Addressing the lattice stability puzzle in the computational determination of intermetallic phase diagrams

TL;DR

This paper investigates the impact of lattice stability data on computational phase diagrams of titanium-transition metal systems, demonstrating that first-principles calculations yield more accurate and realistic phase diagrams than empirical data, especially at intermediate temperatures.

Contribution

The study shows that using first-principles computed lattice stabilities improves the accuracy of phase diagrams for intermetallic systems compared to empirical data.

Findings

Empirical lattice stabilities lead to contradictions with experimental phase diagrams.

First-principles lattice stabilities produce realistic phase diagrams.

Predicted complex phase structures include eutectoid transitions and bcc phase miscibility gaps.

Abstract

The evaluation of phase stabilities of unstable elemental phases is a long-standing problem in the computational assessment of phase diagrams. Here we tackle this problem by explicitly calculating phase diagrams of intermetallic systems where its effect should be most conspicuous, binary systems of titanium with bcc transition metals (Mo, Nb, Ta and V). Two types of phase diagrams are constructed: one based on the lattice stabilities extracted from empirical data, and the other using the lattice stabilities computed from first principles. It is shown that the phase diagrams obtained using the empirical values contain clear contradictions with the experimental phase diagrams at the well known limits of low or high temperatures. Realistic phase diagrams, with a good agreement with the experimental observations, are achieved only when the computed lattice stability values are used. At intermediate temperatures, the computed phase diagrams resolve the controversy regarding the shape of the solvus in these systems, predicting a complex structure with a eutectoid transition and a miscibility gap between two bcc phases.