Transition of Wear Mechanisms of Plasma Source Nitrided AISI 316 Austenitic Stainless Steel Against Ceramic Counterface

A single high-nitrogen face-centered-cubic (f.c.c.) phase (γ_N) layer formed on the plasma source nitrided AISI 316 austenitic stainless steel at a nitriding temperature of 450 °C for a nitriding time of 6 h. An approximately 17 μm-thick γ_N layer has a peak nitrogen concentration of about 20 at. %. Tribological properties of the γ_N phase layer on a ball-on-disk tribometer against an Si₃N₄ ceramic counterface under a normal load of 2 and 6 N with a sliding speed of 0.15 to 0.29 m/s were investigated by friction coefficient and specific wear rate measurement. Worn surface morphology and wear debris were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The microhardness of the γ_N phase layer on the nitrided stainless steel was measured as about 15.1 GPa. The change in the friction coefficient of the γ_N phase layer on the stainless steel was dependent on the applied normal load, which was associated with that in the specific wear rate. Under a lower normal load of 2 N, the lower specific wear rate of the γ_N phase layer with a sliding speed of 0.15 m/s was obtained as 2.8 × 10⁻⁶ mm³/N m with a friction coefficient of 0.60. Under a higher normal load of 6 N, the lower specific wear rate with a sliding speed of 0.29 m/s was 7.9 × 10⁻⁶ mm³/N m with a friction coefficient of 0.80. When the applied load increased from 2 to 6 N, a transition of the wear mechanisms from oxidative to abrasive wear was found, which was derived from the oxidation reaction and the h.c.p. martensite phase transformation of the γ_N phase during the wear tests, respectively.