Primary creep of Zircaloy 4 in the temperature range 923-1073K

The results of uniaxial constant stress creep tests on Zircaloy-4 PWR fuel cladding material are described, together with observations of the creep-induced microstructures. The shapes of the creep curves recorded at stresses below, close to and above the yield stress at temperature are categorised, and discussed in terms of the operative deformation mechanisms. At stresses below the yield stress at temperature, creep is suggested to be dominated by a diffusional mechanism. The shape of the creep curves, however, indicates that the occurrence of some dislocation activity in some grains makes a significant contribution to deformation. The interaction of, the dislocation and diffusional mechanisms needs to to understood if the details of shape of the creep curves are to be predictable. (author)