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

抄録

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.