applied magnetic fields. The MFISs were proportional to the fourth power of the magnetization, and this result is in agreement with Takahashi's spin fluctuation theory of itinerant electron magnetism. The investigation of time response of the MFIS was performed by means of a sweep water-cooled electric magnet, and zero magnetic field to 1.66 T in 8.0 s at 354 K. 2.2 × 10−4 MFIS was observed, which was 80% of the MFIS in a 60-s mode. This indicates that a high-speed transition has occurred on applying magnetic fields.

## **Acknowledgements**

The authors thank Mr. M. Okamoto for helping prepare equipment for MFIS measuring system. This experimental study was partly performed at High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University.

## **Conflicts of interest**

The authors declare no conflict of interest.

## **Author details**

The MFIS effect occurs at the temperature between room temperature and 370 K; therefore, it is useful for magnetic sensors, or actuators in the high temperature region, *ex.* the engine

cooled magnet. The applied magnetic field increased from the zero magnetic field to 1.66 T in 8.0 s.

In order to investigate the magnetic functionality of polycrystalline metamagnetic Heus-

Mn31.5Ga18.5, magnetic field-induced strain (MFIS) measurements were

Mn31.5Ga18.5 at 354 K by means of a water-cooled magnet. The applied magnetic field increased

Mn31.5Ga18.5 at 354 K in increasing magnetic fields by means of a water-

room in the motor vehicles.

from the zero magnetic field to 1.66 T in 60 s.

**Figure 12.** Time dependence of MFIS of Ni41Co9

12 Shape-Memory Materials

**4. Conclusions**

**Figure 13.** MFIS of Ni41Co9

ler alloy Ni41Co9

Takuo Sakon1 \*, Naoki Fujimoto1 , Sho Saruki1 , Takeshi Kanomata2 , Hiroyuki Nojiri3 and Yoshiya Adachi<sup>4</sup>

\*Address all correspondence to: sakon@rins.ryukoku.ac.jp

1 Department of Mechanical and System Engineering, Faculty of Science and Technology, Ryukoku University, Otsu, Shiga, Japan

2 Research Institute for Engineering and Technology, Tohoku Gakuin University, Tagajo, Miyagi, Japan

3 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan

4 Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan

## **References**

[1] Ullakko K, Huang JK, Kantner C, O'Handley RC, Kokorin VV. Large magnetic-fieldinduced strains in Ni2 MnGa single crystals. Applied Physics Letters. 1996;**69**:1966

[13] Seguí C, Cesari E, Lázpita P. Magnetic properties of martensite in metamagnetic Ni–Co–

[14] Kamarád J, Kaštil J, Skourski Y, Albertini F, Fabbrici S, Arnold Z. Magneto-structural

[15] Seguí C. Effects of the interplay between atomic and magnetic order on the properties of metamagnetic Ni-Co-Mn-Ga shape memory alloys. Journal of Applied Physics.

[16] Entel P, Gruner ME, Comtesse D, Sokolovskiy VV, Buchelnikov VD. Interacting magnetic cluster-spin glasses and strain glasses in Ni–Mn based Heusler structured interme-

[17] Porcari G, Fabbrici S, Pernechele C, Albertini F, Buzzi M, Paoluzi A, Kamarad J, Arnold Z, Solzi M. Reverse magnetostructural transformation and adiabatic temperature change

[18] Segui C, Cesari E. Composition and atomic order effects on the structural and magnetic transformations in ferromagnetic Ni–Co–Mn–Ga shape memory alloys. Journal of

[19] Kanomata T, Nunoki S, Endo K, Kataoka M, Nishihara H, Khovaylo VV, Umetsu RY, Shishido T, Nagasako M, Kainuma R, Ziebeck KRA. Phase diagram of the ferromagnetic

[20] Fabbrici S, Albertini F, Paoluzi A, Bolzoni F, Cabassi R, Solzi M, Righi L, Calestani G. Reverse magnetostructural transformation in Co-doped NiMnGa multifunctional alloys.

[21] Kihara T, Xu X, Ito W, Kainuma R, Adachi Y, Kanomata T, Tokunaga M. Magnetocaloric effects in metamagnetic shape memory alloys. In: Shape Memory Alloys—Fundamentals

[22] Yu SY, Cao ZX, Ma L, Liu GD, Chen JL, Wu GH, Zhang B, Zhang XX. Realization of magnetic field-induced reversiblemartensitic transformation in NiCoMnGa alloys. Applied

[23] Sakon T, Sasaki K, Numakura D, Abe M, Nojiri H, Adachi Y, Kanomata T. Magnetic

[25] Sakon T, Kitaoka T, Tanaka K, Nakagawa K, Nojiri H, Adachi Y, Kanomata T. Magneto-

caloric and magnetic properties of meta-magnetic Heusler alloy Ni41Co9

Progress in Metallic Alloys. Rijeka, Croatia: InTech Publisher; 2016. p. 265

. Physical Review B. 2012;**85**:134421

Mn31.5Ga18.5 Heusler alloy. Materials

MnGa ferromag-

Mn31.5Ga18.5. In:

MnGa1−xCox

and Applications. Vol. 59-79. Croatia: InTech Publisher, Rijeka; 2017

[24] Sakon T, Adachi Y, Kanomata T. Magneto-structural properties of Ni<sup>2</sup>

netic shape memory alloy in magnetic fields. Metals. 2013;**3**:202

in Co- and In-substituted Ni-Mn-Ga alloys. Physical Review B. 2012;**85**:024414

MnGa-based Heusler alloys by high magnetic field up

http://dx.doi.org/10.5772/intechopen.76291

15

Magnetic Field-Induced Strain of Metamagnetic Heusler Alloy Ni41Co9Mn31.5Ga18.5

Mn–Ga alloys. Journal of Physics D: Applied Physics. 2016;**49**:165007

transitions induced at 1.2 K in Ni2

Applied Physics. 2012;**111**:043914

Applied Physics Letters. 2009;**95**:022508

field-induced transition in Co-doped Ni41Co9

Physics Letters. 2007;**91**:102507

Transactions. 2013;**54**:9

shape memory alloys Ni2

2014;**115**:113903

to 60 T. Materials Research Express. 2014;**1**:016109

tallics. Physica Status Solidi B. 2014;**251**:2135


[13] Seguí C, Cesari E, Lázpita P. Magnetic properties of martensite in metamagnetic Ni–Co– Mn–Ga alloys. Journal of Physics D: Applied Physics. 2016;**49**:165007

**References**

14 Shape-Memory Materials

in Ni2

pound Ni2

induced strains in Ni2

of Applied Physics. 2005;**97**:083516

Applied Physics Letters. 2004;**85**:4358

alloy. Applied Physics Letters. 2006;**88**:122507

copy. Physical Review B. 2009;**80**:144409

mation. Nature. 2006;**439**:957

Science Forum. 2011;**684**:151

Review B. 2006;**74**:224443

[1] Ullakko K, Huang JK, Kantner C, O'Handley RC, Kokorin VV. Large magnetic-field-

[2] Webster PJ, Ziebeck KRA, Town SL, Peak MS. Magnetic order and phase transformation

[3] Brown PJ, Crangle J, Kanomata T, Matsumoto M, Neumann K-U, Ouladdiaf B, Ziebeck KRA. The crystal structure and phase transitions of the magnetic shape memory com-

[4] Pons J, Santamarta R, Chernenko VA, Cesari E. Long-period martensitic structures of Ni-Mn-Ga alloys studied by high-resolution transmission electron microscopy. Journal

[5] Ranjan R, Banik S, Barman SR, Kumar U, Mukhopadhyay PK, Pandey D. Powder X-ray

[6] Sakon T, Otsuka K, Matsubayashi J, Watanabe Y, Nishihara H, Sasaki K, Yamashita S, Umetsu RY, Nojiri H, Kanomata T. Magnetic properties of the ferromagnetic shape

[7] Sutou Y, Imano Y, Koeda N, Omori T, Kainuma R, Ishida K, Oikawa K. Magnetic and martensitic transformations of NiMnX (X=In,Sn,Sb) ferromagnetic shape memory alloys.

