Preparation of W-Plated Diamond and Improvement of Thermal Conductivity of Diamond-WC-Cu Composite

At a Glance

Metadata	Details
Publication Date	2021-03-07
Journal	Metals
Authors	Xulei Wang, Xinbo He, Zhiyang Xu, Xuanhui Qu
Institutions	University of Science and Technology Beijing
Citations	12
Analysis	Full AI Review Included

Executive Summary

This research successfully developed a high-performance Diamond-WC-Cu composite for advanced thermal management applications, achieving high density and superior thermal conductivity (TC) through optimized surface modification and infiltration techniques.

Core Achievement: A Diamond-WC-Cu composite with 60 vol% diamond achieved a high thermal conductivity of 874 W·m^-1·K^-1.
Interface Optimization: Tungsten (W) plating on diamond particles was achieved using the powder covering sintering method (1100 °C, 90 min), resulting in a dense, uniform W coating of approximately 900 nm.
Mechanism: During composite fabrication, the W coating reacted with diamond carbon to form a stable tungsten carbide (WC) transition layer, which significantly improved the wettability between the non-wetting diamond and the copper matrix.
Interface Resistance: The calculated total interface thermal resistance (R_int) was drastically reduced to 2.11 × 10^-8 m²·K·W^-1 due to the WC layer formation.
Fabrication Method: Composites were prepared using cyclic vacuum pressure infiltration (VPI), yielding a high relative density of >98%.
Modeling Validation: The experimental TC value closely matched theoretical predictions from the Hasselman-Johnson (H-J) and Differential Effective Medium (DEM) models, confirming the effectiveness of the interface modification.

Technical Specifications

Parameter	Value	Unit	Context
Achieved Thermal Conductivity (TC)	874	W·m^-1·K^-1	Diamond-WC-Cu composite (60 vol% diamond)
Relative Density	>98	%	Final Diamond-WC-Cu composite
Diamond Particle Size (Reinforcement)	100	µm	Artificial single crystal diamond (140/170 mesh)
Copper Powder Particle Size (Matrix)	50	µm	Pure copper powder (300 mesh)
W Coating Thickness (Optimal)	900	nm	Prepared by powder covering sintering (1100 °C, 90 min)
Interface Thermal Resistance (R_int)	2.11 × 10^-8	m²·K·W^-1	Calculated total R_int due to WC transition layer
Diamond Volume Fraction Tested	50 to 70	vol%	Range of final composite compositions
Copper Matrix TC (Reference)	400	W·m^-1·K^-1	Red copper baseline
Diamond TC (Reference)	2000	W·m^-1·K^-1	Room temperature
WC TC (Reference)	120	W·m^-1·K^-1	Tungsten Carbide
Cu/Diamond Contact Angle (Uncoated)	122-129	°	Indicating poor wettability

Key Methodologies

The composite preparation involved two main stages: W-plating of diamond particles and cyclic vacuum pressure infiltration (VPI) of the composite.

1. Diamond Surface Modification (W-Plating)

The powder covering sintering method was optimized to create a dense and uniform W coating, which subsequently forms the WC transition layer.

Pre-Treatment (Cleaning/Roughening):
- Boiling/Stirring in 10 wt% NaOH aqueous solution for 15 min.
- Boiling/Stirring in 30 wt% dilute HNO₃ aqueous solution for 30 min.
- Drying at 100 °C.
Sintering Process (Optimal Parameters):
- Mixture: Diamond particles, WO₃ powder, and W powder mixed for 3-5 h.
- Atmosphere: Vacuum condition (4-6 Pa).
- Heating Rate: 10 °C/min.
- Temperature: 1100 °C (Optimal plating temperature).
- Holding Time: 90 min (Optimal holding time).
Result: Formation of elemental W coating, which reacts during infiltration to form WC (Tungsten Carbide).

2. Diamond-WC-Cu Composite Fabrication (Cyclic VPI)

The cyclic vacuum pressure infiltration method was used to ensure high density and uniform infiltration of the copper melt into the diamond preform.

Preform Preparation:
- W-plated diamond mixed with 1-2 wt% Polyvinyl Alcohol (PVA) binder.
- Pre-pressing in graphite mold at 8.5 MPa for 2 min.
- Pre-degassing/Drying in oven at 150 °C for 4-5 h.
Matrix Preparation: Pure copper powder compacted at 80 MPa for 5 min to form a strong Cu body.
Infiltration Cycle (SGL1700 Vacuum Tube Furnace):
- Heat system to infiltration temperature (1200 °C).
- Turn off vacuum pump.
- Fill with Argon gas to 0.5 MPa (Pressure maintained for 10 min).
- Vacuum infiltrate (Ultimate vacuum maintained for 5 min).
- The “vacuum-argon gas” cycle was repeated for 1 h total to promote penetration and eliminate pore defects.

Commercial Applications

The Diamond-WC-Cu composite, characterized by its high thermal conductivity and low thermal expansion coefficient (inherent to diamond), is highly suitable for demanding thermal management applications in modern electronics and aerospace.

High-Power Electronic Packaging: Used as heat sinks and substrates for high-power density devices where traditional materials (Al, Cu, Mo/Cu) fail to dissipate heat effectively.
Semiconductor Circuits: Substrates for integrated circuits (ICs) and microelectronic components requiring stable operation under high thermal loads.
Aerospace Technology: Thermal management components in lightweight, high-integration aerospace systems where minimizing weight and maximizing heat dissipation are critical.
Thermal Interface Materials (TIMs): Advanced composite materials used to bridge the gap between heat sources (chips) and heat sinks.
Power Modules: Heat spreaders for IGBTs (Insulated Gate Bipolar Transistors) and other power electronics.

View Original Abstract

The tungsten (W)-plated diamond process was explored and optimized. A dense and uniform tungsten coating with a thickness of 900 nm was successfully prepared by the powder covering sintering method. The Diamond-WC-Cu composite with high density and high thermal conductivity were successfully prepared by cyclic vacuum pressure infiltration. The microstructure and composition of the W-plated diamond particles were analyzed. The effect of tungsten coating on the microstructure and thermal conductivity of the Diamond-WC-Cu composite was investigated. After calculation, the interface thermal resistance of the composite forming the tungsten carbide transition layer is 2.11 × 10−8 m2∙K∙W−1. The thermal conductivity average value of the Diamond-WC-Cu composite with a diamond volume fraction of 60% reaches 874 W∙m−1∙K−1, which is close to the theoretical prediction value of Hasselman-Johnson (H-J) model and differential effective medium (DEM) model. Moreover, the Maxwell-Eucken (M-E) model, H-J model, and DEM model were used to evaluate the thermal conductivity of the Diamond-WC-Cu composite.

Tech Support

Original Source

DOI: https://doi.org/10.3390/met11030437

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