Effects of grain refinement and strength on friction and damage evolution under repeated sliding contact in nanostructured metals

The early stage sliding contact fatigue behavior of nanocrystalline materials, with average and total range of grain sizes well below 100 nm, was studied. The evolution of friction and damage during repeated sliding contact in the nanocrystalline metals and alloys was systematically compared and contrasted with that in ultrafine-crystalline and microcrystalline materials so as to develop a broad perspective on the effects of grain size on sliding contact fatigue. Some critical experiments were performed to separate the effects of material strength and grain size on friction and damage evolution. Over the range of materials examined, strength rather than grain size appeared to dominate the steady-state friction coefficient and damage accumulation, each diminishing with substantial increases in material strength.