[8] Oikawa K, Ito W, Imano Y, Sutou Y, Kainuma R, Ishida K, Okamoto S, Kitakami O, Kanomata T. Effect of magnetic field on martensitic transition of Ni46Mn41In13 Heusler

[9] Umetsu RY, Kainuma R, Amako Y, Taniguchi Y, Kanomata T, Fukushima K, Fujita A,

[10] Khovaylo VV, Kanomata T, Tanaka T, Nakashima M, Amako Y, Kainuma R, Umetsu RY, Morito H, Miki H. Magnetic properties of Ni50Mn34.8In15.2 probed by Mössbauer spectros-

[11] Kainuma R, Imano Y, Ito W, Morino YSH, Okamoto S, Kitakami O, Oikawa K, Fujita A, Kanomata T, Ishida K. Magnetic-field induced shape recovery by reverse phase transfor-

[12] Albertini F, Fabbrici S, Paoluzi A, Kamarad J, Arnold Z, Righi L, Solzi M, Porcari G, Pernechele C, Serrate D, Algarabel P. Reverse magnetostructural transitions by Co and In doping NiMnGa alloys: Structural, magnetic, and magnetoelastic properties. Materials

diffraction study of the thermoelastic martensitic transition in Ni<sup>2</sup>

memory alloy Ni50+xMn27-xGa23 in magnetic fields. Materials. 2014;**7**:3715

Oikawa K, Ishida K. Mössbauer study on martensite phase in Ni50Mn36.5

magnetic shape memory alloy. Applied Physics Letters. 2008;**93**:042509

MnGa. Journal of Physics. Condensed Matter. 2002;**14**:10159

MnGa. Philosophical Magazine B. 1984;**49**:295

MnGa single crystals. Applied Physics Letters. 1996;**69**:1966

Mn1.05Ga0.95. Physical

57Fe0.5Sn13 meta-


[26] Takahashi Y. Quantum spin fluctuation theory of the magnetic equation of state of weak itinerant-electron ferromagnets. Journal of Physics: Condensed Matter. 2001;**13**:6323

**Chapter 2**

Provisional chapter

**Aspects Regarding Thermal-Mechanical Fatigue of**

DOI: 10.5772/intechopen.77991

This chapter presents advanced researches about the using of metallic alloys with shape memory properties in construction and exploitation of parts subjected to combined stress by thermal and mechanical fatigue during their functioning. The shape memory alloys (SMAs) have a series of properties much different from the usual metallic materials. Their main characteristic is recovery/returning from plastic deformation by heating, considering that in some cases at temperature changing, the shape modification is reversible. In the case of parts made from SMA, which work in conditions by thermal and mechanical stresses and temperature variations, the resistance evaluation at thermal and mechanical fatigue is absolutely necessary. Like researching domain, regarding thermal and mechanical fatigue behavior, it was selected the shape memory Cu-based alloy. The achieved researches, concerning methodology, investigation equipment, experimental results, allow evaluating and estimating the shape memory properties. Losing the shape memory properties of SMA, in requested conditions, namely amnesia, so to the calculation of fatigue resistance must be taken into account by this fundamental property. The expression of the fatigue state, through losing the memorizing capacity, represents a designing indicator, which ensures the guaranty of properties in fatigue conditions, through applying of fatigue cycles. To determine the fatigue resistance of SMA was necessary specific requests. The properties are guaranteed for a certain number of fatigue cycles. The experimental data, presented in this chapter, offer to scientists some information about the SMAs, Cu-based. These data can be used in designing

Aspects Regarding Thermal-Mechanical Fatigue of

**Shape Memory Alloys**

Shape Memory Alloys

Manuela-Cristina Perju

Manuela-Cristina Perju

Abstract

Petrică Vizureanu, Dragoș-Cristian Achiței,

Petrică Vizureanu, Dragoș-Cristian Achiței,

Additional information is available at the end of the chapter

and manufacturing of new parts for different devices.

mechanical fatigue, Cu-based alloy

Keywords: shape memory alloys, properties, shape memory effect, thermal and

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Mirabela-Georgiana Minciună and

Mirabela-Georgiana Minciună and

http://dx.doi.org/10.5772/intechopen.77991


#### **Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys** Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

DOI: 10.5772/intechopen.77991

Petrică Vizureanu, Dragoș-Cristian Achiței, Mirabela-Georgiana Minciună and Manuela-Cristina Perju Petrică Vizureanu, Dragoș-Cristian Achiței, Mirabela-Georgiana Minciună and Manuela-Cristina Perju

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.77991

#### Abstract

[26] Takahashi Y. Quantum spin fluctuation theory of the magnetic equation of state of weak itinerant-electron ferromagnets. Journal of Physics: Condensed Matter. 2001;**13**:6323 [27] Takahashi Y. Spin Fluctuation Theory of Itinerant Electron Magnetism. Berlin/Heidelberg,

[28] Sakon T, Saito S, Koyama K, Awaji S, Sato I, Nojima T, Watanabe K, Sato NK. Experimental

[29] Matsunaga M, Ishikawa Y, Nakajima T. Magneto-volume effect of the weak itinerant fer-

[30] Techapiesancharoenkij R, Kostamo J, Allen SM, O'Handley RC. Frequency response of acoustic-assisted Ni–Mn–Ga ferromagnetic-shape-memory-alloy actuator. Journal of

[31] Gonzalez-Comas A, Obradó E, Mañosa L, Planes A, Chernenko VA, Hattink BJ, Labarta

[32] Khovailo VV, Takagi T, Tani TJ, Levitin RZ, Cherechukin AA, Matsumoto M, Note R. Magnetic properties of Ni2.18Mn0.82Ga Heusler alloys with a coupled magnetostructural

[33] Wang Z, Liu J, Jiang C, Xu H. The stress dependence of magnetostriction hysteresis in

[34] Nishihara H, Komiyama K, Oguro I, Kanomata T, Chernenko V. Magnetization pro-

[35] Takahashi Y. On the origin of the curie-Weiss law of the magnetic susceptibility in itinerant electron magnetism. Journal of the Physical Society of Japan. 1986;**55**:3533

