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MoSiBTiC alloys are promising candidates for next-generation ultrahigh-temperature materials. However, the phase diagram of these alloys has been unknown. We have developed an ultrahigh-temperature thermal analyser based on blackbody radiation that can be used to analyse the melting and solidification of the alloy 67.5Mo–5Si–10B–8.75Ti–8.75 C (mol%). Furthermore, electromagnetic levitation (EML) was used for in-situ observation of solidification and microstructural study of the alloy. On the basis of the results, the following solidification pathway is proposed: Mo solid solution (Moss) begins to crystallize out as a primary phase at 1955 °C (2228 K) from a liquid state, which is followed by a (Moss+TiC) eutectic reaction starting at 1900 °C (2173 K). Molybdenum boride (Mo2B) phase precipitates from the liquid after the eutectic reaction; however, the Mo2B phase may react with the remaining liquid to form Moss and Mo5SiB2 (T2) as solidification proceeds. In addition, T2 also precipitates as a single phase from the liquid. The remaining liquid reaches the (Moss + T2 + TiC) ternary eutectic point at 1880 °C (2153 K), and the (Moss + T2 + Mo2C) eutectic reaction finally occurs at 1720 °C (1993 K). This completes the solidification of the MoSiBTiC alloy.

In situ ultrahigh-temperature XRD measurement of a MoSiBTiC alloy was carried out using a laser-heated diamond anvil cell and synchrotron radiation. This technique revealed the complicated dynamic behavior of phase transitions in the MoSiBTiC alloy on heating above 1950 °C. The MoSiBTiC alloy initially consisted of Mo solid solution (Moss), Mo5B2Si (T2), TiC, Mo2B, Mo3Si, and Mo2C phases. The Mo2B, Mo3Si, and Mo2C phases disappeared on heating at ~1647 °C. The Moss grains coarsened during heating and the Moss, TiC, and T2 phases were present >1950 °C. The obtained results verified the solidification pathway of the MoSiBTiC alloy.