Reliability of alumina ceramics: Effect of grain size

Abstract

The grain size dependence of fracture strength and Weibull modulus of alumina using a high purity, commercial starting powder was investigated. In the regime of an average grain size between 1.7 and 11 μm, fracture strength increases with decreasing grain size. This behaviour could be explained quantitatively by modelling the failure-causing defect as either a spherical pore or a hemispherical surface pit with a circumferential crack proportional to the average grain size. No dependence of Weibull modulus on average grain size and hence on R -curve behaviour could be observed. Theoretical considerations show that the closure stresses in alumina responsible for the R -curve behaviour are too low to affect the Weibull modulus.