Improved Bending Strength and Thermal Conductivity of Diamond/Al Composites with Ti Coating Fabricated by Liquid–Solid Separation Method

At a Glance

Metadata	Details
Publication Date	2024-03-25
Journal	Materials
Authors	Hongyu Zhou, Qijin Jia, Jing Sun, Yaqiang Li, Yinsheng He
Institutions	University of Science and Technology Beijing, State Forestry and Grassland Administration
Citations	8
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Performance Diamond/Al Composites

Executive Summary

This research successfully demonstrates a highly effective method for fabricating high-thermal-conductivity (TC) diamond/aluminum (Al) composites, crucial for next-generation thermal management in high-power electronics (IGBTs, phased array radars).

Process Validation: The Liquid-Solid Separation (LSS) technology was validated for producing 40 vol.% diamond/Al composites, specifically preventing the formation of detrimental aluminum carbide (Al₄C₃) at the interface, thereby preserving mechanical and thermophysical properties.
Thermal Performance: Application of a 100 nm Ti coating on the synthetic single-crystal diamond (SCD) particles resulted in a significant TC increase of 85.9%, raising the composite TC from 149 W/m·K (uncoated) to 277 W/m·K.
Mechanical Enhancement: The Ti coating promoted strong metallurgical bonding (forming Al₃Ti, Al₂Ti, etc.), leading to a 46.25% increase in bending strength, achieving 142.54 MPa.
Interfacial Control: The Ti coating acts as an effective buffer layer, mitigating the severe Coefficient of Thermal Expansion (CTE) mismatch between diamond (1.0-3.0 x 10^-6/K) and Al (23.0 x 10^-6/K), reducing interfacial gaps, and increasing relative density to 98.08%.
Material Comparison: Ti coating proved superior to previously studied Cr coating in maximizing the composite’s bending strength, essential for structural integrity in electronic packaging.
Modeling Discrepancy: Measured TC values (277 W/m·K) reached 71.2%-72.5% of theoretical predictions (DEM/Maxwell models), highlighting the need for precise control over intermetallic layer thickness (observed at ~8 µm) to minimize intrinsic interfacial thermal resistance.

Technical Specifications

The following hard data points were extracted from the analysis of the Ti-coated diamond/Al composites fabricated via the LSS method:

Parameter	Value	Unit	Context
Thermal Conductivity (Ti-Coated)	277	W/m·K	40 vol.% Diamond/Al composite
TC Growth Rate (Ti-Coated)	85.9	%	Increase over uncoated composite (149 W/m·K)
Bending Strength (Ti-Coated)	142.54	MPa	46.25% increase over uncoated composite
Relative Density (Ti-Coated)	98.08	%	High density achieved via LSS
Ti Coating Thickness (Nominal)	100	nm	Applied via vacuum ion plating
Diamond Particle Size (Average)	106	µm	MBD-4 grade synthetic SCD
Diamond CTE	1.0-3.0 x 10^-6/K	/K	Low CTE component
Al Matrix CTE	23.0 x 10^-6/K	/K	High CTE component
Intermetallic Interdiffusion Area	~8	µm	Thickness of the Ti/Al reaction layer
Intrinsic Diamond TC (Calculated)	1121	W/m·K	Based on 330 ppm Nitrogen content
Intermetallic Compounds Formed	Al₃Ti, Al₂Ti, Al₅Ti₃, Ti₉Al₂₃	N/A	Confirmed via XRD

Key Methodologies

The fabrication and characterization of the high-performance diamond/Al composites relied on precise control of material inputs and the Liquid-Solid Separation (LSS) process parameters.

Raw Material Selection: MBD-4 grade synthetic single-crystal diamond (SCD) particles (106 µm average size) were used as the reinforcement phase (40 vol.%). Industrial Al powder (99.81% purity, 37 µm) served as the matrix.
Surface Modification: A Ti coating with a nominal thickness of 100 nm was deposited onto the diamond particles using the vacuum ion plating technique to enhance wettability and bonding.
Mixing and Preparation: Diamond and Al powders were mixed in a 1:4 volume ratio for 8 hours to ensure uniform distribution prior to infiltration.
Liquid-Solid Separation (LSS) Process:
- The mixture was heated to a semi-solid state at 450 °C and held for 20 minutes.
- The temperature was subsequently raised to the liquid state at 685 °C.
- The molten metal was infiltrated into the diamond particle preform by applying a pressure of 60 MPa using a piston, facilitating liquid-solid separation and high-density consolidation.
Interfacial and Phase Characterization:
- Scanning Electron Microscopy (SEM) and Electron Microprobe Analyzer (EMPA) were used to confirm the 8 µm interdiffusion area and metallurgical bonding.
- X-ray Diffraction (XRD) confirmed the formation of intermetallic compounds (Al₃Ti, Al₂Ti, Al₅Ti₃, Ti₉Al₂₃) and, critically, the absence of the deleterious Al₄C₃ phase.
Property Measurement: Thermal diffusion was measured using Laser Flash Analysis (LFA). Bending strength was tested using a three-point bending test at room temperature.

