The Interface of Additive Manufactured Tungsten–Diamond Composites

At a Glance

Metadata	Details
Publication Date	2025-05-30
Journal	Materials
Authors	Xuehao Gao, Dongxu Cheng, Zhe Sun, Yihe Huang, Wentai Ouyang
Institutions	Chinese Academy of Sciences, University of Manchester
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Additive Manufactured Tungsten Composites

Executive Summary

This research successfully demonstrates the critical role of interface engineering using Ni-coated diamond powder in the Laser Powder Bed Fusion (L-PBF) fabrication of Tungsten-Diamond Metal Matrix Composites (MMCs). This work is highly relevant to engineers developing materials for extreme environments, such as nuclear facilities and aerospace hot-end components.

Core Achievement: Fabrication of crack-resistant W+(D-Ni) MMCs via L-PBF, contrasting the highly defective W+D samples.
Interface Mechanism: The Ni coating melts first, acting as a diffusion barrier and solvent, significantly suppressing diamond graphitization and W₂C carbide formation compared to bare diamond.
Microstructure Control: Ni segregation leads to the precipitation of nanocrystalline Diamond-Like Carbon (DLC) phases (tens to hundreds of nanometers) at the interface, enhancing bonding strength.
Defect Mitigation: The addition of Ni promotes W grain refinement (sub-micron dendrite width) and reduces the number and length of critical microcracks, improving the overall structural integrity and potential fracture toughness.
Application Potential: Validates L-PBF as a viable method for producing complex, high-performance W-Diamond MMCs for heat sinks, precision tools, and radiation shielding.
6CCVD Value: 6CCVD offers the necessary high-purity MPCVD diamond materials (SCD/PCD) and custom metalization services (including Ni, Ti, W, Cu) required to replicate and advance this interface engineering approach.

Technical Specifications

The following hard data points were extracted from the L-PBF processing and material analysis of the W-Diamond composites:

Parameter	Value	Unit	Context
W Powder Size Range	15 to 45	µm	Raw material input
Diamond Powder Size Range	25 to 38	µm	Raw material input
Ni Coating Weight Increase	56	wt%	Relative to bare D powder (D-Ni)
L-PBF Layer Thickness	30	µm	Processing parameter
L-PBF Laser Power	400	W	Processing parameter
L-PBF Scanning Speed	725	mm/s	Processing parameter
W Phase Structure	β-bcc	N/A	Confirmed by diffraction pattern
C Content (W+D Interface, W phase)	8.45 to 11.62	at%	Supersaturated solid solution of C in W
Ni Content (W+(D-Ni) Interface, Rich DLC)	16.09	at%	Middle area, Zone #1 (Molten state diffusion)
Nanocrystal Size (Lean Ni DLC Area)	Tens of	nanometers	Limited diffusion in solid D powder
Nanocrystal Size (Rich Ni DLC Area)	Several hundred	nanometers	Stronger diffusion in Ni melt
W Dendrite Width (W+(D-Ni))	Sub-micron	scale	Result of Ni-induced grain refinement
Diamond Hardness	70-150	GPa	Intrinsic property cited for application context
Diamond Thermal Conductivity	3.2	W/(cm·K)	Intrinsic property cited for application context

Key Methodologies

The fabrication and analysis relied on precise L-PBF control and advanced characterization techniques focused on interface chemistry:

Powder Preparation:
- Raw materials included W powder (15-45 µm), bare D powder (25-38 µm), and D-Ni powder (25-38 µm, 56 wt% Ni coating).
- Powders were pre-mixed (85 vol% W - 15 vol% D/D-Ni) using a Y-type blender for over 30 minutes to ensure homogeneity.
L-PBF Processing:
- A self-developed L-PBF system was used.
- Key parameters: Layer thickness 30 µm, Laser power 400 W, Hatch spacing 100 µm, and Scanning speed 725 mm/s.
Phase and Bonding Analysis:
- X-ray Diffraction (XRD) identified primary phases (W, W₂C, WC_1-x, Carbon phase).
- Raman Spectroscopy (633-nm laser) confirmed the presence of sp² bonds (G peak) in the carbon phase, indicating Diamond-Like Carbon (DLC) formation and graphitization.
Interface Microstructure Characterization:
- Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) analyzed surface morphology and element distribution.
- Transmission Electron Microscopy (TEM) and HRTEM, with specimens prepared via Focused Ion Beam (FIB), were used for high-resolution observation of the W/Carbon interface and nanocrystal precipitation.

6CCVD Solutions & Capabilities

6CCVD specializes in providing high-performance MPCVD diamond materials and custom engineering services essential for replicating and advancing research in high-temperature, high-conductivity composites like W-Diamond MMCs.

