The elastic deformation behaviors of perfect $\mathrm{NiAl}$ and $\mathrm{FeAl}$ are investigated using an ab initio electronic structure total energy method. The calculated ideal shear strengths for the $\left\{112\right\}⟨111⟩$ and $\left\{110\right\}⟨111⟩$ slip show qualitatively different features between the two intermetallics. In $\mathrm{NiAl}$, the shear deformation can be understood by exploring the transition among different stress-free structures on the strain paths, while in $\mathrm{FeAl}$ the instabilities under shear are found to be dictated by filling of the unstable anti-bonding $d$ states. The failure modes under uniaxial $⟨100⟩$ tension are also explored for $\mathrm{NiAl}$ and $\mathrm{FeAl}$ using two methods, a straightforward comparison of the resolved shear stress with the ideal shear strength and a detailed examination of the internal stability condition. Both methods yield the same conclusion: $\mathrm{FeAl}$ fails by tension while $\mathrm{NiAl}$ fails by shear. These predictions are consistent with the experimentally observed cleavage behaviors.

• Received 27 June 2005

DOI:https://doi.org/10.1103/PhysRevB.73.024105