Influence of layer number on microstructure, mechanical properties and wear behavior of the TiN/Ti multilayer coatings fabricated by high-power magnetron sputtering deposition

Abstract

In the present research, the TiN/Ti multilayer coatings with different layers were fabricated on Ti6Al4V substrates with same deposition time by high-power DC reactive magnetron sputtering. Their microstructure, phase constituent, mechanical properties and wear behavior were studied to explore the influence of the layer number. The results reveal that increasing of layer number in TiN/Ti multilayer coatings refines the grains and promotes the transformation of the crystal orientation preference of the TiN layer from (111) TiN to a mixture of (111) TiN , (200) TiN and (220) TiN . Moreover, the thickness of the TiN/Ti multilayer coating increases with the increased layer number. The Ti interlayer and TiN layer have a sinuous interface at the atomic scale with many dislocations, and no orientation relationship between these layers is found. With the increasing of layer number, the elastic modulus and hardness of the TiN/Ti multilayer coatings increase firstly and then decrease. The two-layer and four-layer TiN/Ti multilayer coatings obtain the maximum elastic modulus and hardness, respectively. Moreover, the increased layer number improves the adhesion of the TiN/Ti multilayer coating obviously, and the twelve-layer TiN/Ti multilayer coating obtains the highest adhesion, which could be ascribed to the relaxation of interfacial stress. The increased Ti interlayers promote the diversification of the friction coefficient of the TiN/Ti multilayer coatings. With the proceeding of wear test, the friction coefficients of the one-layer and two-layer TiN/Ti multilayer coatings maintain an increasing tendency, but the friction coefficients of the four-layer, eight-layer and twelve-layer TiN/Ti multilayer coatings drop at final, middle and initial stage, respectively. The one-layer, two-layer and four-layer TiN/Ti multilayer coatings have similar wear rates which are less than one twentieth of the wear rate of the Ti6Al4V substrate. While the wear rates of the eight-layer and twelve-layer TiN/Ti multilayer coatings are higher than that of the Ti6Al4V substrate.