Influence of Mo concentration on the structure, mechanical and thermodynamic properties of Mo–Al compounds from first-principles calculations

Abstract

The refractory metal Mo–Al compounds are potential high-temperature materials because of the high melting-point and excellent mechanical properties. However, the structure and related overall performances of Mo–Al alloys are unclear. Here, we apply the first-principles approach to study the influence of Mo concentration on the structure, elastic and thermodynamic properties of Mo–Al compounds. The results show that five phases: cubic MoAl12, rhombohedral MoAl5, monoclinic MoAl4, monoclinic Mo3Al8 and cubic Mo3Al are thermodynamic and dynamical stability. One novel tetragonal Mo2Al(I4/mmm) is predicted. The convex hull shows that Mo3Al8 is more thermodynamically stable than that of the other Mo–Al alloys. Moreover, the bulk modulus of Mo–Al alloys increase gradually with increasing Mo concentration. The bulk modulus, shear modulus and Young's modulus of Mo3Al are 220.7 GPa, 123.5 GPa and 312.3 GPa, respectively, which are larger than the other Mo–Al alloys. The high elastic properties are that the high concentration of Mo forms the numerous Mo–Al bonds due to the interaction between Mo and Al. The calculated Debye temperature of Mo–Al alloys obeys the sequence of Mo3Al8>MoAl4>MoAl5>MoAl12>Mo3Al > Mo2Al. The phonon density of state demonstrates that the high-temperature thermodynamic properties of Mo–Al alloys are determined by the vibration of Al atom and Mo–Al bond.