**4. Conclusion**

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) and is stable.

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

stability of the energy approach is used to predict the wear kinetics in a volume of tribo-systems: Wv = α × Ed Σ, where, α is the energetic coefficient, Wv is the worn volume, and Ed is the dissipated cumulated energy. The multilayered TiAlZrN/ TiAlN/TiAl coatings improve the resistance to the fretting wear of AISI4140 steel by twice as much as the multilayered TiAlCN/TiAlN/TiAl coatings.

In the light of various experimental investigations, the study of the wear mechanisms of the different films was carried out. It follows that the advantages of a multilayer coating over a single-layer coating are mainly presented in three points:

