The effect of plasma nitriding and post oxidation on fretting wear behaviour of a high strength alloy steel

Abstract

The fretting wear performance of the non-nitrided, nitrided and nitrided-post oxidized high strength alloy steel, W460 were investigated in the gross slip regime at ambient condition. Fretting wear tests were performed with an applied normal load of 250 and 650 N at a displacement amplitude of 100 μm using a cylinder-on-flat configuration. X-ray analysis (XRD) revealed the formation of the iron-nitrided Fe3N and Fe4N during plasma nitriding and iron oxide phases of hematite (Fe2O3) and magnetite (Fe3O4) during post-oxidation of the cylindrical steel samples. The steady state tangential force coefficient decreases when the nitrided and post-oxidized samples were fretted against the non-nitrided steel material when compared to the non-nitrided steel contact pair. The steady state tangential force coefficient decreased with an increase in applied normal load across all of the fretting conditions. The total dissipated energy and the total wear volume increased with an increase in applied normal load with total wear volume of the non-nitrided vs nitrided and non-nitrided vs nitrided post-oxidized sample pairs, showing a reduction in the wear volume of approximately 50% compared to the non-nitrided vs non-nitrided combination under the fretting conditions examined. The worn surface morphology of the fretted samples examined using a scanning electron microscope showed the presence of loose wear debris in the wear track, fragmented wear debris, delamination cracks, delamination with large discontinuities, plate-like wear debris, oxide patches and formation of large cavities.