  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.
