Kazuhisa Shobu

Influences of Al content and secondary phase of Mo5(Si,Al)3 on the oxidation resistance of Al-rich Mo(Si,Al)2-base composites

Abstract The microstructures and oxidation behavior of Mo(Si,Al)2-base composites were investigated. A high Al content up to 38 mol% and the effect of the secondary Mo5(Si,Al)3 phase were specifically examined. Microstructure observations indicated that the Al solubility limit at 1680 K extends to 43 and 10 mol% for Mo(Si,Al)2 and Mo5(Si,Al)3, respectively. The composites containing about 10 vol.% Mo5(Si,Al)3 exhibits excellent oxidation resistance in the temperature range between 780 and 1780 K, so that the Mo5(Si,Al)3 up to about 10 vol.% is acceptable and has no detrimental influence on the oxidation resistance. At temperatures from 1480 to 1780 K, a continuous alumina layer develops on the Mo5(Si,Al)3 as well as on the Mo(Si,Al)2. The alumina growth rate is nondistinctive in the Al range investigated, and it is controlled by inward oxygen diffusion through the alumina at 1580 K and higher.

Oxidation behavior of Mo(Si0.6,Al0.4)2/HfB2 composites as aluminum reservoir materials for protective Al2O3 formation

Abstract Mo(Si0.6,Al0.4)2/HfB2 composites containing up to 18 vol% HfB2 have been shown to exhibit good oxidation resistance. Incorporated HfB2 has a minor influence on the scale growth behavior, and the overall behavior is similar to that of Mo(Si0.6,Al0.4)2. A further increase in HfB2 content, however, may lead to substantially fast scale growth.