Effects of Hydrogen on Frictional Properties of DLC Films
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-01-01 |
| Journal | Tribology online |
| Authors | H. Ćkubo, Kenta Oshima, Ryo Tuboi, Chiharu Tadokoro, Shinya Sasaki |
| Institutions | Tokyo University of Science, Daido University |
| Citations | 17 |
| Analysis | Full AI Review Included |
Technical Documentation & Prospectus: Achieving Superlow Friction in Controlled Environments using MPCVD Diamond Precursors
Section titled âTechnical Documentation & Prospectus: Achieving Superlow Friction in Controlled Environments using MPCVD Diamond PrecursorsâExecutive Summary
Section titled âExecutive SummaryâThis research rigorously investigates the conditions required for achieving superlow friction (superlubricity, friction coefficient < 0.01) in hydrogenated Diamond-Like Carbon (a-C:H) films, a critical finding for designing low-wear mechanical systems in sealed or vacuum environments.
- Superlubricity Mechanism: Superlow friction is strictly dependent on the presence of high-pressure hydrogen (H2 > 4500 Pa) in the surrounding atmosphere, which reacts with the DLC surface during sliding.
- Tribofilm Formation: Atmospheric hydrogen is the dominant factor, leading to the rapid formation of a hydrogen-rich tribofilm that acts as an ultra-low shear interface.
- Internal vs. External Hydrogen: While hydrogenated films (18-30 at% H) are necessary precursors, the internal hydrogen content is secondary to the external hydrogen supply for maintaining superlow friction.
- Direct Correlation: Raman analysis established a linear inverse relationship between the average friction coefficient and the hydrogen content (N/(N+S) ratio) of the resulting tribofilm.
- Analytical Techniques: The study successfully employed ERDA and TOF-SIMS (using D2 gas tracing) to confirm that external hydrogen atoms react chemically with the carbon surface (sp2 bonds) to create the passivating tribofilm.
- 6CCVD Relevance: These findings confirm the necessity of highly controlled, high-quality CVD-derived carbon materials and surface chemistry management, areas where 6CCVDâs specialized MPCVD diamond capabilities provide superior wear resistance and purity.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minimum Friction Coefficient | < 0.01 | Dimensionless | Achieved with high-H tribopairs (CVD-DLC/PBIID-DLC) under 5000 Pa H2. |
| Critical H2 Pressure Threshold | > 4500 | Pa | Required atmospheric pressure to sustain superlow friction. |
| Hydrogen Content (CVD-DLC) | 30 | at% | Deposited via PECVD (Amorphous Hydrogenated Carbon). |
| Hydrogen Content (PBIID-DLC) | 18 | at% | Deposited via PBII & D (Amorphous Hydrogenated Carbon). |
| Hydrogen Content (PVD-DLC) | < 1 | at% | Deposited via Arc Ion Plating (Hydrogen-free ta-C). |
| Hardness (CVD-DLC) | 20.5 | GPa | Moderate hardness film used in successful superlubricity pair. |
| Hardness (PVD-DLC) | 72.6 | GPa | Extremely hard film; failed to achieve superlow friction without internal H. |
| Surface Roughness (PBIID-DLC) | 3.5 | nm | Smoothest tested sample (Ra). |
| Load (Standard Tribology Test) | 3.33 | N | Used for comparing tribopairs in fixed air/H2 environments. |
| Tribofilm H Content Increase (ERDA) | 4x Higher | Relative | H content in tribofilm in H2 condition vs. air condition. |
| Laser Wavelength (Raman) | 532 | nm | Used for measuring N/(N+S) ratio to estimate tribofilm hydrogen content. |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized three distinct DLC films deposited via CVD and PVD techniques, tested in a highly controlled atmospheric tribo-tester, followed by rigorous surface analysis to confirm chemical changes.
Material Preparation and Deposition
Section titled âMaterial Preparation and Depositionâ- CVD-DLC Film: Fabricated using Plasma-Enhanced Chemical Vapor Deposition (PECVD), resulting in high hydrogen content (30 at% a-C:H).
- PBIID-DLC Film: Fabricated using Plasma-Based Ion Implantation and Deposition (PBII & D), resulting in moderate hydrogen content (18 at% a-C:H).
- PVD-DLC Film: Fabricated using Arc Ion Plating (AIP), resulting in very low hydrogen content (< 1 at% hydrogen-free ta-C).
Tribological Testing Parameters
Section titled âTribological Testing Parametersâ- Equipment: Ball-on-disk tribo-tester capable of controlling atmospheric pressure from 10-5 to 105 Pa.
- Tribopairs: Tested as PVD-DLC/PBIID-DLC, CVD-DLC/PBIID-DLC, and PBIID-DLC/PBIID-DLC combinations.
