DELAMINATION WEAR IN DUCTILE MATERIALS CONTAINING 2ND PHASE PARTICLES

Plastic deformation and damage accumulation below the contact surfaces play an important role in sliding wear of ductile materials. In this study, metallographic techniques have been developed and used to determine the magnitude of the shear strains and the microhardness gradients in near surface regions in an aluminum-7% silicon alloy. Under dry sliding wear conditions, both the magnitude of plastic strains and the depth of heavily deformed zones increased with sliding distance and applied load. The flow stress and the plastic strains in the deformed zones are shown to obey a work hardening law which can be expressed in the form of a Voce type constitutive equation. Scanning electron microscopy (SEM) studies on the longitudinal sections below the worn surfaces indicated that thin flake-shaped debris particles were generated by a process of subsurface delamination. Delamination occurred via cracks which originated from silicon particles within the deformed zones (but not at the contact surface) and propagated parallel to the surface. A model based on the hypothesis that delamination cracks are formed by the coalescence of voids at a critical depth below the worn surfaces has been proposed. It is shown that the critical depth for maximum rate of damage accumulation is determined by a competition between the plastic strain which enhances void growth and the hydrostatic pressure which suppresses it.