Application of backscattered electron images to the study of fracture in glass ceramics

Abstract

Fracture surfaces of three different glass ceramics were examined to determine the critical flaw sizes and the corresponding microstructures of the materials directly from the fracture surfaces. Standard secondary electron (SE) images and classical topographical back‐scattered electron (BSE) images were used to measure the critical flaw sizes and to observe deviations of the critical flaw interfaces from smooth elliptical fronts. Compositional BSE images were used to characterize the microstructures in and around the critical flaws directly from the unetched fracture surfaces. A direct correlation was found between the critical flaw size and microstructural units effectively acting as grains within the flaw and the fracture toughness. This relationship enabled the discrepancies between the calculated fracture toughness and the measured fracture toughness to be resolved.