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diffusion with D P ΒΌ 10 12 m 2 s 1 : Comparison with cases of Nabarro-Herring creep
calculated for similar conditions indicates that the two types of diffusion creep give
comparable strain rates at 10 MPa stress when the grain size is of the order of
100 lm. However, owing to its stronger stress dependence, the dislocation climb
creep can be expected to predominate down to smaller grain sizes at higher stresses.
Also, for a given D P = D V ratio, the core diffusion mechanism can be expected to be
relatively more important as the stress is increased. However, these predictions rest
on the presumption that the compatibility requirements are met and that the climb
multiplication process is effective. In practice, with minerals, the number of Burgers
vectors available may often be insufficient for the dislocation climb mechanism to
operate exclusively and so climb creep may more commonly appear as a contributing
mechanism, complementary to others.
Harper-Dorn creep ( 1957 ) is another type of creep process that is often thought
to involve dislocation climb at very low stresses but with dislocation density that is
independent of stress, giving rise to linear stress dependence (Nabarro 2000 ;
Poirier 1985 , pp. 114-117).
References
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Burton B (1983) The characteristic equation for superplastic flow. Phil Mag A48:L9-Ll13
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boundaries as vacancy sources or sinks. Scripta Metall 4:171-174
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Theoret. Phys. (U.S.S.R.), 44, 1349-1367; tr. in Soviet Physics JETP 1317(1344), 1909-1920
Nabarro FRN (1948) Deformation of crystals by the motion of single ions. In: Report of a
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1947, London, The Physical Society, 75-90
Nabarro FRN (1967) Steady-state diffusional creep. Phil Mag 16:231-237
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