The Microzone Structure Regulation of Diamond/Cu-B Composites for High Thermal Conductivity - Combining Experiments and First-Principles Calculations

At a Glance

Metadata	Details
Publication Date	2023-02-28
Journal	Materials
Authors	Zhongnan Xie, Wei Xiao, Hong Guo, Boyu Xue, Hui Yang
Institutions	General Research Institute for Nonferrous Metals (China), State Key Laboratory of Nonferrous Metals and Processes
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond/Cu-B Composites for High Thermal Conductivity

Reference Paper: The Microzone Structure Regulation of Diamond/Cu-B Composites for High Thermal Conductivity: Combining Experiments and First-Principles Calculations (Materials 2023, 16, 2021)

Executive Summary

This research successfully demonstrates a highly effective method for dramatically enhancing the thermal conductivity (TC) of diamond-reinforced copper matrix composites, a critical material class for advanced electronic packaging and heat dissipation.

Record Thermal Performance: Achieved a peak thermal conductivity of 694 W/(mK) in Diamond/Cu composites by alloying the copper matrix with 0.5 wt.% Boron (B).
2.5x Improvement: This represents a 2.5-fold increase over the baseline Diamond/Cu composite (261 W/(mK)), overcoming the inherent poor wettability and high thermal boundary resistance (TBR) between diamond and copper.
Interface Mechanism: Boron segregates to the interface, reacting exothermically to form a stable Boron Carbide (B$_{4}$C) interlayer.
Phonon Bridge: First-principles calculations confirm that the B$_{4}$C layer acts as a “phonon transmission bridge,” facilitating efficient heat transfer by providing overlapping phonon spectra between the low-frequency copper and high-frequency diamond.
Optimized Structure: The resulting B$_{4}$C layer exhibits a unique dentate/nano-cone microstructure, which further enhances interface phononic transport efficiency.
Material Basis: The composites were fabricated using high-purity, 100 µm single-crystal diamond (SCD) particles via vacuum pressure infiltration (VPI) at 1250 °C.

Technical Specifications

Hard data extracted from the experimental and computational results:

Parameter	Value	Unit	Context
Peak Thermal Conductivity (TC)	694	W/(mK)	Diamond/Cu-0.5 wt.%B composite
Baseline TC (No B)	261	W/(mK)	Pure Diamond/Cu composite
TC Improvement Factor	2.5	Times	Relative to baseline
Optimal Boron Content	0.5	wt.%	Copper matrix alloying concentration
Diamond Content	60	vol.%	Composite composition
Preparation Temperature	1250	°C	Vacuum Pressure Infiltration (VPI)
Diamond Particle Size	100	µm	Single-crystal reinforcing phase
Boron Diffusion Energy Barrier	0.87	eV	Interstitial B diffusion in bulk Cu
B$_{4}$C Formation Enthalpy	-1.36	eV/atom	Exothermic reaction, highly favorable
Interface Electronic Conductance	1.13	G$_{0}$/nm²	Calculated for pure Cu/Diamond interface
Diamond Phonon Frequency Range	10-40	THz	High-frequency range
Copper Phonon Frequency Range	0-8	THz	Low-frequency range
B$_{4}$C Phonon Frequency Range	5-34	THz	Acts as the bridging spectrum

Key Methodologies

The Diamond/Cu-B composites were prepared and analyzed using a combination of high-temperature fabrication and advanced computational physics.

Material Preparation:
- Reinforcement: Single-Crystal Diamond (SCD) particles (100 µm grain size) were used as the reinforcing phase.
- Matrix: Copper bulks (99.99 wt.% purity) and Boron powder (99.9% purity, 2-3 µm size) were alloyed to create the Cu-B matrix (0, 0.5, and 1.0 wt.% B).
Fabrication Process:
- Diamond particles were formed into preforms and placed in graphite molds.
- The Cu-B alloy was poured into the mold at 1250 °C under vacuum pressure infiltration (VPI).
- Mechanical pressure was applied to ensure copper penetration into the preform gap.
Microstructure Analysis:
- Scanning Electron Microscopy (SEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to confirm the dentate/nano-cone B$_{4}$C microstructure at the interface.
- X-ray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS) confirmed the presence and accumulation of the newly formed B$_{4}$C phase near the interface.
Thermal Measurement:
- Thermal diffusivity was measured at room temperature using a thermal conductivity tester (LFA447).
- Thermal conductivity (K) was calculated using the formula: K = α·ρ${pc}$·C${p}$ (where α is thermal diffusivity, ρ${pc}$ is density, and C${p}$ is specific heat).
First-Principles Calculations (DFT):
- Density Functional Theory (DFT) calculations (using VASP) were employed to model B occupation, diffusion kinetics (NEB method, 0.87 eV barrier), and segregation behavior (driving force of -1.10 eV).
- Phonon Density of States (PDOS, using CASTEP) was calculated for Diamond, Cu, B${4}$C, and Cu${4}$B to validate the phononic transport enhancement mechanism.

