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/partially stabilized zirconia composites prepared by powder metallurgical route, was evaluated up to 1573 K by means of modified small punch test (MSP), which had been originally designed for the evaluation of brittle to ductile transition in metallic materials used for nuclear applications. For the design of thermal barrier type of functionally graded materials, along with the thermomechanical properties in full compositional range, a special attention must be paid for evaluating the transition behavior of deformation and fracture with temperatures because 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, turns into ductile above a certain critical temperature and shows the similar load-deflection curve to those obtained in the case of ductile metallic materials. The brittle to ductile transition temperature which corresponds to the critical temperature was determined accurately by analyzing 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 microstructure, where the variation in transition temperature can be more closely related to the continuity of constituent phases rather than the nominal composition. The brittle to ductile transition behavior has been shown to be dependent not only on the temperature but also on the composition, which was quantitatively represented in an MSP-energy transition map.