Defining the role of ‘zero wear volume’ in percussive impact

Abstract

This work defines the previously undetermined contribution of the ‘zero wear’ volume, that is geometry change due to material compression that occurs before other mechanisms that cause change through actual material loss are initiated during to repetitive impact. Five metal alloys widely used in engineering applications, each with a different bulk hardness, were the subjects of the experiments. Using a reciprocating hammer type impact wear test apparatus, flat coupon type specimens were subjected to repetitive impact from a chrome steel ball acting normal to the surface. 36,000 impacts were applied at a nominal rate of 10 impacts per second, each with an impact energy of 0.23J and an impact force of 3.5 kN. The impact wear crater on selected worn specimens was examined using a 3D non-contact profilometer. Scanning electron microscopy techniques were used to further examine the damage on the specimens. The main damage mechanism was plastic deformation and surface fatigue due to spalling. Microcracks and adhered wear debris were noted on the specimens, but with no evidence of delamination, while subsurface examination showed no possible microcracks under the impacted surface and only surface pitting could be observed from subsurface examination. Analysis of the wear scars suggests that zero wear volume is the main contributor to the total volume ‘loss’ for all materials, and, for specific materials, plastic flow volume and bulk hardness could be a significant parameter in characterising zero-wear volume and crater depth.