Theoretically probing intrinsic properties of γ′ phase in FeCoNiTiAl high-entropy alloys

The intrinsic properties of the gamma ' phase are well known to be of critical importance for the targeted control of the mechanical performance of gamma/gamma ' high entropy alloys (HEAs). In the present work, a composition tuning strategy is employed to modulate the thermal stability, elastic properties, and deformation mechanisms of the gamma ' phase in (FeCoNi)(86)Ti7Al7 HEAs using ab initio methods. Prior to tailoring the alloying elements, the temperature-dependent stability of the gamma ' phase is meticulously investigated by considering both enthalpic and entropic contributions. The findings reveal that the primary vibrational entropy can be effectively substituted by an empirical parameter (delta) to expedite the design of stable HEAs. Subsequently, based on the individual effects of elements on the order-disorder transformation temperatures (Tod) and practical considerations for high-temperature applications, eight substituting elements (Nb, Mo, Ta, W, V, Cr, Mn and Cu) are judiciously selected from the 3d, 4d and 5d transition metal series. The results indicate that Nb and Ta are the most ideal substituting elements for the gamma ' phase, as they concurrently enhance the Tod, shear modulus, hardness, ductility, and antiphase boundary energy. These insights open a promising avenue for the innovative design of strong-yet-ductile gamma/gamma ' HEAs.