A model was presented where the properties of ultrafine-grained materials were explained in terms of the influence of high-angle boundaries on the rates at which dislocations were stored and recovered at the boundaries. The model reproduces the experimental observations that ultrafine-grained materials reach a steady state where the deformation resistance was independent of strain, that the strain rate sensitivity of flow stress was relatively high and that the steady-state flow stress increased inversely with the square root of grain size.

A Simple Dislocation Model of Deformation Resistance of Ultrafine-Grained Materials Explaining Hall–Petch Strengthening and Enhanced Strain Rate Sensitivity. W.Blum, X.H.Zeng: Acta Materialia, 2009, 57[6], 1966-74