Combined plasma carburizing and nitriding of sprayed AISI 316L steel coating for improved wear resistance

Both low-temperature plasma nitriding and carburizing at treatment temperatures below 450 °C are known to increase the surface hardness of a sprayed AISI 316L stainless steel coating to above 1000 HV, while maintaining corrosion resistance, via production of a supersaturated solid solution of expanded austenite, known as the S-phase. In this work, we investigate combined plasma processes for nitriding and carburizing of sprayed AISI 316L coatings. The sequential process, with carburizing first, immediately followed by nitriding, did not produce a significantly thicker S-phase than that produced using plasma nitriding alone. In contrast, the simultaneous process, in which carburizing and nitriding were performed at the same time, was found to form a thick S-phase at 450 °C. Vickers hardness and specific wear amount were improved considerably by both combined plasma processes. In addition, the thickness of the diffusion layers formed on the sprayed 316L coatings was inferior to that of the corresponding diffusion layers formed on AISI 316L steel plates; this was because the sprayed 316L coatings included oxide layers.