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

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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-TiAlT 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.