Newtonian viscous creep in Ti-3Al-2.5V

Biaxial creep tests were performed on fine-grained Ti-3Al-2.5V tubing at 823 and 873 K in the stress range sigma/Epsilon =1.7 10(-4) to sigma/Epsilon =5.9 x 10(-4). Subsequently, the creep data were analysed to determine the stress exponent and activation energy. A stress exponent value of 1 and an activation energy equal to that for grain boundary diffusion were suggestive of a Coble creep-controlled deformation regime. However, discrepancy between the experimental creep rates and Coble creep model predictions along with subsequent observation of deformed microstructures decorated with slip bands implied the operation of a different viscous creep mechanism. A slip band model proposed by Spingarn and Nix was found to provide a better description of the experimental strain rates rather than the conventional viscous creep mechanisms. High-resolution transmission electron microscopy studies confirmed the nature of these bands.