Effects of electro-negativity on the stability of topologically close-packed phase in high entropy alloys

Abstract

Topologically close-packed (TCP) phases with complex structures are often observed in high entropy alloys (HEAs). Currently, these TCP phases are garnering significant interest from both theoretical and experimental perspectives due to the ductility deterioration of the high strength HEAs. Alternatively, there are instances when TCP phases can actually benefit the mechanical performances of alloys, such as the wear resistance. Therefore, the stability of TCP phases should be taken into consideration in the alloy design. In this paper, the relationship between the TCP phase stability and the physicochemical/thermodynamic properties of alloying components in HEAs was systematically studied. The stability of TCP phases was found to correlate well with the electro-negativity difference (ΔX) for most of the reported HEAs. The stability of TCP phases is well delineated by the electro-negativity difference (ΔX): i.e., TCP phases are stable at ΔX > 0.133 except for some HEAs that contain a significant amount of aluminum.