Preface

This book explores the research results dedicated to obtaining, characterizing, and mathematically modeling composite materials, especially metal matrix composites (MMCs), with superior properties having a wide range of applications.

The book consists of seven chapters allocated between four sections:


Authors from different countries (India, Russia, Slovakia, and the United States) have contributed chapters to this book.

*Chapter 1* focuses on the investigation of biocompatible composites obtained using magnetron sputtering for the production of minimally invasive medical implantation devices (stents). Nano- and microdimensional surface layers of Ta, Ti, Ag, and Cu on flat and wire NiTi, Cu, Ti, and SiO2 substrates are created. Phase composition, surface morphology, and layer-by-layer composition are investigated on an X-ray diffractometer, scanning electron microscope (SEM), and Auger spectrometer. It is shown that the thickness and structure of surface layers are affected by sputtering distance, time, power, and bias voltage at the substrate. The presence of the transition layer that contains both substrate and target elements and provides high adhesion of the surface layer to the substrate is demonstrated. The material is tested for corrosion resistance under static conditions by dipping into solutions with various acidities (from pH 1.68 to pH 9.18) for two years, static mechanical properties and biocompatibility in vitro and in vivo. A slight corrosive dissolution is observed only in a medium at a pH of 1.56. Dissolution in the other media is absent. An increase in strength and plasticity in comparison with substrate is attained depending on the nature of the sputtered substance and substrate. The toxicity of samples is not revealed.

*Chapter 2* contains experimental results on the synthesis and characterization of a polyaniline zinc oxide nanocomposite (PAZO) by different analytical techniques such as FT-IR, XTD, TGA-DTG, SEM, and TEM. Nanocomposite material is further explored for the removal of Cr(VI) from aqueous solution, and the effect of various adsorption parameters such as agitation time, solution pH, adsorbent dose, initial metal ion concentration, and temperature is observed and optimized by preliminary experiments. The adsorption of metal ions is highly pH dependent and the maximum removal efficiencies and adsorption capacities of the selected metal ions are obtained at pH 2. The experimental data are tested using Langmuir, Freundlich, D-R, and Temkin models and the data are best followed by the Langmuir model. The maximum monolayer adsorption capacity is 120.92 mg g–1 at 30°C, 134.22

mg g–1 at 40°C, and 139.47 mg g–1 at 50°C. All kinetic parameters suggest that the adsorption of metal ions by PAZO follows second-order kinetics and chemisorption is the rate-determining step. The positive values of ΔH° and negative value of ΔG° indicate that the adsorption process is endothermic and spontaneous in nature.

*Chapter 3* highlights the fact that Al and its composites are the best-suited materials and have better properties than unreinforced materials. Beneficial properties with reduced prices have enlarged their applications. The chapter consists of a literature survey on Al-based MMCs and especially their physical, mechanical, and wear characteristics. These unique properties (high hardness, high strength, high stiffness, high wear, and abrasion and corrosion resistance) make it possible for Al MMC to be used successfully in defense, aerospace, automotive, aviation, and thermal management areas in engine pistons, cylinder barrels, connecting rods, and elements of vehicle braking systems. Physical and mechanical properties and wear behavior of Al-based metal matrix composites are two subsections of the chapter. One of the examples shown in the chapter consists of the Ni contribution to the wear of Al MMCs. Maximum wear resistance is obtained with the addition of 3 wt% Ni to pure Al under both loads and against both counterfaces. The wear resistance of the alloys increases with increasing Ni content up to 3 wt% Ni and tends to decrease to less than 3 wt% Ni. The wear rate of the Al–xNi alloys increases with increasing applied normal load. Many such examples are presented in this chapter. The work is valuable because it presents many ways of improving the properties of Al MMCs.

*Chapter 4* presents an alternative framework for developing objective and thermodynamically consistent hypoelastic-plastic and hyperelastic-plastic-based material models using the first nonlinear continuum theory of finite deformations of elastoplastic media. The theoretical study contains the following steps: a short overview of the nonlinear continuum mechanical theory for finite deformations of elastoplastic media; modeling of plastic flow in the material; constitutive equations of the material; reference definition of the yield surface; calculation of the plastic multiplier; and the ratio of ductile and total damage increment. Furthermore, the chapter presents numerical and experimental results. The related material models are demonstrated in numerical experiments. The most important implication of the presented theory is that the analysis results of the related models are no longer affected by the description and particularities of the mathematical formulation. Nonlinear continuum theory is also briefly presented, while thermodynamic consistency of the formulation is discussed in detail. Another important implication of the theory is that the dissipated plastic power density of the model can be directly related to the dissipated plastic power density of the specimen coming from the uniaxial tensile stress of the modeled material. Multiscale analyses and multiobjective optimization of thermomechanical properties of composite materials, particularly in a nonlinear regime, still need relevant and computationally efficient models. The models presented in this chapter could be useful in the abovementioned field.

*Chapter 5* is focused on specific research with the goal of producing CERMET fuels for nuclear thermal propulsion (NTP) as an alternative to chemical propulsion. Initially, a brief history of NTP by NASA, including fuel element work, followed by more recent research on various fuel systems under consideration is presented. At present, there are a number of fuels under consideration for NTP. These include graphite composites, tricarbides (U-Zr-Nb)C, and CERMETS (MUO2 and W/UO2, Mo/UO2, W/UN, and Mo/UN). For W/UO2,the loss of uranium from the UO2 particles and subsequent migration into the tungsten matrix can be understood in terms of the generation of oxygen vacancies during sintering in a vacuum environment.

