Continuous dynamic recrystallization during severe plastic deformation

Abstract

Severe plastic deformation (strains > 100%) has been shown to create significant grain refinement in polycrystalline materials, leading to a nanometric equiaxed crystalline structure for such metals as aluminum, copper and nickel alloys. This process, termed continuous dynamic recrystallization, is governed by evolution of the dislocation structure, which creates new grain boundaries from dislocation walls. In the proposed model, plasticity occurs which firstly involves dislocation multiplication, leading to strain hardening limited by dynamic recovery. After a critical dislocation density is reached new grain boundaries are formed by condensation of walls of dislocations, creating a new stable configuration that is favored due to a reduction of the system free energy. This evolution of the microstructure continues to develop, with a consequent progressive decrease in the average grain diameter. The proposed model provides a quantitative prediction of the evolution of the average grain size, as well as the dislocation density, during continued plastic strain. The model can be calibrated by use of results from any experiment that involves large plastic deformation of metals, subject to negligible annealing effects. In this paper, the model has been calibrated, and consequently validated, through experiments on machining of Al 6061-T6.

Microstructure and mechanical properties of carbon nanotubes reinforced aluminum matrix composites synthesized via equal-channel angular pressing

“…Grain refinement also decreases dislocation mean free paths leading to more strengthening. In addition, Al is a high stacking fault energy (SFE) material which after a certain amount of straining the hardening will be saturated and further straining does not increase the strength due to dynamic recrystallization (DRX) which is occurring by the nucleation and growth mechanisms of grains with high angle grain boundaries (HAGBs) [99][100][101]. Introducing CNTs postpones the recrystallization and promises higher strength to be obtained.…”

Latent heat saturation in microstructural evolution by severe plastic deformation

“…In the present work, an improved version of the simple model for CDRX developed by Bacca et al (2015) is developed. The basic principles of the original model are explained in this section, with more detail given in Bacca et al (2015), while the proposed new features are explained in the subsequent sections.…”

“…Microstructural evolution occurs via mechanical processes that involve cold working of the material. The resulting change in microstructure is associated with the amount of plastic deformation experienced by the material and becomes significant after severe plastic deformation (SPD) associated with processes such as low-speed machining (Shankar et al 2005, Bacca, Hayhurst andMcMeeking 2015). Experiments performed by Taylor and Quinney (1934) on torsion of metal rods have shown how this evolution is measured by latent heat, i.e.…”

“…Some constitutive models based on latent heat storage have previously been developed with the aim of predicting microstructure evolution in metals (Bernacki et al 2009, Le and Kochmann 2009, Quan et al 2011, Brown and Bammann 2012, Bacca et al 2015, with a focus on the phenomenon of dynamic recrystallization. This phenomenon has also been studied with different approaches such as phase field models (Militzer 2011, Moelans et al 2013, Sreekala and Haataja 2007, Suwa, Saito and Onodera 2008, which considers the nucleation and subsequent growth of new grains within the "old" microstructure, and with the use of finite element techniques as well as other methodologies such as cellular automata (Hallberg 2011).…”

The Influence of Processing Conditions on Microchemistry and the Softening Behavior of Cold Rolled Al-Mn-Fe-Si Alloys

“…This is a general challenge with respect to process optimization and alloy design for "tailor-made" properties of these alloys, and even more so with the introduction of more recycled aluminum where alloying elements like Mn, Fe and Si will accumulate in secondary alloys. More generally the role of dispersoids is of vital importance in the framework of recrystallization induced by severe plastic deformations and the stability of the refined micro-and nanostructure obtained by cold working, with the aim of creating stable grain refined metals with improved properties [16,17].…”