Thermodynamic Properties of Al-Cu-RE Ternary Alloys Calculated with Miedema's Theory

The formation enthalpy is very important for the stability and amorphous forming ability of alloys. A method based on the Miedema's theory and the geometric model was used to calculate the mixing enthalpies of liquid Al-Cu-RE (RE=La similar to Lu) alloys. The calculated results indicate that the mixing enthalpies for Al-Cu-RE ternary alloys are more negative than those of Al-Cu liquid alloys, which arises from chemical potential differences between the rare earth elements and Al, Cu. The maximum for the magnitude of mixing enthalpies for Al-Cu-RE liquid systems increases with the decrease of composition of Cu. It means that the addition of rare earth element is beneficial to the stability and amorphous forming ability for Al-Cu-RE systems. The formation enthalpies of intermetallics AlCuRE and Al8Cu4RE were also calculated. The formation enthalpy of AlCuRE is more negative than that of Al8Cu4RE. The formation enthalpies as a function of composition of rare earth elements for Al(Cu1-xREx)3, Al(Cu1-xREx) and Al-2(Cu1-xREx) were also calculated. The obtained formation or mixing enthalpies could be useful for the investigations of amorphous forming abilities and composition design of Al-Cu-RE alloys.