Calculation of Existence Domains and Optimized Phase Diagram for the Nb-Ti Binary Alloy System Using Computational Methods

Abstract

We present the thermodynamic modeling for the Nb-Ti binary alloy system using CALPHAD (CALculation of PHAse diagram) and CE-CVM (Cluster expansion-cluster variation method) focusing on the solid solution part of the system. Existence domains for the various invariant reactions between the interaction parameters of the system were calculated between BCC and HCP phases. Five different regions viz. Simple Isomorphous, Monotectoid, Simple Isomorphous with congruent maxima, Monotectoid with congruent maxima and Syntectoid were identified in the calculated existence domains, each of which has its own characteristic reactional topology. The calculated existence domains are in good agreement with the earlier thermodynamic assessments made on the Nb-Ti system. Further, we have used the first-principles calculation to generate the thermochemical data for BCC and HCP phases for the Nb-Ti system. Moreover, we have also calculated the optimized phase diagram using the calculated existence domains, earlier experimental data, and the generated thermochemical data for the Nb-Ti system.