Phase Equilibria, Microstructure, and High-Temperature Strength of TiC-Added Mo-Si-B Alloys
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TiC was added to Mo-Si-B alloys using a conventional Ar arc-melting technique, and the phase equilibria, microstructure evolution, and high-temperature strength at 1673 K (1400 °C) were investigated. The primary phase changed to Mo solid solution (Moss), Mo5SiB2 (T2), or TiC depending on the composition. Following the primary phase solidification, a Moss + TiC, Moss + T2, or Moss + T2 + TiC + Mo2C eutectic reaction took place as the secondary solidification step. In some alloys, Moss + T2 + TiC and Moss + T2 + Mo2C eutectic reactions were present as higher-order solidification steps. After annealing at 2073 K (1800 °C) for 24 hours, Moss, T2, TiC, and Mo2C coexisted stably with microstructural coarsening. The coarsening rate was much faster in an alloy with no TiC dispersion, suggesting that TiC has a strong pinning effect on the grain boundary and interface migration. Compression tests conducted at 1673 K (1400 °C) revealed strength properties of almost all the alloys that were better than those of the Mo-Hf-C alloy (MHC). Alloy densities were 9 g/cm3 or less, which is lighter than pure Mo and MHC (≥10 g/cm3) and competitive with Ni-base superalloys. TiC-added Mo-Si-B alloys are promising candidates for ultrahigh-temperature materials beyond Ni-base superalloys.
KeywordsPrimary Phase Ultimate Compressive Strength Colony Boundary Eutectic Area Onset Stress
This work was supported by the funding program for Next Generation World-Leading Researchers (NEXT Program) (No. GR017) and a Grant-in-Aid for Scientific Research (No. 23-4805) from the Japan Society for the Promotion of Science (JSPS).
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