Disclosing mechanical and specific structural characteristics of thick and adherent nanodiamond composite hard coating deposited on WC−Co substrates.

Murasawa, Koki; Diab, Mohamed R.; Atta, Hoda; Naragino, Hiroshi; El-Shaer, Abdelhamid; Yoshitake, Tsuyoshi; Egiza, Mohamed

Abstract

Nanodiamond composite (NDC) films, with a notable hardness of 65 GPa and a substantial thickness of 10 µm, were successfully fabricated on unheated WC−Co substrates using cathodic arc plasma deposition (CAPD) technology. Raman and synchrotron-based structural analysis, comparing NDC films with similarly hard tetrahedral amorphous carbon (ta-C) films and chemical vapor deposition (CVD) diamond, unveiled distinctive features. Visible Raman spectroscopy highlighted NDC's unique nanostructured composition, characterized by nanodiamond grains embedded in an amorphous carbon matrix, resulting in a high fraction of C−C sp3 bonds (70%) and intense σ* C−C resonance contributing to its observed hardness. The small size of diamond crystals induced numerous grain boundaries, as evident through intense t-PA Raman peaks, effectively suppressing internal stress to 2.77 GPa and enabling the deposition of an impressive thickness (10 µm), surpassing the thinness of hard ta-C (< 1 µm). Despite the substantial thickness, NDC films demonstrated remarkable films-substrate adhesion, with no delamination and minimal spallation, in contrast to observed buckling and delamination in CVD diamond during Rockwell testing at various loads (60 Kg and 100 Kg). Additionally, NDC films maintained a stable and low coefficient of friction (≤ 0.1) against an Al2O3 counter-body, compared to the higher coefficient (≥ 0.25) of the bare WC-Co substrate. Furthermore, NDC deposition boasted a rapid rate (3.5 µm/hr), significantly exceeding both ta-C and diamond coatings, enhancing its practical applicability. Significantly, the deposition process for NDC films stands out for its environmental friendliness and cost-effectiveness, involving no external heating, chemical reactions, chemical etching of Co, or nanodiamond seeding. The findings underscore the exceptional potential of NDC as a strong competitor to hard ta-C and CVD diamond coatings, especially in advanced cutting tool applications.

Citation

MURASAWA, K., DIAB, M.R, ATTA, H., NARAGINO, H., EL-SHAER, A., YOSHITAKE, T. and EGIZA, M. [2024]. Disclosing mechanical and specific structural characteristics of thick and adherent nanodiamond composite hard coating deposited on WC−Co substrates. Materials today communications [online], Articles in Press. Available from: https://doi.org/10.1016/j.mtcomm.2024.109839

• Journal Article Type: Article
• Acceptance Date: Jul 14, 2024
• Online Publication Date: Jul 15, 2024
• Deposit Date: Jul 16, 2024
• Publicly Available Date: Jul 16, 2024
• Journal: Materials today communications
• Electronic ISSN: 2352-4928
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• DOI: https://doi.org/10.1016/j.mtcomm.2024.109839
• Keywords: Nanodiamond composites (NDCs); Nanodiamond composite films (NDC films); Nanocomposite films; Hard coatings
• Public URL: https://rgu-repository.worktribe.com/output/2413088