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

摘要

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 micro-structures were characterized by an equiaxed, duplex grain structure (15 ìm diameter) containing lamellar á_2 (Ti_3Al)/? (TiAl) plates ~20 nm. Light optical metallography and transmission electron microscopy illustrated that these microstructures confirmed the (111)_?/(001)_(á2) duplex orientation relationship. Solid components annealed at 1150 °C at 5 h and 1380 °C at 1 h exhibited a fine-grain (3 ìm diameter) duplex structure and a large, equiaxed, fully lamellar grain structure (550 ìm diameter), respectively. The lamellar structure consisted mostly of coherent {111} ? (TiAl) twins with a width of ~0.9 ìm. These diverse annealed microstructures exhibited residual hardness values similar to the as-fabricated EBM components.