ELASTIC AND THERMODYNAMIC PROPERTIES OF NiAl AND Ni3Al FROM FIRST-PRINCIPLES CALCULATIONS

Abstract

The elastic and thermodynamic characteristics of NiAl and Ni 3 Al crystals have been investigated by using a method of density functional theory within the generalized gradient approximation. The three independent elastic constants are C11 = 229.8 GPa , C12 = 124.7 GPa , C44 = 115.7 GPa for NiAl and C11 = 239.6 GPa , C12 = 151.7 GPa , C44 = 123.4 GPa for Ni 3 Al . The bulk moduli, shear moduli, Young's moduli, Poisson's ratios and ratios of B/G of NiAl and Ni 3 Al 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 3 Al crystals are elastically anisotropic. Especially for NiAl crystal, which should be much brittler than Ni 3 Al , lies at the critical point of brittle behavior. In addition, the present results are well in line with experimental and other theoretical results.