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	State Forestry and Grassland Administration, University of Science and Technology Beijing
Citations	8
Analysis	Full AI Review Included

Executive Summary

This research successfully developed high-performance diamond/Al composites using a Liquid-Solid Separation (LSS) method combined with a Ti interfacial coating, targeting advanced thermal management applications.

Performance Enhancement: The Ti coating (approx. 100 nm thick) increased the Thermal Conductivity (TC) of the composite by 85.9%, achieving 277 W/m·K, up from 149 W/m·K for uncoated samples.
Mechanical Improvement: Bending strength saw a 46.25% increase, reaching 142.54 MPa, attributed to enhanced interfacial bonding and higher relative density (98.08%).
Interfacial Integrity: The LSS process, characterized by low heating temperature and short holding time, successfully prevented the formation of detrimental aluminum carbide (Al₄C₃).
Metallurgical Bonding: The Ti coating reacted with the Al matrix to form stable intermetallic compounds (e.g., Al₃Ti, Al₂Ti, Al₅Ti₃, Ti₉Al₂₃), creating a strong metallurgical bond across an interdiffusion area of approximately 8 µm.
Model Comparison: The achieved TC (277 W/m·K) reached 71.2% and 72.5% of the theoretical predictions calculated by the Differential Effective Medium (DEM) and Maxwell models, respectively.
Coating Comparison: While the Ti coating significantly improved bending strength, previous Cr coatings were noted to enhance TC more effectively, suggesting a trade-off between mechanical and thermal properties based on the coating material.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Volumetric Fraction	40	%	Reinforcement phase
Thermal Conductivity (Ti-Coated)	277	W/m·K	Achieved TC (85.9% increase)
Thermal Conductivity (Uncoated)	149	W/m·K	Baseline TC
Bending Strength (Ti-Coated)	142.54	MPa	46.25% increase over uncoated
Relative Density (Ti-Coated)	98.08	%	Fabricated by LSS process
Ti Coating Thickness	~100	nm	Applied via vacuum ion plating
Interdiffusion Layer Thickness	~8	µm	Ti/Al interface region
Theoretical TC (DEM Model)	389	W/m·K	Differential Effective Medium prediction
Theoretical TC (Maxwell Model)	382	W/m·K	Maxwell prediction
Diamond Particle Size (Average)	106	µm	MBD-4 grade synthetic single-crystal
Al Powder Purity	99.81	%	Industrial grade
Diamond TC (Calculated)	1121	W/m·K	Based on 330 ppm N content
CTE of Diamond	1.0~3.0 x 10^-6/K		Target for matching chip CTE

Key Methodologies

The diamond/Al composites were fabricated using the Liquid-Solid Separation (LSS) method under controlled atmospheric conditions.

Raw Material Preparation:
- Synthetic diamond particles (106 µm) were coated with a 100 nm Ti layer via vacuum ion plating.
- Ti-coated diamond and Al powder (37 µm) were mixed in a 1:4 volume ratio for 8 hours using a Turbula Shaker/Mixer.
Blank Formation:
- The homogenous mixture was cold-pressed in a four-column press at 300 MPa for 1 minute to form a blank (6.6 x 38 x 48 mm).
Liquid-Solid Separation (LSS) Process:
- The blank was placed in a custom LSS mold system. Hydrogen gas was used throughout the process to prevent Al oxidation.
- First Heating Stage: Heated at 20 °C/min to 450 °C and held for 20 minutes.
- Second Heating Stage: Heated at 20 °C/min to 683 °C (molten state) and maintained for 40 minutes.
Separation and Consolidation:
- The molten metal was squeezed into the liquid chamber through a 2 mm LSS channel using a piston pressure of 60 MPa. This action trapped the diamond particles and eliminated spillover into the liquid phase.
- The slurry solidified layer by layer under cooling water action to form the final composite (3 x 40 x 50 mm).
Characterization:
- Interfacial bonding was confirmed by SEM, EMPA (showing 8 µm interdiffusion), and XRD (confirming Al₃Ti, Al₂Ti, Al₅Ti₃, and Ti₉Al₂₃ intermetallic compounds, and the absence of Al₄C₃).
- Thermal properties were measured using an LFA laser flash machine (thermal diffusion) and calculated using the Archimedes principle (density) and theoretical specific heat capacity.

Commercial Applications

The fabricated diamond/Al composites offer superior thermal management capabilities due to their high TC and low, matched Coefficient of Thermal Expansion (CTE), making them ideal for next-generation high-power electronics.

High-Performance Electronic Devices: General thermal management for systems requiring high heat flux dissipation.
Power Electronics: Heat spreaders and substrates for Insulated Gate Bipolar Transistors (IGBTs).
Defense and Telecommunications: Thermal substrates for Phased Array Radars.
Optoelectronics: Heat sinks for High-Power Solid-State Lasers.
Integrated Circuits: Packaging materials for Large-Scale Integrated Circuits (LSI) where CTE mismatch must be minimized (matching chip CTE of 4.0~7.0 x 10^-6/K).
Aerospace and Automotive: Components requiring lightweight materials with high thermal stability and mechanical strength.

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

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