Structural stability of NiAl with the L10 structure and local lattice distortion in the Ni3Al alloy around excess Al atoms

For explaining asymmetry in the flow stress of Ni3Al alloy as a function of aluminum content, the structural energy of ordered NiAl alloy with the L10 structure is obtained with the electronic structure calculations based on the density functional theory. Quite a large distortion in the c-direction is found at the equilibrium, which means an L10-like local structure appearing in the Al-rich region of the Ni3Al phase undergoes a large tetragonal strain. This tetragonal strain will give an explanation for the strengthening mechanism using the framework of Cochardt et al. The effect of the Al concentration on the structural stability of L10 in terms of the DOS is also discussed to explain the concentration dependence of the B2-L10 martensitic transition temperature.