Third body effects in fretting

Abstract

Experiments have been carried out, using a tension-compression hydraulic machine, to investigate the fretting behavior of TiN coatings on high speed steel (HSS) against an alumina ball. In the experiments reported here, a range of different normal loads, displacement amplitudes and frequencies was used and the relative humidity of the test atmosphere was held at 5% (RH), 25% (RH), 50% (RH), 75% (RH) and 98% (RH). Compared to uncoated HSS, the fretting maps were modified due to differences in the surface nature and to mechanical properties. With the exception of low relative humidity, the relative motion between TiN and alumina occurs under a gross slip regime and the shape of the friction force versus displacement loop is quasi-rectangular. In the 5% RH and 25% RH atmospheres, the relative motion between TiN and alumina went from partial slip to gross slip when increasing the displacement. All the curves showing the friction coefficient were characterised by an initial transient state where the friction coefficient increased rapidly, followed by a steady state. The coefficient of friction and the wear depth change with the experimental parameters due to different wear mechanisms.