First-principles study of mechanical properties of BCC metals tungsten and molybdenum under high pressure

Abstract:

By using the first principles method based on the density functional theory, the volume, elastic constants, elastic modulus and the phonon dispersion curve as well as the generalized stacking fault energies of bcc metals W and Mo have been investigated at the pressure from 0GPa to 100GPa, and the mechanical stability, the brittle-ductile properties and the shear deformation of the two materials have also been studied at the same pressure. Firstly, by calculating the elastic constants of the two materials at the pressure from 0-100GPa, it is found the elastic constants of each material satisfy the conditions of mechanical stability, moreover, the frequency of the phonon dispersion curves at 100GPa is positive and there is no imaginary frequency, therefore, both the structures of the W and Mo are mechanical stable at the pressure from 0-100GPa. Besides, through analyzing the ratio of the bulk modulus and the shear modulus, it is found that the high pressure can make the ductility of the W and Mo stronger, and the ductility of Mo is better than that of W. Finally, the generalized stacking fault energies, shear modulus G111 along the <111> direction and the anisotropy ratio A of the two materials are all investigated and it is found that, both the generalized stacking fault energies and G111 as well as A all increase when the pressure becomes higher, and the value of A is very close to 1 at 100GPa, all these indicate that the high pressure makes the shear deformation become more difficult and the weakens the anisotropy of W and Mo.