Effects of alloying elements on the structural, elastic and thermodynamic properties of Co3Ta compounds from first-principles calculations

In this work, we investigated the effects of alloying elements X (X = Al, Ti, V, Nb, Mo and W) on the structural stability, elastic, electronic and thermodynamic properties of Co3Ta compounds using the density functional theory (DFT) calculations. The investigations of atomic structure reveal that all of the alloying elements prefer to occupy Co sites rather than Ta sites in both the L12 and D019 structures, by which Mo is found to play the most effective role in the structural stabilization for γ′ phase. Both bulk moduli and shear moduli of Co3Ta compounds are reduced by the additions of alloying elements, except that the shear moduli are slightly increased by alloying Mo and W. By using the quasi-harmonic Debye model, the thermodynamic properties, including thermal expansion coefficients, heat capacity and bulk modulus, are predicted as a function of temperature for these compounds. The results from this work provide fundamental information for the further development of Co-Ta-based superalloys.