First-principles study of phase stability in pseudobinary (Ni1-xPtx)3Al alloys

We studied the phase stability in pseudobinary (Ni1-xPtx)3Al alloys using a combination of first-principles calculations, a cluster expansion technique, and Monte Carlo simulations. Our ground state search yields L10 Ni2PtAl and L10 NiPt2Al as the two stable ground state structures, and the latter has been observed experimentally. The calculated c•a ratio of L10 NiPt2Al is also in good agreement with experiments. By performing Monte Carlo simulations, the order-disorder transition temperatures of L10 Ni2PtAl and L10 NiPt2Al were predicted to be ∼915K and ∼1275K, respectively. The mixing enthalpies of random pseudobinary L12 (Ni1-xPtx)3Al alloys were also predicted using our cluster expansion, and the results agree well with direct first-principles calculations on Special Quasirandom Structures (SQS's) for L12 alloys developed in the present study.