Evaluation of Mechanical Characteristics of Tribofilm Formed on the Surface of Metal Material Due to Friction under Lubrication with Automatic Transmission Fluid
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-11-29 |
| Journal | Tribology online |
| Authors | Takayuki TOKOROYAMA, Takashi Nishimoto, Yasuhiro MurakĂĄmi, Akiyuki HONDA, Hideaki Mitsui |
| Institutions | Nagoya University |
| Citations | 4 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Nano-Tribology
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Nano-TribologyâExecutive Summary
Section titled âExecutive SummaryâThis research validates the use of Atomic Force Microscope (AFM) nano-scratch testing, utilizing a Polycrystalline Diamond tip, as a superior method for accurately determining the hardness of ultra-thin tribofilms (15 nm to 430 nm) compared to conventional nano-indentation.
- Diamond Tool Validation: The study confirms that the extreme hardness and wear resistance of the Polycrystalline Diamond AFM tip are essential for applying precise, repeatable, ultra-low loads (2.19 ”N) during repeated scratch cycles (up to 6 cycles).
- Key Material Differentiation: Hardness values were successfully calculated for ATF tribofilms: Phosphorous-derived (Fluid A) at 2.64 GPa and Sulfur-derived (Fluid B) at 1.89 GPa.
- Methodological Superiority: AFM nano-scratch was deemed effective for thin film analysis because, unlike nano-indentation, it minimizes the influence of the softer SKS3 base substrate, providing reliable data for films < 50 nm thick.
- 6CCVD Relevance: The requirement for high-quality, uniform Polycrystalline Diamond material for the AFM cantilever tip directly aligns with 6CCVDâs core capability in supplying high-grade MPCVD PCD wafers and custom components for advanced metrology.
- Application Focus: This work is critical for engineers developing next-generation Automatic Transmission Fluids (ATF) and low-viscosity lubricants, where precise control over boundary lubrication film properties is paramount.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted, demonstrating the precise mechanical and material requirements of the study.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Tribofilm Hardness (Fluid A) | 2.64 | GPa | Phosphorous-derived film (AFM Nano-scratch) |
| Tribofilm Hardness (Fluid B) | 1.89 | GPa | Sulfur-derived film (AFM Nano-scratch) |
| AFM Cantilever Tip Material | Polycrystalline Diamond | N/A | Used as the abrasive tip for scratching |
| AFM Tip Diameter (r) | 150 | nm | Used in geometric hardness calculation |
| Normal Load (W) - Tribofilm | 2.19 | ”N | Load applied during LFM scratch test on tribofilm |
| Normal Load (W) - SKS3 Steel | 4.07 | ”N | Load applied during LFM scratch test on substrate |
| Fluid A Tribofilm Thickness (AES) | 150 | nm | Calculated thickness based on Fe concentration > 90% |
| Fluid B Tribofilm Thickness (AES) | 430 | nm | Calculated thickness based on Fe concentration > 90% |
| Maximum Nano-Indentation Depth (Fluid A) | 31 | nm | Qualitatively consistent with AFM results |
| Test Temperature (T) | 20-25 | °C | AFM/LFM scratch test conditions |
| Kinematic Viscosity (Fluid A) | 5.8 | mm2/s | 100 °C viscosity |
| Kinematic Viscosity (Fluid B) | 4.2 | mm2/s | 100 °C viscosity |
Key Methodologies
Section titled âKey MethodologiesâThe experiment combined macro-scale friction testing (LFW-1) with micro- and nano-scale metrology (EDS, AFM, Nano-indentation) to characterize the resulting tribofilms.
-
Tribofilm Formation (LFW-1 Test):
- Substrate: SKS3 cold work tool steel.
- Lubricants: ATF Fluids A (Phosphorous additive) and B (Sulfur additive).
- Test Conditions: Block-on-ring method (ASTM D2714-94).
- Temperature: Oil temperature maintained at 110 °C.
- Sliding Speed: Initial 1.0 m/s for 30 min, followed by stepped decreases down to 0.025 m/s.
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Sample Preparation and Positioning:
- Permanent indentations were made using a Micro Vickers hardness tester at 100 ”m intervals for macro-positioning.
- Further indentations were made at 20 ”m intervals to create precise markings for aligning the EDS mapping and AFM nano-scratch tests (same-point measurement).
-
Elemental Analysis (EDS & AES):
- Energy-Dispersive Spectroscopy (EDS) mapping was performed to identify high concentration areas of P (Fluid A) and S (Fluid B) on the wear track.
