Near-surface and depth-dependent residual stress evolution in a piston ring hard chrome coating induced by sliding wear and friction

Abstract

The microstructure, texture and residual stresses of a hard chrome piston ring coating, which was subject to sliding wear in tribological contact with a thermally sprayed, iron-based liner coating, were studied using laboratory X-rays and synchrotron X-rays. The near-surface evolution of residual stresses induced both tribologically and thermally was analyzed in the sliding direction and perpendicular to the sliding direction. The tribologically induced residual stresses correlate with the piston ring tribology as a function of the tribological parameters ‘test duration’, ‘sliding speed’, ‘piston ring load’ and ‘piston ring temperature’ and with the evolution of the piston ring wear, particularly as a function of the accumulated dissipated frictional energy. A tribologically impacted residual stress zone of approximately 15μm was identified and a considerable tribological impact on the residual stresses was detected. A smaller impact depth of only 10μm could be assigned to the thermally impacted residual stress zone. Exposed to high temperatures, the residual stresses tribologically induced in sliding direction within the whole depth range are shifted towards compressive residual stresses. There was a very good agreement between the energetic approach to wear and the evolution of tribologically induced residual stresses as a function of the dissipated frictional energy. Furthermore, the evolution of the wear volume as a function of the tribological parameters, such as ‘sliding speed’, ‘piston ring temperature’ and ‘piston ring load’, could be correlated to the depth-dependent evolution of thermally and tribologically induced residual stresses.