Stainless steel is widely applied in industrial practice thanks to its good corrosion resistance. Nitriding enables a hard and wear resistant layer to be formed and if the process is conducted below 500°C the layers maintain good corrosion resistance thanks to formation of “expanded austenite” or “expanded martensite” . Good corrosion resistance and biocompatibility of the layers together with their high wear resistance makes this process particularly interesting for medical purposes, both for implant and medical equipment and tools. However, these applications demand particular mechanical properties, which should minimise the chance that during exploitation hard wear particles will be formed. Moreover, in specific applications (e.g. implants) the deformation of the layers under load could not produce the sharp and brittle asperities on the surface, which could increase the wear of counterpart. The mechanical properties of the nitrided layers depend mainly on the nitrogen content, which can be controlled by process parameters. The main purpose of this work was to investigate the mechanical properties of gas nitrided layers with various nitrogen contents produced on stainless steel. The nanoidentation and scratch tests were used in combination with GDOES and EMPA techniques. The investigations were particularly focus on determination of the relationship between the mechanical properties (young modulus and hardness) and nitrogen content, which can be used for modelling the layers behaviours under load condition. The several hardness tests were performed from upper surface (continuous stiffness measurement technique) as well as on the cross-sections of the layers. The results were analysed on the base of nitrogen profiles, to overcome two main technical problems: - soft matrix influence (5-times harder layer than matrix) and – gradient nitrogen distribution in the layer. The surface deformation and topography were investigated by atomic force microscopy.

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1. AFM/MFM studies of low temperature nitrided layers on austenitic steel
2. Microstructural changes in upper surface of austenitic steel under low energy plasma