The effect of Ti addition on phase selection of CoCrCu _0.5 FeNi high-entropy alloys

Abstract

With the increasing titanium, the volume fraction of face-centred cubic-structured dendrites decreased, and ordered B2 phase, σ, and Laves phase appeared in CoCrCu 0.5 FeNiTi x alloy when x > 0.5. With the increase of Ti content, Δ S mix , Δ H mix , valence electron concentration (VEC), and Λ (=Δ S mix / δ 2 ) of CoCrCu 0.5 FeNiTi x alloys decreased, while atomic size difference ( δ) and electronegativity difference (Δ χ) increased. Topologically close-packed (TCP) structures are favoured when Δ S mix > 14.53 J K −1 mol −1 . TCP phases can be found when δ > 5.05 and Δ χ ≥ 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.