Contemporary high-temperature alloys for gas turbines operate at 90% of their melting point, necessitating the development of novel materials that withstand higher temperatures. Promising possibilities are alloys located in the system Mo-Si-Ti-B, which have been under investigation for several years and show viable properties in terms of high-temperature mechanical properties and corrosion resistance.
The group of Chang et al. [1] developed a thermodynamic database, which is widely used for CALPHAD-type analyses to guide the development of the materials system. Based on new results, some areas of the phase diagram warrant further investigation. This contribution aims to refine the thermodynamic phase modelling in the metal-rich area of the Mo-Si-Ti diagram, which is important for future applications. For this reason, several additional alloys with varying compositions were produced by vacuum arc melting from high-purity raw materials. After annealing for at least 300 h at 1300 °C and subsequent quenching, the samples were characterized via SEM, EDX and WDX to compare experimental and calculated results.
While several regions could be verified, other parts of the phase diagram need to be reevaluated. Particularly, the solubility of the (Mo,Ti) solid solution for Si is much higher than previously reported. In accordance to the new findings, the location of the technologically relevant two phase and three phase regions of the system need to be readjusted. It is likely that the difference between previously reported results and the new findings stems from quenching the samples in this study. In previous investigations, all samples were furnace-cooled, which appears to have a significant influence on the phase composition and microstructures.

References
[1]     Y. Yang, Y. A. Chang, L. Tan, Y. Du, Materials Science and Engineering A361, pp. 281-293, 2003