Evaluation of lapping and polishing damage in brittle materials by quantitative acoustic microscopy

Surface acoustic wave (SAW) velocities have been measured on polished alumina surfaces. It is found that the major changes (increases) in wave speed occur early on in the polishing process, suggesting that long polishing times lead to little improvement in surface quality. There is little correlation between SAW velocity and surface roughness. Quantitative analysis indicates that the effects of surface roughness and residual stress on Rayleigh wave speed should be small; hence the increase in surface wave speed with increased polishing time is most likely to be due to a reduction in the size and density of micro-cracks.