Effect of Ti interlayer thickness on mechanical properties and wear resistance of TiZrN coatings on AISI D2 steel

Abstract

In the tool industry, adding a soft metallic interlayer to enhance the adhesion of hard coatings is a common practice. This study investigated the effect of Ti interlayer thickness on the residual stress, adhesion strength and wear resistance of TiZrN coatings. The feasibility of using stored elastic energy as an index of wear resistance of the coatings was also studied. The effect of Ti interlayer thickness was evaluated by comparing the mechanical properties of TiZrN films with different Ti interlayer thickness, ranging from 50 to 250 nm. The results showed that the increase of interlayer thickness from 50 to 250 nm reduced the stress of the TiZrN coatings from −5.67 to −3.75 GPa. The optimal Ti interlayer thickness to enhance the adhesion strength of the TiZrN coatings with about 2 μm thickness on D2 steel was 150 nm; however, the adhesion was insignificantly improved compared with the specimen without interlayer. Introducing 250 nm Ti interlayer could slightly increase the wear resistance of the TiZrN coating about 16%, but the adhesion strength of the coating decreased about 6%. The insignificant improvement on mechanical properties and wear resistance of the TiZrN coatings by the Ti interlayer were mainly attributed to the high residual stress of TiZrN top layer. For the coatings with high residual stress (>−4.0 GPa), the stress relief by adding a metal interlayer is limited and insufficient to enhance adhesion strength or wear resistance. Other approaches that can directly lower the intrinsic growth stress in hard coatings may be more effective.