Copper Diamond Composites Research Articles

Simulation of matrix conductivity in copper–diamond composites sintered by field assisted sintering technology

This research investigates thermal conductivity properties of Cu/Zr alloys combined with diamond particles to form a composite that possess superior thermal conductivity. This article describes the use of a theoretical calculation and finite element analysis to compare to previously published experimental observations. Both theoretical calculations and finite element analysis indicate that experimental results cannot be explained solely by an improved interface between the matrix and diamond particles, as originally suggested. This study shows that the experimental results, theoretical calculations, and finite element analysis are in agreement when the thermal conductivity of the matrix is adjusted to compensate for the amount of zirconium lost to the interface. This finding can be used to predict the thermal conductivity of a composite material composed of a Cu/Zr matrix with diamond particles.

Thermal reliability of copper alloy–diamond composites produced by field-assisted sintering technology

This paper highlights the thermal properties of copper–diamond composites fabricated by field assisted sintering technology. The samples were fabricated using a matrix of copper alloyed with silver and zirconium. Previous reports have shown that these samples possess high thermal conductivity. This work examines the thermal conductivity of the samples after being subjected to thermal cycling. Coefficient of thermal expansion is also reported in this work.

Thermal physical properties of Al-coated diamond/Cu composites

To acquire a well bonded interface between the copper and the diamond particles in diamond-copper matrix composites, an available process to apply a vapor deposited aluminum (Al) coating onto diamond particles was used to solve this interfacial problem. The diamond-copper matrix composites were prepared by spark plasma sintering (SPS) process and the effect of Al-coated diamond particles was demonstrated. The experimental results showed that the densification, interfacial bonding and thermal conductivity of Al-coated composites were evidently improved compared to those of the uncoated composites. A maximum thermal conductivity (TC) of 565 W/(m·K) was obtained in the coated composite containing 50vol% diamond particles sintered at 1 163 K. Additionally, the experimental data of thermal conductivity and coefficient of thermal expansion (CTE) were compared with the predictions from several theoretical models.

Relationship between Diamond Particle Size and Thermal Conductivity of Cu-Diamond Composites

Diamond-copper composites were fabricated by ultrahigh pressure sintering (UHPS) technology. The influence of diamond particle size on the microstructure,relative density and thermal conductivity of composites were investigated. The results indicated that the high relative density of more than 99% diamond-copper composite can be prepared by UHPS method. The composite thermal conductivity dramatically increased with increasing diamond particle size and the highest value of 675W/(m·K) were obtained when using 200μm diamond,which is much higher than those of traditional electronic packing materials. The Cu-diamond composite could fulfill the requirement of heat removal of the high-power electronic packaging devices.

Effect of Thermal Loads on Different Modules of DEMO PFCs

The thermal performance of different modules of plasma-facing components (PFCs) is analyzed for the DEMO reactor conditions in steady-state operation with the inclusion of the transient edge-localized modes (ELMs) for mitigated and unmitigated cases. As an example, the effect of these loads is considered for the tungsten (W) alloy mono-block design with a Cu OFHC/EUROFER water coolant tube first proposed in the framework of the Power Plant Physics and Technology (PPP&T) divertor study. A variant of this design with a EUROFER tube connected to the W block with a diamond/copper composite (DCC) used in the diagnostic windows is also analyzed. A design goal is to find the optimal thicknesses of material layers that allow one to keep the maximum temperatures within the allowable design limits under ITER water cooling conditions. Heat transfer and armor erosion due to the plasma impact has been modeled by using the MEMOS code.

Microstructure and thermal properties of copper–diamond composites with tungsten carbide coating on diamond particles

An effective method for preparing tungsten carbide coating on diamond surfaces was proposed to improve the interface bonding between diamond and copper. The WC coating was formed on the diamond surfaces with a reaction medium of WO3 in mixed molten NaCl–KCl salts and the copper–diamond composites were obtained by vacuum pressure infiltration of WC-coated diamond particles with pure copper. The microstructure of interface bonding between diamond and copper was discussed. Thermal conductivity and thermal expansion behavior of the obtained copper–diamond composites were investigated. Results indicated that the thermal conductivity of as-fabricated composite reached 658Wm−1K−1. Significant reduction in coefficient of thermal expansion of the composite compared with that of pure copper was obtained.

Thermal conductivity enhancement of copper–diamond composites by sintering with chromium additive

The thermal diffusivity (TD) and thermal conductivity (TC) of Cu–Cr–diamond composite materials were examined in the temperature range from 50 to 300 °C for diamond volume fractions of 22, 40, 50, 55, and 60 %. The samples were fabricated by the plasma pulse sintering (PPS) method. TC does not increase proportionally with the diamond fraction in the particular composite materials. The highest TD was determined for 50 % diamond volume fraction, and the evaluated TC reached 658 W m−1 K−1 at 50 °C. This article complements earlier articles concerning synthesis and characterization of the diamond–copper composites produced by the PPS method.

