Effects of Chromium Carbide Coatings on Microstructure and Thermal Conductivity of Mg/Diamond Composites Prepared by Squeeze Casting

At a Glance

Metadata	Details
Publication Date	2022-02-09
Journal	Materials
Authors	Jianwei Li, Peng Ren, Jinming Ru, Jianhua Wu, Kaixiang Zhou
Institutions	Qilu University of Technology, Shandong Academy of Sciences
Citations	8
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Performance Mg/Diamond Composites

Executive Summary

This analysis focuses on optimizing Mg/diamond metal matrix composites (MMCs) for high-performance thermal management applications, specifically leveraging chromium carbide (Cr) coatings to control interfacial properties.

Core Achievement: Successful preparation of Mg/diamond (Cr) composites via molten salt coating and squeeze casting, resulting in significantly enhanced thermal properties.
Thermal Conductivity (TC) Enhancement: Achieved a maximum TC of 202.42 W/(m·K), representing an 81.1% improvement over the uncoated composite (111.77 W/(m·K)).
CTE Matching: Demonstrated precise control over the Coefficient of Thermal Expansion (CTE), achieving a minimum value of 5.82 x 10^-6/K, which is highly desirable for matching semiconductor materials.
Interface Control: The study confirmed that Cr coating thickness (ranging from 1.09 µm to 2.95 µm) is the critical parameter governing both TC and CTE performance by optimizing carbide formation (Cr₃C₂ and Cr₇C₃).
Methodology: Cr carbide layers were synthesized at high temperatures (950-1050 °C) using a molten salt bath, followed by Mg infiltration via 10 MPa squeeze casting.
Key Finding: Excessive coating thickness or high processing temperature leads to interface defects (cracking/peeling) and increased interface thermal resistance, thereby reducing overall TC.

Technical Specifications

Parameter	Value	Unit	Context
Maximum Thermal Conductivity (TC)	202.42	W/(m·K)	Achieved with 1.20 µm Cr coating (950 °C/60 min)
Minimum Coefficient of Thermal Expansion (CTE)	5.82 x 10^-6	/K	Achieved with 2.50 µm Cr coating (1000 °C/30 min)
Uncoated Composite TC	111.77	W/(m·K)	Baseline Mg/diamond composite
Diamond Particle Size	212-250	µm	Synthetic single-crystalline powder (HHD90-type)
Cr Coating Thickness Range	1.09 - 2.95	µm	Measured by FIB-SEM dual-beam system
Coating Temperature Range	950 - 1050	°C	Molten salt process
Infiltration Pressure	10	MPa	Squeeze casting process
Infiltration Temperature	800	°C	Mg matrix preparation
Carbide Phases Identified	Cr₃C₂, Cr₇C₃	N/A	Formed spontaneously (Negative Gibbs Free Energy)

Key Methodologies

The composite fabrication involved two primary stages: Cr coating synthesis and Mg matrix infiltration.

Diamond Surface Preparation:
- Diamond particles were washed with diluted acid to remove impurities.
Cr Coating Synthesis (Molten Salt Method):
- Diamond/Cr powder mixture was placed in an alumina crucible, covered by a molten salt bath (NaCl/KCl, 1:1 molar ratio).
- Coating Parameters: Temperature varied (950 °C, 1000 °C, 1050 °C) and holding time varied (30 min, 60 min, 90 min) to control carbide layer thickness.
- Post-Coating: Mixture separated using ultrasonic wave with boiling distilled water and alcohol, followed by vacuum drying at 100 °C.
Composite Preparation (Squeeze Casting Infiltration):
- Cr-coated diamond particles were densely packed into a graphite mold (20 mm x 4 mm).
- Pure Mg bulks were placed on top in a quartz crucible.
- Heating and Protection: Heated to 800 °C for 10 min under a protective SF₆ + CO₂ gas mixture (1:99 ratio) to prevent Mg oxidation.
- Infiltration: Uniaxial pressure of 10 MPa was applied for 60 s at 800 °C.
Characterization:
- Coating thickness and microstructure analyzed using FIB-SEM and EDS line scanning.
- Phase composition confirmed by XRD (Cu-Kα radiation).
- Thermal diffusivity (α) measured by Laser Flash Apparatus (LFA 457).
- Thermal Conductivity (TC) calculated using K_c = α · ρ_c · C_c.

6CCVD Solutions & Capabilities

The research successfully demonstrates that precise control over the diamond-metal interface via carbide coating is essential for achieving high TC and low CTE in thermal management composites. 6CCVD is uniquely positioned to supply the necessary high-quality diamond materials and advanced customization services required to replicate and scale this research.

