Abstract
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.
Highlights
The aim of this study is to show the degree of surface effects upon the measurements
Industry machined or laboratory polished, show an abrasion surface layer with a thickness of tens nanometres and a structure consisting of refined polycrystalline graphite with almost the same La, ~20 nm
The carbon carbon (C\C) σ bonds in this layer are under compression at a level of 367 MPa for the as-polished and 1641 MPa for the asmachined surface
Summary
Whilst nuclear graphite has been developed for this purpose for more than half a century, there is not yet enough understanding of the possible correlations between the microstructure of a virgin graphite grade and the variation of physical properties with increasing neutron irradiation at different temperatures. This understanding is required to guide the design and use of nuclear graphite. Materials engineering and reactor designers still rely on an expensive and time-consuming qualification programme to obtain all necessary physical properties for manufacturing and designing graphite reactor components Such an experimental testing is realised through accelerated neutron irradiation in a materials testing reactor (MTR) with high neutron flux.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
