LOW STRESS VISCOUS CREEP IN A Ti-3Al-2.5V TUBING UNDER INTERNAL PRESSURIZATION

摘要

Biaxial creep tests were performed on a fine grained Ti-3Al-2.5V tubing at 823 and 873 K in the stress range of σ/E=1.7×10~(-4) to σ/E=5.9×10~(-4). Subsequently, the creep data were analyzed 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. HRTEM studies confirmed the nature of these bands.