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Plasma nitriding has become a powerful tool to improve wear resistance of stainless steels and sustain or improve corrosion resistance with an adequate selection of process parameters. In this work, the short treatment route with temperatures above 400°C was selected for AISI 420 stainless steel. After the nitriding process, a wide nitrided layer, with good wear and corrosion properties was simultaneously obtained with selected parameters. A 5 hours treatment at 420 °C resulted in a 10 μm nitrided layer. XRD revealed an expanded Fe-α layer with Fe nitrides but no signal of CrN was found. Wear resistance was improved three and four times in erosion and sliding tests compared to the non-nitrided material. Corrosion resistance was tested in anodic polarization experiments in a NaCl solution. In this test, the samples treated in the short time process presented the best results.

Martensitic AISI 420 stainless steel was plasma nitrided using a DC N2 – H2 pulsed discharge, after thermal treatment at two different tempering temperatures. Sliding wear behavior was determined by means of a ball-on-disk tribometer at room temperature and without lubrication. Wear volume was calculated from the information provided by an optical profilometer and wear scars were analyzed by Scanning Electron Microscopy. The results indicated that the nitrided samples exhibited improved wear resistance when compared to the untreated specimens, but corrosion resistance was diminished due to the presence of the outer nitrided layer. However, when this layer was removed mechanically considerable improvement in the corrosion resistance was achieved without impairing the wear resistance of the whole system, which was 200 % higher compared to the wear resistance of the non-nitrided specimens.

Diamond-like-carbon films (DLC) are hard coatings with a very low friction coefficient, a high wear resistance and chemically inert. However, these coatings have adhesion problems on metallic substrates, because the high residual stresses in the DLC films cause failure of the interface between the film and the substrate. Different methods have been tested to improve the adhesion: deposition of interlayers, multilayer coatings between the substrate and the DLC film have been used as interface, chemical and physical modifications of the carbon coating or diffusion treatments of substrate surface.Plasma nitriding is a well-established method to harden stainless steels and can act as a pretreatment to increase adhesion and improve tribological behaviour of the DLC coating. Hopwever, the characteristics and phases of the nitrided layer can influence on the adhesion and the mechanical behaviour of the system. In this work, the mechanical behaviour of a DLC film deposited over non-nitrided and nitride martensitic stainless steel with two different surface finishing is studied.