The influence of aging on the microstructure and creep behaviour of a γ-Ti-48%A1-2%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 beta(o) along lamellar interfaces, with the beta(o) size increasing with aging time. The beta(o) precipitates nucleate and grow in the alpha(2) lamellar by diffusion of W. Concurrently, the alpha(2) decomposes into discontinuous lamellar. Creep tests at 760 degreesC and 276 MPa indicate that the precipitation of beta(o) along interfaces substantially reduces the primary creep strain, primarily due to the influence of beta(o) 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 beta(o) particles, which serve to initiate intergranular void formation during tertiary creep. The results are discussed in terms of the effect of W solute and beta(o) precipitates on the alpha(2) lamellar stability and are used to infer the influence of microstructural features on the various creep resistance parameters. (C) 2002 Elsevier Science B.V. All rights reserved.