Interface Optimization and Thermal Conductivity of Cu/Diamond Composites by Spark Plasma Sintering Process

At a Glance

Metadata	Details
Publication Date	2025-01-06
Journal	Nanomaterials
Authors	Jun-Feng Zhao, Hao Su, Kai Li, Haijuan Mei, Junliang Zhang
Institutions	Huizhou University
Citations	1
Analysis	Full AI Review Included

Technical Analysis: Interface Optimization and Thermal Conductivity of Cu/Diamond Composites

Executive Summary

This research successfully optimized the interface structure of Copper/Diamond (Cu/Dia) composites using Spark Plasma Sintering (SPS) and Cr alloying, resulting in a significant enhancement of thermal conductivity (TC).

Performance Achievement: Thermal conductivity was increased by approximately 66%, rising from an unoptimized 310 W/mK to a maximum of 516 W/mK.
Interface Modification: The addition of 3 wt% Cr to the Cu matrix facilitated the formation of a Cr₇C₃ carbide layer at the interface, converting the weak physical bond into a strong metallurgical bond.
Particle Size Optimization: Agglomeration was minimized, and uniform distribution was achieved using a 200 µm diamond particle size, which contributed to higher relative density (95.01%).
Process Optimization: The optimal sintering temperature was determined to be 900 °C, balancing sufficient interface reaction with minimizing thermal expansion mismatch gaps upon cooling.
Mechanism: The Cr₇C₃ layer acts as a binder, improving the wettability between Cu and diamond and providing an intermediate acoustic impedance path for efficient phonon transport.

Technical Specifications

Parameter	Value	Unit	Context
Maximum Thermal Conductivity (λ)	516	W/mK	Achieved with 200 µm Dia and 3 wt% Cr at 900 °C.
Thermal Conductivity Improvement	~66	%	Overall increase from unoptimized 310 W/mK.
Optimal Diamond Particle Size	200	µm	Size required for uniform distribution and minimal agglomeration.
Optimal Cr Alloying Content	3	wt%	Content required to form the strong Cr₇C₃ interface phase.
Optimal Sintering Temperature	900	°C	Temperature maximizing interface bonding strength.
Diamond Volume Fraction	~40	%	Constant reinforcing phase content used in all samples.
Relative Density (Optimized)	95.01	%	Achieved with 200 µm Dia particles.
Interface Reaction Product	Cr₇C₃	N/A	Identified via XRD; acts as the metallurgical binder.
Sintering Pressure (SPS)	50	MPa	Applied during the heating phase.
Initial Heating Rate	50	°C/min	Rate used up to 500 °C.
Dwell Time at Sintering Temp	20	min	Time maintained for full densification.

Key Methodologies

The Cu/Dia composites were fabricated using the Spark Plasma Sintering (SPS) technique, preceded by vacuum ball milling to ensure powder homogeneity and prevent oxidation.

Raw Material Selection: Commercial Cu powder (99.99% purity) and diamond crystal grains were used. Cr powder was introduced as the alloying element for interface modification.
Vacuum Ball Milling: Powders (including Cr) were mixed in a ball-to-powder ratio of 10:1 under vacuum for 5 hours using a planetary ball mill. This step ensured homogeneous mixing and prevented Cu oxidation.
- Milling Parameters: 200 rpm rotation speed, alternating 15 min forward/15 min reverse rotation with a 4 min interval.
SPS Preparation: The milled powder was placed into a graphite mold and pressed into 13 mm diameter discs.
SPS Sintering Cycle:
- The sample was heated to 500 °C at 50 °C/min.
- A pressure of 50 MPa was applied and maintained while heating continued to the set sintering temperature (optimized at 900 °C).
- The sample was held at the set temperature for 20 minutes for densification.
- Cooling was performed slowly in the furnace, with pressure released gradually below 200 °C.
Characterization:
- Microstructure: Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to analyze particle distribution and element composition.
- Phase Identification: X-ray Diffraction (XRD) confirmed the presence of the Cr₇C₃ interfacial phase.
- Thermal Properties: Thermal conductivity (λ) was calculated using the formula λ = a × C_p × ρ, where thermal diffusivity (a) was measured using a thermal conductivity tester (LFA467 HyperFlash).
- Density: Actual density (ρ) was determined using the Archimedes principle.

Commercial Applications

The development of high thermal conductivity Cu/Dia composites with tailored interfaces is critical for next-generation thermal management in demanding electronic systems.

High-Power Electronics: Used as heat sinks and spreaders for high-density components like CPUs, GPUs, and power modules where rapid heat dissipation is essential.
Electronic Packaging: Ideal materials for packaging applications requiring both high thermal conductivity (516 W/mK) and tunable coefficients of thermal expansion (CTE).
Electric Vehicles (EVs): Thermal management in high-power electric-drive vehicle power electronics, where heat control is vital for reliability and longevity.
Aerospace and Spacecraft: Applications requiring robust, high-performance thermal management materials in extreme environments.
Miniaturized Devices: Supporting the trend toward miniaturization and high integration in electronic devices by safely transferring large amounts of heat per unit area.

View Original Abstract

Cu/Diamond (Cu/Dia) composites are regarded as next-generation thermal dissipation materials and hold tremendous potential for use in future high-power electronic devices. The interface structure between the Cu matrix and the diamond has a significant impact on the thermophysical properties of the composite materials. In this study, Cu/Dia composite materials were fabricated using the Spark Plasma Sintering (SPS) process. The results indicate that the agglomeration of diamond particles decreases with increasing particle size and that a uniform distribution is achieved at 200 μm. With an increase in the sintering temperature, the interface bonding is first optimized and then weakened, with the optimal sintering temperature being 900 °C. The addition of Cr to the Cu matrix leads to the formation of Cr7C3 after sintering, which enhances the relative density and bonding strength at the interface, transitioning it from a physical bond to a metallurgical bond. Optimizing the diamond particle size increased the thermal conductivity from 310 W/m K to 386 W/m K, while further optimizing the interface led to a significant increase to 516 W/m K, representing an overall improvement of approximately 66%.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano15010073

References

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