- Auger Electron Spectroscopy (AES) depth analysis with Ar ion-beam sputtering (2 kV acceleration voltage) was used to measure tribofilm thickness (calculated range: 150 nm to 430 nm).
-
Mechanical Characterization (AFM Nano-scratch):
- Tool: Polycrystalline Diamond cantilever tip (150 nm radius).
- Mode: Lateral Force Mode (LFM) used for scratching; Dynamic Force Mode (DFM) used for surface shape measurement.
- Scratch Area: 2 ”m x 2 ”m square.
- Procedure: Repeated scratching (up to 6 cycles) was performed at the high-concentration element location identified by EDS.
- Hardness Calculation: Hardness (H) was derived using the abrasive wear model, relating the scratch depth increase (hâ) per cycle to the applied load (W) and tip radius (r) via the wear coefficient (k).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical role of high-quality, precision-engineered diamond materials in advanced tribological metrology. 6CCVD is uniquely positioned to supply the materials necessary to replicate, extend, and industrialize this type of research.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Recommendation | Rationale |
|---|---|---|
| AFM Nano-scratch Tip | Polycrystalline Diamond (PCD) | Provides the necessary extreme hardness and wear resistance for repeatable, ultra-low load scratching (2.19 ”N) without tip degradation. We supply high-uniformity PCD wafers up to 125mm for tip manufacturing. |
| High-Wear Counter-Surfaces | Optical Grade Single Crystal Diamond (SCD) | For extending the research to diamond-on-diamond or diamond-on-DLC contacts (as suggested in references [9]-[12]). SCD offers the highest purity and lowest surface roughness (Ra < 1 nm). |
| Electrochemical Tribology | Boron-Doped Diamond (BDD) | If future studies require simultaneous electrochemical analysis during friction testing, 6CCVD supplies BDD films for use as robust, conductive electrodes. |
Customization Potential
Section titled âCustomization PotentialâThe precision required for nano-tribology demands highly customized material solutions, which 6CCVD specializes in:
- Custom Dimensions: We supply PCD and SCD plates/wafers up to 125mm. For specific tribology rigs, we can provide custom substrate thicknesses (SCD/PCD films from 0.1 ”m to 500 ”m, or substrates up to 10mm).
- Ultra-Precision Polishing: Achieving accurate nano-scratch results requires substrates and tools with minimal surface defects. 6CCVD offers industry-leading polishing services:
- SCD: Ra < 1 nm
- PCD (Inch-size): Ra < 5 nm
- Metalization Services: While this paper focused on steel, if future experiments require integrating diamond films with sensors or heating elements, 6CCVD offers in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for custom electrode or contact pad fabrication.
- Laser Cutting and Shaping: We can supply diamond plates with custom geometries or pre-cut features (e.g., alignment marks or specific cantilever shapes) to facilitate the complex multi-modal metrology alignment used in this study (matching Vickers indentations to AFM/EDS maps).
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team provides authoritative professional support to ensure optimal material selection for complex tribological projects:
- Material Selection: We assist researchers in selecting the correct diamond grade (e.g., high-purity SCD for optical clarity vs. robust PCD for mechanical wear) based on the specific lubricant chemistry and operating temperature (e.g., 110 °C ATF environment).
- Surface Optimization: Consultation on achieving the necessary surface orientation and roughness to minimize friction and accurately isolate the mechanical properties of the ultra-thin tribofilm.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
In this study, nano-scratch tests were conducted using atomic force microscope (AFM) to clarify the hardness of a tribofilm derived from an additive (Fluid A or Fluid B in automatic-transmission fluid) formed on an SKS3 cold work tool steel substrate surface. Comparisons between nano-indentation hardness tests and AFM nano-scratch tests were performed for each specimen. Prior to these tests, the tribofilms on the SKS3 substrate were examined with energy-dispersive spectroscopy (EDS). In order to calculate the hardness of the tribofilm from the nano-scratch results, we assumed that the AFM diamond tip acted as an abrasive to plough the tribofilm. The phosphorous-derived tribofilm formed from Fluid A was harder than the sulfur-derived tribofilm from Fluid B, and it was calculated that the phosphorous-derived tribofilm was approximately 2.64 GPa and the sulfur-derived tribofilm was 1.89 GPa. After 10 nano-indentation hardness tests on each tribofilm, the maximum indentation depth into the tribofilm formed from Fluid A was approximately 31 nm, while it was approximately 36 nm for Fluid B. These results are qualitatively consistent with the hardness results obtained by the AFM nano-scratch test method.