Influence of droplet-free ta-C coatings and lubrication conditions on tribological performance and mechanical characteristics of WC−Co.

Cemented carbide (WC−Co) tools suffer from surface abrasion, limiting their performance. This study explores droplet-free tetrahedral amorphous carbon (ta-C) coatings deposited via arc ion plating as a solution. The coatings possess a dense, sp3-rich structure, leading to a remarkable hardness of 60 GPa compared to 37 GPa of WC−Co, and strong adhesion with a critical scratch load of 41 N. Tribological tests confirm their effectiveness. Dry sliding tests show reduced wear and lower CoF (0.123) compared to uncoated tools (0.159). Notably, water-soluble lubricants yielded the best performance (lowest CoF: 0.092, superior wear resistance), while water and mineral oil also improved performance

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

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

Nanomechanical and structural characteristics of nanodiamond composite films dependent on target-substrate distance.

This study explores the optimization of target-substrate distance (TSD) in coaxial arc plasma deposition technique for depositing nanodiamond composite (NDC) films on unheated WC–Co substrates, with a focus on enhancing properties relevant to cutting tool applications. TSD significantly impacted film growth and adhesion, while hardness and Young's modulus remained stable within the 10–50 mm TSD range. Increased TSD led to reduced deposition rates and film thickness, but improved quality by eliminating macroparticles and reducing surface roughness. Notably, the NDC film deposited at 10 mm TSD exhibited exceptional adhesion resistance, a thickness of 11.45 μm, low compressive internal stress (2.8 GPa), and a surface roughness (Sa) of 280 nm, coupled with an impressive hardness of 49.12 GPa. This film also achieved a favorable deposition rate of 1.05 nm/s. In comparison, the film deposited at 15 mm TSD displayed a maximum hardness of 51.3 GPa, lower Sa of 179 nm, but a reduced deposition rate of 0.29 nm/s. The estimated C sp3 fraction correlated well with the nanoindentation measurements, while internal stress showed a consistent relationship with film adhesion. These findings suggest that a TSD of 10 mm is optimal for balancing hardness, adhesion, deposition rate, and surface roughness, making NDC films a promising candidate for cutting tool applications

Eco-friendly thick and wear-resistant nanodiamond composite hard coatings deposited on WC–Co substrates.

Nanodiamond composite (NDC) films, synthesized using an environmentally friendly PVD coaxial arc plasma deposition technique on commercial cemented carbide (Co6 wt%) substrates without the need for substrate heating, chemical etching of Co, and chemical gases. These NDC coatings, crafted under specific discharge power conditions (5.2 J/pulse, 120 V, and 1 Hz), with or without a substrate biasing (−100V, 40kHz, and 35% duty cycle), exhibit a distinctive nanostructure characterized by nanodiamond grains embedded in an amorphous carbon (a-C) matrix. Highlighting remarkable mechanical characteristics attributed to highly energetic ejected carbon ion. The coatings boast high hardness (H = 65–82 GPa), Young's modulus (E = 688–780 GPa), plasticity index (H/E = 0.094–0.105), and brittle fracture resistance (H3/E2 = 0.58–0.9 GPa). Additionally, these NDC films manifest a substantial thickness of 7 μm due to low internal stress, along with superior adhesion, anti-wear resistance, and a low friction coefficient (0.1–0.09) through dry sliding against an Al2O3 counterpart. Raman analysis substantiates the nanocomposite structure of the film, underscoring the influential role of biasing in enhancing the characteristics of these environmentally friendly and wear-resistant NDC coatings. Nevertheless, the application of a negative bias led to increased internal stress levels (1.28 to 4.53 GPa), adversely impacting the adhesion between the film and substrate, resulting in a decrease from HF3 to HF6 as per Rockwell C indentation. NDC coatings hold significant potential for extending the lifespan of cutting tools and improving overall machining performance

Wetting state and mechanical property alteration for the Fe3Si films using rapid thermal annealing under various temperatures

The current research demonstrates the modification of the wetting behavior and mechanical features as well as structure and morphology of Fe3Si films created via facing target sputtering by the rapid thermal annealing (RTA) with the set RTA temperatures (TRTA) of 200, 400, 600, and 800 °C. Following the RTA process, the crystallinity of Fe3Si developed under 400 °C or below. At the 600 °C and 800 °C TRTA, new crystal orientations emerged for FeSi and then β-FeSi2, respectively. Together with composition results, the Fe3Si films were proven to change into FeSi and then FeSi2 under a high TRTA regime. At temperatures of 600 °C and 800 °C, large crystallites, including the scraggly interface, were observed. The root-mean-square roughness roughened slightly according to the RTA process at TRTA of 600 °C or above. The hydrophobic properties of the Fe3Si film surfaces became hydrophilic after the RTA procedure at a TRTA value above 400 °C. The hardness value of the Fe3Si films evidently increased through RTA at 600 °C and 800 °C. Thus, above 400 °C, the RTA process significantly alters the physical features of as-created Fe3Si films