AlCoCrCuFeNi-Based High-Entropy Alloys: Correlation Between Molar Density and Enthalpy of Mixing in the Liquid State

The density of the liquid equiatomic high-entropy alloys, namely, AlCoCrCuFeNi, AlCoCuFeNi, and CrCoCuFeNi, as well as quaternary alloys AlCoCuFe and AlCoCrNi was determined over a wide temperature range. The measurements were performed by a non-contact technique combining electromagnetic levitation and optical dilatometry. The temperature and composition dependencies of the density were analyzed and the molar excess volumes were calculated. The integral enthalpy of mixing of multi-component alloys was predicted using extended Kohler's model, while Miedema's model was used for binary sub-system alloys. It has been found that a negative excess volume of the investigated Al-containing liquid alloys correlates with a negative enthalpy of mixing. In contrast, a positive excess volume and an endothermic reaction have been estimated for the liquid CoCrCuFeNi alloy. The change of the excess volume in the Al-containing liquid alloys is affected by two basic effects, namely, compression of the Al matrix and formation of compounds in the melt.