TbDyFe [110] oriented crystal. Journal of Applied Physics. 2011;**109**:123923

cesses near the curie temperatures of the itinerant ferromagnets, Ni2

nickel. Journal of Alloys and Compounds. 2007;**442**:191-193

. Physica Scripta. 2007;**75**:546

MnGa. Physical

MnGa and pure

investigation of giant magnetocrystalline anisotropy of UGe2

romagnet MnSi. Journal of the Physical Society of Japan. 1982;**51**:1153

A. Premartensitic and martensitic phase transitions in ferromagnetic Ni2

Germany: Springer-Verlag; 2013

16 Shape-Memory Materials

Applied Physics. 2009;**105**:093923

transition. Physical Review B. 2002;**65**:092410

Review B. 1999;**60**:7085

This chapter presents advanced researches about the using of metallic alloys with shape memory properties in construction and exploitation of parts subjected to combined stress by thermal and mechanical fatigue during their functioning. The shape memory alloys (SMAs) have a series of properties much different from the usual metallic materials. Their main characteristic is recovery/returning from plastic deformation by heating, considering that in some cases at temperature changing, the shape modification is reversible. In the case of parts made from SMA, which work in conditions by thermal and mechanical stresses and temperature variations, the resistance evaluation at thermal and mechanical fatigue is absolutely necessary. Like researching domain, regarding thermal and mechanical fatigue behavior, it was selected the shape memory Cu-based alloy. The achieved researches, concerning methodology, investigation equipment, experimental results, allow evaluating and estimating the shape memory properties. Losing the shape memory properties of SMA, in requested conditions, namely amnesia, so to the calculation of fatigue resistance must be taken into account by this fundamental property. The expression of the fatigue state, through losing the memorizing capacity, represents a designing indicator, which ensures the guaranty of properties in fatigue conditions, through applying of fatigue cycles. To determine the fatigue resistance of SMA was necessary specific requests. The properties are guaranteed for a certain number of fatigue cycles. The experimental data, presented in this chapter, offer to scientists some information about the SMAs, Cu-based. These data can be used in designing and manufacturing of new parts for different devices.

Keywords: shape memory alloys, properties, shape memory effect, thermal and mechanical fatigue, Cu-based alloy

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## 1. Introduction

The SMAs present some properties which are not found to metallic alloys used in practice. Characteristic to these alloys it is the capacity to change the geometric shape at temperature modification. After heating up to a imposed temperature, the part is cooled until ambiance temperature and returns to his initial shape. In some conditions, the shape changing can be reversible and the material can memorize two geometric shapes: the shape from high temperature (hot shape) and the shape from low temperature (cold shape). The shape changing is realized due to shape memory effect (SME). Through SME, the alloy can do mechanical work in the passing time from cold shape to hot shape.

properties, in reduced temperature frame (cca. 15–30C). Although in the two structural states (martensitic and austenitic), the alloy has certain properties of mechanical resistance, his basic function is to memorize. The loss of memory properties of the alloy, in certain conditions of loads, carries the names of amnesia. To keeping of the material integrity in load conditions is necessary the knowledge of the fatigue resistance both of the martensitic state and also the austenitic state. If the SMA element breaks during the load, then the fatigue resistance condition is not accomplished. In these conditions, the value of fatigue resistance will be smaller than the fatigue

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

http://dx.doi.org/10.5772/intechopen.77991

19

Mechanical fatigue resistance is defined through the minimal value of recovered deformation, after a certain number of usage cycles. Determining this size can be realized through different ways of loads, but the most precise is the stretching load. Considering that the shape memory properties are evaluated by the values of recovered deformation, this will be the function which characterizes the material. The basis method for results interpretation of the fatigue resistance is σ(N) diagram, named Wohler curve, in which σ represents the maximum amplitude of alternative load until breakage, after a certain number of cycles. This method can be applied to SMA, both in martensitic state and in austenitic state, characterizing the material resistance in the two states. The attempt consists in deformation in martensitic state at a determined value and its recovery through heating in austenitic domain, by an N number, as long as this value is kept. If the breakage is produced, the fatigue resistance condition is not accomplished. A cycle of fatigue load attempts must contain the following steps: (1) memory imprint at maximum limit or recovery deformation; (2) memory education through a number of cycles at maximum limit deformation; (3) demanding at tensions below the realization tension of memory deformation; (4) heating with the maintaining of the load tension; (5) cooling; (6) after a number of cycles, the recovered deformation value is measured. The diagram which contain variation curves of memory capacity according to the number of

resistance values of the two structural states.

memory cycles and work load is presented in Figure 1.

loading tensions.

There are many fatigue loading types according to the exploitation conditions.

Figure 1. Fatigue under load diagram of CuZnAl alloy: εm—recovered deformation; σm—memory imprint load; σ1, σ2—

SMAs can be classified, according to the alloying elements, in following classes: Nickel-based alloys, Copper-based alloys, Iron-based alloys, and Noble Metals-based alloys, Exotic alloys. Cooper-based alloys, like Cu Al, CuAlNi, AuCd, NiAl, CuZn, CuZnAl are named β phase alloys. There are numerous types of SMAs, but most of them have high manufacturing costs due to noble or rare metals from composition or to complex obtaining technology. Interest presents NiTi, CuZnAl, CuAlNi alloys which are used in various applications. The most important shape memory phenomena are: (1) pseudo-elastic or pseudo elasticity effect (PSE); (2) shape memory simple effect (SME); (3) double sense shape memory effect (DSSME); and (4) vibrations damping effect.

A less studied chapter is the behavior of these alloys at thermal fatigue and that is because SMA can work: with free return, with retained return, with manufacturing of mechanical work, and pseudo-elasticity. In each of these cases, the parts of SMAs will be heated and then cooled to obtain the proposed goal. Between the hot shape and the cold shape of SMA, there exists a difference of energy. The change reversibility of the two shapes stays at the base of many applications. In this case, the reproducibility of the two shapes has a high importance. After a certain number of functioning cycles, the reproducibility of the two shapes is affected, so does the shape memory property.

Nowadays, some SMAs have usages in domains like:


## 2. Mechanical fatigue phenomena at SMA

The SMA from the construction of some installations is subjected to mechanical loads and also thermal loads. The SME supposes the existence of two structural states, with different mechanical properties, in reduced temperature frame (cca. 15–30C). Although in the two structural states (martensitic and austenitic), the alloy has certain properties of mechanical resistance, his basic function is to memorize. The loss of memory properties of the alloy, in certain conditions of loads, carries the names of amnesia. To keeping of the material integrity in load conditions is necessary the knowledge of the fatigue resistance both of the martensitic state and also the austenitic state. If the SMA element breaks during the load, then the fatigue resistance condition is not accomplished. In these conditions, the value of fatigue resistance will be smaller than the fatigue resistance values of the two structural states.

1. Introduction

18 Shape-Memory Materials

in the passing time from cold shape to hot shape.

so does the shape memory property.

