Effect of Ti interlayer on mechanical properties of TiZrN coatings on D2 steel

The objective of this study was to investigate the effect of Ti interlayer on the stress relief and mechanical properties of TiZrN coatings with thickness up to 3 μm. TiZrN coatings with 250-nm Ti interlayer (TiZrN/Ti) were deposited on AISI D2 steel substrate using unbalanced magnetron sputtering. In addition to TiZrN/Ti specimens, two more sets of specimens were prepared for comparison, namely, TiN and TiZrN monolayer coatings. The results showed that Ti interlayer can enhance the (111) preferred orientation of the thinner TiZrN coatings (≤1 μm); however, the preferred orientations of the thicker coatings (>1 μm) showed weak dependence on the Ti interlayer. The stresses in the TiZrN top layer, Ti interlayer and steel substrate were respectively measured using cos2αsin2ψ X-ray diffraction method. The results indicated that the stress in the top TiZrN layer was relieved by both Ti interlayer and the steel substrate for most of the TiZrN/Ti specimens, except for the specimen with 0.53 μm TiZrN, where the stress in the top TiZrN layer was mainly relieved by Ti interlayer. The stress relief reached a maximum in sample with 1.46 μm TiZrN. Then, the stress in TiZrN increased with the film thickness up to 3 μm, where the stress relief was mainly by the steel substrate. The results of scratch test showed that Ti interlayer could increase the adhesive strength. The wear resistance cannot be evaluated by individually considering residual stress or coating thickness. Instead, the elastic stored energy (Gs) combining the residual stress and coating thickness is a better index for evaluating the wear resistance of hard coatings. Adding a Ti interlayer may increase the wear resistance for coatings ≤1 μm; however, the wear resistance may decrease for thicker TiZrN coatings (>1.5 μm) due to the increase of Gs which decreases the capacity in absorbing the external input energy.