Selective Plasma\nTreatment Endowing Low-Friction and\nWear-Resistant Surface of Polycrystalline Diamond against Copper

Despite its unrivaled hardness, polycrystalline diamond\ncan be\nseverely worn under the interaction with softer copper during the\nultrafine copper wire drawing process. The influence of the polycrystalline\ndiamond surface state on its friction behavior is investigated in\nthis work, and argon, oxygen, and hydrogen plasma treatments are adopted\nto regulate the surface state of diamond. When sliding against copper,\nthe original diamond plate exhibits a coefficient of friction (COF)\nexceeding 0.4, copper wears by transferring to the diamond, and diamond\nwears owing to the carbon cluster removal, as confirmed by the TOF-SIMS\nanalyses of the obvious wear tracks. After hydrogen plasma treatment,\nthe tribological performance of diamond sliding against copper is\nmost significantly improved, in which the COF is more stable and reaches\n0.18 with minimal wear debris. Hydrogen plasma treatment generates\nmore hydrogen termination on the diamond surface as well as a hydrogen-containing\namorphous carbon layer, which provides an isolated lubrication effect\nand strongly reduces adhesive wear. Argon plasma treatment also decreases\nthe level of COF to a certain extent, which is attributed to its polishing\nand cleaning action that removes surface contamination and reduces\nroughness. In contrast, oxygen plasma treatment induces a pronounced\netching effect, resulting in groove-like protrusions on the diamond\nsurface that exacerbates abrasive wear. Our research provides a more\nsustainable and residue-free solution for minimizing friction and\nwear of polycrystalline diamond wire drawing dies.