HIGH-TEMPERATURE DEFORMATION AND FRACTURE -BEHAVIOR IN SINTERED MO PSZ COMPOSITES AS EVALUATED BY SMALL PUNCH TEST/

The high-temperature deformation and fracture behavior of molybdenum/p artially stabilized zirconia composites prepared by powder metallurgic al route, was evaluated up to 1573 K by means of modified small punch test (MSP), which had been originally designed for the evaluation of b rittle to ductile transition in metallic materials used for nuclear ap plications. For the design of thermal barrier type of functionally gra ded materials, along with the thermomechanical properties in full comp ositional range, a special attention must be paid for evaluating the t ransition behavior of deformation and fracture with temperatures becau se of definite contribution of inelasticity of materials under thermal loading to the failure often observed during cooling. The results of the dependence of MSP load-deflection curve on temperature have shown apparent transitions in the deformation and fracture of the composites : that is, every composite, which is brittle at room temperature, turn s into ductile above a certain critical temperature and shows the simi lar load-deflection curve to those obtained in the case of ductile met allic materials. The brittle to ductile transition temperature which c orresponds to the critical temperature was determined accurately by an alyzing the temperature dependence of MSP-energy which was figured out as the area below each load-deflection curve. It has been found that the transition temperature is susceptible to the sintered microstructu re, where the variation in transition temperature can be more closely related to the continuity of constituent phases rather than the nomina l composition. The brittle to ductile transition behavior has been sho wn to be dependent not only on the temperature but also on the composi tion, which was quantitatively represented in an MSP-energy transition map.