Abstract:Metal nitride hard coatings, such as TiN and TiAlN, were widely used to protect materials because of their higher hardness and wearing properties. However, these coatings always contain a high degree of internal stress which could arouse adhesion problems. It’s hard to synthesize monolayer TiN or TiAlN coatings thicker than 10μm by PVD method. The multilayer composite structure, offering an efficient way of controlling residual stress, is an effective way to synthesize thicker hard coatings. In this study, a series of multilayer composite Ti/TiN coatings with different composite periods were synthesized by plasma enhanced ion plating and how the multilayered structure affects the coating’s mechanical properties was studied in detail. The result shows that the coating’s mechanical properties are strengthened as increasing the periods of composite Ti/TiN layer. The micro hardness can reach to about 2750HV0.25 albeit possessing better toughness and higher thickness (i.e.>50?m). The coating’s toughness is almost direct proportional to hardness. And also the coating’s tribological performance is improved with a lower dry friction coefficient (about 0.35) and higher wearing resistance by alternating 48 periods of Ti/TiN layer. However, the coating’s bonding strength is weakened as increasing the period of Ti/TiN layer blindly due to the weak interface of coating and substrate.