A Novel Optical Microscopic Approach for Understanding the Formation of Large Defects in Processing of Alumina Ceramics and its Relevance to Fracture

摘要

An outline of two novel characterisation methods is presented, one for observing microstructure of sintered ceramics and the other of green compacts. They show detailed optical images of their internal structures through observation using transmission modes. The origins of large defects were identified as pores in sintered powder granules and low-density regions at the boundaries of granules in compacts. The analysis of the micrographs provided direct information on the defect size distribution in the ceramics. Strength variation was calculated with the Baratta model (spherical pore with circumferential crack) correlated with the defect size population. Comparison of the result to that of measured strength showed that both results agreed well when the crack size around a spherical pore is assumed to be about 4 times the grain size. These results demonstrate the successful and direct establishment of a processing-structure-property relationship for the first time.