The effect of Ti addition on phase selection of CoCrCu0.5FeNi high-entropy alloys

Abstract

ABSTRACTWith the increasing titanium, the volume fraction of face-centred cubic-structured dendrites decreased, and ordered B2 phase, σ, and Laves phase appeared in CoCrCu0.5FeNiTix alloy when x > 0.5. With the increase of Ti content, ΔSmix, ΔHmix, valence electron concentration (VEC), and Λ (=ΔSmix/δ2) of CoCrCu0.5FeNiTix alloys decreased, while atomic size difference (δ) and electronegativity difference (Δχ) increased. Topologically close-packed (TCP) structures are favoured when ΔSmix > 14.53 J K−1 mol−1. TCP phases can be found when δ > 5.05 and Δχ ≥ 0.124. Simple solid solution phase is favoured when VEC ≥ 8.26 but multi-phases including TCP phase coexist when VEC < 8.26. Single-disordered solid solution forms only when Λ > 0.637, solid solution and TCP phases coexist when 0.531 < Λ < 0.637, and TCP phases are favoured when Λ < 0.531.