Erosion of MgO by solid particle impingement at normal incidence

A study has been made of the erosion of almost fully dense, fine-grained MgO by millimeter-scale WC-6 wt% Co spheres impinging at normal incidence with velocities between 10 and 90 m sec^–1. Scanning electron microscopy showed that the damage consisted of a central crater surrounded by an array of intergranular radial and/or median and/or lateral cracks characteristic of an elastic-plastic impact. The crater had a thin lining of plastically deformed material, but appeared to have been formed primarily by localized transgranular and integranular fracture processes, suggesting that any mode of irreversible deformation in the contact region will suffice to produce the changeover from Hertzian cracking to radial, median and lateral cracking. The accompanying gravimetric studies showed that mass loss, which was caused primarily by intersection of lateral cracks with the free surface and with radial and/or median cracks, increased threefold during the short incubation period in which the as-received surface evolved into its steady-state eroded condition. During this period the exponent relating erosion to impact velocity decreased asymptotically towards a value smaller than that predicted by any current theory of erosion in the elastic or the elastic-plastic impact regime. Nor are these theories any more successful at explaining the observed particle-size dependence of the erosion of polycrystalline MgO.