EQUILIBRIA AND MICROSTRUCTURAL EVOLUTION IN THE BETA/BETA'GAMMA' REGION OF THE NI-AL-TI SYSTEM - MODELING AND EXPERIMENT

As part of a comprehensive study of 3-phase alloys in the Ni-Al-Ti system incorporating the beta (B2, NiAl type), beta' (L2(1), Ni2AlTi type) and gamma' (L1(2), Ni3Al type) phases, the phase equilibria for this part of the ternary diagram were modelled by CALPHAD methods. The approach used and the results obtained are presented, and compared with an experimental determination by analytical electron microscopy of the 3-phase equilibrium triangle at 900-degrees-C. The calculated/experimental 3-phase triangle differs significantly from earlier estimates. The theoretical model is also used to predict phase formation sequences for several alloys in the 3-phase triangle and these are critically compared with observed microstructures. An unusual graded antiphase domain structure seen in one alloy is interpreted.