Radiation effects on microstructure and hardness of a titanium aluminide alloy irradiated by helium ions at room and elevated temperatures

Abstract

A 45XD TiAl alloy possessing a lamellar microstructure was irradiated using 5MeV helium ions to a fluence of 5×1021ionm−2 (5000appm) with a dose of about 1dpa (displacements per atom). A uniform helium ion stopping damage region about 17μm deep from the target surface was achieved by applying an energy degrading wheel. Radiation damage defects including helium-vacancy clusters and small helium bubbles were found in the microstructure of the samples irradiated at room temperature. With increasing irradiation temperature to 300°C and 500°C helium bubbles were clearly observed in both the α2 and γ phases of the irradiated microstructure. By means of nanoindentation significant irradiation hardening was measured. For the samples irradiated at room temperature the hardness increased from 5.6GPa to 8.5GPa and the irradiation-hardening effect reduced to approximately 8.0GPa for the samples irradiated at 300°C and 500°C.