In situ creep under helium implantation of titanium–aluminium alloy

The intermetallic alloy Ti–47Al–2W–0.5Si (at.%) has been homogeneously implanted with 4He2+ ions under uniaxial tensile stresses from 20 to 450 MPa to a maximum dose of about 0.16 dpa (1370 appm-He) with displacement damage rates of 2 × 10−6 dpa s−1 at temperatures of 573 and 773 K. Strain under implantation was determined by Linear Variable Displacement Transformer (LVDT), while changes of microstructure were investigated after implantation by Transmission Electron Microscopy (TEM). Irradiation creep strain showed a pronounced transient behaviour, virtually independent of temperature, with a stress dependence which can be approximately described by a creep compliance of 8 × 10−6 dpa−1 MPa−1 up to stresses of 350 MPa. The microstructure of the as-received material consisted of a patch-work of mainly lamellar γ/α2 colonies and equiaxed γ-grains with islands of precipitates. Only ‘black dot’ damage was observed after implantation at 573 K under different stresses, while implantation at 773 K yielded a dense population of bubbles and dislocation loops, mostly mutually attached.