Wear of two-phase metals

Abstract

The effect of the second-phase particle structure on the wear properties of two-phase metals was investigated by using precipitation-hardened copperchromium alloys (Cu-0.58 at.% Cr and Cu-0.81 at.% Cr) aged for different periods of time at 500 °C. The hardness of these materials was found to increase initially with the aging time and then to decrease; the maximum value was reached after about 100 min of aging. Metallographic examination of worn specimens indicated that the wear process proceeded by subsurface deformation, crack nucleation and crack propagation, i.e. by delamination. The friction coefficient was found to be constant for both alloys and for all aging times. In the early stages of precipitation both the wear rate and the wear coefficient decreased. As the aging continued the wear rate and the wear coefficient increased even though the hardness also increased. The wear coefficient remained constant for the overaged alloys. The decrease in both the wear rate and wear coefficient in the early stages of precipitation is due to the fact that particles are small and coherent and require a large amount of subsurface deformation for crack nucleation. With further aging, the particles grow and become incoherent, increasing the wear rate due to easier crack nucleation. For the case of the overaged alloys, the wear coefficient tends to become constant because the wear process is controlled by the crack propagation rate which is found to be independent of the aging time for both alloys.