Study of the ideal strength and electronic structure in B2 transition-metal aluminides

The ideal tensile and shear strengths of the B2-type (CsCl) transition-metal aluminides FeAl, CoAl, and NiAl have been investigated systematically using an \textit{ab initio} electronic structure total energy method. Our calculation explains the unique weakness in FeAl under the $\langle 100 \rangle$ uniaxial tension as compared to NiAl, in which the shear instability intrudes before it approaches the tensile instability at a large critical strain. The weakness of FeAl along $\langle 001\rangle$ direction is attributed to an instability introduced by the filling of antibonding $d$ states. The calculation thus provides a theoretical basis for the observed cleavage behavior of the three materials. This work is supported by Department of Energy, Basic Energy Sciences under the Office of Science under contract DE-AC03-76SF00098.