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

Abstract: The intrinsic properties of the γ′ phase are well known to be of critical importance for the targeted control of the mechanical performance of γ/γ′ 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 γ′ phase in (FeCoNi)₈₆Ti₇Al₇ HEAs using ab initio methods. Prior to tailoring the alloying elements, the temperature-dependent stability of the γ′ 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 (δ) to expedite the design of stable HEAs. Subsequently, based on the individual effects of elements on the order–disorder transformation temperatures (T_od) 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 γ′ phase, as they concurrently enhance the T_od, shear modulus, hardness, ductility, and antiphase boundary energy. These insights open a promising avenue for the innovative design of strong-yet-ductile γ/γ′ HEAs. 摘要.: