Low-temperature plasma nitriding of AISI 304 stainless steel with nano-structured surface layer

A nanostructured surface layer was produced on an AISI 304 stainless steel plate by means of a surface mechanical attrition treatment (SMAT). Low-temperature plasma nitriding of the SMAT stainless steel sample was investigated in comparison with the coarse-grained sample by using structural analysis (X-ray diffraction, scanning electron microscopy, and transmission electron microscopy) as well as mechanical property measurements. It shows a much thicker nitrided layer is formed on the SMAT sample relative to that in the coarse-grained counterpart nitrided under the same condition. The nitrided layer in the SMAT sample is composed of nanostructured austenite expansion and martensite expansion with high supersaturations of nitrogen. The surface hardness and the hardened surface layer thickness, as well as the abrasive and the adhesive wear resistances of the nitrided SMAT sample are much enhanced relative to the nitrided coarse-grained sample.