Long-term creep behaviour of cast TiAl-Ta alloy

Abstract

The long-term creep behaviour of the cast Ti-44.4Al-8.1Ta (at.%) alloy with an initial γ-TiAl(L10)+α2-Ti3Al(D019) microstructure was investigated at 700 °C. The alloy shows a remarkable creep resistance. The minimum creep rate is measured to be as low as 1.47 × 10−10 s−1 and total deformation is only 2.5% after an interrupted 30000 h creep test at 200 MPa. The creep exposure affects the stability of the initial microstructure. The discontinuous precipitation leads to the formation of γ + τ(Ti3Al2Ta) type of microstructure along the lamellar colony and grain boundaries. The decomposition of the α2 phase results in the formation of τ and γ + α2 + L12 segments within the lamellae and cellular γ + α2 + L12 network within the coarse particles. The intensive formation and coalescence of the cavities along the grain boundaries leads to predominantly intergranual type of creep fracture at the applied stresses of 250 and 300 MPa.