An alternative approach to the tribological analysis of Si-doped DLC coatings deposited with different bias voltages using Raman spectroscopy mapping
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-08-10 |
| Journal | Emergent Materials |
| Authors | Bruno J. Rodriguez, Parnia Navabpour, Daniela Proprentner, Marc Walker, Hailin Sun |
| Institutions | Teer Coatings (United Kingdom), University of Warwick |
| Citations | 8 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation: High-Performance Carbon Materials for Extreme Tribology
Section titled âTechnical Analysis and Documentation: High-Performance Carbon Materials for Extreme TribologyâThis document analyzes the research on Si-doped Diamond-Like Carbon (DLC) coatings and connects the findings to 6CCVDâs advanced MPCVD diamond capabilities, focusing on applications requiring extreme hardness, thermal stability, and controlled doping.
Executive Summary
Section titled âExecutive SummaryâThis study successfully demonstrates that increasing the bias voltage during magnetron sputtering deposition significantly enhances the structural and thermal properties of Si-doped DLC coatings, providing critical insights for high-temperature tribological applications.
- Structural Enhancement: Increasing the bias voltage from 65 V to 85 V resulted in a measurable increase in the spÂł C-C content, rising from 21.9% to 23.1%.
- Mechanical Doubling: Hardness (H) was nearly doubled, increasing from 13.6 GPa (65 V bias) to 27.2 GPa (85 V bias), accompanied by a corresponding increase in the Reduced Elastic Modulus (Eâ).
- Thermal Stability Window: The maximum operational temperature before failure was extended by 150 °C, moving from 300 °C (65 V bias) up to 450 °C (85 V bias).
- Tribological Trade-Off: Softer films (lower bias) exhibited the lowest Coefficient of Friction (COF), while the hardest film (85 V bias) provided superior wear resistance due to its higher H/Eâ ratio and thermal stability.
- Novel Analysis: Raman spectroscopy mapping of wear tracks was validated as an effective method for analyzing spÂČ configuration changes and estimating maximum flash temperatures reached during tribological contact.
- 6CCVD Relevance: While DLC provides moderate performance, 6CCVDâs MPCVD Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) offer intrinsic hardness and thermal stability far exceeding the limits demonstrated by these DLC films, making them ideal for next-generation extreme environment applications.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results, detailing the relationship between deposition bias voltage and resulting material properties.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Deposition Method | Magnetron Sputtering | N/A | Used for Si-doped DLC coating |
| Bias Voltage Range | 65 to 85 | V | Controlled ion bombardment energy |
| Silicon Content | 1.3 ± 0.1 to 1.5 ± 0.2 | at. % | Consistent doping level across samples |
| Hardness (H) Range | 13.6 ± 1.0 to 27.2 ± 1.5 | GPa | Increased with bias voltage |
| Reduced Elastic Modulus (Eâ) Range | 157.7 ± 15.9 to 243.5 ± 6.5 | GPa | Increased with bias voltage |
| sp³ C-C Content (XPS) | 21.9 ± 0.4 to 23.1 ± 0.6 | % | Increased with bias voltage |
| Thermal Stability (Failure Temp) | 300 to 450 | °C | Maximum operating temperature |
| G-Peak Position Range | 1556 ± 1 to 1570 ± 2 | cm-1 | Shifted with increasing bias |
| Tribological Load | 10 | N | Applied during ball-on-disk testing |
| Sliding Speed | 1 | cm s-1 | Linear speed |
| Counterpart Material | 6.3 mm diameter Al2O3 | Ball | Used for friction and wear tests |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure focused on controlled deposition parameters, comprehensive structural characterization, and high-temperature tribological assessment.
- Coating Deposition: Silicon-doped DLC (a-C:Si) films were deposited onto M42 high-speed steel specimens (30 mm diameter) using magnetron sputtering. The primary variable was the applied bias voltage (65 V, 75 V, 85 V).
- Structural Characterization (Raman & XPS):
- Raman spectroscopy (λ = 532 nm) was used to analyze the D and G modes, extracting parameters like G-peak position, FWHM (G), and the intensity ratio ID/IG, indicative of spÂČ configuration changes.
- X-ray Photoelectron Spectroscopy (XPS) quantified the silicon content, identified silicon carbide (Si-C) and silicon oxide (Si-O-C) bonds, and measured the spÂł C-C content.
