Effect of Bimodal cBN Particle Size Distribution on Thermal Conductivity of Al/cBN Composite Fabricated by SPS
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-01-01 |
| Journal | Journal of the Japan Society of Powder and Powder Metallurgy |
| Authors | Kiyoshi Mizuuchi, Kanryu Inoue, Yasuyuki Agari, Masami Sugioka, Motohiro Tanaka |
| Institutions | University of Washington, The University of Osaka |
| Citations | 7 |
| Analysis | Full AI Review Included |
Technical Analysis and Material Sourcing Guide: Enhancing Thermal Management via Bimodal Al/cBN Composites
Section titled âTechnical Analysis and Material Sourcing Guide: Enhancing Thermal Management via Bimodal Al/cBN CompositesâExecutive Summary
Section titled âExecutive SummaryâThis study details the fabrication and thermal performance optimization of Aluminum/Cubic Boron Nitride (Al/cBN) metal matrix composites (MMCs) using the Spark Plasma Sintering (SPS) technique in a continuous solid-liquid co-existent state. The core innovation focuses on utilizing a bimodal particle size distribution of the cBN filler to maximize packing density and thermal conductivity (TC).
- Core Value Proposition: Demonstration that engineered bimodal particle distribution (390 ”m and 39 ”m cBN) significantly enhances composite thermal performance compared to traditional monomodal systems.
- Key Achievement: A maximum thermal conductivity of 325 W/mK was achieved at 60 vol% cBN using the bimodal mixture, an 8% increase over the peak monomodal performance (305 W/mK).
- Densification Improvement: Bimodal mixtures maintained high relative packing densities (>99%) up to 60 vol% filler content, whereas monomodal samples suffered a drop below 90% above 50 vol%.
- Fabrication Method: Used a proprietary, two-step pressure SPS process (80 MPa initial, ramped to 300 MPa at 876 K) to facilitate pore filling by the liquid-phase aluminum matrix.
- Critical Observation: Scanning Electron Microscopy (SEM) did not detect significant interfacial reaction layers (e.g., AlN), suggesting that the cBN/Al interface bonding may be weak, presenting an area for future interface engineering optimization.
- Application Relevance: These highly dense, high-TC composites are critical for next-generation thermal management in high-power electronics, advanced LSI, LED headlamps, and electric vehicle (EV) motor systems.
Technical Specifications
Section titled âTechnical SpecificationsâA summary of the critical materials parameters and experimental outcomes extracted from the research paper.
| Parameter | Value | Unit | Context / Condition |
|---|---|---|---|
| Peak Thermal Conductivity (Bimodal) | 325 | W/mK | Al-60 vol% cBN |
| Peak Thermal Conductivity (Monomodal) | 305 | W/mK | Al-45 vol% cBN |
| Maximum Relative Density (Bimodal) | >99 | % | Up to 60 vol% cBN |
| Large cBN Particle Diameter | 390 | ”m | Filler material (Tomei Diamond ISBN-E) |
| Small cBN Particle Diameter | 39 | ”m | Filler material (Tomei Diamond ISBN-E) |
| Optimal Bimodal Ratio (Large:Small) | 73.21 : 26.79 | vol% | Calculated via Furnas model for minimum porosity (17.31%) |
| SPS Sintering Atmosphere | 2 | Pa | Vacuum |
| SPS Sintering Temperature Range | 798 - 878 | K | Solid-liquid co-existent state |
| Maximum Applied Pressure (Load) | 300 | MPa | Applied upon reaching 876 K |
| Low-Rate Heating Temperature Range | 813 - 878 | K | Heating rate 0.05 K/s to ensure efficient pore filling |
| Coefficient of Thermal Expansion (CTE) | 11.65 x 10-6 | K-1 | Al-65 vol% cBN (Bimodal) |
| Interfacial Bonding Assessment | Slightly higher than Kerner upper line | N/A | Suggests weak bonding between cBN and Al matrix |
Key Methodologies
Section titled âKey MethodologiesâThe composite fabrication utilized specialized powder processing and a highly controlled Spark Plasma Sintering (SPS) cycle designed to sustain a solid-liquid co-existent state for maximal densification.
- Raw Material Preparation:
- Filler: Two distinct particle sizes of cubic Boron Nitride (cBN) powder (390 ”m and 39 ”m) were used.
- Matrix: Pure Al powder (99.9%, -45 ”m) mixed with Al-5 mass%Si alloy powder (-45 ”m) at a volume ratio of 9:1. The Al-Si alloy was necessary to maintain a small amount of liquid phase during sintering.
- Bimodal Ratio Calculation: The optimal large:small particle volumetric mixing ratio (73.21:26.79) was determined experimentally using tapping tests on a measuring cylinder and validated against the theoretical Furnas model to achieve minimum porosity (< 18%).
