LMTO/CVM Calculations of Partial BCC Based Phase Relations in the System Ni-Al-Ti

Abstract

Linear Muffin Tin Orbital calculations of equations of state were performed for observed and hypothetical BCC based ordered structures in the Ni-Al-Ti system. Total energies were parameterized in the Connolly-Williams and e-G approximations. The resulting effective cluster interactions (ECI) were used to calculate: 1) BCC based ground-states; 2) The A2→B2 and B2→L21 order-disorder transition temperatures; 3) Quasibinary phase diagrams for the NiAl-NiTi join. The BCC octahedron approximation of the cluster variation method (CVM) was used to calculate Tc(L21→B2) and TC(B2→A2). The simple cubic “cube approximation” of the CVM was used to calculate quasibinary NiAl-NiTi phase diagrams.