The influence of aging on the microstructure and creep behaviour of a γ-Ti–48%Al–2%W intermetallic

The results of aging at 950 C for up to 192 h on the microstructure and creep properties of a fully lamellar Ti–48at.% Al–2at.% W is presented. Aging times as short as 5 h result in acicular precipitates of W rich βo along lamellar interfaces, with the βo size increasing with aging time. The βo precipitates nucleate and grow in the α2 lamellae by diffusion of W. Concurrently, the α2 decomposes into discontinuous lamellae. Creep tests at 760 °C and 276 MPa indicate that the precipitation of βo along interfaces substantially reduces the primary creep strain, primarily due to the influence of βo on interface dislocation emission and motion. However, aging reduces the extent of tertiary creep and slightly reduces creep life, due to larger and more numerous intergranular βo particles, which serve to initiate intergranular void formation during tertiary creep. The results are discussed in terms of the effect of W solute and βo precipitates on the α2 lamellar stability and are used to infer the influence of microstructural features on the various creep resistance parameters.