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Uniaxial tension creep tests have been conducted on polycrystalline alpha zirconium from 50 to 850 C to evaluate the stress and temperature dependence of the second-stage creep rate. Five domains of creep behavior were observed over this temperature range. From 50 to 300 C the activation energy for creep was stress-dependent increasing from approximately 30 to 75 kcal/mole when the stress was decreased from 800 to 400 kg/cm2. Between 300 and 400 C, the activation energy is approximately 70 kcal/mole. From 400 to 500 C, the activation energy increased from 70 to 105 kcal/mole with decreasing stress. From 500 to 700 C, the activation energy was lower with an average value of 66 kcal/mole, which was independent of stress and temperature. From 700 to 800 C, the activation energy was 100 kcal/mole independent of stress. The apparent activation energy decreased to a very low value above 800 C. This apparent decrease in the activation energy is caused by a structural instability which may be related to the alpha-to-beta phase transformation. The creep behavior of alpha zirconium was somewhat different, depending upon whether the specimen was obtained from material fabricated and heat treated in the alpha phase or the beta phase. The various mechanisms controlling the creep behavior in these domains are discussed. The high-temperature activation energies of 100 and 66 kcal/mole are similar to those observed in other hexagonal close-packed (hcp) metals when compared on a homologous temperature basis. The low-temperature creep behavior is analogous in some respects to creep in zirconium-base alloys Zircaloy-2 and 2.5 Nb zirconium which are used for pressure tubes and fuel cladding in water-cooled nuclear reactors.
Gilbert, E. R.
Senior Research Scientist, Pacific Northwest Laboratories, Battelle Memorial Institute, Richland, Wash.
Duran, S. A.
Professor and Chairman, Washington State University, Pullman, Wash.
Bement, A. L.
Manager, Pacific Northwest Laboratories, Battelle Memorial Institute, Richland, Wash.