**2.2 Measurement of tribological parameters**

During the friction process, a complex system is formed in the actual contact areas. This system possesses a number of specific properties which differ from the properties of the contacting body materials when considered separately, without contact during friction. Apparently, to obtain reliable data correlating with the main factors of friction and wear, it is necessary to assess the properties of the contact area directly. However, there are several reasons which make it difficult to measure the tribological parameters directly during the operation of actual products at elevated temperature of the contact forces. Some specific features of the abovementioned reasons are as follows:


It should be noted that while two surfaces are sliding, the tangential contact force is being affected not only by shear strength of adhesive bonds, but also the deformation component of the friction force [30]. The contacting surfaces (especially those subject to wear) can have significant roughness and be heterogeneous in their physical and mechanical properties due to the polycrystalline structure. Thus, the deformation component of the tangential contact force can have a significant influence on the tribological properties of products, but its direct determination in


**Table 1.**

*The samples depending on the turntable rotation frequency.*

the friction process is associated with significant difficulties [30]. It is practically impossible to separate the deformation component from the total tangential forces and thus obtain an adhesion component, especially at an elevated contact temperature, and that fact makes it almost impossible to determine the strength of adhesive bonds immediately during the process of metal cutting [31].

Based on the above, it is physical modeling, which makes it possible to determine the tribological characteristics under conditions most closely simulating the conditions of the cutting area, is the most accurate and effective way to find the indicators of the adhesive interaction between the tool and the material being machined.

The proposed method is based on a physical model [25] (**Figure 1**), which reflects with sufficient accuracy the actual conditions of friction and wear at a local contact in the cutting area. In accordance with this model, a spherical indenter 2 made of a coated tool material (imitating an individual asperity of a contact spot of solids subject to friction), compressed by two plane-parallel counterbodies 1 made of the material being machined (with high precision and cleanliness of the contacting surfaces) rotates under load around its own axis. The force *Fexp*, spent on the rotation of the indenter and applied to the cable 3, laid in a groove of the disk 4, is mainly related to the shear strength τnn of adhesive bonds.

The shear strength τ*<sup>n</sup>* of adhesive bonds is found as follows:

$$
\pi\_n = \frac{3}{4} \frac{F\_{\text{exp}}}{\pi} \frac{R\_{\text{exp}}}{r\_{\text{ind}}^3} \tag{1}
$$

The COF consists of two components, i.e. an adhesion component, which results from the solid body molecular interaction in the actual contact area, and a deformation component, which result from the surface layer deformation on solid bodies during the friction process [31]. In [25], the proposed model demonstrated that the forces to rotate the indenter were mainly related to the shear stress of the adhesive (interatomic and intermolecular) bonds, while in this case, no deformation component of the tangential forces was actually detected. Under the conditions of seizure, no deformation or fracture occur on the contact surface during the sliding, while the detected maximum tangential stresses reflect the hardness of near-surface layer of the softest body out of all the contacting bodies. In case when no seizure occurs, the above stresses are related to the dissipation of energy expended to break the

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on…*

The adhesion (molecular) component of the COF may be defined as follows:

To apply the above method under the conditions of elevated temperatures, a special adhesiometer was developed, which allowed heating the contact area to a temperature of up to 1100°C and providing the typical temperature distribution over the depth of the contacting bodies [25]. Certain shortcomings of the above method include the relatively low rates of deformation and relative sliding. However, in terms of temperature, load, and contact cleanliness, this method is able to simulate well enough the actual conditions of friction and adhesion in the

The indenter is a double-sided spherical cylinder with the radius of 2.5 mm and

After the counterbody and the indenter have been installed, the contact area is heated up to the operating temperature, and then the load N is applied, under the influence of which the indenter with the radius sphere *r1* penetrates into the counterbody surface to the depth *h*. Thus, the plastic contact takes place, and

The accepted loads in combination with low roughness of the contacting surfaces provide both the required area of actual contact between the indenter and the counterbody and the elimination of the formed oxide and sorbed films and the contacting of metal surfaces close to juvenile. At the same time, the oxygen penetration into the contact area is minimized due to the high density of the contact between the indenter and the counterbody. The experiments were carried out at different values of the contact temperature *θ*. Thus, the relationships of τ*<sup>n</sup>* = *f* (*pr*) are obtained for different values of *θ*. The data on the value of τ*<sup>n</sup>* were obtained after the experiment had been repeated three times, with the probable deviation not

The microstructures of the coated samples, including I-a – Ti-TiN-(Ti,Cr,Al,Si)N; I-b – Zr-ZrN-(Nb,Zr,Cr,Al)N; and I-c – Zr-ZrN-(Zr,Al,Si)N, are shown in **Figure 2**. The coatings are nanostructured, the thicknesses of the nanolayers are 30–80 nm, and

The microstructures of the coated samples under the study are depicted in

*Rexp rind*

(3)

*<sup>f</sup> adh* <sup>¼</sup> *<sup>τ</sup><sup>n</sup> pn* ¼ 3 4 *Fexp N*

bonds formed during the contact of the bodies.

