Evaluation on wear behavior of Cr–Ag–N and Cr–W–N PVD nanocomposite coatings using two different types of tribometer

Practice has proven that CrN performs better than TiN under some specific tribological applications. Nevertheless, the relatively soft nature of CrN still remains a problem. This paper reports experimental results on increases in hardness of sputtered PVD CrN coatings by means of additions of varying content of Ag or W. The resulting Cr–Ag–N and Cr–W–N coatings, grown on JIS SKH51 steel substrates, were characterized using SEM, EDS, WDS, XRD, micro-indentation hardness testing and scratch adhesion tests. Moreover, wear behavior was studied on two types of tribometer, employing different contact regimes — a ‘cylinder-on-disk’ line-contact reciprocating-sliding regime and a ‘ball-on-disk’ point-contact rotating-sliding regime.The experimental results can be summarized as follows: The hardness of Cr–W–N coatings increased with increasing W content; reversely, that of Cr–Ag–N coatings decreased with increasing Ag content. The additions of Ag and W resulted in a formation of secondary phases, elemental Ag and WN, respectively, uniformly embedded in the CrN coatings. With the two different types of tribometer, the observed trends for wear behavior, wear and friction coefficient, were nearly identical, indicating that both Ag and W additions to CrN coatings were beneficial. However, the Cr–W–N coatings were significantly more wear resistant than the Cr–Ag–N coatings. With the addition of W at 6.8 at.%, the largest wear improvement of 73%–85% was achieved.