Thermal conductivity of Cu/diamond composites prepared by a new pretreatment of diamond powder

Cu/diamond composites were fabricated by spark plasma sintering (SPS) after the surface pretreatment of the diamond powders, in which the diamond particles were mixed with copper powder and tungsten powder (carbide forming element W). The effects of the pretreatment temperature and the diamond particle size on the thermal conductivity of diamond/copper composites were investigated. It was found that when 300 μm diamond particles and Cu–5 wt.% W were mixed and preheated at 1313 K, the composites has a relatively higher density and its thermal conductivity approaches 672 W (m K)⁻¹.     

Thermal conductivity of diamond/Ag composites with chromium carbide coated diamonds for the building materials of high power modules

Abstract

This paper reports on a study of the preparation and characterisation of diamond/Ag composites for the building materials of high power modules. The Cr₇C₃ coated diamond particles are utilised to improve the interfacial bonding between the Ag and diamond and composites are prepared by hot pressing technique. The characteristics of Cr₇C₃ coating layers were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the Cr₇C₃ coatings on the diamonds result in a strong interfacial bonding and a greatly enhanced thermal conductivity of the composites. A largely enhanced thermal conductivity of 768 W m^?1 K^?1 is obtained in Cr₇C₃ coated composites, which increases 168% relative to that of uncoated composites at 65% diamond volume fraction. The measured thermal conductivity agrees reasonably well with the predictions by a differential effective-medium (DEM) model.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

Fabrication and thermal conductivity of near-net-shaped diamond/copper composites by pressureless infiltration

Near-net-shaped diamond/copper composites with a relative density of over 99% and thermal conductivity of over 350 Wm⁻¹ K⁻¹ are successfully fabricated by powder press-pressureless infiltration processing. The effects of infiltration temperature, infiltration time, interfacial thickness, and type of protective atmosphere on the thermal conductivity of the diamond/copper composites were investigated. The results showed that the diamond-copper composites with complicated shape exhibited better thermal properties, which can be widely used in electronic packaging field. It was found that the properties of diamond-copper composites infiltrated in high vacuum atmosphere were better than that of composites infiltrated in other atmospheres. The thickness of interface showed great effects on the properties of composites. The carbide interfaces were attributed to the decrease of interfacial thermal resistance and enhancement of wetting properties between the diamonds and copper.     

Preparation of high thermal conductivity copper–diamond composites using molybdenum carbide-coated diamond particles

Molybdenum carbide (Mo₂C) coatings on diamond particles were proposed to improve the interfacial bonding between diamond particles and copper. The Mo₂C-coated diamond particles were prepared by molten salts method and the copper–diamond composites were obtained by vacuum pressure infiltration of Mo₂C-coated diamond particles with pure copper. The structures of the coatings and composites were investigated using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicated that the Mo₂C coatings effectively improved the wettability between diamond particles and copper matrix, and Mo₂C intermediate layers were proved to decrease the interfacial thermal resistance of composites. The thermal conductivity of the composite reached 608 Wm^?1 K^?1 with 65 vol.% Mo₂C-coated diamond, which was much higher than that with uncoated diamond. The greatly enhanced thermal conductivity is ascribed to the 1-μm-thick Mo₂C coatings. Mo₂C coatings on diamond particles are proved to be an effective way to enhance the thermal conductivities of copper–diamond composites.     

Effect of copper content on the thermal conductivity and thermal expansion of Al–Cu/diamond composites

Al–Cu matrix composites reinforced with diamond particles (Al–Cu/diamond composites) have been produced by a squeeze casting method. Cu content added to Al matrix was varied from 0 to 3.0 wt.% to detect the effect on thermal conductivity and thermal expansion behavior of the resultant Al–Cu/diamond composites. The measured thermal conductivity for the Al–Cu/diamond composites increased from 210 to 330 W/m/K with increasing Cu content from 0 to 3.0 wt.%. Accordingly, the coefficient of thermal expansion (CTE) was tailored from 13 × 10⁻⁶ to 6 × 10⁻⁶/K, which is compatible with the CTE of semiconductors in electronic packaging applications. The enhanced thermal conductivity and reduced coefficient of thermal expansion were ascribed to strong interface bonding in the Al–Cu/diamond composites. Cu addition has lowered the melting point and resulted in the formation of Al₂Cu phase in Al matrix. This is the underlying mechanism responsible for the strengthening of Al–Cu/diamond interface. The results show that Cu alloying is an effective approach to promoting interface bonding between Al and diamond.     

