The Stress-Relaxation Behaviour of a Polycrystalline Zirconium–Oxygen Alloy between 0·3 and 0·4 T_M

Abstract

Stress-relaxation tests have been performed on a polycrystalline zirconium–8·5 at.-% oxygen alloy at temperatures between 573 and 773 K (0·3 and 0·4 T _M ). At a given strain, the strain-rate sensitivity parameter increases monotonically with temperature, indicating that a single thermally activated process is rate controlling. The activation volume characteristic of the deformation process, in which the stress was found to decrease logarithmically with respect to time, was determined. Activation volumes were found to lie in the range 19–30 b³ (where b is the Burgers vector for prismatic slip in zirconium). A lack of success in obtaining values of the dislocation velocity stress exponent β* has been attributed to the inherent difficulty of applying the particular method of analysis chosen to a material that has a value of β* > 10. The overcoming of interstitial oxygen atoms has been tentatively suggested as the thermally activated ratecontrolling process during stress relaxation.