Rolling contact damage accumulation in two contrasting copper alloys

Rolling contact tests were carried out on two copper alloys with contrasting post-yield properties. The progression of damage was investigated using scanning and transmission electron microscopy. A phosphor bronze alloy showed isotropic hardening and shakedown. In contrast, a precipitation-hardened CuNiSi alloy showed kinematic hardening and ratchetting behaviour and had poor resistance to cracking despite having a higher initial yield stress. The damage was found to be associated with slip band formation and rapid dissolution of the Ni2Si precipitate. Results are consistent with the findings of earlier investigators on the relationship between wear, fatigue and ratchetting in rolling contact and provide a microstructural explanation for the present system. There is a close parallel with classical fatigue in other precipitation-hardened alloy systems.