**V**

It is found that various oxides such as ThO2, Ce2O3, and Y2O3 when added to the CERMET powder reduce fuel loss. It is also found that the oxide additives do not increase the solubility of uranium in UO2, but stabilize UO2 against oxygen loss. Two mechanisms are proposed to explain this stabilization: (1) oxide additives lower the partial molar free energy of oxygen in the UO2 without the possibility of forming free uranium upon cooling and (2) with the addition of metal oxide, uranium is transformed to a hexavalent state, which does not reduce to uranium metal. In conclusion, the most likely candidate to stabilize UO2 during sintering and

thermal cycling in hydrogen will be the addition of a rare earth oxide.

materials with aspirations for a better future.

The book is intended for practical engineers, researchers, students, and others dealing with the reviewed problems. We hope that the book will be beneficial to all readers and initiate further inquiries and developments in the field of advanced

On behalf of all the authors, I want to express our gratitude to publishing author service manager Mr. Luka Cvjetkovic for his patience and understanding.

Institute for Nuclear Research, Nuclear Materials and Corrosion Department,

**Dr. Dumitra Lucan**

Bucharest, Romania

Pitesti, Romania

Technologies for Nuclear Energy State Owned Company,

Technical Sciences Academy of Romania ASTR,

It is found that various oxides such as ThO2, Ce2O3, and Y2O3 when added to the CERMET powder reduce fuel loss. It is also found that the oxide additives do not increase the solubility of uranium in UO2, but stabilize UO2 against oxygen loss. Two mechanisms are proposed to explain this stabilization: (1) oxide additives lower the partial molar free energy of oxygen in the UO2 without the possibility of forming free uranium upon cooling and (2) with the addition of metal oxide, uranium is transformed to a hexavalent state, which does not reduce to uranium metal. In conclusion, the most likely candidate to stabilize UO2 during sintering and thermal cycling in hydrogen will be the addition of a rare earth oxide.

The book is intended for practical engineers, researchers, students, and others dealing with the reviewed problems. We hope that the book will be beneficial to all readers and initiate further inquiries and developments in the field of advanced materials with aspirations for a better future.

On behalf of all the authors, I want to express our gratitude to publishing author service manager Mr. Luka Cvjetkovic for his patience and understanding.

**Dr. Dumitra Lucan**

Technologies for Nuclear Energy State Owned Company, Institute for Nuclear Research, Nuclear Materials and Corrosion Department, Pitesti, Romania

> Technical Sciences Academy of Romania ASTR, Bucharest, Romania

**IV**

mg g–1 at 40°C, and 139.47 mg g–1 at 50°C. All kinetic parameters suggest that the adsorption of metal ions by PAZO follows second-order kinetics and chemisorption is the rate-determining step. The positive values of ΔH° and negative value of ΔG° indicate that the adsorption process is endothermic and spontaneous in nature.

*Chapter 3* highlights the fact that Al and its composites are the best-suited materials and have better properties than unreinforced materials. Beneficial properties with reduced prices have enlarged their applications. The chapter consists of a literature survey on Al-based MMCs and especially their physical, mechanical, and wear characteristics. These unique properties (high hardness, high strength, high stiffness, high wear, and abrasion and corrosion resistance) make it possible for Al MMC to be used successfully in defense, aerospace, automotive, aviation, and thermal management areas in engine pistons, cylinder barrels, connecting rods, and elements of vehicle braking systems. Physical and mechanical properties and wear behavior of Al-based metal matrix composites are two subsections of the chapter. One of the examples shown in the chapter consists of the Ni contribution to the wear of Al MMCs. Maximum wear resistance is obtained with the addition of 3 wt% Ni to pure Al under both loads and against both counterfaces. The wear resistance of the alloys increases with increasing Ni content up to 3 wt% Ni and tends to decrease to less than 3 wt% Ni. The wear rate of the Al–xNi alloys increases with increasing applied normal load. Many such examples are presented in this chapter. The work is valuable because it presents many ways of improving the properties of Al MMCs.

*Chapter 4* presents an alternative framework for developing objective and thermodynamically consistent hypoelastic-plastic and hyperelastic-plastic-based material models using the first nonlinear continuum theory of finite deformations of elastoplastic media. The theoretical study contains the following steps: a short overview of the nonlinear continuum mechanical theory for finite deformations of elastoplastic media; modeling of plastic flow in the material; constitutive equations of the material; reference definition of the yield surface; calculation of the plastic multiplier; and the ratio of ductile and total damage increment. Furthermore, the chapter presents numerical and experimental results. The related material models are demonstrated in numerical experiments. The most important implication of the presented theory is that the analysis results of the related models are no longer affected by the description and particularities of the mathematical formulation. Nonlinear continuum theory is also briefly presented, while thermodynamic consistency of the formulation is discussed in detail. Another important implication of the theory is that the dissipated plastic power density of the model can be directly related to the dissipated plastic power density of the specimen coming from the uniaxial tensile stress of the modeled material. Multiscale analyses and multiobjective optimization of thermomechanical properties of composite materials, particularly in a nonlinear regime, still need relevant and computationally efficient models. The models presented in this chapter could be useful in the abovementioned field.

*Chapter 5* is focused on specific research with the goal of producing CERMET fuels for nuclear thermal propulsion (NTP) as an alternative to chemical propulsion. Initially, a brief history of NTP by NASA, including fuel element work, followed by more recent research on various fuel systems under consideration is presented. At present, there are a number of fuels under consideration for NTP. These include graphite composites, tricarbides (U-Zr-Nb)C, and CERMETS (MUO2 and W/UO2, Mo/UO2, W/UN, and Mo/UN). For W/UO2, the loss of uranium from the UO2 particles and subsequent migration into the tungsten matrix can be understood in terms of the generation of oxygen vacancies during sintering in a vacuum environment.

**1**

Section 1

Obtaining and

Characterization

Section 1
