The Inﬂuence of Site of Co and Holes in PCD Substrate on Adhesive Strength of Diamond Coating with PCD Substrate

At a Glance

Metadata	Details
Publication Date	2023-12-19
Journal	Coatings
Authors	Cen Hao, Guoliang Liu
Institutions	Hong Kong Metropolitan University
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Adhesion Diamond Coatings on PCD Substrates

Executive Summary

This research provides critical insights into maximizing the adhesive strength of CVD diamond coatings on Polycrystalline Diamond (PCD) substrates by controlling interfacial defects.

Core Challenge Addressed: Traditional PCD substrates utilize Cobalt (Co) binder, which, along with residual holes post-removal, severely reduces the adhesive strength of subsequent CVD diamond coatings.
Key Mechanism Identified: Interfacial binding strength (Wad) is highly dependent on the crystallographic orientation of the PCD substrate surface where Co or holes are located.
Optimal Orientation: Both experimental indentation tests and Density Functional Theory (DFT) calculations confirm that the (110) crystal surface yields the highest interfacial binding energy (Wad), maximizing adhesion.
Quantified Improvement: The binding energy on the optimal (110) surface was 31.4% higher than the (100) surface when Co was present (35.17 eV/nm²) and 322.1% higher than the (100) surface when holes were present (22.62 eV/nm²).
Electronic Basis: The superior adhesion on the (110) plane is due to optimal charge transfer and the formation of the strongest C-C covalent bonds between the PCD substrate and the CVD diamond coating.
Strategic Conclusion: To produce high-performance coated PCD tools, engineers must strategically regulate the site of the Co binding phase or ensure holes are preferentially filled/located on the (110) crystal surface.

Technical Specifications

The following hard data points were extracted from the experimental and theoretical sections of the research paper.

Parameter	Value	Unit	Context
Etching Acid Ratio	1:5	Volume Ratio	H₂SO₄ (AR) : H₂O₂ (30%)
Etching Temperature	25	°C	Co removal pretreatment
Etching Time	48	hours	Pretreatment duration
Filament Carbonization Temp	2100 ± 100	°C	Hot Filament CVD (HFCVD) setup
Filament Carbonization Time	2	hours	HFCVD process
Deposition Pressure	3	kPa	Reactive pressure during HFCVD growth
Deposition Time	4	hours	CVD diamond coating growth duration
Carbon Concentration (Deposition)	2	%	Acetone source gas concentration
Interfacial Binding Energy (Wad) - Max Co	35.17	eV/nm²	Co located on (110) surface
Interfacial Binding Energy (Wad) - Max Hole	22.62	eV/nm²	Hole located on (110) surface
Diamond Lattice Parameter (a=b=c)	3.567	Å	Face-centered cubic structure
Indenter Angle	136	°	Square cone diamond indenter (HBRVU-187.5)

Key Methodologies

The study combined physical experimentation (HFCVD deposition and indentation testing) with advanced computational modeling (DFT).

Substrate Selection and Pretreatment: PDC (Polycrystalline Diamond Compact) was used as the substrate. Cobalt (Co) removal was performed by soaking the substrate in corrosive acid reagents (H₂SO₄:H₂O₂) at 25 °C for 48 hours.
CVD Deposition Setup: A custom Hot Filament Chemical Vapor Deposition (HFCVD) system was utilized, employing tungsten filaments (Φ1.0 mm) and using acetone as the carbon source and hydrogen as the auxiliary gas.
Filament Carbonization: A preliminary step performed at 2100 ± 100 °C and 6 kPa for 2 hours.
Diamond Coating Growth: Deposition was conducted at 3 kPa pressure for 4 hours, using a 2% carbon concentration.
Mechanical Characterization: Adhesive strength was assessed via indentation tests using a Brovey hardness tester. SEM imaging was used to observe indentation patterns and compare bonding strengths.
Geometric Modeling: Interfacial structures were built using Device Studio software (2023A) for PCD/diamond and PCD-holes/diamond interfaces on (100), (110), and (111) crystal surfaces. Models included a 1.3 nm vacuum layer.
First-Principles Calculation (DFT): The generalized gradient approximation (GGA) based on the density functional theory (DFT) and the projector augmented wave (PAW) method were used to calculate:
- Interfacial binding energy (Wad).
- Charge density.
- Charge density difference, confirming C-C covalent bond formation.

6CCVD Solutions & Capabilities

6CCVD specializes in providing high-purity, engineered MPCVD diamond materials that meet the stringent requirements necessary to replicate and advance the findings of this research, particularly concerning interface control and adhesion optimization.

