Mo-ZrO2系焼結材におけるZrO2のt→m変態および正方晶ZrO2の残留について

Abstract

In order to investigate the t→m transformation of ZrO2 and the retention of tetragonal-ZrO2 in Mo-ZrO2 composites, the composites containing ∼50 vol%ZrO2 were fabricated by the powder metallurgical process. The t→m transformation temperature (Ms point) was measured by the dilatometric method, and the retention of tetragonal-ZrO2(t-ZrO2) was determined by X-ray diffraction analysis as functions of variables such as powder mixing time, sintered density and zirconia content.The results are as follows:(1) The powder mixing time had a significant influence on Ms point and t-ZrO2. Appropriate mixing time made it possible to retain the t-ZrO2 comparable to that of Al2O3-ZrO2 composite. (2) Although the sintered density did not affect so much, the zirconia content had a great influence, especially in the range from 10 to 15 vol%ZrO2 there was a steep decrease in the t-ZrO2 content with increasing zirconia content. This decrease is due to the growth of zirconia particles. (3) The Ms point and t-ZrO2 content depended on the size of zirconia, and the critical size below which t-ZrO2 was stable lay between 0.4 μm and 0.6 μm. The reason why this size effect occurred could not be explained from the results of this study.