Ab initio studies of Mo-based alloys: Mechanical, elastic, and vibrational properties

Mo-based alloys hold great potential as structural materials for applications at ultra-high temperatures. In order to reliably predict mechanical and thermodynamic properties of Mo-based alloys, the Mo-Si-B model system is studied using first-principles density functional theory methods. Specifically, five intermetallic compounds MoSi2, Mo5Si3, Mo3Si, Mo5SiB2 and MO2B are chosen, and their equilibrium lattice parameters, elastic properties, phonon spectra, and thermodynamic properties are calculated and compared, most of them for the first time. It is shown that for the calculated properties where the measured data are available, the predicted results are in very good agreement with available experiments, thus validate our computational methodologies. Our comprehensive and systematic calculations reveal many interesting and previously unknown features in the mechanical and vibrational properties of these alloys in relation to their structure and composition. It is shown that boron in the Mo-Si-B system enhances elastic and bulk properties without compromising ductility. MoSi2, which has the largest Si concentration, also has the largest elastic anisotropy compared with the other four crystals. (c) 2013 Elsevier Ltd. All rights reserved.