Influence of BCC (A2)-structured elements on Ti2AlMo (B2) for the formation of A2 + B2 structure

The development of two-phase microstructures analogous to the γ/γ' structure in Ni-based superalloys has rarely been achieved in refractory high-entropy alloys (RHEAs). In this study, Ti 2 AlMo-based multi-principal element alloys alloyed with V, Cr, Nb, and Ta were systematically designed to explore phase separation behavior and identify the key elements promoting A2 (disordered BCC) + Ordered B2 structures. Among all investigated compositions, only the Ta20 alloy exhibited a distinct A2 + B2 two-phase microstructure with cuboidal morphology-reported here for the first time in a Ti 2 AlMo-based system. TEM–EDS analysis confirmed that the cuboidal A2 precipitates were formed within an ordered-B2 matrix through spinodal decomposition, resembling the γ/γ' configuration in Ni-based superalloys. This unique microstructure significantly enhanced the high-temperature strength above 1073 K, while the B2 intermetallic matrix limited ductility. The Ta20 alloy represents a unique realization of a γ/γ'-like cuboidal A2 + B2 structure in a refractory alloy system, offering a promising design route toward next-generation high-temperature materials with balanced strength and ductility. • Ti 2 AlMo-based alloys were developed to explore A2 + B2 phase formation. • A unique γ/γ'-like cuboidal A2 + B2 microstructure was obtained. • The cuboidal A2 phase was formed through spinodal decomposition. • Superior high-temperature strength above 1173 K was observed. • Findings propose a new design strategy for lightweight refractory alloys.