Dry sliding wear behavior of copper with nano-scaled twins

A 99.99 wt.% copper plate with a surface layer containing a high density of nano-scaled twins has been synthesized by means of surface mechanical attrition treatment (SMAT). The friction and wear characteristics of the nano-twinned Cu sample were investigated in comparison with those of equiaxed nanocrystalline Cu and coarse-grained (CG) Cu samples. The tribological properties are markedly enhanced with nano-scaled twin surface layer relative to the coarse-grained form at all the loads and the sliding speeds, which is supposed to originate from the strengthening of twin boundaries. The friction coefficients and wear rates of the nano-twinned and the CG Cu increase slowly with an increasing sliding speed, and slightly decrease at a speed of 0.08 m/s. When the speed exceeds 0.08 m/s, there occurs a steep increase of the friction coefficients and wear rates for all the samples, corresponding to the wearing away of the mixed surface layer.