Effects of the In Situ Growth of CNTs on Ti-Coated Diamond Surfaces on the Mechanical Properties of Diamond/Aluminum Composites

At a Glance

Metadata	Details
Publication Date	2024-04-07
Journal	Nanomaterials
Authors	Hao Wu, Ping Zhu, Yixiao Xia, Yifu Ma, Junyao Ding
Institutions	Harbin Institute of Technology, Nanjing University of Science and Technology
Citations	2
Analysis	Full AI Review Included

Executive Summary

This study successfully developed a multi-scale CNT-modified Ti-coated diamond/aluminum composite, achieving enhanced mechanical reliability crucial for advanced thermal management applications.

Enhanced Mechanical Strength: The CNT-modified composite exhibited the highest bending strength (275 ± 6 MPa), representing an approximate 9% increase compared to the uncoated diamond/Al composite (252 ± 9 MPa).
Multi-Scale Interface Architecture: Carbon Nanotubes (CNTs), approximately 1 µm in length, were grown in situ via PECVD on 300 nm Ti-coated diamond particles, creating a robust, multi-phase interface.
Interfacial Bonding Mechanism: The enhanced strength is attributed to the synergistic interfacial reaction during gas pressure infiltration (GPI), forming a complete and uniform layer of TiC, small Al₃Ti precipitates, and Al₄C₃ (from CNT reaction).
Improved Selective Bonding: The multi-product interface successfully improved the selective bonding between aluminum and different diamond crystal planes ({100} and {111}), preventing interfacial debonding observed in untreated composites.
Thermal Trade-off: While mechanical properties improved, thermal conductivity was reduced to 577 W·m^-1·K^-1 (compared to 726 W·m^-1·K^-1 for uncoated D/Al). This reduction is linked to the formation of thicker interface phases (TiC, Al₃Ti, Al₄C₃) which increase phonon scattering.
Strategic Design Insight: This work validates the interface configuration design method as a promising strategy for balancing high mechanical performance and acceptable thermal conductivity in diamond/metal composites.

Technical Specifications

Performance and material parameters of the diamond/aluminum composites (60% diamond volume fraction).

Parameter	Value	Unit	Context
Al Matrix Purity	99.99	wt.%	1060 Bulk Aluminum
Diamond Particle Size (Avg.)	355	µm	Monocrystalline Diamond (MBD4)
Ti Coating Thickness	300	nm	Magnetron Sputtering Layer
CNT Length (In Situ)	~1	µm	PECVD Growth
Max Bending Strength	275 ± 6	MPa	CNT-modified Ti-coated D/Al
Bending Strength (Uncoated)	252 ± 9	MPa	Baseline D/Al Composite
Bending Strength (Ti-Coated)	217 ± 14	MPa	Ti-coated D/Al Composite
Max Thermal Conductivity	726	W·m^-1·K^-1	Uncoated D/Al Composite
Thermal Conductivity (CNT-Mod)	577	W·m^-1·K^-1	CNT-modified Ti-coated D/Al
Dominant Interface Product (CNT-Mod)	TiC, Al₃Ti, Al₄C₃	-	Multi-phase bridging structure
GPI Infiltration Pressure	15	MPa	Fabrication Process

Key Methodologies

The multi-scale CNT-modified Ti-coated diamond particles were prepared using a three-step surface modification process, followed by Gas-Assisted Pressure Infiltration (GPI).

Ti Coating Preparation:
- Method: Magnetron Sputtering.
- Result: Uniform Ti coating with a thickness of 300 nm on diamond particles.
Fe Catalyst Encapsulation:
- Method: Solution Impregnation.
- Precursor: 0.05 mol/L Fe(NO₃)₃·9H₂O solution.
- Process: Ti-coated diamond soaked for 12 h, followed by drying.
In Situ CNT Growth (PECVD):
- Heating: Heated to 650 °C at 10 °C/min, held for 30 min under H₂ protection (20 sccm) to reduce Fe³⁺ to metallic Fe catalyst.
- Plasma Generation: Radio Frequency (RF) set at 13.56 MHz for 20 min.
- Growth Conditions: CH₄/H₂ mixture (20/5 sccm) introduced into the CVD reactor.
- Pressure: Total pressure maintained at 140-160 Pa.
- Result: High-density CNTs (approx. 1 µm length) grown on all crystal faces.
Composite Fabrication (GPI):
- Reinforcement: 60 vol.% modified diamond particles packed into a graphite mold.
- Infiltration: Aluminum ingot placed on top, heated to 800 °C (30 °C/min ramp rate), held for 20 min under vacuum.
- Pressurization: Gas pressure applied up to 15 MPa to complete infiltration.
Interface Analysis:
- The Al matrix was corroded using hydrochloric acid to extract diamond particles for SEM analysis, revealing the retained interfacial products (TiC layer, Al₄C₃).

Commercial Applications

The development of high-strength, thermally conductive diamond/aluminum composites is critical for modern electronics requiring efficient heat dissipation and structural integrity.

High-Density Electronic Packaging: Used as substrates and heat spreaders for high-power semiconductor devices (e.g., IGBTs, MOSFETs) where localized heat flux is extreme.
Thermal Management Systems: Fabrication of heat sinks and thermal interface materials (TIMs) for miniaturized and integrated electronic equipment (e.g., aerospace, automotive power electronics).
High-Reliability Components: Applications requiring materials that maintain mechanical integrity (high bending strength) under severe thermal cycling and mechanical stress, mitigating failure caused by brittle interfacial products (Al₄C₃ hydrolysis).
Adjustable Coefficient of Thermal Expansion (CTE): The ability to tailor the interface structure allows for control over the composite CTE, matching it closely to silicon chips or ceramic components, thereby reducing thermal stress.

View Original Abstract

Diamond/aluminum composites have attracted significant attention as novel thermal management materials, with their interfacial bonding state and configuration playing a crucial role in determining their thermal conductivity and mechanical properties. The present work aims to evaluate the bending strength and thermal conductivity of CNT-modified Ti-coated diamond/aluminum composites with multi-scale structures. The Fe catalyst was encapsulated on the surface of Ti-coated diamond particles using the solution impregnation method, and CNTs were grown in situ on the surface of Ti-coated diamond particles using the plasma-enhanced chemical vapor deposition (PECVD) method. We investigated the influence of interface structure on the thermal conductivity and mechanical properties of diamond/aluminum composites. The results show that the CNT-modified Ti-coated diamond/aluminum composite exhibits excellent bending strength, reaching up to 281 MPa, compared to uncoated diamond/aluminum composites and Ti-coated diamond/aluminum composites. The selective bonding between diamond and aluminum was improved by the interfacial reaction between Ti and diamond particles, as well as between CNT and Al. This led to the enhanced mechanical properties of Ti-coated diamond/aluminum composites while maintaining acceptable thermal conductivity. This work provides insights into the interface’s configuration design and the performance optimization of diamond/metal composites for thermal management.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano14070640

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