As-cast Microstructure of Mo-Si-B Series Alloys

The TCS Mo-based Alloys Database (TCMO) can be used to investigate the solidification path and predict the as-cast microstructure with the help of Scheil simulation.

Read more about Scheil Solidification Simulations on our website, including how to select the right model for your simulation. If you are in Thermo‑Calc, press F1 to search the help to learn about using Scheil.

Mo-Si-B-Cr

Chromium (Cr) is expected to improve the oxidation resistance and reduce the density of Mo-Si-B based alloys. According to the calculations shown below, the three-phase microstructure, i.e., BCC + T2(Mo₅SiB₂) + Mo₃Si, can be retained in solidified Mo-20B-10Si-Cr (at.%) alloys even when the content of Cr reaches up to 35 at.%, which matches with the experimental observations from [2000Sak].

Figure 1: Equilibrium solidification and Scheil solidification simulation of the Mo-20B-10Si-5Cr (at.%) alloy.

Figure 2: Equilibrium solidification and Scheil solidification simulation of the Mo-20B-10Si-20Cr (at.%) alloy.

Figure 3: Equilibrium solidification and Scheil solidification simulation of the Mo-20B-10Si-35Cr (at.%) alloy.

Mo-Si-B-Nb

Niobium (Nb) can improve the high temperature strength of Mo-Si-B alloys by tuning the solidification microstructure. For a series of Mo-Si-B-Nb alloys with 32.6 at.% Nb and different Si and B contents, the TCS Mo-based Alloys Database (TCMO) can not only predict the final as-cast microstructure but also the primary solidification phases, as demonstrated by experiments from [2016Tak]. The simulations shown below are examples with the primary solidification phase of T2 (Mo₅SiB₂), BCC, and T1 (Mo₅Si₃), respectively.

Figure 4: Equilibrium solidification and Scheil solidification simulation of the Mo-32.6Nb-14Si-10B alloy.

Figure 5: Equilibrium solidification and Scheil solidification simulation of the Mo-32.6Nb-18Si-2.5B alloy.

Figure 6: Equilibrium solidification and Scheil solidification simulation of the Mo-32.6Nb-27Si-2B (at.%) alloy.

References

[2000Sak] R. Sakidja, J. Myers, S. Kim, J. H. Perepezko, The effect of refractory metal substitution on the stability of Mo(ss) + T2 two-phase field in the Mo–Si–B system. Int. J. Refract. Met. Hard Mater. 18, 193–204 (2000).

[2016Tak] N. Takata, N. Sekido, M. Takeyama, J. H. Perepezko, M. Follett-Figueroa, C. Zhang, Solidification of Bcc/T1/T2 three-phase microstructure in Mo–Nb–Si–B alloys. Intermetallics 72, 1–8 (2016).