*DOI: http://dx.doi.org/10.5772/intechopen.93973*

the height of 25 mm made of tool material (carbide).

external friction is detected during the punch rotation [31].

where *N* is the load applied (N).

cutting area.

exceeding 5%.

**Figure 2** [3].

**155**

**3. Results and discussion**

the total coating thickness reaches about 3 μm.

where *Fexp* is the circumferential force on the disc, rotating the indenter;

*Rexp* is the radius of the disk in which the indenter is fixed; and.

*rind* is the radius of the indent on the samples.

Due to the small dimension of the indenter, it possible to make an assumption about the normal stresses acting on the sphere surface as constant and equal in the entire indentation area (a purely plastic contact).

The above normal stresses are determined as follows:

$$p\_n = \frac{N}{\pi \, r\_{ind}^2} \tag{2}$$

#### **Figure 1.**

*Friction contact model considered by [3, 4, 25, 31]. 1 – Two plane-parallel counterbodies; 2 – Spherical indenter; 3 – Cable; 4 – Disk; 5 – Copper plates; 6 – Thermal pads; N – Load applied.*

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on… DOI: http://dx.doi.org/10.5772/intechopen.93973*

The COF consists of two components, i.e. an adhesion component, which results from the solid body molecular interaction in the actual contact area, and a deformation component, which result from the surface layer deformation on solid bodies during the friction process [31]. In [25], the proposed model demonstrated that the forces to rotate the indenter were mainly related to the shear stress of the adhesive (interatomic and intermolecular) bonds, while in this case, no deformation component of the tangential forces was actually detected. Under the conditions of seizure, no deformation or fracture occur on the contact surface during the sliding, while the detected maximum tangential stresses reflect the hardness of near-surface layer of the softest body out of all the contacting bodies. In case when no seizure occurs, the above stresses are related to the dissipation of energy expended to break the bonds formed during the contact of the bodies.

The adhesion (molecular) component of the COF may be defined as follows:

$$f\_{adh} = \frac{\tau\_n}{p\_n} = \frac{3}{4} \frac{F\_{exp}}{N} \frac{R\_{exp}}{r\_{ind}} \tag{3}$$

where *N* is the load applied (N).

the friction process is associated with significant difficulties [30]. It is practically impossible to separate the deformation component from the total tangential forces and thus obtain an adhesion component, especially at an elevated contact temperature, and that fact makes it almost impossible to determine the strength of adhesive

Based on the above, it is physical modeling, which makes it possible to determine the tribological characteristics under conditions most closely simulating the conditions of the cutting area, is the most accurate and effective way to find the indicators of the adhesive interaction between the tool and the material being

The proposed method is based on a physical model [25] (**Figure 1**), which reflects with sufficient accuracy the actual conditions of friction and wear at a local contact in the cutting area. In accordance with this model, a spherical indenter 2 made of a coated tool material (imitating an individual asperity of a contact spot of solids subject to friction), compressed by two plane-parallel counterbodies 1 made

contacting surfaces) rotates under load around its own axis. The force *Fexp*, spent on the rotation of the indenter and applied to the cable 3, laid in a groove of the disk 4,

> *Rexp r*3 *ind*

(1)

(2)

of the material being machined (with high precision and cleanliness of the

*<sup>τ</sup><sup>n</sup>* <sup>¼</sup> <sup>3</sup> 4 *Fexp π*

*Rexp* is the radius of the disk in which the indenter is fixed; and.

where *Fexp* is the circumferential force on the disc, rotating the indenter;

Due to the small dimension of the indenter, it possible to make an assumption about the normal stresses acting on the sphere surface as constant and equal in the

> *pn* <sup>¼</sup> *<sup>N</sup> π r*<sup>2</sup> *ind*

*Friction contact model considered by [3, 4, 25, 31]. 1 – Two plane-parallel counterbodies; 2 – Spherical*

*indenter; 3 – Cable; 4 – Disk; 5 – Copper plates; 6 – Thermal pads; N – Load applied.*

is mainly related to the shear strength τnn of adhesive bonds. The shear strength τ*<sup>n</sup>* of adhesive bonds is found as follows:

*rind* is the radius of the indent on the samples.

entire indentation area (a purely plastic contact).

The above normal stresses are determined as follows:

bonds immediately during the process of metal cutting [31].

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

machined.

**Figure 1.**

**154**

To apply the above method under the conditions of elevated temperatures, a special adhesiometer was developed, which allowed heating the contact area to a temperature of up to 1100°C and providing the typical temperature distribution over the depth of the contacting bodies [25]. Certain shortcomings of the above method include the relatively low rates of deformation and relative sliding. However, in terms of temperature, load, and contact cleanliness, this method is able to simulate well enough the actual conditions of friction and adhesion in the cutting area.

The indenter is a double-sided spherical cylinder with the radius of 2.5 mm and the height of 25 mm made of tool material (carbide).

After the counterbody and the indenter have been installed, the contact area is heated up to the operating temperature, and then the load N is applied, under the influence of which the indenter with the radius sphere *r1* penetrates into the counterbody surface to the depth *h*. Thus, the plastic contact takes place, and external friction is detected during the punch rotation [31].

