Fig.7 amplified images of the slip and stick regions in Fig.6(b) and Fig.6(d)
The surface of the sample continuously undergoes plastic deformation due to the fretting friction between the sample and the fretting pad in the slip region. After repeated sliding, rolling, and smoothing, plastic failure occurs on the surface. Lamellar spalling occurs in the slip zone, forming pits and wear debris with different depths and shapes. The overall damage in the slip region is relatively large, the scratches are deep, and the surface is extremely rough. Because of the wiping effect of abrasive particles on the surface of the slip region, there are almost no microcracks on the normal surface, and the microcracks occur only at the edges of the pits where stress is concentrated. Kozo Nakazawa et al. 23 made similar findings in their research. In the stick region, due to the coupling effect of adhesion and fretting, the surface material of the sample is severely torn, and many small pits are connected to form a large pit. The surface damage is small in the stick region where no tearing of the surface material has occurred, and basically no slip marks similar to the slip region.
The morphology of the stick region and the slip region with an equivalent stress of 400 MPa and a contact stress of 150 MPa under SP is shown in Fig7.(h)(i); There are a lot of abrasive debris in the slip region of SP, and furrows caused by the sliding effect can be seen everywhere, and the surface is very rough; The surface of the stick region is smoother than that of the slip region, and the surface is free of scratches caused by the sliding effect, but there are pits of different shapes caused by the surface material tearing. Compared with DP, the area and depth of the pits generated in SP are less.