- SPS Sample Preparation: Mixed powders were loaded into WC/Co hard metal dies to produce disc samples (10 mm diameter, approx. 2 mm thickness).
- SPS Sintering Profile (Two-Stage Load/Rate):
- Initial Stage (RT to 813 K): Heating rate of 1.08 K/s applied under low initial pressure (80 MPa).
- Solid-Liquid Filling Stage (813 K to 878 K): Heating rate slowed drastically to 0.05 K/s to promote sustained solid-liquid co-existence, allowing the liquid Al phase to effectively fill particle gaps (pores). Pressure maintained at 80 MPa.
- Final Consolidation Stage (At 876 K): Heating stopped, and pressure was ramped immediately from 80 MPa to 300 MPa and held for 180 seconds to ensure final dense bonding and compression.
- Characterization: Samples were tested for microstructure (SEM), thermal conductivity (Laser Flash method, Netzsch LFA-457), relative density (Archimedes method), and thermal expansion (Rigaku TMA8310).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research confirms the crucial role of optimal particle size distribution and high-quality interface engineering in achieving exceptional thermal performance in metal matrix composites (MMCs). 6CCVD, as an expert in MPCVD diamond technology, provides the advanced materials and customization services necessary to replicate, extend, and surpass the results achieved in this study.
| Applicability Area | 6CCVD Material Solutions | Customization Potential & Engineering Support |
|---|---|---|
| High-Performance Filler Materials | Polycrystalline Diamond (PCD) & Single Crystal Diamond (SCD): While cBN was used (TC up to 1300 W/mK), 6CCVD specializes in MPCVD diamond, possessing intrinsic thermal conductivities up to 2000 W/mK. Sourcing our materials offers a direct pathway to significantly higher composite TC. | 6CCVD can supply custom-sized PCD powder or small SCD fragments designed for use as high-conductivity filler particles, optimized for use in bimodal or multimodal packing configurations. |
| Material Dimensions & Geometry | Large-Area Diamond Wafers: We supply CVD diamond plates and wafers up to 125 mm (PCD) and custom SCD pieces. This capacity far exceeds the 10 mm disc size used in the research, enabling commercial-scale production feasibility studies. | Precision Machining: Our in-house services include CNC laser cutting for complex geometries, ensuring researchers receive exact dimensions required for advanced testing (e.g., thermal diffusivity samples, specialized heat sinks). |
| Interface Engineering & Bonding | Custom Metalization Services: The paper noted slightly weak bonding between the cBN and Al matrix. 6CCVD provides in-house metalization crucial for enhancing thermal interface conductance (TIC) and mechanical cohesion. | We offer deposition of standard refractory layers (Ti, W) followed by noble metals (Pt, Pd, Au, Cu). This capability is vital for preparing diamond filler particles or diamond substrates for subsequent sintering, brazing, or bonding into advanced MMCs. |
| Precision Substrates | Ultra-Low Roughness SCD & PCD: For thermal measurement and testing similar to the Laser Flash method used, surface quality is critical. | 6CCVD guarantees ultra-low surface roughness: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD. This precision ensures accurate, repeatable thermal analysis. |
| Process Replication & Optimization | Expert PhD Engineering Support: The success of the SPS process relies heavily on controlling temperature (798 K - 878 K) and pressure (up to 300 MPa) accurately. | Our in-house PhD team can consult on material selection and surface preparation necessary to adapt high-performance diamond materials for use in solid-liquid co-existent sintering or similar high-pressure thermal management projects. |
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Cubic boron nitride (cBN)-particle-dispersed-aluminum (Al) matrix composites were fabricated in solid-liquid co-existent state by Spark plasma sintering (SPS) process from the mixture of cBN powders, Al powders and Al-5 mass%Si powders. As the cBN powders, two kind of powders, monomodal cBN powders of 390 ÎŒm in diameter and a bimodal cBN powder mixture of 390 ÎŒm and 39 ÎŒm in diameter, were used. The microstructures and thermal conductivities of the composites fabricated were examined. These composites were all well consolidated by heating at a temperature range between 798 K and 876 K for 1.56 ks during SPS process. No reaction at the interface between the cBN particle and the Al matrix was observed by scanning electron microscopy for the composites fabricated under the sintering conditions employed in the present study. Although the relative packing density of the monomodal composite decreased from 99.5 % to 89.5 % with increasing the cBN volume fraction in a diamond volume fraction range between 50 % and 60 %, that of the bimodal composite was higher than 98.6 % in a cBN volume fraction range up to 65 %. The thermal conductivity of the bimodal composite was 306-325 W/mK, which is higher than that of the monomodal composite in a diamond volume fraction range higher than 45 %. The coefficients of thermal expansion of the composites were a little higher than the theoretical values estimated by the upper line of Kernerâs model, indicating the bonding between the cBN particle and the Al matrix in the composite is weak a little.