Near-surface structure and residual stress in as-machined synthetic graphite
B Marz and K Jolley and R Smith and HZ Wu, MATERIALS & DESIGN, 159, 103-116 (2018).
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 I-D/I-G ratios evidencing graphite crystal refinement from an La of similar to 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 subsurface region, measured by L-a, showed an exponential relationship with depth (z) to a depth of 35-40 mu m. The positive shift of the G band in the Raman spectrum indicates a residual compression accompanied by refinement with the highest average of similar to 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 similar to 200 mu m. Mechanisms for the refinement and residual compression are discussed with the support of atomistic modelling. (C) 2018 The Authors. Published by Elsevier Ltd.
Return to Publications page