Role of α2/γ and γ/γ phase boundaries in cavity formation in a TiAl intermetallic compound irradiated with He-ions

A Ti–48at.%Al intermetallic compound has been irradiated with 200 keV He-ions at 623 and 773 K. The helium cavity density decreases with decreasing α2 and γ lamella width. A plot of the cavity density and lamella width reveals a linear relationship after irradiation to 15 dpa. Cavity density in regions with 300 nm wide lamella is about half of that in large γ grains of the specimen. The α2/γ lamellar boundaries supply a preferential nucleation site for cavities. Although the cavities are also formed on the γ/γ lamellar boundaries, the nucleation is limited to misfit dislocations on the boundaries. Defect-free zones are in the regions of about 50 nm width immediately adjacent to the lamellar boundaries at 773 K. These results suggest that the lamellar boundaries are effective sinks for radiation defects and contribute to the suppression of radiation-induced defect cluster development in TiAl alloys.