Microstructure and micro-abrasive wear of sintered yttria-containing 316L stainless steel treated by plasma nitriding

Plasma nitriding of austenitic stainless steel may result in the formation of a nitrided layer, which is responsible for the increase in hardness, as well as wear and corrosion resistance of this material. In this work, the effect of yttria on the micro-abrasive wear behavior of plasma nitrided stainless steel was investigated. Powder metallurgy (P/M) 316L austenitic stainless steel samples, without and with 1 wt.% Y2O3, were plasma nitrided at 450 °C for different nitriding times (from 2 h up to 10 h). The nitrided samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, instrumented indentation and micro-abrasive wear tests. The XRD analysis confirmed the presence of nitrogen expanded austenite (γN) phase for all nitrided layers and the formation of iron and chromium nitrides. The nitride content in the nitrided layer increased with the nitriding time. However, alloying the sintered 316L stainless steel with yttria particles increased the nitrogen content in the nitrided layer, which consequently increased the lattice distortion and the amount of nitrogen expanded austenite and decreased the content of iron and chromium nitrides in the nitrided layer. Micro-abrasive wear tests showed that the addition of yttria to the bulk of the sintered material promotes a more wear-resistant material for all nitriding times. This behavior was related to the hardness, thickness and amount of the nitrogen expanded austenite of the nitrided layer.