The accepted loads in combination with low roughness of the contacting surfaces provide both the required area of actual contact between the indenter and the counterbody and the elimination of the formed oxide and sorbed films and the contacting of metal surfaces close to juvenile. At the same time, the oxygen penetration into the contact area is minimized due to the high density of the contact between the indenter and the counterbody. The experiments were carried out at different values of the contact temperature *θ*. Thus, the relationships of τ*<sup>n</sup>* = *f* (*pr*) are obtained for different values of *θ*. The data on the value of τ*<sup>n</sup>* were obtained after the experiment had been repeated three times, with the probable deviation not exceeding 5%.

### **3. Results and discussion**

The microstructures of the coated samples, including I-a – Ti-TiN-(Ti,Cr,Al,Si)N; I-b – Zr-ZrN-(Nb,Zr,Cr,Al)N; and I-c – Zr-ZrN-(Zr,Al,Si)N, are shown in **Figure 2**. The coatings are nanostructured, the thicknesses of the nanolayers are 30–80 nm, and the total coating thickness reaches about 3 μm.

The microstructures of the coated samples under the study are depicted in **Figure 2** [3].

the deeper deformation of contact layers depends [F1, F2]). **Figures 4** and **5** exhibit

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on…*

relationships demonstrate that the shear stresses *τnn* first increase for all the samples under study and then decrease with an increasing temperature. At the same time, for the sample with the Zr-ZrN-(Nb,Zr,Cr,Al)N coating, the shear stresses *τnn* initially grow noticeably with an increase in temperature, but when the temperature exceeds 400°C, they begin to decrease, while the process intensity grows with an increase in temperature. In particular, the conducted experiments found that at temperature of 400°C, for samples of carbide WC–Co, the parameter of *τnn* was significantly (almost by 2 times) higher for a sample with the Zr-ZrN-(Nb,Zr,Cr, Al)N coating compared to uncoated samples, but at temperature above 400°C, an uncoated sample demonstrated higher τnn. The samples with the Ti-TiN-(Ti,Cr,Al, Si)N coating demonstrated the lowest relationship between τnn and temperature among all the samples under the study. With an increasing temperature, τnn first increases slightly; however, when at temperatures exceeding 300°C, the parameter of τnn starts decreasing with an increase in temperature. It should be noted that at the maximum temperature of 550°C, τnn is approximately equal to τnn at room

*Influence of temperature on tribotechnical properties of tribopair in the "steel AISI 321–carbide (WC-Co) with coating" interface [3]. 1 – Uncoated sample; 2 – Zr-ZrN-(Zr,Al)N coating; 3 –Ti-TiN-(Ti,Cr,Al,Si)N*

*Influence of temperature on tribotechnical properties of tribopair in the "steel S31600–carbide (WC-Co) with coating" interface [3]. 1 – Uncoated; 2 – Zr-ZrN-(Zr,Al)N coating; 3 – Ti-TiN-(Ti,Cr,Al,Si)N coating;*

*Prn*, and temperature. The above

curves reflecting the relationship between *τnn*, *Prn*, *<sup>τ</sup>nn*

*DOI: http://dx.doi.org/10.5772/intechopen.93973*

temperature.

**Figure 4.**

**Figure 5.**

**157**

*4 – Zr-ZrN-(Nb,Zr,Cr,Al)N coating.*

*coating; 4 –Zr-ZrN-(Nb,Zr,Cr,Al)N coating.*

#### **Figure 2.**

*The structure of the coated samples under the study. a – Ti-TiN-(Ti,Cr,Al,Si)N coating; b – Zr-ZrN-(Nb,Zr, Cr,Al)N coating; c – Zr-ZrN-(Zr,Al,Si)N coating [3]; I-c – Zr-ZrN-(Zr,Al,Si)N coating. 1 –WC-Co substrate; 2 – adhesion sublayer; 3 – transitional layer; 4 – internal zone of wear-resistant layer; 5 – intermediate sublayer; 6 – external zone of wear-resistant layer.*

The results of the studies of the nanolayer coating Ti-TiN-(Ti,Al,Cr)N structure (samples of Group II) are presented in **Figure 3** [4].

As seen from **Figure 3**, all the coatings under study have a nanolayer structure. The experiments found the nanolayer thicknesses, which ranged from 10 nm to 302 nm, depending on the coating type. The earlier studies [4,34,35] revealed that each nanolayer of the II-a coating had a complex structure, formed due to the planetary rotation of the toolset during the deposition process [4, 25, 32]. In [4, 25], it is also found that the coatings with the nanolayer thicknesses of 70–10 nm also have a similar complex structure. At the same time, the nanolayers of the II-a and II-c coatings affect the formation of the crystalline structure, and the growth of crystals during the deposition is limited by the boundaries of one nanolayer. The IId and II-e coatings demonstrate the growth of crystals, which is not limited by the nanolayer boundaries.

