Coble creep of zirconium at homologous temperatures of 0.35 to 0.46

It is shown that at homologous temperatures T/TM of 0.35 to 0.46 (748 to 973 K) in the stress interval 4x10-6 G to 9x10-5 G (G is the shear modulus) and at intercept grain sizes L-bar less than ∼120 μm, Coble diffusion creep takes place in zirconium. At intercept grain sizes greater than ∼125 μm, the Harper-Dorn creep dominates under the same external conditions (temperature, stress). For the homologous temperature range under consideration, no interval of intercept grain sizes exists in which Nabarro-Herring creep would dominate. Bingham-type behaviour is characteristic of the Coble creep in the region of external conditions under consideration. The threshold stress is relatively low and its temperature dependence, if any, is weak. Employing the results of the present work together with those of previous papers on power-law creep in zirconium by M. Pahutova and J. Cadek and on Harper-Dorn creep by J. Fiala, J. Novotny and J. Cadek, creep mechanism maps were constructed using as coordinates the normalized mean intercept grain size L-bar/b (b is Burgers vector) and normalized stress σ/G for 873 K, or normalized stress σ/G and reciprocal homologous temperature TM/T for mean intercept grain sizes L-bar=100 μm and L-bar>125 μm