Preparation of Boron-Doped Diamond Films on Cemented Tungsten Carbide
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-12-01 |
| Journal | Journal of The Surface Finishing Society of Japan |
| Authors | Kunio Saito, Asuka Suzuki, Atsuo Kawana, Yukihiro Sakamoto |
| Institutions | Chiba Institute of Technology |
| Citations | 1 |
| Analysis | Full AI Review Included |
Expert Technical Analysis: Boron-Doped Diamond Synthesis on Cemented Tungsten Carbide via MPCVD
Section titled âExpert Technical Analysis: Boron-Doped Diamond Synthesis on Cemented Tungsten Carbide via MPCVDâExecutive Summary
Section titled âExecutive SummaryâThis paper details a successful methodology for the direct synthesis of high-adhesion Boron-Doped Diamond (BDD) films on Cemented Tungsten Carbide (WC-Co) using Microwave Plasma Enhanced Chemical Vapor Deposition (MPCVD). This research is highly relevant for advanced tooling and electrochemical applications requiring robust, conductive diamond coatings.
- Adhesion Breakthrough: Demonstrated excellent film adhesion (Rockwell HF1-2 classification) on WC-Co substrates, a notoriously challenging material due to Co binder reactivity.
- Process Innovation: Achieved continuous BDD deposition without the conventional acid pretreatment step necessary to remove Co, thereby preserving the structural integrity and toughness of the WC-Co tool body.
- Mechanism Confirmation: A two-step process involving a Boride Pretreatment successfully formed $\text{CoB}$ and $\text{CoO}$ layers on the substrate surface, effectively suppressing the Co catalytic action that inhibits diamond nucleation.
- Material Safety: Utilized the safer, less toxic Trimethyl Borate ($\text{B}(\text{OCH}{3}){3}$) as the boron source, avoiding the special handling required for highly toxic and explosive sources like Diborane ($\text{B}{2}\text{H}{6}$) or Trimethyl Boron ($\text{B}(\text{CH}{3}){3}$).
- Substrate Dependency: Demonstrated that optimal pretreatment time varies inversely with the Cobalt (Co) content of the substrate; lower Co content (K10) requires less pretreatment time for effective BDD nucleation and robust growth.
- Application Relevance: The resulting BDD films are conductive, opening avenues for application in EDM (Electrical Discharge Machining) electrodes and advanced cutting tools requiring electrical discharge positioning or superior wear resistance.
Technical Specifications
Section titled âTechnical SpecificationsâThe following parameters define the optimized MPCVD conditions for the synthesis of high-adhesion BDD films on WC-Co.
| Parameter | Value | Unit | Context / Condition |
|---|---|---|---|
| CVD System Type | Mode-conversion MPCVD | N/A | Microwave frequency: 2.45 GHz |
| Microwave Power | 1 | kW | Applied during both pretreatment and deposition |
| Plasma Pressure | 20 | kPa | Applied during both pretreatment and deposition |
| Pretreatment Duration | 30 | minutes | Optimized for boride formation |
| Deposition Duration | 60 | minutes | Achieved continuous, adherent BDD film |
| Boron Source | Trimethyl Borate ($\text{B}(\text{OCH}{3}){3}$) | N/A | Less toxic B source alternative |
| Boron Source Concentration | 0.05 | g/L | $\text{H}{3}\text{BO}{3}$ / $\text{CH}_{3}\text{OH}$ ratio for precursor mixture |
| Adhesion Result (VDI 3198) | HF1 - HF2 | N/A | Excellent adhesion (Boride Pretreatment) |
| Substrate Types | K10, K20, K30 | WC-Co grades | Co content ranging from 4% to 11% by weight |
| BDD Raman Peak | 1333 | cm-1 | Characteristic diamond peak (broadened due to high B-doping) |
WC-Co Substrate Composition (Weight %)
Section titled âWC-Co Substrate Composition (Weight %)â| Substrate Grade | W | Co | Ti | Ta | C |
|---|---|---|---|---|---|
| K10 | 84 ~ 90 | 4 ~ 7 | 0 ~ 1 | 0 ~ 2 | 5 ~ 6 |
| K20 | 83 ~ 89 | 5 ~ 8 | 0 ~ 1 | 0 ~ 2 | 5 ~ 6 |
| K30 | 81 ~ 88 | 6 ~ 11 | 0 ~ 1 | 0 ~ 2 | 5 ~ 6 |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a two-step continuous MPCVD process to achieve optimal BDD adhesion on WC-Co.
- Substrate Preparation:
- WC-Co substrates (K10, K20, K30) were mechanically scratched using diamond powder.
- Substrates were subsequently cleaned via ultrasonic bath in acetone prior to chamber loading.
- CVD Setup:
- A mode-conversion type MPCVD reactor was used.
- The boron source ($\text{B}(\text{OCH}{3}){3}$ mixed with $\text{H}{3}\text{BO}{3}$ and $\text{CH}{3}\text{OH}$) was bubbled into the vacuum chamber using $\text{H}{2}$ as a carrier gas.