6CCVD Solutions & Capabilities

The success of this research hinges on controlling the diamond interface structure and utilizing high-quality diamond material. 6CCVD is uniquely positioned to supply the foundational materials and advanced surface engineering required to replicate, optimize, and scale this technology for commercial thermal management applications.

Research Requirement	6CCVD Solution & Value Proposition
High-Purity Diamond Reinforcement (100 µm Single-Crystal Diamond)	Optical Grade SCD Wafers/Plates: 6CCVD supplies high-purity Single Crystal Diamond (SCD) material, crucial for maximizing intrinsic thermal properties (TC > 2000 W/(mK) for high-purity SCD). We offer SCD in thicknesses from 0.1 µm up to 500 µm, suitable for use as filler particles or as high-performance substrates.
Interface Modification & Carbide Formation (B$_{4}$C layer)	Custom Metalization Services (Ti, W, Cu): While the paper used VPI/B alloying, 6CCVD offers direct, controlled surface modification. We provide internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) on SCD/PCD surfaces, allowing engineers to pre-coat diamond fillers or substrates to ensure robust chemical bonding and minimize Thermal Boundary Resistance (TBR) in subsequent composite fabrication steps (e.g., sintering or infiltration).
Scaling for Thermal Management (High-power electronics)	Large Area PCD Substrates: For scaling up high-performance thermal management solutions, 6CCVD offers Polycrystalline Diamond (PCD) plates/wafers up to 125mm in diameter, polished to Ra < 5nm. This provides the necessary large-area heat spreading capability for modern chip packages.
Advanced Material Design (DFT/Phonon Spectrum Analysis)	Expert Engineering Consultation: Our in-house PhD material science team specializes in CVD diamond physics, surface termination, and interface engineering. We can assist researchers in selecting the optimal diamond grade (SCD vs. PCD) and surface preparation technique to achieve specific interface chemistries required for low-TBR metal matrix composites.
Boron Doping for Semiconductors (Alternative Application)	Boron-Doped Diamond (BDD): 6CCVD also offers Boron-Doped Diamond (BDD) materials, which are critical for electrochemical and semiconductor applications, demonstrating our expertise in precise boron incorporation into the diamond lattice.

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View Original Abstract

The interface microzone characteristics determine the thermophysical properties of diamond/Cu composites, while the mechanisms of interface formation and heat transport still need to be revealed. Here, diamond/Cu-B composites with different boron content were prepared by vacuum pressure infiltration. Diamond/Cu-B composites up to 694 W/(mK) were obtained. The interfacial carbides formation process and the enhancement mechanisms of interfacial heat conduction in diamond/Cu-B composites were studied by HRTEM and first-principles calculations. It is demonstrated that boron can diffuse toward the interface region with an energy barrier of 0.87 eV, and these elements are energetically favorable to form the B4C phase. The calculation of the phonon spectrum proves that the B4C phonon spectrum is distributed in the range of the copper and diamond phonon spectrum. The overlapping of phonon spectra and the dentate structure together enhance the interface phononic transport efficiency, thereby improving the interface thermal conductance.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma16052021

References

2018 - Effect of Ti interlayer on interfacial thermal conductance between Cu and diamond [Crossref]
2019 - Tailoring interface structure and enhancing thermal conductivity of Cu/diamond composites by alloying boron to the Cu matrix [Crossref]
2017 - Design of interfacial Cr3C2 carbide layer via optimization of sintering parameters used to fabricate copper/diamond composites for thermal management applications [Crossref]
2020 - High thermal conductivity and strong interface bonding of a hot-forged Cu/Ti-coated-diamond composite [Crossref]
2012 - High thermal conductivity composite of diamond particles with tungsten coating in a copper matrix for heat sink application [Crossref]
2013 - Microstructure and thermal conductivity of Cu-B/diamond composites [Crossref]
2019 - Graphene interlayer for enhanced interface thermal conductance in metal matrix composites: An approach beyond surface metallization and matrix alloying [Crossref]
2021 - Unveiling the interface characteristics and their influence on the heat transfer behavior of hot-forged Cu-Cr/Diamond composites [Crossref]