- Standard Conditions: Load set to 3.33 N, Rotation Speed 10 rpm, Rotation Radius 5 mm, conducted in ambient air or fixed H2 (5000 Pa).
- Variable Pressure Conditions (CVD-DLC/CVD-DLC): Load reduced to 2.5 N, Speed 6 rpm. H2 pressure ramped sequentially: Increased from 500 Pa to 5000 Pa, then decreased back to 500 Pa, in 500 Pa increments held for three minutes each.
Surface Analysis Techniques
Section titled âSurface Analysis Techniquesâ- ERDA (Elastic Recoil Detection Analysis): Used for predictive evaluation of hydrogen content profiles in the DLC balls post-test.
- Raman Spectroscopy: Utilized the G-peak method and the N/(N+S) ratio to estimate the relative hydrogen content of the thin tribofilm layer.
- TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry): Used deuterium (D2) gas as a tracer to chemically map and confirm that surrounding atmospheric hydrogen reacted directly with surface carbon atoms during sliding.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe findings in this paper underscore the critical need for precision-engineered carbon surfaces capable of maintaining structural integrity under extreme tribological conditions while interacting reliably with controlled atmospheres. 6CCVD provides the high-purity, structural materials necessary to advance research in controlled tribology and superlubricity, particularly where conventional DLC films may lack necessary stability or size.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research into industrial, high-load, or extreme-wear environments (such as satellite mechanisms or specialized bearings), 6CCVD offers high-quality MPCVD materials that serve as superior wear surfaces or durable substrates for coating:
| Material Recommendation | Grade / Specification | Relevance to Research |
|---|---|---|
| Polycrystalline Diamond (PCD) | High-Purity MPCVD, Inch-Size Wafers | Excellent mechanical and thermal stability, serving as the ultimate wear counterface in high-load tribopairs. Can be polished to Ra < 5 nm (inch-size) to meet high surface quality requirements seen in the paper (3.5-6.0 nm Ra). |
| Single Crystal Diamond (SCD) | Optical/Electronic Grade (0.1”m - 500”m thickness) | Ideal for fundamental research requiring highly predictable, anisotropic surfaces. Can be used as a substrate for highly controlled CVD film deposition. Polished to Ra < 1 nm. |
| Custom DLC Substrates | Engineered CVD/MPCVD Materials | If researchers require a base material structurally superior to ISO100Cr6 steel for the DLC coating, 6CCVD can supply specialized diamond substrates (up to 10mm thick) capable of handling higher loads and temperatures. |
Customization Potential
Section titled âCustomization PotentialâThe constraints of the experiments (24 mm disks, specific coating thicknesses) are standard offerings for 6CCVD, ensuring seamless scalability for R&D projects:
- Custom Dimensions: We supply plates and wafers up to 125mm (PCD) and offer precision laser cutting services to match the exact 24 mm disk dimensions or any custom geometry required for specialized tribo-testers.
- Thickness Control: 6CCVD provides highly controlled material thicknesses ranging from 0.1 ”m to 500 ”m for both SCD and PCD, enabling precise control over mechanical properties and thermal management, crucial for high-speed tribology tests.
- Integrated Metalization: Although not the primary focus of this tribology paper, 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu). This allows researchers to integrate heating elements, temperature sensors, or complex contacts directly onto the diamond surface for sophisticated, real-time tribochemical analysis and feedback control.
Engineering Support
Section titled âEngineering SupportâThe core conclusionâthat hydrogen surface chemistry dominates frictionâis a key insight applicable across many extreme environments. 6CCVDâs in-house PhD engineering team specializes in tailoring diamond material specifications (surface termination, impurity levels, crystallinity) for unique requirements, including advanced Superlubricity and High-Load Tribology projects. We can assist in selecting the optimal MPCVD material and surface preparation method to ensure maximum stability and minimum friction coefficients in controlled atmospheric or vacuum applications.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The tribological behavior of diamond-like carbon films (DLC) is strongly dependent on the hydrogen content, sp2/sp3 ratio, and sliding environment. Some hydrogenated amorphous carbon films (a-C:H) exhibit superlow friction in hydrogen conditions. However, previous works have not clarified the dominant factors of the superlow friction phenomena of DLC films. In this research, we focused on the effects of hydrogen derived from the surrounding atmosphere and the hydrogen within the DLC films on superlow friction phenomena. To investigate these effects, friction tests were conducted on three DLC films having different hydrogen contents (0, and 18, 30 at%) in the air and in low-pressure-hydrogen conditions at various hydrogen pressures. After the friction tests, the wear tracks were examined by confocal laser scanning microscopy, Raman spectroscopy, elastic recoil detection (ERDA) analysis, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The hydrogen derived from the surrounding atmosphere and the formation of the hydrogen-rich tribofilm were key factors for the superlow friction phenomena.