Design and development of a novel non-equiatomic Ti-Nb-Mo-Ta-W refractory high entropy alloy with a single-phase body-centered cubic structure

Element segregation and consequent phase separation are challenging problems in refractory high entropy alloys (RHEAs). In this study, thermodynamic parameters and calculation of phase diagrams (CALPHAD) were implemented for RHEA design to suppress segregation and phase separation. A novel non-equiatomic RHEA, Ti1(NbMoTa)2W0.5 alloy, was designed with a minimized difference between liquidus and solidus temperatures (ΔTl−s) and a wide temperature range between solidus temperature and transformation temperature (ΔTsingle) and compared with equiatomic RHEA. As-cast Ti1(NbMoTa)2W0.5 alloy maintained a single-phase body-centered cubic (BCC) structure, corresponding to the Scheil–Gulliver model, and segregation of constituent elements was suppressed owing to the minimized ΔTl−s. Ti1(NbMoTa)2W0.5 alloy showed excellent strength (approximately 1100 MPa) and ductility (1.6 times higher than TiNbMoTaW alloy). This study demonstrated a novel approach for obtaining single-phase BCC-structured RHEAs with suppressed elemental segregation and phase separation by utilizing combined use of ΔTl−s and ΔTsingle as alloy design indexes.