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arXiv · 2111.08187

Effect of a weak magnetic field on ductile-brittle transition in micro-cutting of single-crystal calcium fluoride

Yunfa Guo·Yan Jin Lee·Yu Zhang·Anastassia Sorkin·Sergei Manzhos·Hao Wang
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Abstract

Magneto-plasticity occurs when a weak magnetic field alters material plasticity and offers a viable solution to enhance ductile-mode cutting of brittle materials. This study demonstrates the susceptibility of non-magnetic single-crystal calcium fluoride (CaF2) to the magneto-plastic effect. The influence of magneto-plasticity on CaF2 was confirmed in micro-deformation tests under a weak magnetic field of 20 mT. The surface pile-up effect was weakened by 10-15 nm along with an enlarged plastic zone and suppressed crack propagation under the influence of the magnetic field. Micro-cutting tests along different crystal orientations on the (111) plane of CaF2 revealed an increase in the ductile-brittle transition of the machined surface with the aid of magneto-plasticity where the largest increase in ductile-brittle transition occurred along the [11-2] orientation from 512 nm to a range of 664-806 nm. Meanwhile, the subsurface damage layer was concurrently thinner under magnetic influence. An anisotropic influence of the magnetic field relative to the single-crystal orientation and the cutting direction was also observed. An analytical model was derived to determine an orientation factor M that successfully describes the anisotropy while considering the single-crystal dislocation behaviour, material fracture toughness, and the orientation of the magnetic field. Previously suggested theoretical mechanism of magneto-plasticity via formation of non-singlet electronic states in defected configurations was confirmed with density functional theory calculations. The successful findings on the influence of a weak magnetic field on plasticity present an opportunity for the adoption of magnetic-assisted micro-cutting of non-magnetic materials.

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Yunfa Guo, Yan Jin Lee, Yu Zhang, Anastassia Sorkin, Sergei Manzhos, Hao Wang. 2021-11-16. Effect of a weak magnetic field on ductile-brittle transition in micro-cutting of single-crystal calcium fluoride. https://arxiv.org/abs/2111.08187

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