A phenomenological model based on nanostructured dislocation cluster interactions to predict the work hardening behavior of cryodeformed materials

Abstract

In the present work, a phenomenological model was developed to understand the different stages of strain hardening in cryodeformed FCC materials with different stacking fault energy (SFE) level, i.e., high, medium, and low. The strain hardening in the materials consists of three stages, i.e. (i) easy-glide (stage-I) (ii) hardening (stage-II) and (iii) dynamic recovery (DRV) (stage-III). The proposed model considers the microstructure of cryodeformed materials which contains a mixture of discrete dislocation clusters including twin boundaries, and randomly arranged dislocations (dislocation debris). The model output predicts the work hardening behavior by using three deciding parameters: (i) normalized nanostructured dislocation cluster velocity (vDC)nor, (ii) normalized nanostructured dislocation cluster acceleration (aDC)nor and (iii) normalized dislocation debris velocity (vDD)nor. The deformation mechanisms during stage-II of strain hardening can be predicted by the nature of (aDC)nor curve. The cyclic trend in the (aDC)nor curve indicates the simultaneous occurrence of dislocation-based strengthening and DRV. The mono-cyclic (aDC)nor curve indicates hardening behavior due to combined effect of twin and dislocations-based deformation. The (aDC)nor curve fails to segregate stage II and stage III of deformation. In order to identify the transition from stage II and stage III mode of deformation, the relationship between (vDC)nor and (vDD)nor was formulated. A new parameter: DRV factor (Sx), was used to estimate the fraction of DRV in the materials. The uniaxial stress vs strain curves at varying strain rates and defect densities calculated from XRD analysis were used as input parameter for the model. A transmission electron microscopy (TEM) was performed to validate the dislocation interactions concluded from the model.