EFFECT OF ION-IMPLANTATION ON THERMAL-SHOCK RESISTANCE OF MAGNESIA AND GLASS

Monocrystals of magnesia together with glass samples have been subject ed to ion implantation prior to thermal shock testing in an impulse pl asma of continuously varied intensity. Measurements of the separation between fragments have been used to estimate the surface temperature. Fracture and deformation characteristics of the surface layer are meas ured in ion implanted and unimplanted samples using optical and scanni ng electron microscopy. Implantation-induced nearsurface damage is ana lysed by ion channelling using 2 MeV He+ ions. Ion implantation is sho wn to modify the nearsurface structure of magnesia samples by introduc ing damage, which makes crack initiation easier under thermal stresses . The fracture threshold and maximum crack density are shifted towards the lower temperature range. Ion implanted MgO crystals show a ten-fo ld increase in surface crack density. An increased crack density resul ts in a decreased degree of damage characterized by the depth of crack penetration. The thermal stress resistance parameter of glass samples is increased at relatively small doses and decreased at higher doses. The results suggest that crack density and the degree of fracture dam age in brittle ceramics operating under thermal shock conditions can b e effectively controlled by ion implantation which provides crack init iating defects in the near-surface region.