The experiments have been conducted at temperatures ranging from 20 to 550°C to investigate the influence of temperature on the tribotechnical properties of tribopairs in the "the material being machined–carbide with wear-resistant complex" interface (shear strength τnn of adhesive bond, normal stress on contact *Prn*, and relation *<sup>τ</sup>nn Prn*, actually representing the adhesion component of the COF, on which

**Figure 3.**

*The nanolayer structure of coatings on samples (TEM) [4]. a – λ = 304 nm, b - λ = 70 nm, c - λ = 53 nm, d - λ = 10 nm.*

## *The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on… DOI: http://dx.doi.org/10.5772/intechopen.93973*

the deeper deformation of contact layers depends [F1, F2]). **Figures 4** and **5** exhibit curves reflecting the relationship between *τnn*, *Prn*, *<sup>τ</sup>nn Prn*, and temperature. The above relationships demonstrate that the shear stresses *τnn* first increase for all the samples under study and then decrease with an increasing temperature. At the same time, for the sample with the Zr-ZrN-(Nb,Zr,Cr,Al)N coating, the shear stresses *τnn* initially grow noticeably with an increase in temperature, but when the temperature exceeds 400°C, they begin to decrease, while the process intensity grows with an increase in temperature. In particular, the conducted experiments found that at temperature of 400°C, for samples of carbide WC–Co, the parameter of *τnn* was significantly (almost by 2 times) higher for a sample with the Zr-ZrN-(Nb,Zr,Cr, Al)N coating compared to uncoated samples, but at temperature above 400°C, an uncoated sample demonstrated higher τnn. The samples with the Ti-TiN-(Ti,Cr,Al, Si)N coating demonstrated the lowest relationship between τnn and temperature among all the samples under the study. With an increasing temperature, τnn first increases slightly; however, when at temperatures exceeding 300°C, the parameter of τnn starts decreasing with an increase in temperature. It should be noted that at the maximum temperature of 550°C, τnn is approximately equal to τnn at room temperature.

#### **Figure 4.**

The results of the studies of the nanolayer coating Ti-TiN-(Ti,Al,Cr)N structure

*The structure of the coated samples under the study. a – Ti-TiN-(Ti,Cr,Al,Si)N coating; b – Zr-ZrN-(Nb,Zr, Cr,Al)N coating; c – Zr-ZrN-(Zr,Al,Si)N coating [3]; I-c – Zr-ZrN-(Zr,Al,Si)N coating. 1 –WC-Co substrate; 2 – adhesion sublayer; 3 – transitional layer; 4 – internal zone of wear-resistant layer; 5 –*

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

As seen from **Figure 3**, all the coatings under study have a nanolayer structure. The experiments found the nanolayer thicknesses, which ranged from 10 nm to 302 nm, depending on the coating type. The earlier studies [4,34,35] revealed that each nanolayer of the II-a coating had a complex structure, formed due to the planetary rotation of the toolset during the deposition process [4, 25, 32]. In [4, 25], it is also found that the coatings with the nanolayer thicknesses of 70–10 nm also have a similar complex structure. At the same time, the nanolayers of the II-a and II-c coatings affect the formation of the crystalline structure, and the growth of crystals during the deposition is limited by the boundaries of one nanolayer. The IId and II-e coatings demonstrate the growth of crystals, which is not limited by the

The experiments have been conducted at temperatures ranging from 20 to 550°C

*Prn*, actually representing the adhesion component of the COF, on which

to investigate the influence of temperature on the tribotechnical properties of tribopairs in the "the material being machined–carbide with wear-resistant complex" interface (shear strength τnn of adhesive bond, normal stress on contact *Prn*,

*The nanolayer structure of coatings on samples (TEM) [4]. a – λ = 304 nm, b - λ = 70 nm, c - λ = 53 nm,*

(samples of Group II) are presented in **Figure 3** [4].

*intermediate sublayer; 6 – external zone of wear-resistant layer.*

nanolayer boundaries.

and relation *<sup>τ</sup>nn*

**Figure 3.**

**156**

*d - λ = 10 nm.*

**Figure 2.**

*Influence of temperature on tribotechnical properties of tribopair in the "steel AISI 321–carbide (WC-Co) with coating" interface [3]. 1 – Uncoated sample; 2 – Zr-ZrN-(Zr,Al)N coating; 3 –Ti-TiN-(Ti,Cr,Al,Si)N coating; 4 –Zr-ZrN-(Nb,Zr,Cr,Al)N coating.*

#### **Figure 5.**

*Influence of temperature on tribotechnical properties of tribopair in the "steel S31600–carbide (WC-Co) with coating" interface [3]. 1 – Uncoated; 2 – Zr-ZrN-(Zr,Al)N coating; 3 – Ti-TiN-(Ti,Cr,Al,Si)N coating; 4 – Zr-ZrN-(Nb,Zr,Cr,Al)N coating.*

The specific features of the variation of the adhesion (molecular) component *fadh* of the COF with an increase in temperature were considered. Coated samples demonstrated noticeably lower values of *fadh* compared to an uncoated sample, at all temperatures and for all types of carbides. Meanwhile, *fadh* reaches its maximum at temperature of about 400–450°C, and after that, *fadh* begins to decrease. The sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating demonstrated the lowest value of the adhesion (molecular) component fadh of the COF. However, when the limit temperature of 550°C is reached, fadh decreases sharply for the sample with the Zr-ZrN- (Nb,Zr,Cr,Al)N coating. Thus, at temperature of 550°C, the samples with the both coatings under consideration demonstrate approximately the same values of *fadh*, while the substantially lower value of *fadh* was detected for the uncoated sample. The conducted experiments make it possible to predict that with a further increase in temperature, the sample with the Zr-ZrN-(Nb,Zr,Cr,Al)N coating will demonstrate the minimum value of *fadh*.