Applicable Materials for High-Adhesion Applications

To achieve the highest possible adhesive strength, researchers require substrates with controlled purity and surface characteristics.

6CCVD Material Solution	Specification & Advantage	Relevance to Research
High Purity MPCVD PCD	Plates/wafers up to 125mm. Superior purity compared to HPHT PCD, minimizing initial Co contamination.	Provides a cleaner, more uniform substrate, simplifying the Co removal pretreatment and reducing residual defects.
Optical Grade SCD	SCD thickness from 0.1µm to 500µm. Ra < 1nm polishing capability.	Ideal for fundamental studies requiring precise, single-crystal orientation (e.g., (110) or (100)) to isolate and validate DFT predictions regarding crystal plane effects.
Custom Substrates	Substrates up to 10mm thick, available in custom dimensions and shapes.	Allows researchers to test the optimized coating process on application-specific tool geometries, moving beyond simple wafer formats.

Customization Potential & Surface Engineering

The research highlights that surface preparation and defect control are paramount. 6CCVD offers capabilities essential for engineering the optimal interface:

Precision Polishing: 6CCVD provides ultra-smooth polishing (Ra < 5nm for inch-size PCD), which is critical for achieving the uniform, high-quality surface required for controlled HFCVD nucleation and maximizing interfacial bonding.
Custom Dimensions: We supply PCD plates up to 125mm in diameter, enabling the scale-up of this high-adhesion coating process from laboratory samples to industrial-sized tools.
Metalization Services: Although the paper focuses on C-C bonding, 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for researchers who need to integrate these high-adhesion coated tools into electronic or sensor applications requiring robust ohmic contacts.
Surface Termination Control: Our MPCVD expertise allows for control over the diamond surface termination (e.g., hydrogen or oxygen termination), a crucial factor influencing charge transfer and subsequent coating adhesion, which can be tailored to complement the findings on the (110) plane.

Engineering Support

6CCVD’s in-house PhD material science team is equipped to assist researchers and engineers in applying these findings to real-world applications.

Material Selection Consultation: We provide expert guidance on selecting the optimal PCD substrate grade and surface preparation technique necessary to achieve the high interfacial binding strength demonstrated in this study.
Process Optimization: Our team can collaborate on projects focused on high-adhesion diamond coating for superhard cutting tools, leveraging our deep understanding of MPCVD growth parameters to optimize deposition recipes for specific crystal orientations.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of engineered diamond solutions worldwide.

View Original Abstract

Polycrystalline diamond (PCD) prepared by the high temperature and pressure method often uses Co as a binder, which had a detrimental effect on the cutting performance of PCD, thus Co needed to be removed. However, the removal of Co would cause residual holes and also make the cutting performance of PCD poorer. To address this issue, hot filament chemical vapor deposition (HFCVD) was used. During deposition, the residual holes cannot be filled fully, and Co would diffuse to the interface between CVD diamond coatings and the PCD substrate, which influenced the adhesive strength of the diamond coating with the PCD substrate. In order to investigate the influencing mechanism, both experiments and the density functional theory (DFT) calculations have been employed. The experimental results demonstrate that Co and the holes in the interface would reduce the interfacial binding strength. Further, we built interfacial structures consisting of diamond (100), (110), (111) surfaces and PCD to calculate the corresponding interfacial binding energy, charge density and charge density difference. After contrast, for Co and the holes located on the (110) surface, the corresponding interfacial binding energy was bigger than the others. This means that the corresponding C-C covalent bond was stronger, and the interfacial binding strength was higher. Based on this, conducting cobalt removal pretreatment, optimizing the PCD synthetic process and designing the site of Co can improve the performance of the PCD substrate CVD diamond coating tools.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings14010001

References

2022 - Polishing of polycrystalline diamond using synergies between chemical and mechanical inputs: A review of mechanisms and processes [Crossref]
2020 - The manufacturing and the application of polycrystalline diamond tools-A comprehensive review [Crossref]
2020 - Application of an innovative ridge-ladder-shaped polycrystalline diamond compact cutter to reduce vibration and improve drilling speed [Crossref]
2013 - A study on PDC drill bits quality [Crossref]
2022 - Effect of transition metal carbides on mechanical properties of polycrystalline diamond by HPHT sintering [Crossref]
2018 - Study on Co-enhancement of polycrystalline diamond composite sheets
2017 - Effect of decobalting on thermal stability of polycrystalline diamond