6CCVD Solutions & Capabilities

The research highlights the critical role of high-quality diamond material, precise coating thickness, and controlled metalization in achieving superior thermal and mechanical performance. 6CCVD is uniquely positioned to supply the necessary materials and engineering services to replicate, optimize, and scale this technology for industrial applications.

Research Requirement	6CCVD Solution & Capability	Technical Advantage for Replication/Extension
High-Quality Diamond Reinforcement (SCD, controlled N content)	Single Crystal Diamond (SCD) & Polycrystalline Diamond (PCD)	We provide MPCVD-grown diamond with precise control over purity and doping (e.g., nitrogen content), allowing engineers to select materials optimized for intrinsic TC (up to >2000 W/m·K) or specific defect engineering.
Interfacial Bonding Layer (Ti coating, 100 nm thickness)	In-House Custom Metalization Services	6CCVD offers precise, controlled deposition of carbide-forming elements, including Titanium (Ti), Tungsten (W), and Chromium (Cr), critical for forming stable intermetallic compounds and maximizing Interfacial Thermal Conductance (ITC). We guarantee thickness control necessary to avoid excessive thermal resistance (as noted for the 8 µm layer).
Scaling and Substrate Size (Future large-scale packaging)	Large Area PCD Plates/Wafers	We manufacture Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, suitable for scaling up thermal management substrates used in high-power modules (IGBTs, phased array radar).
Material Thickness & Geometry (Custom composite preforms)	Custom Dimensions and Thicknesses	6CCVD supplies SCD and PCD materials in thicknesses ranging from 0.1 µm to 500 µm, and substrates up to 10 mm. We offer precision laser cutting and grinding services to meet exact geometric requirements for LSS or infiltration processes.
Surface Quality (Minimizing phonon scattering)	Ultra-Low Roughness Polishing	Our SCD materials are polished to Ra < 1 nm, and inch-size PCD to Ra < 5 nm. This superior surface finish minimizes phonon scattering at the diamond-matrix interface, a key factor in maximizing composite TC.
Boron Doping for Functionality (Future BDD applications)	Boron-Doped Diamond (BDD)	For applications requiring simultaneous thermal management and electrochemical stability (e.g., sensors or electrodes), 6CCVD offers BDD materials, leveraging the versatility of MPCVD synthesis.

Engineering Support

6CCVD’s in-house PhD engineering team specializes in the physics of diamond interfaces and thermal transport modeling. We can assist researchers and engineers in selecting the optimal diamond material grade and metalization scheme (Ti, Cr, W, etc.) required to achieve specific TC and mechanical targets for similar Diamond/Al Composite Thermal Management projects.

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

View Original Abstract

In response to the rapid development of high-performance electronic devices, diamond/Al composites with high thermal conductivity (TC) have been considered as the latest generation of thermal management materials. This study involved the fabrication of diamond/Al composites reinforced with Ti-coated diamond particles using a liquid-solid separation (LSS) method. The interfacial characteristics of composites both without and with Ti coatings were evaluated using SEM, XRD, and EMPA. The results show that the LSS technology can fabricate diamond/Al composites without Al4C3, hence guaranteeing excellent mechanical and thermophysical properties. The higher TC of the diamond/Al composite with a Ti coating was attributed to the favorable metallurgical bonding interface compounds. Due to the non-wettability between diamond and Al, the TC of uncoated diamond particle-reinforced composites was only 149 W/m·K. The TC of Ti-coated composites increased by 85.9% to 277 W/m·K. A simultaneous comparison and analysis were performed on the features of composites reinforced by Ti and Cr coatings. The results suggest that the application of the Ti coating increases the bending strength of the composite, while the Cr coating enhances the TC of the composite. We calculate the theoretical TC of the diamond/Al composite by using the differential effective medium (DEM) and Maxwell prediction model and analyze the effect of Ti coating on the TC of the composite.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma17071485

References

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2023 - Thermal characterization of metal-diamond composite heat spreaders using low-frequency-domain thermoreflectance [Crossref]
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2020 - A review on fabrication methods, reinforcements and mechanical properties of aluminum matrix composites [Crossref]