Effect of Multilayered Structure on Properties of Ti/TiN Coating

Metal nitride hard coatings, such as TiN and TiAlN are widely used to protect materials because of their higher hardness and wear properties. However, these coatings always contain a high degree of internal stress which could arouse adhesion problems. It is hard to synthesize monolayer TiN or TiAlN coatings thicker than 10 μm by PVD (physical vapor deposition). The multilayer composite structure, offering efficient means of controlling residual stress, is a successful way to synthesize thicker hard coatings. In the present study, a series of multilayer composite Ti/TiN coatings with different composite periods were synthesized by plasma enhanced ion plating and the effects of multilayered structure mechanical properties of the coating was studied. The result shows that the mechanical properties of the coating are strengthened with increasing the periods of composite Ti/TiN layer. The micro hardness (HV0.25) can reach to about 27 500 MPa and better toughness and higher thickness (≥50 μm) are obtained. The toughness of the coating is almost directly proportional to hardness. Meanwhile, the tribological performance of the coating is improved with a lower dry friction coefficient (about 0.35) and higher wear resistance by alternating 48 periods of Ti/TiN layer. However, the bonding strength of the coating is weakened with further increasing the period of Ti/TiN layer due to the weak interface of coating and substrate.