Residual-stress predictions in polycrystalline alumina

Microstructure-level residual stresses occur in polycrystalline ceramics during processing, as a result of thermal expansion anisotropy and crystallographic misorientation across the grain boundaries. Depending on the grain size, the magnitude of these stresses can be sufficiently high to cause spontaneous microcracking when cooled from the processing temperature. They are also likely to affect where cracks initiate and propagate under macroscopic loading. The magnitudes of residual stresses in untextured and textured alumina samples have been predicted using experimentally determined grain orientations and object-oriented finite-element analysis. The crystallographic orientations have been obtained using electron-backscattered diffraction. The residual stresses are lower and the stress distributions are narrower in the textured samples, in comparison with those in the untextured samples. Crack initiation and propagation also have been simulated, using a Griffith-like fracture criterion. The grain-boundary-energy:surface-energy ratios required for computations are estimated using atomic-force-microscopy thermal-groove measurements.