Phase Stability and Thermo-Physical Properties of Nickel-Aluminum Binary Chemically Disordered Systems via First-Principles Study

Abstract

The effect of Al content and crystal structures on ground state, phase stability, elasticity and thermodynamics of Ni1−xAlx (x = 0.25, 0.50 and 0.75) binary chemically disordered systems are investigated using first-principles method in combination with quasi-harmonic Debye-Gruneisen model. The special quasirandom structures are applied to model disordered body-centered cubic (bcc) and face-centered cubic (fcc) phases. The Gibbs free energy of mixing of equiatomic Ni0.5Al0.5 is the lowest. The nonmagnetic fcc structure’ Ni1−xAlx are predicted to be more favorable phases. Disordered Ni1−xAlx are less stable than ordered L21 Ni3Al and B2 NiAl, and L21 phase is the most likely to form a nuclear growth. The somewhat different impact of Al content on elastic properties has been extracted that the resistance to volume change, shear deformation and elastic deformation of Ni1−xAlx decrease with increasing Al content. For bcc and fcc phases, Ni0.75Al0.25 and Ni0.25Al0.75 are predicted to be ductile behavior, while Ni0.5Al0.5 exhibit brittleness. The structural, vibrational and electronic contributions are taken into account to study the thermodynamic properties at finite temperature. The lattice constants a and volumetric thermal expansion coefficient α of Ni1−xAlx systems increase with the increase of Al content. Nevertheless, it is decreasing for heat capacity Cv and C. The vibrational entropy Svib of bcc Ni0.25Al0.75 is the largest in considered temperature. The α, C and Svib of disordered Ni1−xAlx are larger than that of ordered Ni3Al and NiAl. Vibrational and electronic entropy are the dominating at finite temperature stabilization mechanism.