Abstract
Amorphous Ni60Mo30B10 powders have been hot-pressed, crystallized and heat-treated to control microstructures for excellent mechanical properties.
In materials (HP) hot-pressed at 1373 K, borides such as Mo2NiB2 are dispersed in Ni solutions saturated with alloy elements. These boride precipitates are quite fine and homogeneous. Materials of HP are solution-treated at 1373 K and aged to precipitate within its Ni solutions (973STA, 1073STA, 1273STA). Symbols of 973, 1073 and 1273 signify aging temperatures. In materials of 973STA and 1073STA, the borides, and Ni3Mo and NiMo compounds are dispersed, but little Ni solution exists. On the other hand, materials of 1273STA are formed of the borides and the NiMo compounds within the Ni solutions.
Materials of 1073STA give higher hardness in the temperature range between 300 and 800 K compared with HP materials. Its high hardness is about 8.3 GPa and compressive strength at room temperature is about 3.0 GPa. On the other hand, 1273STA materials of relatively high hardness exhibit large ductility because of the existence of the Ni solutions.
It is found that these composites maintain an excellent hardness and a moderate ductility up to about 800 K due to the thermal stability of its microstructures.