While studying the variation of *fadh* upon the contact with the counterbody made of S31600 steel (**Figure 5**), it is possible to notice that the dynamics of the change in *fadh* is similar for all the samples under consideration: the value of *fadh* first increases, but begins to decrease after a certain temperature is reached. However, for different samples, the value of *fadh* begins to fall at different temperatures. In particular, for the sample with the ZrN-(Nb,Zr,Cr,Al)N coating, fadh begins to decrease when the temperature reaches 750°C, while for the sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating – at temperature of 850°C. If upon the contact with the counterbody made of American Iron and Steel Institute (AISI) 321 steel, the sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating exhibits the minimum value of *fadh* in a range from 300 to 550°C, then upon the contact with the counterbody made of S31600 steel, the sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating demonstrates the highest value of fadh among all the samples under consideration. Meanwhile, the remaining samples showed largely the same dynamics of the variation in *fadh* for counterbodies made of the both materials under consideration.

temperatures above 800°C, while for the coatings with larger values of λ (II-a, II-b, and II-c), the oxidation processes start already at a temperature of 700°C. Thus, it can be concluded that a smaller value of λ provides better resistance to thermal oxidation, due to an increased number of interlayer interfaces inhibiting the processes of ther-

*The results of the investigation into the tribological properties of the samples II in the "steel AISI 1045–carbide (WC-Co) with coating" interface [4]: A – Normal stresses* **Prn***; b – Strengths on cut* **τn***; c – Coefficient of friction*

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on…*

*DOI: http://dx.doi.org/10.5772/intechopen.93973*

There is a significant difference between the tribological characteristics of the II-d and II-e samples. In particular, when the value of λ decreases from 16 nm (II-d) to 10 nm (II-e), the value of *fadh* increases significantly, and the most significant difference in *fadh* is demonstrated by the II-d and II-e samples in the temperature range from 800 to 900°C. When the above temperatures are reached, the spinodal decomposition of the (Ti,Al,Cr)N phase begins, accompanied by the formation of a soft hexagonal AlN phase and also a release of pure Ti,Al and Cr [4, 11]. The interlayer interfaces can slow down the formation of the decomposition zone, although, if the value of λ is too small, this effect becomes significantly weaker, and as a result, more intense spinodal decomposition is detected for the II-e sample and less intense – for the II-d sample. **Figure 7** depicts the influence of λ on the adhesion component *fadh* of the COF. Based on the obtained approximating curves, it is possible to distinguish two distinct extrema of *fadh*, including the maximum in a range of λ = 70–53 nm and the minimum in a range of λ = 16–10 nm. A decrease in the value of λ from 16 to 10 nm leads to a noticeable increase in *fadh* at all the temperatures under consideration. Temperature has a significant influence on the value of *fadh* and the nature of its

variation depending on the value of λ. Based on the data presented in **Figure 7**, three temperature ranges can be distinguished, characterized by the different influence of the nanolayer period λ on the adhesion component *fadh* of the COF. When temperatures are within a range from 500 to 600°C, the influence of λ on *fadh* is not significant, and the maximum values of *fadh* are typical for coatings with

At temperatures of 700–900°C, the influence of λ on fadh enhances noticeably. There is a significant decline in the value of *fadh* with a decrease in λ from 53 to

the maximum (302 nm) and minimum (10 nm) values of λ.

mal destruction of the surface layer of the coating [4, 11].

**Figure 6.**

**159**

**fadh = τn***/***Prn***.*

The results of the investigation into the tribological parameters of the samples II-a – II-e are presented in **Figure 6**.

The investigation of the relationship between the tribological properties and temperature for samples with various coatings demonstrated that with an increase in temperature, the value of *fadh* varies nonmonotonically and is of extreme nature. Within a temperature range from 500 to 800°C, an increase in the parameters of the fictional contact is related to an increase in the adhesive interaction on the contact surface. At 800°C, the adhesion on the contacting surface of friction is maximum, which can negatively affect the wear resistance of the product. The sample with the II-e coating demonstrates the higher value of *fadh*, which begins to decrease at elevated temperatures. This phenomenon can relate to the formation of tribological oxide films (titanium and aluminum oxides), while the thicknesses of the coating layers are of key importance.

