Papers by Keyword: Stage IV

Abstract: A constant strain hardening rate is characteristic for large strain deformation at low temperatures and often observed during wire drawing. This stage of deformation, in the following referred to as stage IV, is determined by the microstructural evolution of dislocation cells. At elevated temperatures, rapid stress saturation is typically reached and no stage IV behavior is observed. This behavior is modelled in the present work, following the concept of state-parameter based plasticity, evolving dislocation density and subgrain formation as functions of strain rate, strain and temperature. It is demonstrated that the temperature dependence of state parameters at different deformation stages is closely related. The present model is compared to a series of compression tests carried out on a Gleeble 1500 thermo-mechanical simulator. EBSD micrographs of the same material reveal the microstructural evolution during plastic deformation. It is shown experimentally that the transition from cell forming behavior to subgrain formation correlates well with the disappearance of stage IV and the overall change in the dominant mechanism for overcoming obstacles. In combination with thermally activated yield stress prediction, this model, recently implemented in the software package MatCalc, offers a powerful tool for flow-curve simulation.

Abstract: The eect of deformation-induced disorientations on work-hardening of metals is modelled by dislocation dynamics. By incorporating excess dislocations related to disori- entations, Kocks' dislocation model describing stage III hardening is extended to stage IV. Disorientations evolving from purely statistical reasons still lead to stage III behavior and a saturation of the ow stress, but deterministic contributions to the development of disorienta- tions, as dierences in activated slip systems across boundaries, cause a linear increase of the flow stress at large strains. Such a constant work-hardening rate is characteristic for stage IV.