First-Principles Investigation of Perfect and Diffuse Anti-Phase Boundaries in HCP-Based Ti-Al Alloys

TL;DR

This study uses first-principles methods to analyze the thermodynamics and energies of anti-phase boundaries in Ti-Al alloys, revealing significant short-range order and quantifying boundary energies relevant to alloy deformation.

Contribution

It provides a comprehensive first-principles analysis of both diffuse and perfect anti-phase boundaries in Ti-Al alloys, including energies, stresses, and displacements, enhancing understanding of their mechanical behavior.

Findings

Substantial short-range order exists in Ti-6 Al alloys.

Diffuse antiphase boundary energies can reach 25 mJ/m² at typical processing temperatures.

Minimal anisotropy observed between basal and prism plane DAPB energies.

Abstract

First-principles thermodynamic models based on the cluster expansion formalism, monte-carlo simulations and quantum-mechanical total energy calculations are employed to compute short-range-order parameters and diffuse-antiphase-boundary energies in hcp-based $\alpha$-Ti-Al alloys. Our calculations unambiguously reveal a substantial amount of SRO is present in $\alpha$-Ti-6 Al and that, at typical processing temperatures concentrations, the DAPB energies associated with a single dislocation slip can reach 25 mJ/m$^{2}$. We find very little anisotropy between the energies of DAPBs lying in the basal and prism planes. Perfect antiphase boundaries in DO$_{19}$ ordered Ti$_3$Al are also investigated and their interfacial energies, interfacial stresses and local displacements are calculated from first principles through direct supercell calculations. Our results are discussed in light of mechanical property measurements and deformation microstructure strudies in $\alpha$ Ti-Al alloys.