Primary creep behavior of Ti-48Al-2W as a function of stress and lamellar morphology

The fully lamellar microstructure of powder metallurgy Ti-48Al-2W after cooling from the alpha region to 1280 degreesC, followed by air cooling and aging at 950 degreesC for up to 96 hours, is presented. Aging times as short as 5 hours result in acicular-shaped precipitates of W-rich beta(0) along lamellar interfaces, with the beta(0) size increasing with aging time. The beta(0) precipitates nucleate and grow in the alpha(2) lamellae. Concurrently, with the formation of go, the a, decomposes into discontinuous lamellae. Aging to precipitate beta(0) along lamellar interfaces increases the 760 degreesC tensile strength (with a slight reduction of ductility) and reduces the instantaneous creep strain, since beta(0) precipitates at lamellar interfaces hinder interface dislocation mobility. The deformed microstructures from interrupted creep tests at 140 to 276 MPa at 760 degreesC indicate that the precipitation of beta(0) along interfaces substantially reduces the primary creep strain, primarily due to the influence of beta(0) on interface dislocation emission and motion. These results are discussed in terms of the influence of lamellar morphology on the instantaneous creep strain and primary creep transient, and the possible creep mechanisms are highlighted.