Stability of the B2 phase among refractory metals

Energy efficiency demands finding new materials for applications at elevated temperatures. Refractory multicomponent alloys with a BCC/B2 microstructure promise to serve as alternatives to the current state-of-the-art, Ni-based superalloys for applications at higher temperatures. With the vast compositional space of these alloys, the first fundamental question is whether the B2 phase can form among refractory metals. In this study, we span through the periodic table to investigate the potential for creating ordered B2 intermetallics among the refractory metals, using first principles calculations, and establish the correlation between the nature of the atomic bonds and stability of the B2 structure. We use our newly developed Multi-Cell Monte Carlo method to explore the extensive compositional space of these alloys, refine the trends in ordering, and pinpoint the most promising combinations for detailed analysis. We discover that B2 phases form exclusively with the inclusion of elements from groups VII and VIII, such as Re, Ru, and Os, and we identify these phases among a total of eleven elements. Further analysis of the electronic structure and bonding characteristics of these B2 systems reveals a pseudogap in the electronic density of states at the Fermi level. This pseudogap is attributed to the hybridization of d orbitals, leading to the formation of strong covalent bonds in the most stable compounds. This finding explains why B2 formation is restricted to elements from groups IV-VIII and V-VII refractory metals.