First results on duplex coatings without intermediate mechanical treatment

Duplex coatings consisting of a nitrided steel substrate and a CrN PVD layer were produced. Plasma nitriding of the steel was performed at a pressure below 0.01 mbar in commercially available PVD equipment. Microstructural investigations and hardness measurements revealed that both the hardening and the nitriding rate were comparable to those of conventional nitriding processes. Bright nitriding was achieved. Duplex coatings were produced in a single cycle process, depositing the CrN layer after the nitriding treatment without intermediate venting of the vacuum chamber. Smooth duplex coatings were obtained with good adhesion between the nitrided substrate and the PVD layer. In both scratch and impact fatigue tests the duplex coatings produced were superior as compared with CrN coatings deposited on unnitrided steel.