CREEP MECHANISMS IN MULTIPHASE CERAMIC MATERIALS

Hard, refractory particles long have been added to ceramic materials t o impart creep resistance. The nature of such particles and the volume fraction added may vary widely between different systems. As a result , a rich variety of creep behavior and of attendant mechanisms is foun d. A critical survey is presented of the experimental data and of the models developed to rationalize them. Particular attention is paid to three materials systems: whisker-reinforced ceramics (e.g., SiC-whiske r-reinforced Al2O3); infiltrated powder compacts (e.g,, siliconized Si C); and glass-bonded ceramics (e.g., sintered Si3N4). A microstructura l classification system is presented based on the nature of the networ k developed by the hard particles. This is useful as a guideline in de veloping mechanistic models. The current state of such models is revie wed critically. Although models for the high- and low-volume-fraction regions are well advanced, those applicable at intermediate volume fra ctions-relevant to whisker reinforcement for example-remain at an earl y stage. Finally, the experimental data on a range of materials are re viewed and classified. These data are compared with the models.