Elastic and thermodynamic properties of NiAl and Ni_3Al from first-principles calculations

摘要

The elastic and thermodynamic characteristics of NiAl and Ni_3Al crystals have been investigated by using a method of density functional theory within the generalized gradient approximation. The three independent elastic constants are C_(11) = 229.8 GPa, C_(12) = 124.7 GPa, C _(44) = 115.7 GPa for NiAl and C_(11) = 239.6 GPa, C _(12) = 151.7 GPa, C_(44) = 123.4 GPa for Ni_3Al. The bulk moduli, shear moduli, Young's moduli, Poisson's ratios and ratios of B/G of NiAl and Ni3Al are also calculated. In addition, the dependences of the bulk moduli on temperatures and pressures as well as the linear thermal expansion coefficients (α_L) versus temperatures are evaluated and discussed. Both NiAl and Ni_3Al crystals are elastically anisotropic. Especially for NiAl crystal, which should be much brittler than Ni_3Al, lies at the critical point of brittle behavior. In addition, the present results are well in line with experimental and other theoretical results.