Elevated temperature creep behavior and microstructure of a cryomilled aluminum-titanium alloy

The dependence of flow stresses on the strain rates was studied at temperatures from 503 K to 773 K. Pronounced threshold stresses were observed at all temperatures of testing and decrease with increasing temperature. At slower strain rates of testing, the threshold stresses are dominant in the stress-strain rate curves, and prevent formation of master curves after normalization of strain rates and flow stresses. The data at higher strain rates appear to be much less influenced by the threshold stresses.; At high temperatures, strong yield points with stress drop are seen at the faster strain rates. At slower strain rates, serrated yielding is found. This behavior is seen in submicron-grained materials with dispersoids, and very low dislocation densities. Using a model by Johnston and Gilman, a model was developed incorporating dislocation annihilation effects of higher temperatures. Numerical integration yields stress-strain plots which agree qualitatively with discontinuous yielding.