Interfacial design of Cu/SiC composites prepared by powder metallurgy for heat sink applications

In order to dissipate the heat generated in electronic packages, suitable materials must be developed as heat spreaders or heat sinks. Metal matrix composites (MMCs) offer the possibility to tailor the properties of a metal (Cu) by adding an appropriate reinforcement phase (SiC) to meet the demands for high thermal conductivities in thermal management applications. Copper/SiC composites have been produced by powder metallurgy. Silicon carbide is not stable in copper at the temperature needed for the fabrication of Cu/SiC. The major challenge in development of Cu/SiC is the suppression of this reaction between copper and SiC. Improvements in bonding strength and thermo-physical properties of the composites have been achieved by a vapour deposited molybdenum coating on SiC powders to control the detrimental interfacial reactions.     

Effect of titanium carbide coating on the microstructure and thermal conductivity of short graphite fiber/copper composites

Graphite fiber–Cu composites have drawn much attention in electronic packaging due to its excellent machinability and thermal properties. However, the weak interface bonding between graphite fiber and copper resulted in low thermo-mechanical properties of composites. In this work, a titanium carbide coating with thickness of 0.1 μm or 1 μm was synthesized on the surface of graphite fiber through molten salts method to strengthen interfacial bonding. The enhanced composites present 24–43 % increase in thermal conductivity and achieve the thermal conductivity of 330–365 W m^?1 K^?1 as well as the coefficient of thermal expansion of 6.5 × 10^?6–14 × 10^?6 K^?1. A Maxwell–Garnett effective medium approach on the anisotropic short fiber reinforcement with interfacial thermal resistance was established. The obtained enhancement was in good agreement with the estimates. The results suggest that the major factor that influences the thermal conductivities is not the interfacial thermal resistance but the low thermal conductivity of fiber in transversal direction when a well interfacial bonding is obtained.     

Thermal conductivity of Cu–Zr/diamond composites produced by high temperature–high pressure method

Copper matrix composites reinforced with about 90 vol.% of diamond particles, with the addition of zirconium to copper matrix, were prepared by a high temperature–high pressure method. The Zr content was varied from 0 to 2.0 wt.% to investigate the effect on interfacial microstructure and thermal conductivity of the Cu–Zr/diamond composites. The highest thermal conductivity of 677 W m⁻¹ K⁻¹ was achieved for the composite with 1.0 wt.% Zr addition, which is 64% higher than that of the composite without Zr addition. This improvement is attributed to the formation of ZrC at the interface between copper and diamond. The variation of thermal conductivity of the composites was correlated to the evolution of interfacial microstructure with increasing Zr content.     

添加微量Ti 元素对Diamond/Cu复合材料组织及性能的影响

分别采用在Cu基体添加0. 1 wt%的Ti 元素形成Cu₂Ti合金和在Diamond 颗粒表面镀钛(DiamondTi) 的方法, 制备了含Diamond 体积分数为60 %的Diamond/Cu₂Ti 复合材料和DiamondTi/Cu 复合材料。对比分析了Ti 元素对复合材料微观组织、界面结合及性能的影响规律。结果表明: 添加0. 1 wt%Ti 元素能改善Diamond与Cu 的界面结合, 在界面处观察到明显的碳化物反应层; 且以Cu₂Ti合金的方式添加Ti 元素改善界面的效果优于在Diamond 颗粒表面镀Ti 的方式。所制备的Diamond/Cu₂Ti 复合材料的热导率为621 W(m·K) - 1, 而DiamondTi/Cu复合材料的热导率仅为403. 5 W(m·K) -1, 但均高于未添加Ti 制备的Diamond/Cu 复合材料。      

Fabrication and thermal conductivity of copper matrix composites reinforced with Mo2C or TiC coated graphite fibers

Graphite fiber reinforced Cu-based composites have good thermal conductivity, low coefficient of thermal expansion for heat sink applications. In these composites, the quality of interfacial bonding between the copper matrix and the graphite fibers has significant influence on the thermal properties of composites. In this study, two different carbide coatings (Mo₂C or TiC) were synthesized on graphite fiber to promote the interfacial bonding in composites. Fibers/Cu composites had been produced by spark plasma sintering process. The results showed that the densification, interfacial bonding and thermal conductivity of coated composites were improved distinctly compared to that of uncoated ones. The enhanced composites present 16–44% increase of thermal conductivity in X–Y plane. An original theoretical model was proposed to estimate the interface thermal resistance. The result showed that the interfacial thermal resistance was largely reduced by one order of magnitude with the introduction of carbide interlayer.     

