A model for experimentally-observed high-strain-rate dynamic strain aging in titanium

Recent high-strain-rate experimental results have shown an anomalous response by commercially pure titanium at relatively high temperatures: for a fixed high strain rate and a suitable strain, the flow stress which is a monotonically decreasing function of the temperature, suddenly begins to increase with increasing temperature, and then begins to decrease, displaying a dynamic strain-aging behavior. This phenomenon may be caused by the interaction between moving dislocations and mobile point defects in the dislocation core area. Based on this supposition, a model is developed which, both qualitatively and quantitatively. describes the experimentally observed results. This model assumes that the anomalous response is, in fact, dynamic strain aging caused by the drag of the core atmosphere, the evolution of the dislocation structural and the associated interaction processes. The model combines the concepts of athermal long-range and thermally activated, short-range barriers, with the model of a "trough" for the thermally activated breakaway of dislocations from the core atmosphere. The evolution of the core atmosphere concentration is included in the model, based on the strong interaction force between dislocations and point defects in the core area. The final product is a unified model which seems to accurately predict the response of commercially pure titanium, over a broad range of strain rates and temperatures. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.