First-principles calculations of thermal expansion path of the Co7Mo6 Mu-phase

Abstract

The Mu-phase, which is an intermetallic compound, can form in steels and superalloys, and significantly degrade their mechanical properties. The thermal expansion of Co7Mo6 Mu-phase have been investigated by first-principles based quasi-harmonic Debye-Gr\"uneisen approximation and by comparing the free energies calculated along different paths of thermal expansion. The calculations were carried out for temperatures from 0 K to 1500 K which below the decomposition temperature of Co7Mo6. The electronic, vibrational and magnetic energy contributions to the free energy were accounted. The thermal expansion of Co7Mo6 is not isotropic. The influence of physical factors on the stability of Co7Mo6 was analyzed. The isobaric heat capacity, thermal expansion, elastic constants, bulk modulus, sound wave velocities, Debye and Curie temperatures were reported. The calculated results analyzed and are in an agreement with the available experimental and theoretical data.