The Interface of Additive Manufactured Tungsten–Diamond Composites
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-05-30 |
| Journal | Materials |
| Authors | Xuehao Gao, Dongxu Cheng, Zhe Sun, Yihe Huang, Wentai Ouyang |
| Institutions | Hubei University of Technology, Ningbo Institute of Industrial Technology |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study investigates the interface bonding and microstructure evolution in Tungsten-Diamond Metal Matrix Composites (MMCs) fabricated via Laser Powder Bed Fusion (L-PBF), focusing on the critical role of Nickel (Ni) coating on diamond particles.
- Enhanced Composite Quality: The use of Ni-coated diamond (W+(D-Ni)) significantly reduced microcracks and improved the overall integrity of the composite compared to uncoated W+D samples.
- Interface Phase Formation: L-PBF processing, characterized by high cooling rates, resulted in the formation of an amorphous Diamond-Like Carbon (DLC) phase (ta-C structure) at the W/C interface in both composites.
- Ni Coating Functionality: The Ni coating acted as a barrier, delaying and reducing the diffusion between W and C, thereby suppressing diamond graphitization and minimizing the precipitation of brittle W2C carbides.
- Grain Refinement Mechanism: The addition of Ni promoted W grain refinement at the interface (sub-micron dendrite width) through a combination of Ni solid solution softening and C element expulsion during rapid W dendrite growth.
- Nanocrystal Precipitation: Ni segregated into the DLC phase, leading to the precipitation of Ni-rich nanocrystals. In the Ni-rich (molten) areas, nanocrystals reached several hundred nanometers, while in the Ni-lean (solid diffusion) areas, they were limited to tens of nanometers.
- Supersaturated W Phase: In the W+D sample, the W matrix formed a supersaturated solid solution of C, with concentrations reaching 11.62 at% at the interface, far exceeding the equilibrium solubility (0.7 at%).
Technical Specifications
Section titled “Technical Specifications”The following table summarizes the key material and process parameters used in the L-PBF fabrication of the W-D MMCs.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| W Powder Size | 15 to 45 | µm | Raw material specification. |
| Diamond Powder Size (D/D-Ni) | 25 to 38 | µm | Raw material specification. |
| Ni Coating Weight Increase | 56 | % | Relative to D powder weight. |
| Composite Volume Ratio (W:D) | 85:15 | vol% | Powder mixture composition. |
| Laser Power (P) | 400 | W | L-PBF processing parameter. |
| Scanning Speed (v) | 725 | mm/s | L-PBF processing parameter. |
| Layer Thickness (t) | 30 | µm | L-PBF processing parameter. |
| Hatch Spacing (h) | 100 | µm | L-PBF processing parameter. |
| Max C Content in W Phase (W+D) | 11.62 | at% | Supersaturated solid solution at the interface. |
| Average C Content in W Dendrites (C-rich) | 8.39 | at% | W+(D-Ni) C expulsion zone. |
| Average Ni Content in Ni-Rich DLC Nanocrystals | 29.87 | at% | Middle area of the carbon phase interface. |
| W-C Heat of Mixing | -60 | kJ/mol | High bond energy difference, driving carbide formation. |
| Ni-C Heat of Mixing | -39 | kJ/mol | Moderate bond energy difference. |
| W Dendrite Width (W+(D-Ni)) | Sub-micron | scale | Refined grain size due to Ni addition. |
| DLC Phase Structure | Amorphous | N/A | Confirmed as ta-C (Diamond-Like Carbon) by Raman/TEM. |
Key Methodologies
Section titled “Key Methodologies”The study employed L-PBF to fabricate the composites and utilized advanced microscopy and spectroscopy techniques to analyze the resulting interface microstructures.
- Powder Mixing: Tungsten (W) powder was pre-mixed with 15 vol% Diamond (D) or Ni-coated Diamond (D-Ni) powder using a Y-type powder blender for over 30 minutes to ensure homogeneous distribution.
- L-PBF Fabrication: A custom-developed L-PBF system was used with fixed parameters: 400 W laser power, 725 mm/s scanning speed, 30 µm layer thickness, and 100 µm hatch spacing.
- Interface Melting Behavior (W+D): During L-PBF, W powder melted while D powder remained in a solid state. W and C elements underwent gradual interdiffusion, forming a DLC phase due to the high cooling rate.
- Interface Melting Behavior (W+(D-Ni)): The Ni coating melted first, followed by the W powder. C and W diffused into the Ni melt (forming a rich Ni DLC area), and Ni/W diffused into the solid D powder (forming a lean Ni DLC area).
- Phase and Compositional Analysis:
- X-ray Diffraction (XRD) was used to identify bulk phases (W, W2C, WC1-x, and C phase).
- Raman Spectroscopy (633-nm laser) confirmed the presence of amorphous carbon (DLC) at the interface by detecting broadened D (sp3) and G (sp2) peaks.
- Focused Ion Beam (FIB) was used to prepare thin lamellae for Transmission Electron Microscopy (TEM).
- TEM, HRTEM, and Energy-Dispersive X-ray Spectroscopy (EDX) were used to map element distribution (W, C, Ni) and analyze the microstructure (nanocrystal size, dendrite morphology) at the interface.
Commercial Applications
Section titled “Commercial Applications”The enhanced properties and controlled interface bonding achieved through Ni coating make these L-PBF fabricated W-D MMCs highly suitable for demanding engineering environments.
- Nuclear Energy and Fusion:
- Application: Plasma-facing components (PFCs) and shielding materials.
- Benefit: Tungsten’s excellent resistance to neutron radiation and high density, combined with improved fracture toughness due to Ni-induced grain refinement, ensures structural integrity under extreme conditions.
- Thermal Management Systems:
- Application: High-performance heat sinks and thermal spreaders for high-power electronics and aerospace components.
- Benefit: Leveraging diamond’s ultra-high thermal conductivity (3.2 W/(cm·K)) while ensuring robust bonding via the DLC interface layer, allowing for efficient heat dissipation.
- Precision Tooling and Machining:
- Application: Precision cutting, grinding, and drilling tools.
- Benefit: The composite combines the ultra-high hardness of diamond (70-150 GPa) with a crack-resistant W matrix, extending tool life and improving machining accuracy.
- Aerospace Hot-End Components:
- Application: Components exposed to high temperatures and mechanical stress.
- Benefit: High melting point and excellent fracture toughness of the W matrix, enhanced by the Ni coating strategy, provide reliability in extreme thermal environments.
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
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2023 - Research status of tungsten-based plasma-facing materials: A review [Crossref]
- 2016 - A study on diamond grinding wheels with regular grain distribution using additive manufacturing (AM) technology [Crossref]
- 2015 - Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 1: ELID assisted precision conditioning of grinding wheels [Crossref]
- 2024 - Application and development of superhard materials in geological drilling field
- 2023 - Synthesizing SiC layer on diamond by heat treatment and its effects on density and thermal conductivity of diamond/W composite [Crossref]
- 2019 - State-of-the-art of surface integrity in machining of metal matrix composites [Crossref]
- 2014 - Interaction of the cutting tools and the ceramic-reinforced metal matrix composites during micro-machining: A review [Crossref]
- 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]