*3.3.2 Prediction energy wear coefficient*

Investigations at various loads and slip amplitudes confirm that there exists a correlation between the wear volume extension of the TiAlZrN/TiAlN/TiAl multilayer coating and dissipated energy. For all the different loading conditions previously defined in Section 2.4, **Figure 12** shows the rates of the wear volume as a function of the dissipated energy. The used volume is measured using a 3D optical profilometer, and the dissipated energy is estimated directly by the area of the fretting loop for each cycle. As a separate form of this behavior, when the energy approach is applied, all of the test parameters are represented by the one and only linear equation from which a single overall energy wear coefficient (α = slope of the curve ) can be detreminated for each antagonist. In fact, the energy coefficient represents the slope of the straight line which connects the lost volume and the energy dissipated by friction: VLost = αEd. In the case under consideration, αTiAlZrN = 104 μm3 /J, and TiAlCN coating provides an energetic wear coefficient of αTiAlCN = 23.103 μm3 /J [3].

This result shows that the TiAlZrN coating improves its higher capacity to wear in fretting. The principal factors favoring this tendency are generally related to the presence of compression residual stress, the decrease of friction coefficient, the increase of superficial hardness, and the roughness effect of the surface [20]. Without measuring the residual stress, the contribution of the reduction of friction coefficient and the increase in hardness are confirmed in this study. One can notice as in **Figure 13** that hard coatings quickly give rise to particle detachment and prevent the partial slip regime by accommodating the displacement in the powder bed, and favor debris formation. A large amount of debris has been observed during fretting tests, and coatings are damaged by material transfer due to adhesion and/or abrasion. It can be seen that a small amount of debris remains within the contact area, while a large amount of debris is ejected outside and located near to the border of the fretting scar. However, fretting scars have three characteristic regions, which are clearly visible for the multilayered TiAlZrN/TiAlN/TiAl coating; central convex region with slight abrasion traces, outer annular region covered with debris, and transition region where the abrasion traces parallel to the sliding direction can be easily identified. **Figure 14** compares the energetic wear coefficients with those reported in the literature [3, 20, 21]. Magnetron-sputtered TiAlZrN coatings in the as-deposited condition possess a better fretting wear resistance (104 μm3 /J) than TiAlCN coatings (23 μm3 /J) for tests performed in ambient air. According to energetic considerations, the multilayered TiAlZrN coatings improve the resistance to fretting wear by a factor 6.5, compared with non-coated steel [3]. But the TiAlCN multilayer has a lower performance as it improves the resistance only by a factor of 2.8. This result is acceptable since the addition of Al, Zr forms stable oxides, especially Zr, which forms a very thin oxide layer similar to Al2O3 [2, 21, 22, 26] that strongly influences the energetic wear coefficient and provides good tribological properties [2].

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and is stable.

*Fretting Wear Performance of PVD Thin Films DOI: http://dx.doi.org/10.5772/intechopen.93460*

In this work, we reviewed the deposition parameters and properties of titanium and titanium-aluminum-based quaternary coatings. It is found that the effect of the individual as well as multiple alloying elements are manifested in further modifying the properties of (Ti, Al) N coatings. Research and developments on simple binary and ternary coatings in previous studies are discussed. This was followed by the investigations on quaternary multicomponent coatings (TiAlZrN/TiAlN/TiAl and TiAlCN/TiAlN/TiAl); the behaviors in these coatings in fretting wear are compared. The main conclusions are the following. The local card solicitation obtained for the two layers of quaternary studied shows the delimitation of both sliding rates. It is shown that the gross slip regime region (GSR) of the coated AISI4140 steel is extended by the presence of the TiAlZrN layer in comparison with the TiAlZrN layer. These results are being very useful in the tribology. Indeed, the GSR is always associated to wear, but the partial slip regime (PSR) is accompanied to a crack that can be disastrous and leads to the failure. To reduce the instantaneous friction coefficient and stabilized friction coefficient, it is necessary to choose the coating-based zirconium coating instead of the coating-based carbon. In general, the stability of the coefficient of friction observed under the fretting conditions tested for a PVD coating was linked to the presence of a third multilayer body: a first layer consisting of particles mainly of submicron size; a second, discontinuous lamellar layer; and a third layer consisting of particles having a microstructure with ultrafine grains (refinement). In steady state, the third body formed easily remains trapped in contact. The third body, less than 50 μm thick, protects the surface (reduced wear)

*Energy wear rates of different substrates and hard coatings in fretting wear tests [27].*

However, the gap between these two coatings is governed by the amplitude of the loading parameters. The thin coatings formed by physical vapor deposition may provide an initial friction reduction but it is not sufficiently durable for this application. However, the beneficial effect of the PVD coatings on fretting wear diminishes with increasing normal force and decreasing fretting stroke. In this chapter, the worn volume of the two quaternary layers is very influenced by loading conditions. Therefore, special attention should be given to better distinguish the effect of zirconium. Adding Zr improves the wear resistance of Al-Ti-N coating. Zr stabilizes Ti-Al-N lattice and also forms a very thin stable oxide layer similar to Al2O3. These two effects together enhance the wear resistance of the Ti-Al-Zr-N coatings. The

**4. Conclusion**

**Figure 14.**

**Figure 13.** *Wear volume as a function of cumulated dissipated energy.*

**Figure 14.**

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

condition possess a better fretting wear resistance (104 μm3

considerations, the multilayered TiAlZrN coatings improve the resistance to fretting wear by a factor 6.5, compared with non-coated steel [3]. But the TiAlCN multilayer has a lower performance as it improves the resistance only by a factor of 2.8. This result is acceptable since the addition of Al, Zr forms stable oxides, especially Zr, which forms a very thin oxide layer similar to Al2O3 [2, 21, 22, 26] that strongly influences the energetic wear coefficient and provides good tribological

/J) for tests performed in ambient air. According to energetic

coatings (23 μm3

properties [2].

/J) than TiAlCN

This result shows that the TiAlZrN coating improves its higher capacity to wear in fretting. The principal factors favoring this tendency are generally related to the presence of compression residual stress, the decrease of friction coefficient, the increase of superficial hardness, and the roughness effect of the surface [20]. Without measuring the residual stress, the contribution of the reduction of friction coefficient and the increase in hardness are confirmed in this study. One can notice as in **Figure 13** that hard coatings quickly give rise to particle detachment and prevent the partial slip regime by accommodating the displacement in the powder bed, and favor debris formation. A large amount of debris has been observed during fretting tests, and coatings are damaged by material transfer due to adhesion and/or abrasion. It can be seen that a small amount of debris remains within the contact area, while a large amount of debris is ejected outside and located near to the border of the fretting scar. However, fretting scars have three characteristic regions, which are clearly visible for the multilayered TiAlZrN/TiAlN/TiAl coating; central convex region with slight abrasion traces, outer annular region covered with debris, and transition region where the abrasion traces parallel to the sliding direction can be easily identified. **Figure 14** compares the energetic wear coefficients with those reported in the literature [3, 20, 21]. Magnetron-sputtered TiAlZrN coatings in the as-deposited

**330**

**Figure 13.**

*Wear volume as a function of cumulated dissipated energy.*

*Energy wear rates of different substrates and hard coatings in fretting wear tests [27].*
