Phase Composition of Some Mo-Si-B Series Alloys
The multiphase composite Mo-based alloys are candidate materials to replace Ni-based superalloys that generally operate at temperatures below 1200 °C. To achieve the optimal combinations of strength, fracture toughness, and oxidation resistance, knowledge of phase relations between the ductile BCC solid solution and intermetallic compounds such as Mo5SiB2 (T2), Mo3Si, Mo5Si3 (T1) and D88 (Ti5Si3) is crucial.
The TCS Mo-based Alloys Database (TCMO) can be used to predict the phase stability and compositions for a given chemistry, which is the prerequisite for Mo-based alloy design.
Mo-Ti-Si-B Calculated Phase Compositions
The quaternary Mo-Ti-Si-B alloys are expected to exhibit superior performance compared to the ternary Mo-Si-B alloys due to the introduction of the Ti5Si3 phase. The table confirms that when using the TCS Mo-based Alloys Database (TCMO) database, the predicted stable phases and phase compositions for 10 Mo-Ti-Si-B alloys at 1600 °C are in good agreement with the experimental results from [2005Yan].
| Alloy Chemistry, at.% | Ti Composition in Each Phase, at.% | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| T2 | Mo3Si | BCC | T1 | Ti5Si3 | ||||||||
| B | Si | Ti | Exp. | Calc. | Exp. | Calc. | Exp. | Calc. | Exp. | Calc. | Exp. | Calc. |
| 19 | 11 | 10 | 12.9±1 | 11.8 | 9.3±1 | 14.3 | 1±0.5 | 1.4 | ||||
| 20 | 22.7±1.5 | 22.0 | 22.1±2 | 23.3 | 14.4±3 | 11.0 | ||||||
| 30 | 29.1±2 | 28.7 | 33.6±3 | 32.3 | 52.1±1 | 50.4 | ||||||
| 9 | 18 | 28.5 | 26±2 | 26.4 | 33.5±2 | 27.2 | 24±1 | 24.1 | 41±1.5 | 39.4 | ||
| 32.5 | 26.5±2 | 27.4 | 27±1 | 27.7 | 42.3±2 | 40.4 | 49.2±1 | 48.9 | ||||
| 35 | 26.7±2 | 27.5 | 27.8±1 | 28.1 | 50.5±1 | 49.0 | ||||||
| 37.5 | 27.2±2 | 28.9 | 35±1 | 33.0 | 53±1 | 51.0 | ||||||
| 10 | 10 | 25 | 27±3 | 26.2 | 30±2 | 27.0 | 23.8±1 | 23.2 | ||||
| 27.5 | 27.8±3.5 | 26.8 | 26.4±0.4 | 25.5 | 43±3 | 40.0 | ||||||
| 30 | 29±3 | 27.6 | 29.5±1 | 28.2 | 50±1 | 49.1 | ||||||
Mo-Re-Si-B Calculated Phase Compositions
Rhenium (Re) is effective in toughening the BCC Mo solution phase and thus improving the ductility of Mo alloys. The TCS Mo-based Alloys Database (TCMO) can successfully predict the effect of Re addition on phase stability and composition of Mo-Si-B based multiphase alloys, as shown in the tables below. The experiment results are from [2013Yan].
Mo-13Re-13Si-6B (at.%)
| Mo-13Re-13Si-6B (at.%) | ||||||||
|---|---|---|---|---|---|---|---|---|
| at.% | BCC | Mo3Si | T2 | Sigma | ||||
| Exp | Calc | Exp | Calc | Exp | Calc | Exp | Calc | |
| B | ~0 | 0.1 | ~0 | 0 | 22 | 25.0 | ~0 | 0 |
| Mo | 75.6 | 82.2 | 73.4 | 71.0 | 61.7 | 60.6 | 64.1 | 62.4 |
| Re | 19.7 | 13.2 | 4.4 | 4.0 | 3.1 | 1.9 | 23.8 | 26.3 |
| Si | 4.7 | 4.5 | 22.3 | 25.0 | 13.2 | 12.5 | 12.1 | 11.3 |
Mo-13Re-7Si-15B (at.%)
| Mo-13Re-7Si-15B (at.%) | ||||||||
|---|---|---|---|---|---|---|---|---|
| at.% | BCC | Mo2B | T2 | Sigma | ||||
| Exp | Calc | Exp | Calc | Exp | Calc | Exp | Calc | |
| B | ~0 | 0.2 | 34 | 33.3 | 22 | 25.1 | ~0 | 0 |
| Mo | 72.8 | 77.8 | 56.5 | 55.1 | 61.4 | 59.8 | 63.5 | 57.6 |
| Re | 24.4 | 19.1 | 8.9 | 11.5 | 4 | 2.7 | 26.3 | 34.8 |
| Si | 2.8 | 2.9 | 0.6 | 0 | 12.6 | 12.4 | 10.2 | 7.6 |
References
[2005Yan] Y. Yang, Y. A. Chang, L. Tan, W. Cao, Multiphase equilibria in the metal-rich region of the Mo–Ti–Si–B system: thermodynamic prediction and experimental validation. Acta Mater. 53, 1711–1720 (2005).
[2013Yan] Y. Yang, H. Bei, J. Tiley, E. P. George, Re effects on phase stability and mechanical properties of MoSS+Mo3Si+Mo5SiB2 alloys. J. Alloys Compd. 556, 32–38 (2013).