Microstructures for Two-Phase Gamma Titanium Aluminide Fabricated by Electron Beam Melting

Abstract

Pre-alloyed (Ti-48Al-2Cr-2Nb) powder was used to fabricate solid, fully dense (3. 85 g/cm3) components by electron beam melting (EBM). Foam components with densities from 0. 33 to 0. 46 g/cm3 were also fabricated by EBM. Both the solid and the foam component microstructures were characterized by an equiaxed, duplex grain structure (15 μm diameter) containing lamellar α2 (Ti3Al)/γ (TiAl) plates ~20 nm. Light optical metallography and transmission electron microscopy illustrated that these microstructures confirmed the (111)γ/(001)α2 duplex orientation relationship. Solid components annealed at 1150 °C at 5 h and 1380 °C at 1 h exhibited a fine-grain (3 μm diameter) duplex structure and a large, equiaxed, fully lamellar grain structure (550 μm diameter), respectively. The lamellar structure consisted mostly of coherent {111} γ (TiAl) twins with a width of ~0. 9 μm. These diverse annealed microstructures exhibited residual hardness values similar to the as-fabricated EBM components. © 2012 Springer Science+Business Media, LLC and ASM International.