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	Zhejiang University of Technology, Ningbo Institute of Industrial Technology
Citations	1
Analysis	Full AI Review Included

Executive Summary

This research details the fabrication and evaluation of Diamond/Diamond-like Carbon (DLC) composite coatings designed to overcome the high friction and wear issues associated with rough, single-layer diamond films in dry sliding environments.

Enhanced Architecture: Composite coatings (MCD/DLC and UNCD/DLC) were successfully fabricated using a combination of Hot-Filament Chemical Vapor Deposition (HFCVD) for the diamond base and magnetron-sputtering-assisted ion beam deposition for the DLC top layer.
Superior Tribological Performance: The composite coatings demonstrated significantly improved performance compared to monolithic diamond. The UNCD/DLC coating achieved the lowest average friction coefficient (0.074 ± 0.007) and the lowest wear rate (5.31 x 10^-6 mm³/Nm).
MCD/DLC Improvement: The MCD/DLC composite showed a 33.73% reduction in the average friction coefficient and a 39.55% decrease in the average wear rate relative to single-layer MCD.
Surface Smoothing: The DLC overlayer effectively reduced surface roughness, particularly on the finer-grained UNCD coating, achieving a 27.4% reduction in arithmetic mean roughness (Ra).
Lubrication Mechanism: The enhanced performance is attributed to a synergistic effect: the DLC layer creates a smoother interface, minimizing abrasive wear, and accelerates friction-induced graphitization (sp² phase transition) during sliding, which provides superior lubricity.

Technical Specifications

Parameter	Value	Unit	Context
Best Average COF	0.074 ± 0.007	Dimensionless	UNCD/DLC composite coating
Best Wear Rate	5.31 x 10^-6	mm³/Nm	UNCD/DLC composite coating
MCD/DLC COF Reduction	33.73	%	Relative to MCD (0.169 to 0.112)
MCD/DLC Wear Rate Reduction	39.55	%	Relative to MCD (1.684 x 10^-5 to 1.018 x 10^-5 mm³/Nm)
UNCD Ra (Initial)	137	nm	Before DLC deposition
UNCD/DLC Ra (Final)	99.45	nm	After DLC deposition (27.4% reduction)
DLC Film Thickness	~1	µm	Deposited via ion beam
MCD Coating Thickness	14.2	µm	HFCVD deposition
UNCD Coating Thickness	9.04	µm	HFCVD deposition
Tribotest Load	15	N	Normal load, SiC ball counterbody
Tribotest Speed	30	mm/s	Average sliding speed, dry environment
DLC Deposition Temperature	50	°C	Low-temperature process
DLC Substrate Bias	-100	V	Applied during DLC deposition
Diamond (111) Lattice Spacing	0.206 - 0.207	nm	Measured via HRTEM
Graphitization Marker (ID/IG)	1.01	Dimensionless	UNCD/DLC wear track (Highest graphitization)

Key Methodologies

The composite coatings were fabricated on SiC substrates using a two-step process combining Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) techniques.

Diamond Base Layer Preparation (HFCVD):
- Substrate Pretreatment: SiC substrates were mechanically roughened using a W40 diamond abrasive slurry, followed by ultrasonic cleaning and nanodiamond particle seeding (30 min ultrasonic treatment in ethanol suspension).
- MCD Deposition Parameters: CH₄/H₂ ratio of 3%, N₂/H₂ ratio of 0%, Power 4.4 kW, Pressure 2.3 kPa, Deposition time 12 h.
- UNCD Deposition Parameters: CH₄/H₂ ratio of 3%, N₂/H₂ ratio of 5%, Power 3.6 kW, Pressure 2.0 kPa, Deposition time 24 h.
DLC Top Layer Deposition (Magnetron-Sputtering-Assisted Ion Beam):
- Chamber Preparation: Vacuum reached 3 x 10^-5 Torr.
- Argon Etching: Ionized argon was used for 30 min etching at a bias voltage of -200 V to clean and activate the diamond surface. Ion-source operating voltage was 1200 ± 100 V.
- DLC Growth: Argon was replaced by methane/acetylene gas mixture. Acetylene flow rate was 35 sccm.
- DLC Parameters: Substrate bias was -100 V, ion-source current 0.2 A, resulting in a growth rate of 800 nm/h to achieve a target thickness of approximately 1 µm. Deposition temperature was maintained at 50 °C.
Tribological Testing:
- Conditions: Reciprocating ball-on-flat tribometer under ambient laboratory temperature and dry sliding.
- Counterbody: SiC ball (radius 6 mm).
- Test Parameters: Normal load of 15 N, 5 mm stroke length, 30 mm/s average sliding speed, total duration 1 h.

Commercial Applications

The development of highly stable, low-friction, and wear-resistant diamond/DLC composite coatings is critical for components operating under severe, dry sliding conditions where conventional lubrication is insufficient or impossible.

Aero-Engine Components: High-temperature, dry-sliding parts requiring exceptional wear resistance and stability, such as bearings or seals in high-performance turbines.
Mining and Heavy Machinery: Components exposed to abrasive environments (e.g., hydraulic rods, drill bits, or sliding surfaces) where lubrication failure is common.
Precision Molds and Dies: Tools requiring ultra-hard surfaces with low friction coefficients to reduce sticking and improve release, extending mold service life.
High-Temperature Applications: Components where traditional liquid lubricants break down, relying on the intrinsic solid lubrication properties of the graphitized sp² phase formed by the DLC layer.
Space Tribology: Mechanisms operating in vacuum or extreme temperature environments where dry friction solutions are mandatory.

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]