Understanding the mechanisms of electroplasticity from a crystal plasticity perspective

Abstract

Electroplasticity is defined as the reduction in flow stress of a material undergoing deformation on passing an electrical pulse through it. The lowering of flow stress during electrical pulsing has been attributed to a combination of three mechanisms: softening due to Joule-heating of the material, de-pinning of dislocations from paramagnetic obstacles, and the electron-wind force acting on dislocations. However, there is no consensus in literature regarding the relative magnitudes of the reductions in flow stress resulting from each of these mechanisms. In this paper, we extend a dislocation density based crystal plasticity model to incorporate the mechanisms of electroplasticity and perform simulations where a single electrical pulse is applied during compressive deformation of a polycrystalline FCC material with random texture. We analyze the reductions in flow stress to understand the relative importance of the different mechanisms of electroplasticity and delineate their dependencies on the various parameters related to electrical pulsing and dislocation motion. Our study establishes that the reductions in flow stress are largely due to the mechanisms of de-pinning of dislocations from paramagnetic obstacles and Joule-heating, with their relative dominance determined by the specific choice of crystal plasticity parameters corresponding to the particular material of interest. (Arka Lahiri), pratheek.shanthraj@manchester.ac.uk (Pratheek Shanthraj), f.roters@mpie.de (Franz Roters) not only during the pulses but also between the pulses [2-4]. Thus, repeated electropulsing during deformation mimics the attributes of hot working, albeit at a much lower energy cost. This has prompted development of industrial manufacturing paradigms like Electrically-assisted manufacturing (EAM) and Electroplastic manufacturing processing (EPMP) which leverage the phenomenon of EP on an industrial scale. There are several reviews of EAM, EPMP, and the phenomenon of EP which can serve as useful references in this regard [5-8].Even as there are increased efforts to harness the benefits of EP in the manufacturing industry, the mechanisms contributing to EP continue to be poorly understood. Researchers over the years have proposed several different theories to explain the reductions in flow stress during

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“…However, the effect of electron wind is considered lower than Joule heating [ 17 ]. Using a numerical approach, Lahiri [ 18 ] showed that the effect of the electron wind force is negligible. Both Molotskii and Lahiri proposed the de-pinning of dislocation via the magnetic field that is generated while the current is flowing in the conductor [ 17 , 18 , 19 ].…”

“…Using a numerical approach, Lahiri [ 18 ] showed that the effect of the electron wind force is negligible. Both Molotskii and Lahiri proposed the de-pinning of dislocation via the magnetic field that is generated while the current is flowing in the conductor [ 17 , 18 , 19 ]. However, both these studies were undertaken using face-centered cubic (fcc) metals; this study proves that the effect of an induced magnetic field on plasticity is also observable in hcp metals.…”

One Step Forward to Electrically Assisted Forming Mechanisms and Computer Simulation: A Review

“…Three wellknown theories for EAF, that is, Joule heating, depinning of dislocations, and the electron wind force, were explored individually in the case of their effect on stress drop. [7] Dislocation density-based CP model. Open-source CP software DAMASK were used for simulations.…”

“…A CP model can provide an understanding of the nature and magnitude of the reductions in flow stress due to different causative factors, including the depinning of dislocations, the electron wind force, and Joule heating, but there are some drawbacks that should be properly addressed for the widespread application of the CP. According to the study by Lahiri et al, [7] the model lacks the generality and should be modified for other…”

“…(JH denotes Joule heating, F ew denotes electron wind force, 'All' refers to all mechanisms of EP being active, andτ sol and v 0 represent flow stress reductions due to changes in those terms). Reproduced with permission [7]. Copyright 2019 IOPscience.…”