Evaluation of the mechanical behaviour of a DLC film on plasma nitrided AISI 420 with different surface finishing

DLC films have a high hardness, extremely low friction coefficient, and they are chemically inert. Plasma nitriding can serve as a pre-treatment to increase adhesion and improve tribological performance of the DLC coating. s work, the mechanical and tribological behaviour of a DLC film deposited on martensitic stainless steel is studied. Two different surface finishing techniques were accomplished before the nitriding process: paper grinding and polishing with diamond powder. Plasma nitriding was carried out in a DC pulsed discharge, and the DLC film was deposited by Plasma Assisted CVD. The nitrided layer and film were observed with an optical microscope and SEM. The tribological behaviour was analysed in sliding wear tests and adhesion was tested. The coating was 3 μm thick, and the nitrided layers were about 11 μm in the polished samples and only 8 μm in the grounded ones. The coated samples yielded a better wear resistance than the pre-nitrided samples but only on the polished nitrided samples did the film present an acceptable adhesion.