Erosion and strength degradation in alumina

Abstract

The effect of multiparticle impact at 23 700 and 1000 °C on the erosion and strength degradation of sintered alumina was determined. Impact damage at normal incidence was characterized by numerous small pits consistent with grain boundary cracking. Neither erosion rate nor strength degradation for normal impingement depended strongly on temperature. Although erosion rate increased with increasing kinetic energy of the impacting particle, strength degradation leveled off at high kinetic energies, contrary to predictions based on elastic-plastic fracture. An alternative theory was developed on the basis of the observed damage morphology. This theory assumes that the kinetic energy of the impacting particle goes into grain boundary cracking and the subsequent grain fallout creates a hemispherical pit with an annular crack. This model correctly predicts the dependence of both erosion rate and strength degradation on the kinetic energy of the impacting particle. For impingement at low angles, impact damage was primarily by a ductile ploughing process. This caused erosion rates to be greater than that predicted on the basis of the brittle chipping mode of erosion, but strength degradation was less because the shallow elongated flaws are less severe than the pits produced by normal impact.