Clementine satellite;

Nowadays, some SMAs have usages in domains like:

2. Mechanical fatigue phenomena at SMA

The SMAs present some properties which are not found to metallic alloys used in practice. Characteristic to these alloys it is the capacity to change the geometric shape at temperature modification. After heating up to a imposed temperature, the part is cooled until ambiance temperature and returns to his initial shape. In some conditions, the shape changing can be reversible and the material can memorize two geometric shapes: the shape from high temperature (hot shape) and the shape from low temperature (cold shape). The shape changing is realized due to shape memory effect (SME). Through SME, the alloy can do mechanical work

SMAs can be classified, according to the alloying elements, in following classes: Nickel-based alloys, Copper-based alloys, Iron-based alloys, and Noble Metals-based alloys, Exotic alloys. Cooper-based alloys, like Cu Al, CuAlNi, AuCd, NiAl, CuZn, CuZnAl are named β phase alloys. There are numerous types of SMAs, but most of them have high manufacturing costs due to noble or rare metals from composition or to complex obtaining technology. Interest presents NiTi, CuZnAl, CuAlNi alloys which are used in various applications. The most important shape memory phenomena are: (1) pseudo-elastic or pseudo elasticity effect (PSE); (2) shape memory simple effect (SME); (3) double sense shape memory effect (DSSME); and (4) vibrations damping effect. A less studied chapter is the behavior of these alloys at thermal fatigue and that is because SMA can work: with free return, with retained return, with manufacturing of mechanical work, and pseudo-elasticity. In each of these cases, the parts of SMAs will be heated and then cooled to obtain the proposed goal. Between the hot shape and the cold shape of SMA, there exists a difference of energy. The change reversibility of the two shapes stays at the base of many applications. In this case, the reproducibility of the two shapes has a high importance. After a certain number of functioning cycles, the reproducibility of the two shapes is affected,

• aerospace and naval: flaps for aircrafts, solar panels benders for Hubble telescope or

• medical: medical instruments, crack bones restoration clamps, coronary dilators, glasses frames, locomotor prostheses, arches for dental corrections, stents, brain spatulas;

• others: fire extinguishers, automatic sprinklers, pipe couplings, disassembly devices, automotive thermostats, filter holders, gas switches, solar actuators, steam valves, and vibration dampers.

The SMA from the construction of some installations is subjected to mechanical loads and also thermal loads. The SME supposes the existence of two structural states, with different mechanical

• robotics: devices for channel drainage, actuators for tasks manipulation robots;

Mechanical fatigue resistance is defined through the minimal value of recovered deformation, after a certain number of usage cycles. Determining this size can be realized through different ways of loads, but the most precise is the stretching load. Considering that the shape memory properties are evaluated by the values of recovered deformation, this will be the function which characterizes the material. The basis method for results interpretation of the fatigue resistance is σ(N) diagram, named Wohler curve, in which σ represents the maximum amplitude of alternative load until breakage, after a certain number of cycles. This method can be applied to SMA, both in martensitic state and in austenitic state, characterizing the material resistance in the two states. The attempt consists in deformation in martensitic state at a determined value and its recovery through heating in austenitic domain, by an N number, as long as this value is kept. If the breakage is produced, the fatigue resistance condition is not accomplished. A cycle of fatigue load attempts must contain the following steps: (1) memory imprint at maximum limit or recovery deformation; (2) memory education through a number of cycles at maximum limit deformation; (3) demanding at tensions below the realization tension of memory deformation; (4) heating with the maintaining of the load tension; (5) cooling; (6) after a number of cycles, the recovered deformation value is measured. The diagram which contain variation curves of memory capacity according to the number of memory cycles and work load is presented in Figure 1.

There are many fatigue loading types according to the exploitation conditions.

Figure 1. Fatigue under load diagram of CuZnAl alloy: εm—recovered deformation; σm—memory imprint load; σ1, σ2 loading tensions.

## 3. Fatigue solicitation with free recovery of deformation

This type of fatigue resistance property is guaranteed by the SMA producers. The function of these alloys being the recovered deformation and the variable is the number of memory cycles. If memory imprint deformation is higher, the recovery deformation is higher, but the number of exploitation cycles is reduced. The most encountered fatigue solicitation is solicitation with constant keeping of load during the test.

The fatigue tests are proceeding at the determination of the maximum memory effect through traction and dilatometry, in order to establish both maximum load deformation, and also the

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

http://dx.doi.org/10.5772/intechopen.77991

21

The establishment of the thermal cycle temperature is based on critical transformation temperatures. The test can be done on a specialized traction machine, provided with load and heat programmer. The test can be done at load or deformation values below the maximum memorizing value.

The grippers of sample in traction machine must allow the release adjustment of the sample with resulted remanent deformation, which is recovered through a later heating. From the diagram (Figure 2a), it results that every values are synchronized in time through repeating

In addition, solicitation at fatigue with constant keeping of deformation is found in the practice (Figure 2b) at mechanical systems with memory element with contrast spring, with limiter. The admitted maximum value of deformation corresponded to maximum memorizing deformation.

4. Solicitation at fatigue with recovery under load of recovery deformation

Often, the SMA element from a device does not deform freely; it makes a mechanical work in memory recovery period. Because of that, the fatigue test with free recovery is not matching

Figure 3. Load cycle (σ) and thermal cycle (T) for fatigue testing under load: σd—load in the time of shape recovery.

corresponding tension of this deformation.

the fatigue test cycle.

This type of load is found in the practice at a mechanical system with SMA element, which lifts a weight. The maximum load admitted is the one corresponding to the maximum memorized deformation. The value of free recovery deformation depends on the produced deformation in cold state (martensitic) and the constant load applied. The value of deformation produced by the constant load can be different throughout the test cycles.

Figure 2. The graphic of fatigue test with constant load keeping (a) and constant deformation keeping (b): σm—load tension; εm—maximum memory deformation; ε—elastic recovery; Ti—temperature of heating cycle; εrec—recovery deformation; n—number of load cycles.

The fatigue tests are proceeding at the determination of the maximum memory effect through traction and dilatometry, in order to establish both maximum load deformation, and also the corresponding tension of this deformation.

3. Fatigue solicitation with free recovery of deformation

the constant load can be different throughout the test cycles.

constant keeping of load during the test.

20 Shape-Memory Materials

mation; n—number of load cycles.

This type of fatigue resistance property is guaranteed by the SMA producers. The function of these alloys being the recovered deformation and the variable is the number of memory cycles. If memory imprint deformation is higher, the recovery deformation is higher, but the number of exploitation cycles is reduced. The most encountered fatigue solicitation is solicitation with

This type of load is found in the practice at a mechanical system with SMA element, which lifts a weight. The maximum load admitted is the one corresponding to the maximum memorized deformation. The value of free recovery deformation depends on the produced deformation in cold state (martensitic) and the constant load applied. The value of deformation produced by

Figure 2. The graphic of fatigue test with constant load keeping (a) and constant deformation keeping (b): σm—load tension; εm—maximum memory deformation; ε—elastic recovery; Ti—temperature of heating cycle; εrec—recovery deforThe establishment of the thermal cycle temperature is based on critical transformation temperatures. The test can be done on a specialized traction machine, provided with load and heat programmer. The test can be done at load or deformation values below the maximum memorizing value.

The grippers of sample in traction machine must allow the release adjustment of the sample with resulted remanent deformation, which is recovered through a later heating. From the diagram (Figure 2a), it results that every values are synchronized in time through repeating the fatigue test cycle.

In addition, solicitation at fatigue with constant keeping of deformation is found in the practice (Figure 2b) at mechanical systems with memory element with contrast spring, with limiter. The admitted maximum value of deformation corresponded to maximum memorizing deformation.

## 4. Solicitation at fatigue with recovery under load of recovery deformation

Often, the SMA element from a device does not deform freely; it makes a mechanical work in memory recovery period. Because of that, the fatigue test with free recovery is not matching

Figure 3. Load cycle (σ) and thermal cycle (T) for fatigue testing under load: σd—load in the time of shape recovery.

with the exploitation conditions. For determination of fatigue resistance in these conditions, the traction machine must be provided with a special program for load cycle (Figure 3).

