Structural stability of NiCoFeCrAlxhigh-entropy alloy fromab initiotheory

First-principles alloy theory predicts that at room temperature the paramagnetic NiCoFeCrAl${}_{x}$ high entropy alloys adopt the face centered cubic (fcc) structure for $x\ensuremath{\lesssim}0.60$ and the body centered cubic (bcc) structure for $x\ensuremath{\gtrsim}1.23$, with an fcc-bcc duplex region in between the two pure phases. The calculated single- and polycrystal elastic parameters exhibit strong composition and crystal structure dependence. Based on the present theoretical findings, it is concluded that alloys around the equimolar NiCoFeCrAl composition have superior mechanical performance as compared to the single-phase regions.