Applicable Materials

To replicate or extend this research, 6CCVD recommends the following materials:

Polycrystalline Diamond (PCD) Feedstock: We supply high-purity PCD material, which can be processed into custom powder sizes (e.g., 25-38 µm) suitable for L-PBF feedstock. Our PCD offers excellent thermal stability and mechanical properties required for MMCs used in precision cutting/grinding tools.
Optical Grade Single Crystal Diamond (SCD): For applications demanding the highest thermal performance (e.g., advanced heat sinks), 6CCVD provides SCD plates up to 500 µm thick, offering superior intrinsic thermal conductivity compared to PCD.

Customization Potential

The success of the W+(D-Ni) composite hinges on precise interface engineering, a core capability of 6CCVD:

Research Requirement	6CCVD Customization Capability	Technical Advantage
Ni Coating Replication	Internal Metalization Services: We offer precise, uniform coating of diamond materials (substrates or powders) using Ni, Ti, W, Cu, Pt, Pd, or Au. This allows researchers to replicate the 56 wt% Ni coating or explore multi-layer systems (e.g., Ti/Ni) to further optimize W-C diffusion kinetics.	Enables direct control over the interface reaction layer, maximizing bonding strength and minimizing graphitization.
Custom Substrate Dimensions	Large-Area PCD Wafers: 6CCVD fabricates PCD plates up to 125 mm in diameter and up to 500 µm thick. These can serve as high-quality, thermally stable build substrates for L-PBF systems, supporting scale-up.	Facilitates the transition from small research coupons to industrial-sized components (e.g., large nuclear shielding tiles).
Surface Finish Requirements	Precision Polishing: We achieve surface roughness (Ra) < 1 nm on SCD and Ra < 5 nm on inch-size PCD. This is crucial for applications like heat sinks where surface quality dictates thermal contact resistance.	Ensures optimal performance in high-power density thermal management applications.

Engineering Support

6CCVD’s in-house PhD material science team can assist with material selection and process optimization for similar Tungsten-Diamond MMC projects. We provide consultation on:

Feedstock Optimization: Tailoring diamond powder morphology and size distribution to improve powder bed quality and flowability in L-PBF (addressing challenges noted in related literature).
Carbide Mitigation: Selecting appropriate metal coatings and thicknesses to manage the high cooling rates of L-PBF and minimize detrimental W₂C and WC_1-x phase formation.
BDD Exploration: Investigating Boron-Doped Diamond (BDD) materials for potential use in composites requiring specific electrical or electrochemical properties alongside extreme hardness.

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

View Original Abstract

Tungsten-diamond metal matrix composites (MMCs) fabricated via L-PBF show potential for applications in nuclear facility shielding, heat sinks, precision cutting/grinding tools, and aerospace hot-end components. In this paper, tungsten (W), diamond (D), and diamond with Ni coating (D-Ni) powders are used to fabricate W+D and W+(D-Ni) composites by L-PBF technology. The results show that at the interface of the W+D sample, the W powder melts while the D powder remains in a solid state during L-PBF processing, and W and C elements gradually diffuse into each other. Due to the high cooling rate of L-PBF processing, the C phase forms a diamond-like carbon (DLC) phase with an amorphous structure, and the W phase becomes a supersaturated solid solution of the C element. At the interface of the W+(D-Ni) sample, the diffusion capacity of Ni and W elements in the solid state is weaker than in the molten state. C and W elements diffuse into the Ni melt, forming a rich Ni area of the DLC phase, while Ni and W elements diffuse into the solid D powder, forming a lean Ni area of the DLC phase. In the rich Ni area of the DLC phase, Ni segregation leads to the precipitation of nanocrystals (several hundred nanometers), whereas in the lean Ni area of the DLC phase, the diffusion capacity of Ni and W elements in the solid D powder is limited, resulting in nanocrystalline sizes of only about tens of nanometers. During W dendrite growth, the addition of the Ni coating and the expelling of the C phenomenon leads to W grain refinement at the interface, which reduces the number and length of cracks in the W+(D-Ni) sample. This paper contributes to the theoretical development and engineering applications of tungsten-diamond MMCs fabricated by L-PBF.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma18112574

References

2023 - Research status of tungsten-based plasma-facing materials: A review [Crossref]
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2024 - Application and development of superhard materials in geological drilling field
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2024 - Research Progress of Diamond-reinforced Metal Matrix Composites
2023 - Effect of Si-coated diamond on the relative density and thermal conductivity of diamond/W composites prepared by SPS [Crossref]