Imprint tension of the cold shape (σ) must not exceed the maximum memory deformation, and the tension in the recovery period of the shape must be constant. The number of test cycles is determined after the sample breakage or after the loss a certain of memory capacity, determined through dilatometry. The determination involves a large number of samples and high volume of attempts. The graphic of fatigue resistance is compound from a family of curves.

Thermal fatigue represents the loss of some properties under the influence of a number of thermal cycles. In the case of SMA, the loss of memory properties is pursued. The application domain of thermal cycles must be contained in transformation critical points area, where the

Figure 5. Diagram of thermal fatigue resistance.

Figure 6. Thermal fatigue of the double sense memory component of a SMA: εds—double sense recovery deformation.

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

http://dx.doi.org/10.5772/intechopen.77991

23

Figure 4. Graphic of fatigue test with recovery under load of deformation recovery.

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys http://dx.doi.org/10.5772/intechopen.77991 23

Figure 5. Diagram of thermal fatigue resistance.

with the exploitation conditions. For determination of fatigue resistance in these conditions, the traction machine must be provided with a special program for load cycle (Figure 3).

22 Shape-Memory Materials

Imprint tension of the cold shape (σ) must not exceed the maximum memory deformation, and the tension in the recovery period of the shape must be constant. The number of test cycles is determined after the sample breakage or after the loss a certain of memory capacity, determined through dilatometry. The determination involves a large number of samples and high volume of attempts. The graphic of fatigue resistance is compound from a family of curves.

Thermal fatigue represents the loss of some properties under the influence of a number of thermal cycles. In the case of SMA, the loss of memory properties is pursued. The application domain of thermal cycles must be contained in transformation critical points area, where the

Figure 4. Graphic of fatigue test with recovery under load of deformation recovery.

Figure 6. Thermal fatigue of the double sense memory component of a SMA: εds—double sense recovery deformation.

memory property manifests. The test for the determination of this property consists in determination of maximum recovery deformation, after a number of applied thermal cycles (Figure 3).

To increase the resistance to mechanical fatigue, is applied a hot rolling, followed a quenching in water, through the grains limits gets an irregular shape. During mechanical education, this shape is recovering, absorbing an extra energy, thanks to which the tenacity of the limits is improved. The main method of enhancing the resistance at mechanical fatigue of SMA is grains finishing. The thermal fatigue is tied especially by the irreversible forming of defects, which leads to a considerable hardening in the case of a binary, biphasic brass (Cu-40%Zn).

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

http://dx.doi.org/10.5772/intechopen.77991

25

In the case of CuZnAl SMA, the mechanical education affects the critical temperatures of transformation, but in much lower ways than the thermal one. The influences of the two types of education are opposite, such that the thermal education strongly reduced the temperature

Fatigue cracking is the phenomenon which leads to breakage at a repeated or fluctuating load, which is smaller than the elastic material load. Fatigue breaking is progressive, at the begin-

The place where the cracking begins is never extended at more than 2–5 grains around starting point [1]. The location of breaking beginning is dictated by the loads concentration and can be extremely diverse as a position and hard to distinguish in the successive stages of the propagation or increase cracking. The location of breaking beginning is placed in a parallel plan with the direction of shear load. At continuous repetitive loads, the cracks direction is changed perpendicular to the direction of elastic load. After which the initial crack is formed, it becomes a load concentrator, which tends to drive the crack deeper in metal with every repetition of load.

The local loads at the pick of the cracking are extremely high because the cracking and any open crack causes the deepening of the crack. The striations are really thin and it appears at a certain time and although they a certain shape, specific to the breakage through thermal fatigue. At the propagation of fatigue cracking, a continuous reducing of section area is observed, which weakens the material until in the end the breakage is complete. In the end,

The SMAs are very sensitive at fatigue. In addition to the phenomena encountered at classic crystalline materials, the SMAs have additional mechanisms tied to phase change which characterized it. These mechanisms are regrouped in a way of thermal fatigue and three ways

In most of the applications, according temperatures, applied load, imposed deformation and Ms transformation temperature, the various mechanisms which control the fatigue process are

Improving life and breaking of SMAs. The break type depends on the application mode of mechanical fatigue. At superelasticity, the break is generally intergranular. The improving life

hysteresis, and the mechanical education accentuate it, but very lightly.

the breakage can be ductile or fragile or a combination between the two.

6. Causes of properties degradation

of mechanical fatigue, which are defined in Table 1.

combined and the phenomenon becomes very complex.

ning there are small cracks, which increase under the action of fluctuant loads.

To determine the thermal fatigue of a SMA, a traction deformation (εm) is performed, after is subjected to a number heating and cooling cycles, without load, and then it is loaded to traction with the same deformation (εm) and is checked through thermal dilatometry the recovery deformation through heating (Figure 4).

Taking into account the precipitation produced through aging, the value of recovery deformation will decrease. At traction load for a remanent deformation (εm), the elastic recovery should be taken into account.

Depending on the number of points needed on the thermal fatigue diagram, a specific number of samples are subjected to thermal cycles. Then a sample is extracted and subjected to dilatometric test after a deformation (εm). Considering that the SMA has double sense component, a test of memory degradation through thermal fatigue (Figure 5) can be done.

For this purpose, the deformed sample with ε<sup>m</sup> value is subjected to thermal cycles on dilatometer following the recovery deformation value without load (Figure 6).

The heating range of the heating cycle must contain the critical points. Through this method, it is measured the memory component from heating process through free recovery and the deformation component at cooling. To determine, this property is used a single sample.

## 5. SMAs fatigue

In the case of a device in which the memory element makes double sense shape memory effect (DSSME) in the system, fatigue resistance limit is defined through the number of cycles until the recovery load decreases at a minimum value (usually 70% from initial value).

SMA can present various phenomena of irreversible deterioration of microstructure and which define specific categories of fatigue. Therefore, in the case of conventional behavior and superelasticity, although there is a difference because of martensitic transformation induced under load, the same type of mechanical fatigue occurs. In the case of education through DSSME, if the applied load is maintained constantly, the fatigue phenomenon is thermal. In the case when the applied load is modifying SME, thermal-mechanical fatigue appears.

Mechanical fatigue involves breaking cracks in four stages: (1) defects accumulation; (2) cracks formation; (3) cracks propagation, in stationary and unsteady regime; (4) final breaking.

On the other hand, when more different SMAs, CuZnAl type, are mechanically educated at room temperature until the same load, was found that the alloys have the resistance to mechanical fatigue lower their Ms are lower. For SMAs, CuZnAl type, the resistance to mechanical fatigue is higher in a martensitic state. This fact is explained by the high fragility of austenite grains limits, that is a particularity of SMAs, CuZnAl type.

To increase the resistance to mechanical fatigue, is applied a hot rolling, followed a quenching in water, through the grains limits gets an irregular shape. During mechanical education, this shape is recovering, absorbing an extra energy, thanks to which the tenacity of the limits is improved. The main method of enhancing the resistance at mechanical fatigue of SMA is grains finishing. The thermal fatigue is tied especially by the irreversible forming of defects, which leads to a considerable hardening in the case of a binary, biphasic brass (Cu-40%Zn).

In the case of CuZnAl SMA, the mechanical education affects the critical temperatures of transformation, but in much lower ways than the thermal one. The influences of the two types of education are opposite, such that the thermal education strongly reduced the temperature hysteresis, and the mechanical education accentuate it, but very lightly.

