Role and effect of mechanical polishing on the enhancement of the duplex mechanical attrition/plasma nitriding treatment of AISI 316L steel

This paper analyses a recently developed duplex process combining a Surface Mechanical Attrition Treatment (SMAT) with low-temperature plasma nitriding. The thickness of the nitrided layer significantly increased by adding a polishing step between SMAT and plasma nitriding at 425°C for AISI 316 austenitic steel. Contrarily it was also observed that without this polishing step the hardness decreased and the thickness and the homogeneity of the nitrided layer diminished with respect to the standard duplex process. The reason for this phenomenon is not well understood.