Equilibrium high entropy phases in X-NbTaTiZr (X = Al,V,Cr and Sn) multiprincipal component alloys

Abstract

X-NbTaTiZr, with X=Al,V,Cr and Sn, potential High Entropy Alloys obtained by arc melting were annealed to reveal the equilibrium constitution. AlNbTaTiZr and VNbTaTiZr alloys, made of two bcc solid solutions in the as-cast state, are composed of a bcc solid solution plus a minority phase, a Al–Zr intermetallic compound and a Zr–Ti hcp phase, respectively, while Cr and Sn containing alloys always present an intermetallic phase together with a bcc solid solution. Isochronal annealing on V- and Al- alloys revealed the mechanism of formation of the equilibrium microstructure.It is shown with an example in the AlNbTaTiZr system that stable high entropy phases (configurational entropy higher than 1.5 R) can be identified in equimolar alloys and synthesized.The inspection of the equilibrium microstructures in equimolar compositions together with the data available in literature on single phase HEAs confirm the usefulness of the selection criterion to design equilibrium HEAs previously developed, provided the relevant parameters are employed within the suggested limiting values.