The transitions between microscopic wear modes during repeated sliding friction observed by a scanning electron microscope tribosystem

In order to analyse the microscopic wear mechanism in repeat-pass sliding, the wear process was observed successively over ten cycles of sliding in a newly developed scanning electron microscope tribosystem. The wear process was recorded with a video tape recorder. The type of wear test was pin-on-disk. The pin specimen was made of tungsten carbide. The hemispherical pin tip radius was 30 μm. The disk specimen was made of SUS 304 stainless steel. The sliding velocity was 40 μm s^-1. The normal load could be varied from 0.07 to 1.5 N. The following principal results were obtained. 1. (1) Wear mode transition during repeated sliding progresses from cutting, to wedge forming, to shear-tongue forming and then to ploughing. 2. (2) The critical conditions for the transitions between wear modes are expressed as follows: 0.27 < D_p cutting; 0.09 < D_p < 0.27 wedge forming; 0.06 < D_p < 0.09 shear-tongue forming; D_p < 0.06 ploughing; where D_p is the ratio of the depth of penetration to the length of contact parallel to the sliding direction. It is expressed as a function of normal load, disk specimen hardness, pin specimen radius and number of friction cycles. 3. (3) The conditions for wear mode transition can be explained theoretically by using a wear mode diagram.