For the composite target properties, GBR with custom features has been used, and the performance is represented in Fig. (and Table , SI). The prediction follows the ideal fit for lower strength values but underestimates at higher strength region because of the lack of enough training data in this regime. The alloy composition having the largest EI value is Nb87Zr1.1Hf0.6W11.3 which is consistent with the alloy composition suggested by YS and UTS individual ML model. Mean, standard deviation, and expected improvement values for the first seven suggested alloy compositions for the composite properties are presented in the supplementary information (Table -S8, SI). The key alloying elements in the suggested compositions are W, Hf, Zr, Ta, and Re. The maximum solid solubility limit of W, Hf, Zr, and Ta in Niobium is 100 atom percent, and Re has a solid solubility limit of 45.5 atom percent . Thus, the suggested alloy compositions most likely form a single-phase solid solution contributing to the alloy strengthening mechanism. We used the CALPHAD approach to study the equilibrium phase diagrams for these suggested alloy candidates. As the alloy systems are quaternary and quinary, we constructed pseudo-binary phase diagrams. We derived the pseudo-binary phase diagrams for Nb87Zr1.1Hf0.6W11.3 and Nb85Zr1.2Ta3.5W9.7Re0.6 alloy systems using Thermo-Calc software . These phase diagrams are constructed by varying the mole percentage of tungsten while keeping the mole percentage ratio of other elements fixed. The analysis of the pseudo-binary phase diagrams (Fig. , SI) suggests that for a wide temperature range from about 550 o C to 2500 o C, single-phase BCC is the only thermodynamically stable phase. This Thermo-Calc calculation provides a good agreement that the suggested alloy candidates are likely to have high strengths due to the single-phase solid solution.