Steady-State Creep of a-Zirconium at Temperatures up to 850 8C

Cumulative zirconium creep data over a broad range of stresses (0.1 to 115 MPa) and temperatures (300 8C to 850 8C) were analyzed based on an extensive literature review. Zirconium obeys traditional power-law creep with a stress exponent of approximately 6.4 over stain rates and temperatures usually associated with the conventional “five-power-law ” regime. Thus, dislocation climb, rather than the often assumed glide mechanism, may be rate controlling. Power-law breakdown occurs at values of «̇ss/D greater than approximately 109 cm22, consistent with most traditional five-power-law materials. The creep rate of zirconium at low values of s /G varies proportionally to the applied stress. The rate-controlling mechanism(s) for creep within this regime is unclear. A grain-size dependency may exist, particularly at small (,90 mm) sizes, suggesting a diffusional mechanism. A grain-size independ-ence at larger grain sizes supports a Harper–Dorn mechanism, but the low observed activation energy (,90 kJ/mol) is not consistent with those observed at similar temperatures at higher stresses in the five-power-law regime (270 kJ/mol) where creep is also believed to be lattice self-diffusion controlled. The stress dependence in this regime is not consistent with traditional grain-boundary sliding mechanisms. I. INTRODUCTION and diffusional (Coble[9,10,12–15] or Nabarro–Herring[9,15]