Effect of plasma nitriding on adhesion strength of CrTiAlN coatings on H13 steels by closed field unbalanced magnetron sputter ion plating

A duplex treatment, i.e. plasma nitriding followed by closed field unbalanced magnetron sputter ion plating, is used to strengthen the bonding of CrTiAlN coatings to H13 steels in the paper. A nitride layer is first formed on H13 steel samples by plasma nitriding and then two chromium transition layers are prepared on the surface of the nitrided H13 steels using closed field unbalanced magnetron sputter ion plating. The adhesion between the substrate and the coating is evaluated using the Rockwell indentation and scratch tests. Meanwhile, the composition, phase structure and the morphologies for CrTiAlN coatings as well as the worn surfaces are characterized by EDX, SEM and XRD, respectively. Dry sliding wear behavior of the duplex-treated H13 steels is analyzed by using ball-on-disk wear tests compared with those of untreated and plasma-nitrided H13 steels. The results show that the adhesion strength and wear resistance for duplex-treated coatings increase significantly due to a gradient-hardness support, one favorable gradient of chemical composition, an intermediate hardening effect and a diffusion reaction of the nitrided layer-coating interface.