Deformation processes during creep of single and polycrystalline CaO

Abstract

When the variation of the creep rate, ∊_s, with stress, [sgrave], is described as ∊_s α [sgrave]ⁿ, the stress/creep rate relationships are found to be similar for both single and polycrystalline lime at 1473 K. Since creep of single crystals can only occur by the generation and movement of dislocations, the observed transition in stress exponent, n, from ∼ 5 at high stresses to almost unity at low-stress levels cannot be interpreted in terms of a change from dislocation to diffusional creep processes. Moreover, the forms of the primary creep curves are similar, the primary stage can be restored by a recovery anneal, and incubation periods of zero creep rate are invariably recorded before creep recommences after small stress reductions during creep over the entire stress range studied for both the single and polycrystalline materials. The similarity of the behaviour patterns exhibited at all stress levels suggests that the recovery-controlled dislocation processes governing the creep properties differ only in detail in the n ⋍ 5 and n ⋍ 1 regimes.