Thermodynamic modeling and optimization of the Fe–Ni–Ti system

A thermodynamic assessment of the ternary Fe–Ni–Ti system together with a partial reassessment of the binary sub-systems Ni–Ti and Fe–Ti was made following the CALPHAD method and using the compound energy formalism (CEF). Two and four sublattices were used to model the bcc and fcc phases respectively. This allows describing the order–disorder transformations occurring not only in the ternary Fe–Ni–Ti system, but also in the quaternary Al–Fe–Ni–Ti system. The description of the C14 Laves phase TiFe2 was modified to three sublattices in order to be consistent with other Al–Fe–Ni–Ti sub-systems in which a three sublattice model is needed. Thermodynamic parameters were optimized using the available experimental data. On the basis of this optimization the stable phase diagram is calculated. Moreover stable and metastable equilibria between ordered and disordered phases based on fcc and bcc respectively are calculated.