The effect of transformation stresses on the devitrification kinetics of a minory phase in liquid phase sintered ceramics

The crystallization of minory amorphous constituens in liquid phase sintered ceramics, for example in Si3N4, is usually accompanied by a volume change. The resulting mismatch between crystallizing second phase inclusions and the surrounding matrix or the primary phase leads to the formation of transformation stresses. The strain energy stored in the stress field reduces the thermodynamic driving force of crystallization. The coupling on crystallization, stress formation and relaxation is modelled. The extended duration of the crystallization process due to an intermediate stress induced decrease of the crystallization rate is assessed. The properties of amorphous grain boundary films are discussed with respect to stress relaxation and creep resistance at high temperatures. The main fraction of the second phase in the real microstructure is likely to be located in an interconnected network which provides a possibility of stress relaxation.