The sample with the II-d coating demonstrated the most favorable value of *fadh*, as well as the lowest shear strength *τ<sup>n</sup>* of adhesive bonds. The advantages of this coating are especially clearly demonstrated at temperatures above 600°C. It is important to note that for the samples with the minimum nanolayer thicknesses (II-d and II-e), the value of *fadh* continuously increases up to the temperature of 800°C and then begins to noticeably decrease, and such a decline is especially clear for the II-e coating). For the coatings with large values of the nanolayer period λ (II-a, II-b, and II-c), a decrease of *fadh* is observed at temperatures above 700°C, and such a decline intensifies with a decrease in λ. Such a decrease is least pronounced in the II-a coatings with the maximum nanolayer period λ. Thus, it can be assumed that for the coatings with the minimum value of λ (II-d and II-e), the active oxidation begins at

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on… DOI: http://dx.doi.org/10.5772/intechopen.93973*

#### **Figure 6.**

The specific features of the variation of the adhesion (molecular) component *fadh* of the COF with an increase in temperature were considered. Coated samples demonstrated noticeably lower values of *fadh* compared to an uncoated sample, at all temperatures and for all types of carbides. Meanwhile, *fadh* reaches its maximum at temperature of about 400–450°C, and after that, *fadh* begins to decrease. The sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating demonstrated the lowest value of the adhesion (molecular) component fadh of the COF. However, when the limit temperature of 550°C is reached, fadh decreases sharply for the sample with the Zr-ZrN- (Nb,Zr,Cr,Al)N coating. Thus, at temperature of 550°C, the samples with the both coatings under consideration demonstrate approximately the same values of *fadh*, while the substantially lower value of *fadh* was detected for the uncoated sample. The conducted experiments make it possible to predict that with a further increase in temperature, the sample with the Zr-ZrN-(Nb,Zr,Cr,Al)N coating will demon-

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

While studying the variation of *fadh* upon the contact with the counterbody made of S31600 steel (**Figure 5**), it is possible to notice that the dynamics of the change in *fadh* is similar for all the samples under consideration: the value of *fadh* first increases, but begins to decrease after a certain temperature is reached. However, for different samples, the value of *fadh* begins to fall at different temperatures. In particular, for the sample with the ZrN-(Nb,Zr,Cr,Al)N coating, fadh begins to decrease when the temperature reaches 750°C, while for the sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating – at temperature of 850°C. If upon the contact with the counterbody made of American Iron and Steel Institute (AISI) 321 steel, the sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating exhibits the minimum value of *fadh* in a range from 300 to 550°C, then upon the contact with the counterbody made of S31600 steel, the sample with the Ti-TiN-(Ti,Cr,Al,Si)N coating demonstrates the highest value of fadh among all the samples under consideration. Meanwhile, the remaining samples showed largely the same dynamics of the variation in *fadh* for

The results of the investigation into the tribological parameters of the samples

The investigation of the relationship between the tribological properties and temperature for samples with various coatings demonstrated that with an increase in temperature, the value of *fadh* varies nonmonotonically and is of extreme nature. Within a temperature range from 500 to 800°C, an increase in the parameters of the fictional contact is related to an increase in the adhesive interaction on the contact surface. At 800°C, the adhesion on the contacting surface of friction is maximum, which can negatively affect the wear resistance of the product. The sample with the II-e coating demonstrates the higher value of *fadh*, which begins to decrease at elevated temperatures. This phenomenon can relate to the formation of tribological oxide films (titanium and aluminum oxides), while the thicknesses of

The sample with the II-d coating demonstrated the most favorable value of *fadh*, as well as the lowest shear strength *τ<sup>n</sup>* of adhesive bonds. The advantages of this coating are especially clearly demonstrated at temperatures above 600°C. It is important to note that for the samples with the minimum nanolayer thicknesses (II-d and II-e), the value of *fadh* continuously increases up to the temperature of 800°C and then begins to noticeably decrease, and such a decline is especially clear for the II-e coating). For the coatings with large values of the nanolayer period λ (II-a, II-b, and II-c), a decrease of *fadh* is observed at temperatures above 700°C, and such a decline intensifies with a decrease in λ. Such a decrease is least pronounced in the II-a coatings with the maximum nanolayer period λ. Thus, it can be assumed that for the coatings

with the minimum value of λ (II-d and II-e), the active oxidation begins at

counterbodies made of the both materials under consideration.

strate the minimum value of *fadh*.

II-a – II-e are presented in **Figure 6**.

the coating layers are of key importance.

**158**

*The results of the investigation into the tribological properties of the samples II in the "steel AISI 1045–carbide (WC-Co) with coating" interface [4]: A – Normal stresses* **Prn***; b – Strengths on cut* **τn***; c – Coefficient of friction* **fadh = τn***/***Prn***.*

temperatures above 800°C, while for the coatings with larger values of λ (II-a, II-b, and II-c), the oxidation processes start already at a temperature of 700°C. Thus, it can be concluded that a smaller value of λ provides better resistance to thermal oxidation, due to an increased number of interlayer interfaces inhibiting the processes of thermal destruction of the surface layer of the coating [4, 11].

There is a significant difference between the tribological characteristics of the II-d and II-e samples. In particular, when the value of λ decreases from 16 nm (II-d) to 10 nm (II-e), the value of *fadh* increases significantly, and the most significant difference in *fadh* is demonstrated by the II-d and II-e samples in the temperature range from 800 to 900°C. When the above temperatures are reached, the spinodal decomposition of the (Ti,Al,Cr)N phase begins, accompanied by the formation of a soft hexagonal AlN phase and also a release of pure Ti,Al and Cr [4, 11]. The interlayer interfaces can slow down the formation of the decomposition zone, although, if the value of λ is too small, this effect becomes significantly weaker, and as a result, more intense spinodal decomposition is detected for the II-e sample and less intense – for the II-d sample.

