Thermal expansion, strength and oxidation resistance of Mo/Mo5SiB2 in-situ composites at elevated temperatures

Four Mo/Mo5SiB2 in-situ composites with different volume fractions of Mo solid solution, VfMo, were produced by ingot metallurgy and their microstructure, thermal expansion, compressive strength and oxidation behavior were investigated relating to VfMo. Mo-8.5Si-13.2B annealed at 2073 K for 24 h has nearly eutectic microstructure consisting of Mo solid solution and Mo5SiB2. For higher VfMo, there are micro-cracks in Mo5SiB2 phase probably induced by thermal stress during the cooling process. Mo-8.5Si-13.2B shows the highest yield stress among the four Mo/Mo5SiB2 in-situ composites, and about 1 GPa even at 1773 K. For lower VfMo than that of Mo-8.5Si-13.2B, the steady state oxidation behavior is observed at temperatures between 1173 and 1473 K, indicating that the oxidation resistance is relatively good, whereas the oxidation resistance is catastrophic for higher VfMo than that of Mo-8.5Si-13.2B.