Fatigue cracking is the phenomenon which leads to breakage at a repeated or fluctuating load, which is smaller than the elastic material load. Fatigue breaking is progressive, at the beginning there are small cracks, which increase under the action of fluctuant loads.

The place where the cracking begins is never extended at more than 2–5 grains around starting point [1]. The location of breaking beginning is dictated by the loads concentration and can be extremely diverse as a position and hard to distinguish in the successive stages of the propagation or increase cracking. The location of breaking beginning is placed in a parallel plan with the direction of shear load. At continuous repetitive loads, the cracks direction is changed perpendicular to the direction of elastic load. After which the initial crack is formed, it becomes a load concentrator, which tends to drive the crack deeper in metal with every repetition of load.

The local loads at the pick of the cracking are extremely high because the cracking and any open crack causes the deepening of the crack. The striations are really thin and it appears at a certain time and although they a certain shape, specific to the breakage through thermal fatigue. At the propagation of fatigue cracking, a continuous reducing of section area is observed, which weakens the material until in the end the breakage is complete. In the end, the breakage can be ductile or fragile or a combination between the two.

## 6. Causes of properties degradation

memory property manifests. The test for the determination of this property consists in determination of maximum recovery deformation, after a number of applied thermal cycles (Figure 3).

To determine the thermal fatigue of a SMA, a traction deformation (εm) is performed, after is subjected to a number heating and cooling cycles, without load, and then it is loaded to traction with the same deformation (εm) and is checked through thermal dilatometry the

Taking into account the precipitation produced through aging, the value of recovery deformation will decrease. At traction load for a remanent deformation (εm), the elastic recovery

Depending on the number of points needed on the thermal fatigue diagram, a specific number of samples are subjected to thermal cycles. Then a sample is extracted and subjected to dilatometric test after a deformation (εm). Considering that the SMA has double sense compo-

For this purpose, the deformed sample with ε<sup>m</sup> value is subjected to thermal cycles on dila-

The heating range of the heating cycle must contain the critical points. Through this method, it is measured the memory component from heating process through free recovery and the deformation component at cooling. To determine, this property is used a single sample.

In the case of a device in which the memory element makes double sense shape memory effect (DSSME) in the system, fatigue resistance limit is defined through the number of cycles until

SMA can present various phenomena of irreversible deterioration of microstructure and which define specific categories of fatigue. Therefore, in the case of conventional behavior and superelasticity, although there is a difference because of martensitic transformation induced under load, the same type of mechanical fatigue occurs. In the case of education through DSSME, if the applied load is maintained constantly, the fatigue phenomenon is thermal. In the case when the applied load is modifying SME, thermal-mechanical fatigue appears.

Mechanical fatigue involves breaking cracks in four stages: (1) defects accumulation; (2) cracks formation; (3) cracks propagation, in stationary and unsteady regime; (4) final breaking.

On the other hand, when more different SMAs, CuZnAl type, are mechanically educated at room temperature until the same load, was found that the alloys have the resistance to mechanical fatigue lower their Ms are lower. For SMAs, CuZnAl type, the resistance to mechanical fatigue is higher in a martensitic state. This fact is explained by the high fragility

of austenite grains limits, that is a particularity of SMAs, CuZnAl type.

the recovery load decreases at a minimum value (usually 70% from initial value).

nent, a test of memory degradation through thermal fatigue (Figure 5) can be done.

tometer following the recovery deformation value without load (Figure 6).

recovery deformation through heating (Figure 4).

should be taken into account.

24 Shape-Memory Materials

5. SMAs fatigue

The SMAs are very sensitive at fatigue. In addition to the phenomena encountered at classic crystalline materials, the SMAs have additional mechanisms tied to phase change which characterized it. These mechanisms are regrouped in a way of thermal fatigue and three ways of mechanical fatigue, which are defined in Table 1.

In most of the applications, according temperatures, applied load, imposed deformation and Ms transformation temperature, the various mechanisms which control the fatigue process are combined and the phenomenon becomes very complex.

Improving life and breaking of SMAs. The break type depends on the application mode of mechanical fatigue. At superelasticity, the break is generally intergranular. The improving life of these alloys imposes to reduce the internal tensions between grains and increasing their resistance to cracking.

resistance, its basic function is memorizing. The fatigue resistance will consider the loss of the

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

http://dx.doi.org/10.5772/intechopen.77991

27

The equipment used for testing the resistance at mechanical fatigue, reproduces the loads at which are subjects the parts in exploitation. The equipments used for testing the resistance at thermal fatigue study the modifications that appear in a sample subjected to a thermal load

The study of optimal exploitation time of an parts made from SMAs is necessary for the knowledge of the exploitation time in maximum parameters. This study proposes the necessity to realize thermal and mechanical combined loads for fatigue tests. The samples for the tests are samples with standard dimensions and will be subjected to traction, being caught between

According to the weights attached to lever system, the sample will be loaded with a load directly proportionally with the weight placed (4.5 kg). The proportionality is obtained through a lever system. The alloy has certain mechanical resistance properties, which can be altered through fatigue in cyclic exploitation conditions. The sample will be heated and cooled cyclic, in 40–150C temperatures interval, with an installation which blow hot or cold air. The heating time is 4 min

An important problem of this installation is the synchronization of thermal cycle with mechanical cycle, an important fact in the case of SMAs and the study of their thermal-mechanical

The prototype installation for thermal-mechanical fatigue tests (Figure 8) respect the principles of functioning for testing installation at mechanical and thermal fatigue. The control of parameters and result recording are made automatically with computer and XMEM original soft-

Elaboration is a first step in obtaining process of shape memory alloy. The elaboration procedures are different according to the alloy type or the tracked properties. The alloy elaboration was made in an induction furnace, with graphite crucible (Figure 9a), using high purity

–104 cycles, and the

grippers. The samples load is made by mechanical means (Figure 7).

and cooling time is 2 min. The cycle's number (N) needed for a sample is 103

exploitation time for realizing of these cycles is in the order of tens of hours.

memorizing capacity in cyclic load conditions.

(heating-cooling).

fatigue phenomenon.

alloying elements.

1. Elaboration of shape memory alloy

Figure 7. Shape and dimensions of samples used for experiments.

ware.

To obtain these results, the following factors must be realized: (1) creating a rolling texture, which reducing the orientation differences between grains; (2) possibility to obtain of plastic deformation at grains limit level; (3) heat treatment to reduce the grains size and phase uniformization of structure; (4) decreasing of the martensite plates (Table 2).

Regarding the standard chemical composition and the values of specific mechanical characteristics of SMAs, Cu-based alloy, little information is found. Some specific conditions to obtain SMAs are distinguishing: (1) chemical compositions which variants between very tied limits; (2) obtaining of alloy from high purity components with very strict limitation of impurities; (3) low physical and chemical anisotropy in the alloy volume, and (4) optimal correlation of elaboration and thermal-mechanical treatment parameters. Most of the SMAs obtaining method contain three steps: (1) elaboration-forging; (2) primary heat treatment; (3) obtaining of hot and cold shapes.

Analyzing (1) SMAs types, (2) shape memory properties, and (3) obtaining costs were chosen for the study of the thermo-mechanical fatigue on Cu-based alloys. Between the Cu-based alloys, CuZnAl types were chosen, that is, Cu75Zn18Al6.