**Figure 7** depicts the influence of λ on the adhesion component *fadh* of the COF. Based on the obtained approximating curves, it is possible to distinguish two distinct extrema of *fadh*, including the maximum in a range of λ = 70–53 nm and the minimum in a range of λ = 16–10 nm. A decrease in the value of λ from 16 to 10 nm leads to a noticeable increase in *fadh* at all the temperatures under consideration.

Temperature has a significant influence on the value of *fadh* and the nature of its variation depending on the value of λ. Based on the data presented in **Figure 7**, three temperature ranges can be distinguished, characterized by the different influence of the nanolayer period λ on the adhesion component *fadh* of the COF.

When temperatures are within a range from 500 to 600°C, the influence of λ on *fadh* is not significant, and the maximum values of *fadh* are typical for coatings with the maximum (302 nm) and minimum (10 nm) values of λ.

At temperatures of 700–900°C, the influence of λ on fadh enhances noticeably. There is a significant decline in the value of *fadh* with a decrease in λ from 53 to

**Figure 7.**

*Relationship between the adhesion component* fadh *of the COF and the nanolayer period λ at different temperatures [4].*

16 nm, and equally significant growth is detected with a further decrease in λ from 16 to 10 nm. At a temperature of 1000°C, a decrease in λ from 302 to 16 nm leads to a continuous decrease in *fadh* and then to a noticeable increase at λ = 10 nm.

can be noticed in the interface area between the steel adherent and the coating. This layer is also characterized by the phenomenon of spinodal decomposition and active diffusion of Fe. The nanolayer structure of the coating was completely destroyed in this area. Below the mentioned layer there is a layer characterized by active growth of coating grains under the influence of the elevated temperature. This layer also contains signs of diffusion of O and Fe, but in much smaller volumes. Finally, below there is an area of the coating with the preserved nanostructure. The area demon-

*Structure of the surface layers in I-a – Ti-TiN-(Ti,Cr,Al,Si)N coating at the boundary with the steel adherent*

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on…*

The study focused on the distribution of chemical elements in the area of the "coating – steel adherent" finds (see **Figure 9**) the presence of diffusing Fe in the surface layers of the coating at a depth not exceeding 200 nm and diffusing O at a depth not exceeding 300 nm from the coating surface. There is also a diffusion of Ti from the coating into the steel adherent to a depth not exceeding 100 nm. Thus, under the influence of such factors as temperature, oxidation, and diffusion of Fe, a

*Study of the oxidation layer. (a) Diagram of research areas (TEM), and (b) distribution of chemical elements*

strates no presence of diffused Fe and O.

*DOI: http://dx.doi.org/10.5772/intechopen.93973*

**Figure 8.**

**Figure 9.**

*by areas.*

**161**

*(TEM) [39].*

The specified temperature ranges can be related to the temperature in the cutting area under various conditions of machining. In particular, temperatures within a range from 500 to 800°C are usually detected at relatively low cutting speeds *vc*, when the mechanisms of adhesive and abrasive wear play a key role, while oxidation and diffusion processes are relatively weakly expressed [33–35]. A range of temperatures within 800–900°C is typical for significantly high cutting speeds, when oxidation and diffusion processes begin to play an important role, and the destruction of the external layers of the coating begins due to spinodal decomposition [11, 36–38]. At the same time, such elevated temperatures trigger the formation of protective oxide films, which have a positive influence on the tribological parameters of the cutting process. A range of temperatures within 900–1000°C is typical during dry cutting at the highest possible cutting speed. At the temperatures within the above range, the oxidation and diffusion processes prevail, and a coating can fail as a result of active oxidation and spinodal decomposition [11, 33–35].

Thus, at relatively low cutting speeds, the best cutting properties can be demonstrated by a tool with the II-d coating, characterized by the minimal tendency to adhesion to the material being machined in combination with the significantly high hardness, which provides good resistance to both adhesive and abrasive wear. During the cutting at high cutting speeds (and, accordingly, elevated temperatures in the cutting area), the best cutting properties can be expected from a cutting tool with the II-e coating, characterized by better resistance to oxidation and propagation of spinodal decomposition due to the maximum number of interlayer interfaces that restrain the indicated phenomena. The II-e coating is also characterized by the highest hardness. Meanwhile, a significantly high value of the adhesion component of the COF for the II-e coating can even play a positive role in the turning of difficult-to-cut materials. This effect can be associated with a decrease in the contact stresses due to an increase in the contact area of the chips with the rake face of the tool at a significantly lower intensity of the increase in the normal forces, acting on the contact area of the rake face, which in turn reduces cracking and brittle fracture in the coated tool [39]. The above assumptions were confirmed by the conducted cutting tests [3, 4]. The processes occurring in the surface layers of the coatings under the simultaneous action of elevated temperature, oxidation, and diffusion were considered in detail using the example of coating I-a – Ti-TiN-(Ti, Cr,Al,Si)N (**Figure 8**) [39]. The formation of a layer with signs of active oxidation

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on… DOI: http://dx.doi.org/10.5772/intechopen.93973*

