First-principles study of atomic ordering in fcc Ni-Cr alloys

We investigate atomic ordering in fcc Ni-rich Ni-Cr alloys using first-principles techniques and statistical mechanics simulations based on the Ising Hamiltonian with effective cluster interactions computed by the screened generalized perturbation method (SGPM) and projector augmented wave (PAW) method. We demonstrate that effective chemical interactions in this system are quite sensitive to alloy composition and in fact to the specific configurational state. The chemical interactions for the high-temperature random state produce the atomic short-range order (SRO) with intensity maximum close to the $(\frac{2}{3}\frac{2}{3}0)$ point of the reciprocal space in agreement with the previous first-principles investigation. A consistent with diffuse neutron scattering data maximum at the $(1\frac{1}{2}0)$ position is obtained only when we take into consideration relatively small strain-induced interactions, which solves a long-standing inconsistency between theory and experiment in this system. The calculated transition temperature of order-disorder transition of Ni${}_{2}$Cr alloy, 880 K, is in good agreement with the experimental value of 863 K.