Friction, wear and deformed structure of Ag and Ni under early stages of scratching

We report here the investigation of the effect of stacking fault energy (SFE) on the friction, wear, and deformed microstructure of Ag and Ni following one and ten cycles of scratching. For this purpose, low and high SFE face centered cubic (fcc) metals, were evaluated. Scratching of the samples was conducted in the reciprocal motion using a diamond indenter. To provide similar contact conditions we applied the parameter of virgin contact area, P/H-i similar to 0.055, where P is the load and H-i the initial hardness. The tests were performed during 1 and 10 scratching cycles using sliding velocity of 30 mu m/s. The microhardness before and after scratching was measured. Friction surfaces were carefully examined with a field emission scanning electron microscope (SEM) and an atomic force microscope (AFM). The cross-sectional transmission electron microscopic (TEM) lamellae were prepared using a focused ion beam (FIB). It was found that the deformation hardening of Ag is significantly greater than that of Ni. The size of scratch tracks of Ag was smaller than for Ni. This phenomenon can be explained by a high rate of deformation hardening and formation of the refined structure at upper surface layers of Ag due to the limitation of the cross slip during plastic deformation.