Revisiting intrinsic brittleness and deformation behavior of B2 NiAl intermetallic compound: A first-principles study

For NiAl intermetallic compound with B2 structure, there is still no calculation combining models of single and multiple layers while using the same basic set. Furthermore, some recently proposed criteria for brittleness and toughness have not been used to analyze its deformation behavior. Thus, first-principles calculation was applied to comprehensively study the elastic properties, ideal strength, generalized stacking fault energy and surface energy of B2-NiAl intermetallic compound. The results suggest that calculations based on the current basic set give more accurate lattice parameters and elastic moduli. The Pugh criterion and Cauchy pressure cannot be used to interpret the intrinsic brittleness of NiAl. In comparison, the ductility parameter based on the strain energy under elastic instability and ZCT and Rice criteria based on generalized stacking fault energy and surface energy successfully identify the intrinsic brittleness of the NiAl intermetallic compound. The reason why [111] slip always occurs in the deformation along [100] direction was clarified by examining the critical value for brittle-ductile transition. The results of density of state indicate shear deformation has less impact on structural stability, and the change of charge density difference implies that <001> shear induces more intensive redistribution of charge density, which is well correlated to the brittleness and deformation behavior of NiAl intermetallic compound.