First-Principles Study of Mechanical and Thermodynamic Properties of Binary and Ternary CoX (X = W and Mo) Intermetallic Compounds

In this study, the structural, elastic, and thermodynamic properties of DO(19) and L1(2) structured Co(3)X (X = W, Mo or both W and Mo) and μ structured Co(7)X(6) were investigated using the density functional theory implemented in the pseudo-potential plane wave. The obtained lattice constants were observed to be in good agreement with the available experimental data. With respect to the calculated mechanical properties and Poisson’s ratio, the DO(19)-Co(3)X, L1(2)-Co(3)X, and μ-Co(7)X(6) compounds were noted to be mechanically stable and possessed an optimal ductile behavior; however, L1(2)-Co(3)X exhibited higher strength and brittleness than DO(19)-Co(3)X. Moreover, the quasi-harmonic Debye–Grüneisen approach was confirmed to be valid in describing the temperature-dependent thermodynamic properties of the Co(3)X and Co(7)X(6) compounds, including heat capacity, vibrational entropy, and Gibbs free energy. Based on the calculated Gibbs free energy of DO(19-)Co(3)X and L1(2)-Co(7)X(6), the phase transformation temperatures for DO(19-)Co(3)X to L1(2)-Co(7)X(6) were determined and obtained values were noted to match well with the experiment results.