THERMAL-SHOCK BEHAVIOR OF OPEN-CELL CERAMIC FOAMS

Specimens of heated, open-cell ceramics were thermally shocked by immersion in water or oil. It was found the strength retained after thermal shock underwent a gradual decrease with increasing quench temperature, indicative of a cumulative damage mechanism which manifests itself with increasing thermal stress. This damage could also be monitored using measurements of the elastic constants before and after quenching. The thermal shock resistance of the open-cell materials was found to be strongly dependent on cell size (increased with increasing cell size) and weakly dependent on density (increased with increasing density). Two possible sources of thermal stress were considered; one was associated with the temperature gradient across the microscopic struts and the other with the heating of the quenching medium as it infiltrates the cellular structure. Such heating was confirmed and it was concluded that this was the dominant source of thermal stress in this particular study, controlling the thermal shock resistance of the open-cell ceramics.