The thermal-mechanical fatigue phenomenon of SMA cannot be avoided. Although in the two structural states (martensite and austenite), the alloy has certain properties of mechanical



Table 1. Ways of thermal and mechanical fatigue at SMA.

Table 2. Values of fatigue resistance coefficients.

resistance, its basic function is memorizing. The fatigue resistance will consider the loss of the memorizing capacity in cyclic load conditions.

The equipment used for testing the resistance at mechanical fatigue, reproduces the loads at which are subjects the parts in exploitation. The equipments used for testing the resistance at thermal fatigue study the modifications that appear in a sample subjected to a thermal load (heating-cooling).

The study of optimal exploitation time of an parts made from SMAs is necessary for the knowledge of the exploitation time in maximum parameters. This study proposes the necessity to realize thermal and mechanical combined loads for fatigue tests. The samples for the tests are samples with standard dimensions and will be subjected to traction, being caught between grippers. The samples load is made by mechanical means (Figure 7).

According to the weights attached to lever system, the sample will be loaded with a load directly proportionally with the weight placed (4.5 kg). The proportionality is obtained through a lever system. The alloy has certain mechanical resistance properties, which can be altered through fatigue in cyclic exploitation conditions. The sample will be heated and cooled cyclic, in 40–150C temperatures interval, with an installation which blow hot or cold air. The heating time is 4 min and cooling time is 2 min. The cycle's number (N) needed for a sample is 103 –104 cycles, and the exploitation time for realizing of these cycles is in the order of tens of hours.

An important problem of this installation is the synchronization of thermal cycle with mechanical cycle, an important fact in the case of SMAs and the study of their thermal-mechanical fatigue phenomenon.

The prototype installation for thermal-mechanical fatigue tests (Figure 8) respect the principles of functioning for testing installation at mechanical and thermal fatigue. The control of parameters and result recording are made automatically with computer and XMEM original software.

1. Elaboration of shape memory alloy

of these alloys imposes to reduce the internal tensions between grains and increasing their

To obtain these results, the following factors must be realized: (1) creating a rolling texture, which reducing the orientation differences between grains; (2) possibility to obtain of plastic deformation at grains limit level; (3) heat treatment to reduce the grains size and phase

Regarding the standard chemical composition and the values of specific mechanical characteristics of SMAs, Cu-based alloy, little information is found. Some specific conditions to obtain SMAs are distinguishing: (1) chemical compositions which variants between very tied limits; (2) obtaining of alloy from high purity components with very strict limitation of impurities; (3) low physical and chemical anisotropy in the alloy volume, and (4) optimal correlation of elaboration and thermal-mechanical treatment parameters. Most of the SMAs obtaining method contain three steps: (1) elaboration-forging; (2) primary heat treatment; (3) obtaining

Analyzing (1) SMAs types, (2) shape memory properties, and (3) obtaining costs were chosen for the study of the thermo-mechanical fatigue on Cu-based alloys. Between the Cu-based

The thermal-mechanical fatigue phenomenon of SMA cannot be avoided. Although in the two structural states (martensite and austenite), the alloy has certain properties of mechanical

Martensite formation through

max(N = 105 cycles) 75 MPa 250 MPa 100 MPa 150 MPa emax simple effect 4% 8% 5% 10% N = 10<sup>3</sup> 2% 3% 3% 6% N = 104 1% 2% 2% 4% emax double effect 2% 5% 2% — N = 102 1% — 1.2% — N = 103 0.8% 1% 0.8% —

Classic fatigue in austenitic

Policristalyne Monocristalyne

state

uniformization of structure; (4) decreasing of the martensite plates (Table 2).

Fatigue T < Mf Af <T<Ms T>Ms

contraction

alloys, CuZnAl types were chosen, that is, Cu75Zn18Al6.

Thermal Thermal education in stability domain of the two phases

Solicitation cycles CuZnAl NiTi CuAlNi

max—maximum load; emax—maximum effect; N—cycles number of load.

Table 2. Values of fatigue resistance coefficients.

Table 1. Ways of thermal and mechanical fatigue at SMA.

resistance to cracking.

26 Shape-Memory Materials

of hot and cold shapes.

Mechanical Reorient of martensite variants

s

s

Elaboration is a first step in obtaining process of shape memory alloy. The elaboration procedures are different according to the alloy type or the tracked properties. The alloy elaboration was made in an induction furnace, with graphite crucible (Figure 9a), using high purity alloying elements.

Figure 7. Shape and dimensions of samples used for experiments.

Figure 8. The prototype installation for thermal-mechanical fatigue tests. (1) control panel; (2) rigid metallic frame; (3, 4) bearings and levers system for mechanical load; (5) counter-weight; (6) motor-reducing gear-arm assembly for lift the weights; (7) weights; (8) comparator watch; (9) heating enclosure housing; (10) SMA test sample; (11) grippers; (12) fixed fastening system.

At elaboration temperature, the interaction between metallic charge and furnace atmosphere consist from oxidation reactions or gases dissolution. The elaboration stages are the following: (1) copper introducing in crucible; (2) after copper melting, aluminum adding; (3) zinc adding.

The melting temperature is limited to 1200C to reduce the evaporation losses. There is a risk of zinc burning and dissolution of resulted gases in the metallic bath. The protection of metallic bath against oxidation was made with borax (Na2B4O7).

After homogenization of alloy in graphite crucible (Figure 9a), heating in induction furnace with high frequencies (8000 Hz), the alloy is casted in a metallic die (Figure 9b) and was obtained the samples (Figure 9c).

2. Experimental determination of chemical composition

The analysis of chemical composition on cast samples was made on Foundry Masters spectrometer, 01 J0013 type [4]. With WASLAB software and the extensible calibration programs, is obtained an analysis bulletin, which present the determined values (Table 3).

The presence of chemical compounds is distinguished with the formula:

Figure 9. (a) Graphite crucible; (b) metallic dies for SMA casting; (c) cast samples.

which was coupled with EDX detector, QUANTAX QX2 type [8].

4. Structural analysis of sample in cast state through optical and SEM microscopy

Optical analysis of microstructure for studied alloy was made on a metallographic microscope, AxioObserver D1m type [7]. The SEM microscopy was made on VEGA II LSH microscope,

Cu\* Zn\* Al\* Fe Co Si Ni Ag As Mn 75.4 18.6 5.85 0.021 0.015 0.026 0.005 0.002 0.008 0.073

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

http://dx.doi.org/10.5772/intechopen.77991

29

The Cu75Zn18Al6 alloy presents various types of martensite, with parallel plates, zig-zag and

• copper-zinc Cu5Zn8 in 53%

Table 3. Chemical composition (%).

\*

arrow heads (Figures 11 and 12).

• aluminum-copper Al4Cu9 in 47%

Conventional notation of studied alloy—Cu75Zn18Al6.

Through the quantitative spectral analysis, we want to have the certainty that the resulted percentages of alloying elements from sample are in the limits imposed for charge. In the calculation of charge was considered that impurifying elements exist: Fe (0.021–0.033), Co (<0.015), Si (0.009–0.026), Ni (< 0.005), Ag (0.002), As (0.008–0.01), Mn (0.02–0.08).