- Step 1: Boride Pretreatment (30 minutes)
- Objective: Form borides ($\text{CoB}$, $\text{CoO}$) on the WC-Co surface to deactivate the catalytic effect of Cobalt.
- Reactive Gases: $\text{H}{2}$ (100 sccm) and $\text{B}(\text{OCH}{3}){3}$ precursor mixture. Methane ($\text{CH}{4}$) was not introduced during this step.
- Process Confirmation: XPS analysis confirmed the formation of $\text{CoB}$ and $\text{CoO}$, and Raman spectroscopy indicated the presence of amorphous carbon (a-C), particularly strong on low-Co K10 substrates, which aids nucleation.
- Step 2: BDD Deposition (5 to 60 minutes)
- Objective: Continuous growth of highly conductive BDD film.
- Reactive Gases: Methane ($\text{CH}{4}$ 15 sccm), $\text{H}{2}$ (100 sccm), and $\text{B}(\text{OCH}{3}){3}$ precursor mixture.
- Growth Confirmation: SEM showed rapid diamond crystal growth and coalescence, forming a continuous film by 60 minutes. Raman and XPS confirmed the presence of highly boron-doped diamond characteristics (broadened 1333 $\text{cm}^{-1}$ peak, and B-related peaks near 500 $\text{cm}^{-1}$ and 1200 $\text{cm}^{-1}$).
- Adhesion Testing:
- Rockwell hardness indentation test (60 kgf load, 200 ”m indenter) was used.
- Adhesion was evaluated according to the VDI 3198 standard (HF1-2 ranking confirms excellent bond strength).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research validates a crucial technique for creating high-performance, conductive diamond tooling. 6CCVD stands ready to supply the advanced MPCVD diamond materials necessary to replicate and scale this innovation globally.
Applicable Materials
Section titled âApplicable MaterialsâThe successful, robust adhesion of BDD to WC-Co opens significant opportunities for advanced cutting tools and electrodes.
| Research Requirement | 6CCVD Recommended Solution | Technical Rationale |
|---|---|---|
| Conductive Diamond Film | Heavy Boron-Doped Polycrystalline Diamond (BDD/PCD) | BDD is essential for applications like EDM/ECD, offering chemical inertness and necessary conductivity. We offer custom BDD doping levels. |
| High Adhesion Tooling | Custom Grade PCD Substrates | Our PCD is grown specifically for robust industrial applications, compatible with the optimized boride pretreatment methods outlined in the research. |
| Thick Coatings | PCD Thickness up to 500 ”m | For maximum tool life or thick electrodes, 6CCVD provides PCD films up to half a millimeter thick on various substrates. |
Customization Potential
Section titled âCustomization PotentialâThe utilization of proprietary WC-Co grades (K10, K20, K30) highlights the need for tailored material solutions. 6CCVDâs comprehensive in-house capabilities directly address these requirements.
- Custom Dimensions and Geometries: While the paper implies tool inserts, 6CCVD can supply diamond plates and wafers up to 125mm (PCD). We offer precise laser cutting and shaping services to produce complex geometries required for specialized tool inserts or unique electrode designs.
- Surface Preparation and Polishing: The research emphasizes the critical role of surface condition. 6CCVD provides industry-leading polishing services, achieving roughness of $\text{Ra}$ < 5 nm for inch-size PCD, ensuring optimal starting conditions for both advanced coating (like the BDD/boride process) and final device integration.
- Integrated Solutions: If subsequent metal contacts are required for electrochemical integration or sensor applications, 6CCVD offers in-house custom metalization services (e.g., Au, Pt, Pd, Ti, W, Cu) that can be applied directly onto the BDD surface.
Engineering Support
Section titled âEngineering SupportâThis study demonstrates that successful diamond coating on carbide relies heavily on correlating substrate composition (Co content) with optimized CVD pretreatment time.
- Process Optimization Consultation: 6CCVDâs in-house PhD team provides specialized engineering support for projects involving conductive diamond deposition on metal or carbide interfaces. We assist clients in refining pretreatment recipes and boron incorporation levels to match specific application demands (e.g., maximizing adhesion for extreme impact tooling or fine-tuning conductivity for electrochemical sensors).
- Material Selection for Tooling: We offer expert guidance on selecting the ideal diamond material (SCD, PCD, or BDD) based on the clientâs existing WC-Co grade composition, ensuring high performance in demanding cutting and wear protection projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Diamond coating on cemented tungsten carbideïŒWC-CoïŒis quite difficult. Generally, to reduce the reactivity of cobaltïŒCoïŒ, which is the binder of WC-Co, an acid pretreatment is applied. Recent reports have described that the adhesion of nanostructured diamond coating was improved using diboraneïŒB2H6ïŒto reduce the reactivity of Co as a catalyst. To obtain boron-doped diamondïŒBDDïŒ, B2H6 and trimethyl boronïŒBïŒCH3ïŒ3ïŒare often used as boron sources. However, special apparatus must be prepared because of the toxicity, flammability, and explosiveness of these sources.