Nanocrystallized layer formed by sliding wear under high stress for pure Cu

When metallic materials become worn, a nanocrystallized layer is often observed under the worn surface. This layer is called the wear-induced layer (WIL). In this study, the mechanism behind the formation of the WIL by sliding wear under high stress for pure Cu is investigated. The microstructure around the worn surface changes discontinuously between the WIL and the plastically deformed region (PDR). The grain size in the WIL is much smaller than that in the PDR, whereas grains in the PDR underneath the WIL are refined by huge strain due to wear. From the results of crystallographic texture analysis, the WIL has recrystallization texture, whereas deformation texture with a 〈110〉 fiber is observed in the PDR. Hence, in the WIL, frictional heat causes recrystallization, which induces further grain refinement. It is concluded that the WIL is formed by both severe plastic deformation (SPD) due to wear and the recrystallization due to frictional heat.