**Figure 8.**

16 nm, and equally significant growth is detected with a further decrease in λ from 16 to 10 nm. At a temperature of 1000°C, a decrease in λ from 302 to 16 nm leads to

The specified temperature ranges can be related to the temperature in the cutting area under various conditions of machining. In particular, temperatures within a range from 500 to 800°C are usually detected at relatively low cutting speeds *vc*, when the mechanisms of adhesive and abrasive wear play a key role, while oxidation and diffusion processes are relatively weakly expressed [33–35]. A range of temperatures within 800–900°C is typical for significantly high cutting speeds, when oxidation and diffusion processes begin to play an important role, and the destruction of the external layers of the coating begins due to spinodal decomposition [11, 36–38]. At the same time, such elevated temperatures trigger the formation of protective oxide films, which have a positive influence on the tribological parameters of the cutting process. A range of temperatures within 900–1000°C is typical during dry cutting at the highest possible cutting speed. At the temperatures within the above range, the oxidation and diffusion processes prevail, and a coating can fail as a result of active oxidation and spinodal decomposition [11, 33–35]. Thus, at relatively low cutting speeds, the best cutting properties can be demonstrated by a tool with the II-d coating, characterized by the minimal tendency to adhesion to the material being machined in combination with the significantly high hardness, which provides good resistance to both adhesive and abrasive wear. During the cutting at high cutting speeds (and, accordingly, elevated temperatures in the cutting area), the best cutting properties can be expected from a cutting tool with the II-e coating, characterized by better resistance to oxidation and propagation of spinodal decomposition due to the maximum number of interlayer interfaces that restrain the indicated phenomena. The II-e coating is also characterized by the highest hardness. Meanwhile, a significantly high value of the adhesion component of the COF for the II-e coating can even play a positive role in the turning of difficult-to-cut materials. This effect can be associated with a decrease in the contact stresses due to an increase in the contact area of the chips with the rake face of the tool at a significantly lower intensity of the increase in the normal forces, acting on the contact area of the rake face, which in turn reduces cracking and brittle fracture in the coated tool [39]. The above assumptions were confirmed by the conducted cutting tests [3, 4]. The processes occurring in the surface layers of the coatings under the simultaneous action of elevated temperature, oxidation, and diffusion were considered in detail using the example of coating I-a – Ti-TiN-(Ti, Cr,Al,Si)N (**Figure 8**) [39]. The formation of a layer with signs of active oxidation

a continuous decrease in *fadh* and then to a noticeable increase at λ = 10 nm.

*Relationship between the adhesion component* fadh *of the COF and the nanolayer period λ at different*

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

**Figure 7.**

**160**

*temperatures [4].*

*Structure of the surface layers in I-a – Ti-TiN-(Ti,Cr,Al,Si)N coating at the boundary with the steel adherent (TEM) [39].*

can be noticed in the interface area between the steel adherent and the coating. This layer is also characterized by the phenomenon of spinodal decomposition and active diffusion of Fe. The nanolayer structure of the coating was completely destroyed in this area. Below the mentioned layer there is a layer characterized by active growth of coating grains under the influence of the elevated temperature. This layer also contains signs of diffusion of O and Fe, but in much smaller volumes. Finally, below there is an area of the coating with the preserved nanostructure. The area demonstrates no presence of diffused Fe and O.

The study focused on the distribution of chemical elements in the area of the "coating – steel adherent" finds (see **Figure 9**) the presence of diffusing Fe in the surface layers of the coating at a depth not exceeding 200 nm and diffusing O at a depth not exceeding 300 nm from the coating surface. There is also a diffusion of Ti from the coating into the steel adherent to a depth not exceeding 100 nm. Thus, under the influence of such factors as temperature, oxidation, and diffusion of Fe, a

**Figure 9.**

*Study of the oxidation layer. (a) Diagram of research areas (TEM), and (b) distribution of chemical elements by areas.*

surface layer with new special properties, influencing, among other phenomena, a decrease in the value of fadh is being formed in the coating.

**Acknowledgements**

**Conflict of interest**

**Author details**

Alexey Vereschaka<sup>1</sup>

1 IDTI RAS, Moscow, Russia

Nikolay Sitnikov<sup>5</sup>

This study was supported by a grant of the Russian Science Foundation

*The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on…*

[Agreement No. 18–19–00312 dated 20 April 2018].

*DOI: http://dx.doi.org/10.5772/intechopen.93973*

The authors declare no conflict of interest.

\*, Sergey Grigoriev<sup>2</sup>

3 Ulyanovsk State Technical University, Ulyanovsk, Russia

5 National Research Nuclear University MEPhI, Moscow, Russia

6 National University of Science and Technology MISiS, Moscow, Russia

© 2020 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,

4 Ufa State Aviation Technical University, Ufa, Russia

\*Address all correspondence to: dr.a.veres@yandex.ru

provided the original work is properly cited.

**163**

2 Moscow State Technological University STANKIN, Moscow, Russia

, Filipp Milovich<sup>6</sup>

, Vladimir Tabakov<sup>3</sup>

, Nikolay Andreev<sup>6</sup> and Caterine Sotova<sup>2</sup>

, Mars Migranov<sup>4</sup>

,
