Equations were derived for the apparent stress exponent and activation energy in materials whose deformation was controlled by double kink nucleation and propagation on dislocations. The apparent activation energy (determined from Arrhenius plots of creep rate versus reciprocal temperature) could be 10 to 20% lower than the true activation energy; depending upon the stress. The apparent stress exponent (determined from the strain rate dependence of the stress or the stress dependence of the creep rate) was shown to be strongly dependent upon stress (and therefore upon temperature) and could decrease from above 10 at low temperatures, to unity at high temperatures; even though a single mechanism was controlling. Reasonable agreement was found between experimental and theoretical values of the stress exponent for yielding in single crystals of Ni3Al and NiAl; except that the calculated high-temperature values tended to be somewhat lower than the observed values. The analysis was expected to apply to yielding in many single crystals (or large-grained polycrystals) where the double kink mechanism was rate-controlling.

Apparent Activation Energy and Stress Exponent in Materials with a High Peierls Stress. T.E.Mitchell, J.P.Hirth, A.Misra: Acta Materialia, 2002, 50[5], 1087-93