Fabrication of Titanium and Copper-Coated Diamond/Copper Composites via Selective Laser Melting

At a Glance

Metadata	Details
Publication Date	2022-04-30
Journal	Micromachines
Authors	Lu Zhang, Yan Li, Simeng Li, Ping Gong, Qiaoyu Chen
Institutions	China University of Geosciences
Citations	16
Analysis	Full AI Review Included

Executive Summary

This research successfully utilized Selective Laser Melting (SLM) to fabricate dense Titanium (Ti) and Copper (Cu)-coated diamond/copper (D/Cu) Metal Matrix Composites (MMCs), focusing on optimizing interfacial bonding and thermal performance for advanced heat management applications.

Core Achievement (Thermal Conductivity): A maximum Thermal Conductivity (TC) of 336 W/mK was achieved in the 1 vol.% Cu-coated D/Cu composite, significantly exceeding the performance of corresponding Ti-coated composites (174 W/mK).
Interfacial Solution: Electroless plating of copper onto diamond particles proved superior to titanium evaporation coating, resulting in better wettability, strong interfacial bonding, and the elimination of micro-cracking in the 1 vol.% composite.
Mechanical Superiority: Cu-coated D/Cu composites exhibited significantly higher bending strengths (up to 150 MPa) and lower Coefficients of Thermal Expansion (CTE) compared to Ti-coated counterparts, indicating enhanced thermal stability.
Processing Optimization: High relative densities (up to 96%) were achieved by optimizing SLM parameters, specifically targeting a Volumetric Laser Energy Density (D) of 300 J/mm³ (180 W laser power, 200 mm/s scanning rate).
Manufacturing Advancement: The successful integration of coated diamond particles via SLM opens new pathways for 3D printing complex, micro-sized diamond-reinforced MMCs for next-generation electronic packaging.

Technical Specifications

Parameter	Value	Unit	Context
Maximum Thermal Conductivity (TC)	336	W/mK	1 vol.% Cu-coated D/Cu composite (D=300 J/mm³)
Maximum Bending Strength	150	MPa	1 vol.% Cu-coated D/Cu composite
Minimum Surface Roughness (Sa)	5.751	µm	Achieved at 180 W laser power, 200 mm/s scanning rate
Optimal Volumetric Energy Density (D)	300	J/mm³	For 1 vol.% Cu-coated D/Cu (180 W, 200 mm/s)
Relative Density (1 vol.% Ti-coated)	96	%	Highest density achieved for Ti-coated composites
Copper Powder Purity	99.99	%	Pure gas atomized copper
Copper Powder Average Size	18.856 ± 15	µm	Matrix material
Diamond Particle Average Size	~25	µm	Reinforcement material
Copper Coating Thickness (on Diamond)	0.99 to 1.77	µm	Applied via electroless plating
Titanium Coating Thickness (on Diamond)	93.04 to 122.8	nm	Applied via vacuum evaporation
SLM Laser Wavelength	1060	nm	Neodymium-doped yttrium aluminum garnet fiber laser
SLM Laser Spot Size	30	µm	Fixed parameter
Optimal Layer Thickness (t)	0.025	mm	Optimized to prevent scraper rubbing
Optimal Melt Pool Overlap Rate (Hr)	60	%	Target for achieving peak density

Key Methodologies

The fabrication process involved three primary stages: surface modification of diamond particles, powder mixing, and Selective Laser Melting (SLM) optimization.

1. Diamond Particle Surface Modification

Copper Coating (Electroless Plating):
- Method: Chemical plating solution used with mechanical agitators.
- Purpose: To significantly improve the wettability of diamond with molten copper, addressing the inherent incompatibility between the materials.
- Result: Produced a dense copper layer ranging from 0.99 to 1.77 µm thick.
Titanium Coating (Evaporation Process):
- Method: Vacuum evaporation using a source boat and heater.
- Purpose: Titanium acts as an active element, forming titanium carbide (TiC) at the interface to chemically bond the diamond and copper matrix.
- Result: Produced a titanium layer ranging from 93.04 to 122.8 nm thick.

2. Powder Preparation and Mixing

Materials: Pure gas atomized copper powder (18.856 µm) and coated diamond particles (~25 µm).
Composition Ratios: Composites were prepared at 1, 3, and 5 vol.% diamond content (Table 1).
Mixing: Powders were combined in a ball mill at 100 rpm for 3 hours, followed by drying at 60 °C and sifting through a 400 mesh.

3. Selective Laser Melting (SLM)

Equipment: SISMA MYSINT100 system (180 W max power).
Atmosphere Control: High-purity N₂ atmosphere maintained (residual oxygen content < 0.5 vol.%) to prevent oxidation of Ti and Cu.
Scanning Strategy:
- Cubic Samples (5x5x5 mm³): Chessboard scan strategy used, where the scanning direction in each of the four squares per layer was perpendicular to the adjacent square.
- Rectangular Contour Samples (1x3 mm²): Single-line scan strategy used for initial parameter determination.
Parameter Optimization (1 vol.% Cu-coated D/Cu):
- Optimal Laser Power (P): 180 W.
- Optimal Scanning Rate (v): 200 mm/s.
- Optimal Layer Thickness (t): 0.025 mm.
- Optimal Hatch Distance (h): Approximately 100 µm (corresponding to a 60% melt pool overlap rate).

Commercial Applications

The successful fabrication of high-TC, low-CTE diamond/copper MMCs via SLM targets critical sectors requiring superior thermal management and complex component geometries.

Application Area	Specific Use Case	Technical Advantage Provided
Electronic Packaging	High-power semiconductor substrates (e.g., IGBTs, MOSFETs).	High TC (336 W/mK) ensures rapid heat dissipation, preventing device failure.
Thermal Management	Advanced heat sinks and heat spreaders.	Tailored CTE minimizes thermal stress and fatigue when bonded to silicon or ceramic components.
Aerospace and Defense	Components in radar systems and avionics requiring high thermal stability.	Superior bending strength (150 MPa) and low CTE provide reliability under extreme temperature cycling.
Additive Manufacturing (AM)	Complex 3D printed thermal components and micro-structures.	SLM capability allows for the creation of intricate internal cooling channels and custom geometries impossible via traditional methods.
RF and Microwave Devices	High-frequency power amplifiers and modules.	Excellent combination of electrical conductivity (copper matrix) and thermal performance.

View Original Abstract

The poor wettability and weak interfacial bonding of diamond/copper composites are due to the incompatibility between diamond and copper which are inorganic nonmetallic and metallic material, respectively, which limit their further application in next-generation heat management materials. Coating copper and titanium on the diamond particle surface could effectively modify and improve the wettability of the diamond/copper interface via electroless plating and evaporation methods, respectively. Here, these dense and complex composites were successfully three-dimensionally printed via selective laser melting. A high thermal conductivity (TC, 336 W/mK) was produced by 3D printing 1 vol.% copper-coated diamond/copper mixed powders at an energy density of 300 J/mm3 (laser power = 180 W and scanning rate = 200 mm/s). 1 and 3 vol.% copper-coated diamond/copper composites had lower coefficients of thermal expansions and higher TCs. They also had stronger bending strengths than the corresponding titanium-coated diamond/copper composites. The interface between copper matrix and diamond reinforcement was well bonded, and there was no cracking in the 1 vol.% copper-coated diamond/copper composite sample. The optimization of the printing parameters and strategy herein is beneficial to develop new approaches for the further construction of a wider range of micro-sized diamond particles reinforced metal matrix composites.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi13050724

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