First-principles calculations of thermodynamic properties and planar fault energies in Co3X and Ni3X L12 compounds

We do Density Functional Theory based total-energy calculations of the L12 phase in Co3X and Ni3X compounds, X being a transition metal element. The lattice parameters, magnetic moments and formation enthalpies are determined and compared with the available experimental data. The (111) superlattice intrinsic stacking fault energy (SISF), a crucial factor affecting materials strength and their mechanical behavior, is calculated using the axial interaction model. We have applied the quasiharmonic Debye model in conjunction with first-principles in order to establish the temperature dependence of the lattice parameters and the (111) SISF energies. We investigate our prediction of a low formation enthalpy in the system Ni −25 at.%Zn by doing auxiliary simulations for the fcc random alloy at the composition 25 at.%Zn. Our simulations indicate that the elements Ti, Zr, Hf, Nb, and Ta can help stabilizing the promising and extremely important Co3Al0.5W0.5 alloy.