- Mechanical Testing: Hardness (H) and Reduced Elastic Modulus (Eâ) were measured using NanoTest Xtreme with a Berkovich indenter. Indentation depth was strictly controlled (< 200 nm) to minimize substrate influence.
- Tribological Testing (MFT-5000): Ball-on-disk friction tests were performed using a 10 N load and 6.3 mm Al2O3 balls as the counterpart. Tests were conducted at increasing temperatures (Room Temperature up to 450 °C) until coating failure.
- Wear Analysis: Specific Wear Rates (SWR) were calculated based on volume removal, measured using an Alicona InfiniteFocus instrument. Raman mapping was applied across the wear tracks to analyze localized graphitization and estimate maximum flash temperatures.
- High-Temperature Integrity: Cross-sections of tested coatings were analyzed using TEM (HAADF detector) and EDS to study oxygen diffusion depth and structural integrity after high-temperature annealing (300 °C).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the need for materials with extreme hardness, superior thermal stability, and precise doping control for advanced tribological applications. 6CCVDâs MPCVD diamond materials offer performance metrics that significantly surpass the limits of the Si-doped DLC films studied.
Applicable Materials for Replication and Extension
Section titled âApplicable Materials for Replication and Extensionâ| Application Requirement | 6CCVD Material Recommendation | Technical Rationale |
|---|---|---|
| Extreme Hardness & Wear Resistance | Electronic Grade SCD (Single Crystal Diamond) | Intrinsic hardness > 90 GPa, providing wear resistance orders of magnitude greater than the 27.2 GPa achieved by the best DLC film. |
| High Thermal Stability & Large Area | Polycrystalline Diamond (PCD) Plates | PCD is stable up to 700 °C in air and > 1000 °C in inert environments, vastly exceeding the 450 °C DLC limit. Available in large formats up to 125 mm diameter. |
| Controlled Surface Chemistry/Conductivity | Boron-Doped Diamond (BDD) Films | BDD allows for precise, tunable doping (light or heavy) to control electrical and electrochemical properties, essential for specialized tribological environments or sensor integration. |
| Optical/Raman Analysis | Optical Grade SCD Wafers | SCD offers ultra-low defect density and high transparency, ideal for advanced spectroscopic analysis (like the Raman mapping technique used in this paper) without background interference. |
Customization Potential for Advanced Tribology
Section titled âCustomization Potential for Advanced Tribologyâ6CCVD provides comprehensive engineering services necessary to transition research findings into robust, scalable components:
- Custom Dimensions and Substrates: While the paper used 30 mm steel specimens, 6CCVD can supply PCD plates up to 125 mm in diameter or SCD wafers up to 10 mm thick, allowing for the scaling of tribological components far beyond typical DLC limits.
- Precision Thickness Control: 6CCVD offers precise thickness control for both SCD and PCD films, ranging from 0.1 ”m to 500 ”m, enabling optimization of the H/Eâ ratio and compressive stress for specific load-bearing applications.
- Integrated Metalization: The study utilized protective Pt layers and Cr-C interlayers. 6CCVD offers in-house metalization capabilities (including Au, Pt, Pd, Ti, W, and Cu) for creating robust electrical contacts, specialized interlayers, or protective caps on diamond surfaces.
- Ultra-Low Roughness: To ensure accurate tribological measurements and minimize frictional energy generation, 6CCVD guarantees ultra-precision polishing (Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD).
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the structural and electronic properties of MPCVD diamond. We can assist engineers and scientists in selecting the optimal diamond material (SCD, PCD, or BDD) and surface preparation techniques required to replicate or extend this research into high-performance High-Temperature Tribology projects.
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract A series of diamond-like carbon (DLC) coatings were deposited with increasing bias voltage using magnetron sputtering techniques. Structural changes were observed in the sp 2 -configuration across the films which were accompanied by a slight increase in the sp 3 fraction. With an increasing bias voltage, the thermal stability of the coatings increased from 300 to 450 °C. Oxygen diffusion was observed through the coating as a result of the high-temperature annealing and found to slow down with increasing bias voltage. Coefficients of friction (COF) remained stable with temperature for the individual coatings, with the softer films reporting the lowest COF. Our approach employed Raman spectroscopy to map the wear tracks at different temperatures, providing a deeper understanding of the coating performance and suggested maximum flash temperatures endured during testing.