Effect of grinding, lapping and various surface treatments on the strength of silicon nitride

Abstract

Fully dense sintered reaction-bonded silicon nitride was manufactured as test bars in a variety of surface conditions (as-sintered, commercially diamond ground to a coarse and fine grit finish in both the longitudinal and transverse directions, and lapped), and lapped specimens were further treated by annealing at 1000°C in argon, annealing at 600°C in air, thermally cycling from 600°C to ambient in air and etching in hydrofluoric acid. The nature of the surface in each condition was characterised using scanning electron microscopy and profilometry measurements, and the flexural strength measured and analysed using the Weibull function. Machining considerably increased the strength of the fired material, but the effects of the various surface and thermal treatments were relatively small. Lapping increased the strength of the ground specimens by about 10%, and both annealing and etching reduced the strength of the lapped specimens. © 1990.