Abstract
Diamond is the hardest material on Earth1. Nevertheless, polishing diamond is possible with a process that has remained unaltered for centuries and is still used for jewellery and coatings: the diamond is pressed against a rotating disc with embedded diamond grit2. When polishing polycrystalline diamond, surface topographies become non-uniform because wear rates depend on crystal orientations3. This anisotropy is not fully understood4 and impedes diamond’s widespread use in applications that require planar polycrystalline films, ranging from cutting tools5 to confinement fusion6. Here, we use molecular dynamics to show that polished diamond undergoes an sp3–sp2 order–disorder transition resulting in an amorphous adlayer with a growth rate that strongly depends on surface orientation and sliding direction, in excellent correlation with experimental wear rates7. This anisotropy originates in mechanically steered dissociation of individual crystal bonds8. Similarly to other planarization processes9, the diamond surface is chemically activated by mechanical means. Final removal of the amorphous interlayer proceeds either mechanically or through etching by ambient oxygen10.
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Acknowledgements
This work was financially supported by the BMBF (project OTRISKO) and the Deutsche Forschungsgemeinschaft (Gu 367/30).
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L.P., P.G. and M.M. designed the study, developed the amorphization model and wrote the paper. L.P. and S.M. carried out molecular dynamics simulations.
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Pastewka, L., Moser, S., Gumbsch, P. et al. Anisotropic mechanical amorphization drives wear in diamond. Nature Mater 10, 34–38 (2011). https://doi.org/10.1038/nmat2902
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DOI: https://doi.org/10.1038/nmat2902
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