3. Diffractometric analysis of sample in cast state

The diffractometric analysis was made on X-ray diffractometer, XPert Pro Philips Analytical type [5]. The obtained results are presented in Figure 10.

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys http://dx.doi.org/10.5772/intechopen.77991 29

Figure 9. (a) Graphite crucible; (b) metallic dies for SMA casting; (c) cast samples.


Conventional notation of studied alloy—Cu75Zn18Al6.

Table 3. Chemical composition (%).

At elaboration temperature, the interaction between metallic charge and furnace atmosphere consist from oxidation reactions or gases dissolution. The elaboration stages are the following: (1) copper introducing in crucible; (2) after copper melting, aluminum adding; (3) zinc adding. The melting temperature is limited to 1200C to reduce the evaporation losses. There is a risk of zinc burning and dissolution of resulted gases in the metallic bath. The protection of metallic

Figure 8. The prototype installation for thermal-mechanical fatigue tests. (1) control panel; (2) rigid metallic frame; (3, 4) bearings and levers system for mechanical load; (5) counter-weight; (6) motor-reducing gear-arm assembly for lift the weights; (7) weights; (8) comparator watch; (9) heating enclosure housing; (10) SMA test sample; (11) grippers; (12) fixed

After homogenization of alloy in graphite crucible (Figure 9a), heating in induction furnace with high frequencies (8000 Hz), the alloy is casted in a metallic die (Figure 9b) and was

The analysis of chemical composition on cast samples was made on Foundry Masters spectrometer, 01 J0013 type [4]. With WASLAB software and the extensible calibration programs, is

Through the quantitative spectral analysis, we want to have the certainty that the resulted percentages of alloying elements from sample are in the limits imposed for charge. In the calculation of charge was considered that impurifying elements exist: Fe (0.021–0.033), Co

The diffractometric analysis was made on X-ray diffractometer, XPert Pro Philips Analytical

obtained an analysis bulletin, which present the determined values (Table 3).

(<0.015), Si (0.009–0.026), Ni (< 0.005), Ag (0.002), As (0.008–0.01), Mn (0.02–0.08).

bath against oxidation was made with borax (Na2B4O7).

2. Experimental determination of chemical composition

3. Diffractometric analysis of sample in cast state

type [5]. The obtained results are presented in Figure 10.

obtained the samples (Figure 9c).

fastening system.

28 Shape-Memory Materials

The presence of chemical compounds is distinguished with the formula:


Optical analysis of microstructure for studied alloy was made on a metallographic microscope, AxioObserver D1m type [7]. The SEM microscopy was made on VEGA II LSH microscope, which was coupled with EDX detector, QUANTAX QX2 type [8].

The Cu75Zn18Al6 alloy presents various types of martensite, with parallel plates, zig-zag and arrow heads (Figures 11 and 12).

Figure 10. Chemical compounds distribution for Cu75Zn18Al6 alloy, in cast state.

#### 5. Thermal conductivity analysis of cast sample

The measurements of thermal conductivity were made because the SMAs are used in applications like actuators, fact which impose the correct establish of the values for this coefficient and his mode by electric activation. TCi system [6] determines directly the thermal conductivity and other parameters, for different types of materials: solids, liquids, powders, foams. The achieved analyses are nondestructive, and for tests they are necessary small samples (Table 4).

The Cu75Zn18Al6 alloy present a good thermal conductivity in cast state, the medium value is fit in the limits which are specific to the copper alloys casted in parts.

6. Hot plastic deformation

Thermal conductivity

(W/mK)

thickness of material, to ensure a mono-phasic structure.

Figure 12. SEM microscopy, cast state, HNO3 30% attack, (1000).

Table 4. Thermal conductivity for sample in cast state.

Figure 13c presents the forged sample during plastic deformation.

The presence of chemical compounds is distinguished with the formula:

7. Diffractometric analysis of sample in forged state (Figure 14)

For structure finishing, the cast samples are subjected to a hot plastic deformation. The heating temperatures for plastic deformation is 850 10C, with maintain period by 0.5 h/25 mm

Caloric capacity (J/kgK) 437.750 438.040 438.059 438.059 438.058 438.058 438.054 438.056 438.051 438.052

No. 1 2 3 4 5 6 7 8 9 10

43.900 41.140 40.450 40.650 40.300 40.310 40.950 40.850 41.050 41.050

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys

http://dx.doi.org/10.5772/intechopen.77991

31

The plastic deformation was made in 850–800C thermal interval, what is means the obtaining of deformation grade through repeating the plastic deformation operation (10–20 cycles).

Figure 11. Optical microscopy, cast state, HNO3 30% attack, (100).

Aspects Regarding Thermal-Mechanical Fatigue of Shape Memory Alloys http://dx.doi.org/10.5772/intechopen.77991 31

Figure 12. SEM microscopy, cast state, HNO3 30% attack, (1000).


Table 4. Thermal conductivity for sample in cast state.

#### 6. Hot plastic deformation

5. Thermal conductivity analysis of cast sample

30 Shape-Memory Materials

Figure 11. Optical microscopy, cast state, HNO3 30% attack, (100).

Figure 10. Chemical compounds distribution for Cu75Zn18Al6 alloy, in cast state.

fit in the limits which are specific to the copper alloys casted in parts.

The measurements of thermal conductivity were made because the SMAs are used in applications like actuators, fact which impose the correct establish of the values for this coefficient and his mode by electric activation. TCi system [6] determines directly the thermal conductivity and other parameters, for different types of materials: solids, liquids, powders, foams. The achieved analyses are nondestructive, and for tests they are necessary small samples (Table 4). The Cu75Zn18Al6 alloy present a good thermal conductivity in cast state, the medium value is

> For structure finishing, the cast samples are subjected to a hot plastic deformation. The heating temperatures for plastic deformation is 850 10C, with maintain period by 0.5 h/25 mm thickness of material, to ensure a mono-phasic structure.

> The plastic deformation was made in 850–800C thermal interval, what is means the obtaining of deformation grade through repeating the plastic deformation operation (10–20 cycles). Figure 13c presents the forged sample during plastic deformation.

7. Diffractometric analysis of sample in forged state (Figure 14)

The presence of chemical compounds is distinguished with the formula:

Figure 13. (a) Heating furnace and forged parts; (b) forging of cast; (c) hot forged sample (850–900C).

Figure 14. Chemical compounds distribution for Cu75Zn18Al6 alloy, in a forged state.


8. Structural analysis of sample in forged state through optical and SEM microscopy (Figures 15 and 16)

The same martensitic structure, mixed, with different shapes: parallel plates, arrow head, is found and also in the case of forged sample.

9. Thermal conductivity analysis of samples in forged state (Table 5)

The hot plastic deformation has a lower influence on thermal conductivity; the measured values are falling in specific limits of SMA, based on cooper, found in different stages of processing through plastic deformation and obtaining of parts.

10. Heat treatment of quenching to put in solution

Table 5. Thermal conductivity for sample in forged state.

Thermal conductivity

(W/mK)

Figure 16. SEM microstructure, in forged state, HNO3 30% attack, (5000).

Figure 15. Optical microstructure, in forged state, HNO3 30% attack, (100).

The forged samples were processed through machining at standard dimensions according to the experimental tests. These samples are subjected to quenching heat treatment. The

Caloric capacity (J/kgK) 438.015 437.853 437.713 437.662 437.569 437.592 437.500 437.428 437.442 437.268