Applicable Materials

To replicate or extend this research into commercial thermal management devices, 6CCVD recommends the following materials:

High-Purity SCD Powder: For direct use in MMC fabrication methods like squeeze casting or powder metallurgy, 6CCVD can supply high-purity Single Crystal Diamond (SCD) powder with controlled particle size distribution, ensuring optimal packing density and thermal performance.
Optical Grade SCD Wafers: For advanced electronic packaging where large, defect-free heat spreaders are required, 6CCVD offers SCD plates up to 500 µm thick with surface roughness Ra < 1 nm, providing superior intrinsic thermal properties (TC up to 2000 W/(m·K)).
Inch-Size PCD Plates: For scaling up large-area thermal management solutions, 6CCVD provides Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, polished to Ra < 5 nm, offering a cost-effective alternative for high-volume applications.

Customization Potential

The paper highlights the critical role of the Cr carbide interface layer (1.09-2.95 µm) in optimizing thermal performance. 6CCVD offers comprehensive customization capabilities essential for industrializing this technology:

Research Requirement	6CCVD Customization Capability	Value Proposition
Interface Layer Control	Custom Metalization Services: We offer in-house deposition of carbide-forming elements including Ti, W, Cu, Pt, Pd, and Au. We can precisely control layer thickness and composition to optimize interfacial thermal resistance (hd).	Enables replication of Cr carbide layers or exploration of superior interfaces (e.g., TiC, WC) for enhanced bonding and thermal performance.
Custom Dimensions	Large-Area Diamond: Plates/wafers up to 125 mm (PCD) and substrates up to 10 mm thick.	Allows researchers and engineers to move beyond small-scale lab samples (20 mm x 4 mm mold) to develop full-scale electronic packaging components.
Precision Polishing	Ultra-Low Roughness: Ra < 1 nm (SCD) and Ra < 5 nm (PCD).	Ensures minimal surface defects and optimal contact when integrating diamond heat spreaders into composite structures or bonding directly to semiconductor chips.
Global Logistics	Global Shipping: DDU default, DDP available.	Ensures rapid, reliable delivery of custom diamond materials worldwide, accelerating R&D timelines.

Engineering Support

The complex relationship between carbide phase evolution (Cr₃C₂ vs. Cr₇C₃), CTE mismatch, and phonon scattering requires deep material science expertise.

6CCVD’s in-house PhD team specializes in optimizing diamond interfaces for high-power thermal and electronic applications. We provide expert consultation on:

Interface Engineering: Selecting the optimal carbide-forming metal (e.g., Ti, W, Cr) and deposition parameters to minimize interface thermal resistance (hd) and maximize TC.
CTE Matching: Assisting in material selection and coating design to ensure the final composite CTE closely matches that of target semiconductor materials (e.g., Si, GaAs, SiC), preventing thermal stress and failure in electronic packaging.
Material Specification: Guiding customers in selecting the appropriate diamond type (SCD vs. PCD) and dimensions for specific thermal management projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Magnesium matrix composites are considered a desired solution for lightweight applications. As an attractive thermal management material, diamond particle-reinforced Mg matrix (Mg/diamond) composites generally exhibit thermal conductivities lower than expected. To exploit the potential of heat conduction, a combination of Cr coating on diamond particles and squeeze casting was used to prepare Mg/diamond (Cr) composites. The thickness of the Cr coating under different coating processes (950 °C/30 min, 950 °C/60 min, 950 °C/90 min, 1000 °C/30 min, and 1050 °C/30 min) was measured by FIB-SEM to be 1.09-2.95 μm. The thermal conductivity (TC) of the Mg/diamond composites firstly increased and then decreased, while the coefficient of thermal expansion (CTE) of Mg/diamond (Cr) composite firstly decreased and then increased with the increase in Cr coating thickness. The composite exhibited the maximum TC of 202.42 W/(m·K) with a 1.20 μm Cr coating layer, while a minimum CTE of 5.82 × 10−6/K was recorded with a coating thickness of 2.50 μm. The results clearly manifest the effect of Cr layer thickness on the TC and CTE of Mg/diamond composites.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15041284

References

2018 - Present and future thermal interface materials for electronic devices [Crossref]
2019 - Recent advances in nano-materials for packaging of electronic devices [Crossref]
2017 - Carbon fiber reinforced metal matrix composites: Fabrication processes and properties [Crossref]
2018 - Thermal conductivity of high purity synthetic single crystal diamonds [Crossref]
2019 - Thermal expansion coefficient of diamond in a wide temperature range [Crossref]
2015 - Nano- and micro-/meso-scale engineered magnesium/diamond composites: Novel materials for emerging challenges in thermal management [Crossref]
2018 - Multi-scale design of novel materials for emerging challenges in active thermal management: Open-pore magnesium-diamond composite foams with nano-engineered interfaces [Crossref]
2018 - Optimized thermal conductivity of diamond/Cu composite prepared with tungsten-copper-coated diamond particles by vacuum sintering technique [Crossref]
2018 - Enhanced thermal conductivity in Cu/diamond composites by tailoring the thickness of interfacial TiC layer [Crossref]