Analysis of phase formation in multi-component alloys

An attempt has been made to predict phase formation using a CALPHAD-based approach for a large number of compositions that are known to form FCC, BCC and a mixture of FCC and BCC phases. The stable phase is assumed to be the first phase that is formed upon cooling from liquid state with the highest driving force. The driving force for other phases at the transition for various compositions is also presented. A comparison between the parametric approach of phase prediction by study of thermodynamic and topological parameters on one hand and the CALPHAD approach on the other is also presented. CALPHAD approach appears to predict BCC phase formation much more accurately than the FCC phase formation. The results indicate that solid solution formation in multicomponent alloys is favored when the ratio of ΔSconfig/ΔSfusion is greater than 1 and 1.2 for equiatomic and non-equiatomic alloys, respectively. The results also point out that BCC phase is favored when the atomic size difference is larger, which is reflected by a higher value of ΔSσ/k. Formation of FCC phase appears to be governed mainly by ΔHmix, while BCC phase governed by ΔSσ/k, which is representative of strain in the structure.

► CALPHAD approach appears to predict BCC phase formation more accurately than FCC phase formation.
► Solid solution is favored when the ΔSconfig/ΔSfusion > 1 for equiatomic alloys.
► Solid solution is favored when the ΔSconfig/ΔSfusion > 1.2 for non-equiatomic alloys.
► BCC phase is favored when atomic size difference is larger, as reflected by a higher value of ΔSσ/k.
► FCC and BCC phase formation appears to be governed mainly by ΔHmix and ΔSσ/k, respectively.