MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF BORIDE-DISPERSED COMPOSITES FABRICATED BY HOT-PRESSING AMORPHOUS NI60MO30B10 POWDERS

Amorphous Ni60Mo30B10 powders have been hot-pressed, crystallized and heat-treated to control microstructures for excellent mechanical prope rties. In materials (HP) hot-pressed at 1373 K, borides such as Mo2NiB , are dispersed in Ni solutions saturated with alloy elements. These b oride precipitates are quite fine and homogeneous. Materials of HP are solution-treated at 1373 K and aged to precipitate within its Ni solu tions (973STA, 1073STA, 1273STA). Symbols of 973, 1073 and 1273 signif y aging temperatures. In materials of 973STA and 1073STA, the borides, and Ni3Mo and NiMo compounds are dispersed, but little Ni solution ex ists. On the other hand, materials of 1273STA are formed of the boride s and the NiMo compounds within the Ni solutions. Materials of 1073STA give higher hardness in the temperature range between 300 and 800 K c ompared with HP materials. Its high hardness is about 8.3 GPa and comp ressive strength at room temperature is about 3.0 GPa. On the other ha nd, 1273STA materials of relatively high hardness exhibit large ductil ity because of the existence of the Ni solutions. It is found that the se composites maintain an excellent hardness and a moderate ductility up to about 800 K due to the thermal stability of its microstructures.