Fatigue behavior of duplex-treated samples coated with Cr(C,N) film

The effect of a Cr(C,N) PVD coating on the fatigue behavior of 42CrMo4 steel grade was investigated both in a quenched and tempered condition and after nitriding treatment. The latter, so-called “duplex process”, combines a nitriding pre-treatment in order to obtain a hard and stiff substrate and a PVD coating in order to reduce the friction coefficient and improve the wear resistance of tools and mechanical components. Prior to fatigue testing, the surface modifications were characterized by means of X-ray diffraction (XRD), residual stress distribution, Vickers nano-hardness measurements and scanning electron microscopy (SEM) analysis. For the quenched and tempered steels, the PVD coating acts as a high compressive residual stressed zone able to increase the fatigue resistance of the coated component. On the contrary, for the duplex-treated samples, a limited increase in the fatigue limit was detected with respect to uncoated nitrided samples. This result was interpreted by means of the residual stress gradient which does not show high differences for nitrided coated and uncoated samples.