Influence of atomic and mechanical attrition on low temperature plasma nitriding of ferrous alloys

AISI 316 austenitic stainless steel samples were plasma nitrided in variable process times at low temperature (300 deg. C). Two different pretreatments were performed where ball milling (mechanical attrition) and argon plasma (atomic attrition) were used in order to study their posterior effects on plasma nitriding. X-ray diffraction, scanning electron microscopy and nano-indentation experiments were performed for characterization before and after plasma nitriding. Mechanical attrition produces a phase transformation of the original crystalline structure while atomic attrition creates preferential planes in the same crystalline structure. After plasma nitriding and although both pretreatments increase the hardness, the atomic attrition shows the highest hardness values. The mechanical attrition decreases the nitrided layer thickness due to surface oxidation that creates a potential barrier for nitrogen incorporation.