Creep and damage processes in multi-phase ceramic materials

A brief review is presented of the creep and creep fracture behaviour of a range of multi-phase ceramic systems. Three main classes of material are considered, ranging from soft ceramic matrices reinforced with strong particles such as whiskers, through metal infiltrated ceramic compacts, to glass bonded ceramics. Thus a wide range of matrix volume fraction from 90 to 1%, is considered. The creep resistance is seen to depend generally on that of the soft phase, and on the rheological influence of the hard phase. At intermediate volume fractions, network formation plays a major role. The creep fracture behaviour in all classes of material shows two regimes - at high stress, failure is due to a single dominant crack emanating from a flaw; while at low stress, generalized damage is seen. A modified Monkman-Grant relationship is often found, suggesting that increasing creep resistance is the main route to improved lifetime at high temperatures.