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Near-surface structure and residual stress in as-machined synthetic graphite

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posted on 10.09.2018 by Benjamin Maerz, Kenny Jolley, Roger Smith, Houzheng Wu
We have used optical and electron microscopy and Raman spectroscopy to study the structural changes and residual stress induced by typical industrial machining and laboratory polishing of a synthetic graphite. An abrasion layer of up to 35 nm in thickness formed on both machined and polished surfaces, giving the same ID/IG ratios evidencing graphite crystal refinement from an La of ~110 nm down to an average of 21 nm, but with different residual compression levels. For the as-polished sample, structural change was limited to the near surface region. Underneath the as-machined surface, large pores were filled with crushed material; graphite crystals were split into multi-layered graphene units that were rearranged through kinking. Graphite crystal refinement in the sub-surface region, measured by La, showed an exponential relationship with depth (z) to a depth of 35–40 μm. The positive shift of the G band in the Raman spectrum indicates a residual compression accompanied by refinement with the highest average of ~2.5 GPa on top, followed by an exponential decay inside the refined region; beyond that depth, the compression decreased linearly down to a depth of ~200 μm. Mechanisms for the refinement and residual compression are discussed with the support of atomistic modelling.

Funding

We gratefully acknowledge the support of the EPSRC Advanced Materials for Nuclear Fission programme under UNIGRAF: Understanding and Improving Graphite for Nuclear Fission with the grant numbers EP/M018822/1, EP/M018598/1 and EP/M018679/1.

History

School

  • Science

Department

  • Chemistry

Published in

Materials and Design

Citation

MAERZ, B. ... et al, 2018. Near-surface structure and residual stress in as-machined synthetic graphite. Materials and Design, 159, pp.103-116.

Publisher

Elsevier © The Authors

Version

VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution 4.0 International (CC BY 4.0) licence. Full details of this licence are available at: http://creativecommons.org/licenses/ by/4.0/

Acceptance date

20/08/2018

Publication date

2018

Notes

This is an Open Access Article. It is published by Elsevier under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/

ISSN

0264-1275

Language

en

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