On the thermal conductivity of Cu–Zr/diamond composites

Interfaces and close proximity between the diamond and the metal matrix are very important for their thermal conductance performance. Matrix-alloying is a useful approach to greatly enhance the interfacial bonding and thermal conductivity. In this study, the copper–diamond (Cu/Dia) composites with addition of 0.8, 1.2 and 2.4 wt.% zirconium (Zr) are prepared to investigate the influence of minor addition of Zr on the microstructure and thermal conductivity of the composites. The thermal conductivity of the composites is analyzed both experimentally and theoretically. It is demonstrated that moderate interfacial modification due to the Zr added is beneficial to improve the thermal conductivity of the Cu/Dia composites.     

Identification and characterization of diffusion barriers for Cu/SiC systems

The promise of CuSiC metal matrix composites (MMCs) as a thermal management material is to provide increased power density and high reliability for advanced electronic systems. CuSiC will offer high thermal conductivity between 250 and 325 W/mK with corresponding adjustable thermal expansion coefficient between 8.0 and 12.5 ppm/^∘C. The major challenge in development of these materials is control of the interface interactions. Cu and SiC react at high temperatures between 850 and 1150^∘C, needed for fabrication of the CuSiC material, with an expected decrease in thermal conductivity of the CuSiC MMCs as the Si product of reaction dissolves into the Cu. The application of barrier coatings onto SiC was observed to control chemical reaction of Cu and SiC. In the current study, the effectiveness of four barriers to prevent Cu diffusion and reaction with SiC were evaluated between 850 to 1150^∘C. Immersion experiments were conducted at 1150^∘C to understand the reaction between copper and silicon carbide. Reaction products were identified with transmission electron microscopy (TEM) and electron diffraction. Laser flash thermal diffusivity measurements confirmed thermal conductivity to decrease with increasing silicon content of the copper as determined by induction coupled plasma mass spectrometry (ICPMS) and glow discharge mass spectrometry (GDMS). An erratum to this article is available at .     

Microstructure and Ablation Behavior of W Coating Prepared by Atmospheric Plasma Spraying for Zr/Cu Infiltrated C/C Composites

To improve the ablation resistance of carbon/carbon (C/C) composites, W coating prepared by atmospheric plasma spraying (APS) for Zr/Cu infiltrated C/C composites are fabricated, the Zr/Cu infiltrated C/C composites are prepared by reactive melt infiltration (RMI). The microstructural features of the composites are examined by scanning electron microscopy coupled with energy dispersive spectrometry (SEM‐EDS), X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The ablation resistance of the W coated Zr/Cu infiltrated composites are tested in the oxyacetylene torch environment at heat flux of 4186 kW m^?2 for 150 s. The results show that the diameter of ablation center and line ablation rate (LAR) of W coated composites are about 3.92 mm and 5.16 × 10^?3 mm s^?1. Compared to pure C/C and the Zr/Cu infiltrated composites, the diameters of ablation center of W coated composites are reduced by 18.00% and 15.52%, the LAR of W coated composites decreases by 74.52% and 23.55%. Overall, the W coated composites depict good ablation property due to the high melting point of W coating, which can be resistant to high‐temperature oxidation and ablation, the sublimation of WO₃ carries away the heat.

     

Effect of chromium carbide coating on thermal properties of short graphite fiber/Al composites

A chromium carbide coating was synthesized onto graphite fibers by molten salts method to improve the interfacial bonding and thermal properties of short graphite fiber/Al composites which were fabricated by vacuum pressure infiltration technique. The graphite fiber/Al composites with different thicknesses of chromium carbide coatings were prepared through varying plating times to investigate the influence of chromium carbide layer on the microstructures and thermal properties of the composites. The combined Maxwell–Garnett effective medium approach and acoustic mismatch model schemes were used to theoretically predict thermal conductivities of the composites. The results indicated that the chromium carbide coating formed on graphite fiber surface in molten salts consists mainly of the Cr₇C₃ phase. The Cr₇C₃-coating layer with plating time of 60 min and thickness of 0.5 μm was found to be most effective in improving the interfacial bonding and decreasing the interfacial thermal resistance between graphite fiber and aluminum matrix. The 40 vol% Cr₇C₃-coated graphite fiber/Al composite with Cr₇C₃ thickness of 0.5 μm exhibited 45.4 % enhancement in in-plane thermal conductivity of 221 W m^?1 K^?1 compared to that of uncoated composite, as well as the coefficient of thermal expansion of 9.4 × 10^?6 K^?1, which made it as very interesting material for thermal management applications.     

