Transmission electron microscopy characterization of interfacial boundaries in heat-treated Ti₃Al + TiAl two-phase alloy

Abstract

A Ti₃Al(α₂) + TiAl(γ) two-phase alloy made of Ti-44 at.% Al was heat treated to refine the microstructure for improving ductility. Quantitative transmission electron microscopy was carried out on the interfacial boundaries in this alloy which is characterized by lamellar structure with numerous Ti₃Al-TiAl and TiAl-TiAl_T interfaces, and with the antiphase domain boundaries (APBs) in Ti₃Al lamellae. Two types of intrinsic interfacial dislocation which accommodate the interfacial misfits were seen on the Ti₃Al-TiAl interfaces. Extrinsic interfacial dislocations were also present on most of the interfaces. Three different types of defect structure which depend upon the mechanism of twinning during heat treatment were observed on the twin boundaries in TiAl lamellae. The APBs in Ti₃Al which appear as a maze pattern without preferential crystallographic orientation are of the type (a′₀/6)〈1010〉 and (a′_o/6)〈1120〉. The potential contribution of these interfaces to the mechanical properties is discussed.