Creep mechanisms in TI-3Al-2.5V alloy tubing deformed under closed-end internal gas pressurization

Creep tests were carried out on Ti-3Al-2.5V alloy tubing in the temperature range of 723-873 K under closed-end internal pressurization. The data thus obtained were analyzed to obtain the mechanistic creep parameters (stress exponent and activation energy). Transitions in creep mechanisms were noted as the stress exponent varied from a lower value of 1 through 2 to a higher value of 5 with increasing stress where the activation energy assumed values of 232 and 325 kJ mol(-1), respectively. The creep mechanisms were elucidated in the light of standard creep models supported by the substructures studied by transmission electron microscopy. Newtonian viscous creep (n = 1) at lower stresses was identified to be in accordance with a slip band model named after Spingarn and Nix. Grain boundary sliding with n = 2 was noted in an intermediate stress region while climb of edge dislocations was observed to control creep at higher stresses. Microstructural observations along with parametric variations of creep rates were useful ill identifying the underlying deformation mechanisms. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.