Effect of Cr/CrNx transition layer on mechanical properties of CrN coatings deposited on plasma nitrided austenitic stainless steel

In this work, two types of transition layers (pure Cr and gradient CrNx) were fabricated between plasma-assisted nitrided (PAN) stainless steel and magnetron sputtering CrN coating to investigate the effect of transition layer on mechanical properties of CrN coating on PAN stainless steel substrates. For comparison, samples without transition layer were also synthesized. The phase structure, morphology, abrasive resistance and adhesion of the CrN coatings, as well as the nano-hardness and Young's modulus were investigated by XRD, SEM, ball-on-disk tribometer, scratch tester and nano-indentation tester, respectively. The results showed the transition layers of pure Cr and gradient CrNx absorbed the excess nitrogen diffusing outwards from the nitrided layer, and thus suppressed partly the precipitation. As a result, the adhesion force was improved to 22.5 and 25.7 N, respectively. The nano-hardness and Young's modulus of modified layers were improved to the range of 22.8-25.8 GPa and 331-347.3 GPa, corresponding to the substrate of 7.2 GPa and 230.5 GPa. The modified layer with no transition layer had the best wear resistance for nitriding of 1 h; while the layer with gradient CrNx had the best wear resistance for nitriding of 4 h.