Subsurface zones created under lubrication conditions studied by positron annihilation

We present positron annihilation studies of the subsurface zones induced in the sliding contact of two metals under lubrication conditions. The surfaces of copper samples were exposed to the sliding of a small steel ball and the open volume defects induced under the surface were detected using both a positron beam experiment and a conventional positron experiment. From our studies we deduced that the total range of subsurface zones was almost independent of the lubrication conditions. For the highest load of the ball we observed that the subsurface zone created under lubrication condition extends deeper than for the case where the zone was induced in the dry sliding contact. We found that sliding with lubricant induces a layer on the surface whose properties, as detected by positrons, were different than those of other samples. It seems that this layer could contain open volume defects that are larger than those in deeper layers. Our studies have shown that the positron beam technique is a suitable tool for defect characterization in tribotested samples.