Fracture Toughness of Massively Transformed and Subsequently Heat Treated TiAl Intermetallic Compound

The effects of massive transformation and subsequent heat treatments on the microstructure of Ti-46Al-7Nb-0.7Cr-0.2Ni-0.1Si (mol%) intermetallic compounds are studied. Massive transformation occurs at the center region of the specimen by cooling from α single phase state. At the surface side of the specimen, α phase has remained. Fine convoluted microstructure with α2, γ phases and lamellar structure has formed by heating at (α+γ) two phase state after massive transformation. Colony size or grain size is about 25 μm. Fine fully lamellar structure is obtained after heat treatment of convoluted microstructure at α phase for 60 s. Fracture toughness seems to be increasing with the increase in lamellar colony size. However, some massively transformed specimens show lower toughness due to the formation of microdamage present in samples before the test.