超高压熔渗法制备铜/金刚石复合材料的热导率*

用超高压熔渗法制备了金刚石体积分数为90%的铜/金刚石复合材料, 其热导率为662 Wm^-1K^-1, 比用其它方法制备的这种材料的热导率高。SEM、EDS和XRD的表征结果表明, 这种铜/金刚石复合材料的界面结合良好, 金刚石与铜之间有过渡层, 部分金刚石相互连通。     

Cu Nanospring Films for Advanced Nanothermal Interfaces

An advanced thermal interface material comprised of dense and orderly arrays of 10‐µm high Cu nanosprings with tunable normal and shear compliance, lateral stability due to spring intertwining, and thermal resistance below 1 mm²KW^?1 is presented. The Cu nanospring films possess the compliance of soft polymers but up to 100 times higher thermal conductivity than materials with similar elastic modulus. This unique combination of mechanical and thermal properties makes it possible for the first time to populate the large empty space in the materials selection chart of thermal conductivity versus elastic modulus.

     

Effect of metalloid silicon addition on densification,microstructure and thermal–physical properties of Al/diamond composites consolidated by spark plasma sintering

Aluminum matrix composites reinforced with diamond particles were consolidated by spark plasma sintering. Metalloid silicon was added (Al–Si/diamond composites) to investigate the effect. Silicon addition promotes the formation of molten metal during the sintering to facilitate the densification and enhance the interfacial bonding. Meanwhile, the alloying metal matrix precipitates the eutectic-Si on the diamond surfaces acting as the transitional part to protect the improved interface during the cooling stage. The improved interface and precipitating eutectic-Si phase are mutually responsible for the optimized properties of the composites. In this study, for the Al–Si/diamond composite with 55 vol.% diamonds of 75 μm diameter, the thermal conductivity increased from 200 to 412 Wm⁻¹ K⁻¹, and the coefficient of thermal expansion (CTE) decreased from 8.9 to 7.3 × 10⁻⁶ K⁻¹, compared to the Al/diamond composites. Accordingly, the residual plastic strain was 0.10 × 10⁻³ during the first cycle and rapidly became negligible during the second. Additionally, the measured CTE of the Al–Si/diamond composites was more conform to the Schapery’s model.     

Ein neues Werkstoffkonzept zur trockenen Bearbeitung mineralischer Materialien

A new material concept for machining of mineral materials For the machining of mineral materials like rock, concrete and asphalt ultra hard cutting‐tools such as diamond tools are used. During the use diamond tools are cooled with water to remove the heat and to prevent an early deterioration of the diamonds. Without water cooling the diamonds at the cutting edge as well as in lower levels are damaged. For ecological and economic reasons a dry machining of mineral materials is of great interest. The consumption of coolant and the pollution of occupied buildings by alkaline water would be decreased. But specific diamonds tools are necessary to realise a dry machining. The Institute of Materials Engineering pursues a novel material concept for diamond impregnated composites to protect diamonds in deeper layers. Materials with a very low thermal conductivity are inserted in the diamond‐composites to protect the diamonds against heat and to reduce the deterioration of diamonds in lower levels. Cobalt and bronze (CuSn 85/15) with particle sizes of 45–90 μm and < 40 μm, diamonds with particle sizes of 300–450 μm and alumina with particle sizes of 350–500 μm, 150–210 μm and < 70 μm were used. The diamond‐alumina‐composites were powder metallurgically produced and were examined by light‐ and electron microscopy and digital image analysis.     

界面结合强度对C/Cu 复合材料热膨胀性能的影响

本文通过在C/C u 复合材料的Cu 基体中添加不同的合金元素(Sn,Ni, Fe) 获得不同的界面结合强度, 研究了界面结合强度对C/C u 复合材料热膨胀特性的影响规律, 并分析了界面结合强度对降温过程中复合材料的收缩特性及残余应变的影响。