On wear mechanisms and microstructural changes in nano-scratches of fcc metals

Abstract

Sliding and scratching are fundamental tribological phenomena which affect the surface and surface-near zones of materials. To clarify ongoing tribological and microstructural mechanisms, a thorough analysis of three fcc materials (aluminium, austenitic steel and copper) was performed via nano-sliding and scratching at different load levels. Nanoindentation was used to evaluate the phases’ mechanical properties, namely hardness H, Young’s modulus E and the ratios H/E (yield strain) and H³/E2 (resistance against plastic indentation), which proved to be good measures to understand the abrasive wear behaviour. Electron backscatter diffraction (EBSD) measurements and focused ion beam (FIB) cross-sections of the scratches provided deeper insight into the degree of deformation and deformation induced phase changes.Results show a distinct influence of the materials’ mechanical parameters and phase changes on the deformation and wear mechanisms, and the thereby entailed apparent coefficient of friction (FT/FN). The mechanical properties were a key factor for a change in wear mechanism from sliding to ploughing to chipping. The thresholds were investigated for the three materials and increase from Aluminium to Copper to Austenite with H³/E2 being a good descriptor of the necessary contact pressures entailing changes of the wear mechanism.