Tribological Properties of Diamond/Diamond-like Carbon (DLC) Composite Coating in a Dry Environment

At a Glance

Metadata	Details
Publication Date	2025-08-19
Journal	Materials
Authors	Chengye Yang, Zhengxiong Ou, Yuanyuan Mu, Xingqiao Chen, Shihao Yang
Institutions	Chinese Academy of Sciences, University of Chinese Academy of Sciences
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond/DLC Composite Coatings

Executive Summary

This research validates a synergistic composite architecture—Diamond/Diamond-Like Carbon (DLC)—as a superior solution for mitigating high wear and friction associated with single-layer polycrystalline diamond (PCD) coatings in dry sliding environments.

Core Achievement: Successful fabrication of MCD/DLC and UNCD/DLC composite coatings using a combined CVD (diamond base) and ion-beam deposition (DLC top) approach on SiC substrates.
Performance Enhancement (MCD/DLC): Achieved a 33.73% reduction in the average friction coefficient (COF) and a 39.55% decrease in the average wear rate compared to monolithic MCD.
Optimal Tribology: The UNCD/DLC composite demonstrated the best performance, achieving an ultra-low stable COF of 0.074 ± 0.007 and the lowest wear rate (5.31 x 10^-6 mm³/Nm).
Surface Modification: The DLC overlayer effectively reduced the surface roughness (Ra reduction up to 27.4% for UNCD/DLC), minimizing abrasive wear and smoothing the contact interface.
Friction Mechanism: Enhanced lubrication is driven by the DLC layer accelerating friction-induced graphitization (sp³ to sp² phase transition) at the sliding interface, forming a lubricious tribolayer.
Viable Strategy: Confirms that surface modification of high-roughness PCD coatings with a thin, conformal DLC layer is a highly effective strategy for enhancing wear resistance in industrial dry friction applications.

Technical Specifications

The following hard data points were extracted from the tribological evaluation of the as-prepared coatings under dry sliding conditions (15 N load, 30 mm/s speed, SiC counterbody).

Parameter	Value	Unit	Context
Optimal Stable COF	0.074 ± 0.007	Dimensionless	UNCD/DLC Composite
MCD/DLC Stable COF	0.112 ± 0.010	Dimensionless	33.73% reduction vs. MCD
UNCD/DLC Wear Rate	5.31 x 10^-6	mm³/Nm	Lowest observed wear rate
MCD/DLC Wear Rate	1.018 x 10^-5	mm³/Nm	39.55% reduction vs. MCD
UNCD Base Thickness	9.04	µm	Average growth rate: 0.38 µm/h
MCD Base Thickness	14.2	µm	Average growth rate: 1.18 µm/h
DLC Overlayer Thickness	~1	µm	Deposited via Ion Beam
UNCD Initial Roughness (Ra)	137	nm	Reduced to 99.45 nm (27.4% reduction)
MCD Initial Roughness (Ra)	214.5	nm	Reduced to 204.5 nm (4.7% reduction)
DLC Deposition Temperature	50	°C	Low temperature process

Key Methodologies

The composite coatings were fabricated using a two-step process combining Hot-Filament Chemical Vapor Deposition (HFCVD) for the diamond base layer and Magnetron-Sputtering-Assisted Ion Beam Deposition for the DLC top layer.

1. Diamond Base Layer (HFCVD)

Parameter	MCD Recipe Value	UNCD Recipe Value
Substrate	SiC (20 mm x 20 mm x 2 mm)	SiC (20 mm x 20 mm x 2 mm)
Filament Material	Tantalum wires (0.35 mm diameter)	Tantalum wires (0.35 mm diameter)
CH₄/H₂ Gas Flow Ratio	3%	3%
N₂/H₂ Gas Flow Ratio	0%	5%
Power	4.4 kW	3.6 kW
Barometric Pressure	2.3 kPa	2.0 kPa
Deposition Time	12 h	24 h

2. DLC Overlayer (Ion Beam Deposition)

Pre-Etching: Substrate surface etched using ionized Argon (Ar) ion beam for 30 minutes to enhance adhesion.
- Bias Voltage: -200 V.
- Ion-Source Current: 0.2 A.
- Ion-Source Operating Voltage: 1200 ± 100 V.
Gas Replacement: Argon gas replaced by Methane/Acetylene mixture.
DLC Deposition: DLC film deposited to a target thickness of ~1 µm.
- Bias Voltage: -100 V.
- Ion-Source Current: 0.2 A.
- Acetylene Flow Rate: 35 sccm.
- Growth Rate: 800 nm/h.
- Chamber Temperature: 50 °C.

