TiAl alloys are being developed for future use as lightweight, high strength structural materials for the aerospace and automotive industries. The growth of titanium borides in-situ in a TiAl melt can lead to a variety of structures, such as TiB (Bf and B27 structures) and TiB2, depending on the Ti/Al ratio in the melt, and on the presence of further alloying additions [1,2]. The morphologies of the boride particles can be significantly altered if they grow coupled with other boride or intermetallic phases [2-4]. Since the morphology and distribution of the borides with the intermetallic matrix can significantly affect their effectiveness as creep reinforcements, the structures and growth mechanisms of these composites need to be quantified at the atomic scale.
In a Ti-45.5at.%Al-1.6at.%Fe-l.lat.%V-0.7at.%B alloy know to contain TiB2 precipitates [2,3], the morphology of the boride particles have been investigated using HREM. The Stuttgart JEOL-ARM, operated at 1250kV using the side-entry pole-piece with 0.12nm point resolution, enables the distinction between individual boron and titanium columns in the titanium borides to be achieved for the first time.