Figure 8

(a) The optical images of the wear scars on the Al₂O₃ balls after rubbing against TC4 titanium alloy and its Ni-B coatings, and (b) the corresponding cross-sectional profile lines of the Al₂O₃ balls in (a) (The white dashed line in (a) is the location of the cross-sectional profile lines, which is perpendicular to the sliding direction, and the gray dashed line in (b) is the schematic profile line of the non-wear Al₂O₃ ball’s surface)