6CCVD Solutions & Capabilities

This research highlights the critical role of the diamond base layer’s quality (MCD vs. UNCD) and the subsequent surface modification (DLC) in achieving superior tribological performance. 6CCVD is uniquely positioned to supply the high-quality, customized diamond materials necessary to replicate and advance this composite coating strategy.

Applicable Materials

The study utilized Microcrystalline Diamond (MCD) and Ultrananocrystalline Diamond (UNCD), both falling under the category of Polycrystalline Diamond (PCD).

Recommended Material: Optical Grade PCD (Polycrystalline Diamond).
- MCD Replication: 6CCVD can supply PCD with controlled grain size (3-8 µm range, similar to the MCD used) for applications requiring high hardness and adhesion strength.
- UNCD Replication: 6CCVD can supply PCD with ultra-fine grain structures suitable for achieving the low initial roughness (Ra < 137 nm) required for optimal DLC performance, mirroring the UNCD base layer.
Substrate Compatibility: While the paper used SiC, 6CCVD can deposit PCD films on various substrates, including Si, Mo, and W, tailored to the client’s specific thermal or mechanical requirements.

Customization Potential

6CCVD’s advanced MPCVD and post-processing capabilities directly address the requirements for scaling and optimizing this composite architecture:

Research Requirement	6CCVD Capability & Advantage
Custom Thickness Control	The paper used 9-14 µm diamond films. 6CCVD offers precise thickness control for PCD films from 0.1 µm up to 500 µm, allowing engineers to optimize the diamond layer for specific load-bearing requirements.
Large Area Substrates	The paper used small 20 mm x 20 mm substrates. 6CCVD can supply PCD plates and wafers up to 125 mm in diameter, enabling industrial-scale component coating.
Ultra-Low Roughness PCD	The success of the DLC layer depends on the initial diamond roughness. 6CCVD provides advanced polishing services, achieving roughness values of Ra < 5 nm on inch-size PCD wafers, providing an ideal starting surface for subsequent DLC deposition.
Interface Engineering	The DLC deposition utilized ion-beam etching for adhesion. 6CCVD offers custom metalization services (Au, Pt, Pd, Ti, W, Cu) which can be used as adhesion layers or interlayers between the diamond base and the subsequent DLC layer, further enhancing bond strength and thermal management.

Engineering Support

The enhanced tribological performance of the Diamond/DLC composite is highly dependent on the quality and structure of the underlying diamond film. 6CCVD’s in-house PhD team specializes in optimizing diamond crystal structure (MCD vs. UNCD) and surface morphology for demanding applications.

Wear Resistance Projects: Our experts can assist clients in selecting the optimal PCD grain size and thickness to maximize abrasive wear resistance while providing a surface suitable for subsequent low-friction DLC modification.
Dry Friction Optimization: We provide consultation on material specifications for similar high-load, dry sliding projects, ensuring the supplied PCD base layer is engineered to accelerate the desired friction-induced graphitization mechanism.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In this study, a diamond/diamond-like carbon (DLC) composite coating was designed and fabricated utilizing a combination of chemical vapor deposition (CVD) and magnetron-sputtering-assisted ion beam deposition. This was designed to cope with severe problems such as high wear due to insufficient lubrication under dry sliding conditions with a single diamond. The tribological properties of the fabricated coatings under dry conditions were comparatively evaluated. The results demonstrate that the diamond/DLC composite coatings significantly enhance the tribological performance relative to their single-layer diamond counterparts. Specifically, a 33.73% reduction in the average friction coefficient and a 39.55% decrease in the average wear rate were observed with the MCD (microcrystalline diamond/DLC coating. Similarly, a 16.85% reduction in the average friction coefficient and a 9.69% decrease in the average wear rate were observed with the UNCD (ultrananocrystalline diamond)/DLC coating. Analysis of the worn track morphology and structure elucidated the underlying friction mechanism. It is proposed that the DLC top layer reduces the surface roughness of the underlying diamond coating and mitigates abrasive wear in the dry environment. Furthermore, the presence of the DLC film promotes graphitization via phase transition during sliding, which enhances lubricity and facilitates the establishment of a smooth friction interface.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma18163879

References

2023 - A review of diamond synthesis, modification technology, and cutting tool application in ultra-precision machining [Crossref]
2022 - Micropatterning of synthetic diamond by metal contact etching with Ti powder [Crossref]
2021 - Fabrication, tribological properties and cutting performances of high-quality multilayer graded MCD/NCD/UNCD coated PCB end mills [Crossref]
2022 - Fracture mechanics of microcrystalline/nanocrystalline composited multilayer chemical vapor deposition self-standing diamond films [Crossref]
2020 - Cutting performances of MCD, SMCD, NCD and MCD/NCD coated tools in high-speed milling of hot bending graphite molds [Crossref]