Optimization of Multi-phase Mo-12Si-8.5B Alloy by SiC Whisker
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Fine-grained and multi-phase Mo-Si-B alloy contains many grain/phase interfaces, which allows for optimizing its performances by modifying its interfaces. Based on the structure design, this study introduces the SiC whisker in a multi-phase Mo-Si-B alloy. The Mo-12Si-8.5B-SiC alloy, which used a liquid–liquid doping method to mix the SiC whiskers in the mechanical alloyed powder, was also synthesised by hot pressing. The microstructure, strength and toughness were experimentally examined, and the solid-state reaction and thermodynamic calculations were analysed to evaluate the effect of the SiC whisker. Microstructural observations showed that the SiC addition could regulate the phase constitution by markedly increasing the intermetallic content and, moreover, decrease the α-Mo content in the Mo-Si-B alloy. This effect resulted in a change in the microstructure, which was transformed from a continuous α-Mo matrix of the SiC-free Mo-12Si-8.5B alloy to a fine-grained intermetallic matrix of the Mo-12Si-8.5B-SiC alloy. Some SiO2 particles distributed at the grain and phase boundaries could be decreased by the SiC addition, which was mainly related to the grain/phase boundary purifying effect derived from the interfacial reactions of the whisker and matrix. The high strength of the intermetallic matrix with a small amount of silica in the Mo-Si-B-SiC alloy is beneficial for enhancing the strength and fracture toughness.
This subject was supported by the National Natural Science Foundation of China (Grant Nos. 51701162 and 51674196), the China Postdoctoral Science Foundation (Grant No. 2016M602885), and the Shaanxi Postdoctoral Research Program (Grant No. 2016BSHEDZZ07).