On the materials properties of thin film plasma-nitrided austenitic stainless steel

A series of experiments were performed to study the composition and mechanical properties of the surface layers formed on the austenitic stainless steel after plasma nitriding in the temperature range of 400–500 °C with different N2–H2 gas mixtures. The thin layer at the nitrided surface was examined by the glancing-angle XRD and the differential load penetration from the microhardness measurements. The formation of the expanded austenite phase was detected at temperatures below 450 °C and/or 10% N2 in the treatment gas. The distortion of equivalent lattice constant after plasma nitriding was as high as 10%. The modulus of elasticity in the nitrided surface was increased by 33% after the plasma nitriding. The coating-only hardness was measured and it was equivalent to the hardness of coating containing CrN. Thus, it is possible to obtain thin coatings with superior resistance to corrosion and high hardness on the austenitic stainless steel.