Primary creep in nickel: Experiments and theory

Abstract

Primary creep in both polycrystalline and single crystalline pure nickel has been studied at a temperature range of 0.54–0.62 T m and stress range of 1−5 × 10 −4 σ/ μ. Although constant strain rate experiments and stress jump experiments in primary creep suggest that dynamic recovery controls fast deformation, diffusion controlled static recovery was found dominant at all but the very earliest stages of primary creep. Both deformation resistance and internal stress was found to evolve systematically during primary creep. While such evolution reached steady state in single crystals at steady state in creep, this was not the case for polycrystals at the minimum creep rate. Theoretical scaling-law models are provided for the primary creep strain rate based on a combination of dynamic and static recovery for an evolving deformation resistance. These scaling laws, normalized with steady state properties, and in dimensionless time, demonstrate that while the time constants for dynamic recovery controlled creep are typically of only 10 2 s duration, those for static recovery controlled creep are of the order of 10 4 s, in the range of stress and temperature investigated here. These scaling laws also provide a general behavior pattern which can cope with the creep strain portion of any transient during primary creep. Fast, dynamic recovery controlled plastic portions of transient deformation require further study. Andrade's famous −2 3 time law for creep strain rate is shown to be a general by-product of dynamic recovery controlled transient deformation.