Effect of Liquid Phase Additions on Microstructure and Thermal Properties in Copper and Copper-Diamond Composites

This study details a new approach to creating copper-diamond composite materials for thermal management applications by using a two-phase (solid-liquid) approach in powder metallurgy using Field Assisted Sintering Technology (FAST). Silver-copper alloyed powder at eutectic compositions was used as a nonreactive liquid phase while Cu5Si was used as a reactive liquid phase. Microstructure results are reported favorably comparing the additions of a small amount of liquid phase to pure solid state sintering. Additionally, EDX results indicate that the liquid phase material fills gaps at the interface of the matrix and diamond particle resulting in improved microstructure and density. Thermal conductivity results show that liquid phase additions improve the thermal conductivity of composites compared to composites without any liquid phase, but Si additions cause a severe drop in baseline conductivity.

Improved Thermal Performance of Diamond-Copper Composites with Boron Carbide Coating

B4C-coated diamond (diamond@B4C) particles are used to improve the interfacial bonding and thermal properties of diamond/Cu composites. Scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy were applied to characterize the formed B4C coating on diamond particles. It is found that the B4C coating strongly improves the interfacial bonding between the Cu matrix and diamond particles. The resulting diamond@B4C/Cu composites show high thermal conductivity of 665 W/mK and low coefficient of thermal expansion of 7.5 × 10−6/K at 60% diamond volume fraction, which are significantly superior to those of the composites with uncoated diamond particles. The experimental thermal conductivity is also theoretically analyzed to account for the thermal resistance at the diamond@B4C-Cu interface boundary.

Preparation of copper–diamond composites with chromium carbide coatings on diamond particles for heat sink applications

Cr7C3 coatings were formed on diamond particles for improving the wettability between diamond particles and copper. The coatings were formed with a reaction medium of chromium in mixed molten salt. Copper–diamond composites with Cr7C3 coatings on diamond particles have been fabricated by vacuum pressure infiltration method. The microstructure of interfacial bonding between diamond and copper was discussed. Thermal conductivity and thermal expansion behavior of the obtained copper–diamond composites with various fractions of diamond particles were investigated. The as-fabricated composite exhibit a thermal conductivity of 562 W m−1 K−1 associated with coefficient of thermal expansion of 7.8 × 10−6 K−1 with a Cr7C3-coated diamond volume fraction of 65%. These results indicate that the obtained composites are suitable for being heat sink applications.

Effect of molybdenum carbide intermediate layers on thermal properties of copper–diamond composites

Abstract Molybdenum carbide (Mo 2 C) coated diamond particles were prepared by molten salts method and the copper–diamond composites were obtained by vacuum pressure infiltration of Mo 2 C-coated diamond particles with pure copper. The formation mechanism of the Mo 2 C layers was investigated, and the microstructure, thermal conductivity and thermal expansion behavior of the obtained copper–diamond composites were studied. The coated layers were formed by using a reaction medium of MoO 3 in mixed molten salts, and the formation mechanism of the Mo 2 C layers on diamond particles was investigated. The result indicates that the formation of Mo 2 C layers occurred in two steps, that is, the reduction of MoO 3 to MoO 2 and the reduction of MoO 2 to Mo 2 C. The wettability between diamond particles and copper was effectively improved, and the relative density of the copper–diamond composites achieved 99.5%. The thermal conductivity reached 596 W m −1 K −1 , and the coefficient of thermal expansion was 7.15 × 10 −6 K −1 of the composites with 60 vol.% Mo 2 C-coated diamond. This composite is expected to be suitable for electronic packaging applications.

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 Spark Plasma Sintering Temperature on Microstructures and Properties of Copper-Diamond Composites

Temperature being one of the most important parameters of Spark plasma sintering (SPS) and its effects on the microstructures as well as on the physical properties of copper diamond composites fabricated by mechanical mixing of copper with 70 vol.% diamond powders, precoated with 1 wt% chromium has been studied. Experiments were performed at 900°C, 1000°C and 1100 °C for 10 minutes under 50 MPa. The results reveal that sintering temperature highly influences the copper/diamond interface bonding and microstructures. The composite’s properties like thermal conductivity (T.C), specific heat (Cp), diffusivity (Dff) and relative density (ρr) were also highly influenced by temperature variations. Except the relative density, all the other properties increased respectively with increasing sintering temperature.

New model of heat transport across the metal-insulator interface by the example of boundaries in a diamond-copper composite

A model of heat transport from an insulator (diamond) to a metal (copper) has been proposed taking into account energy transport to the oscillations inherent in the insulator but having frequencies much higher than the frequencies inherent in the fundamental oscillations of the metal. This problem is solved exactly in the one-dimensional case and in the one-constant approximation of bonding at the interface. It has been established that energy transport occurs in a thin layer near the metal boundary.

Multiscale Copper-µDiamond Nanostructured Composites

Nanostructured copper-diamond composites can be tailored for thermal management applications at high temperature. A novel approach based on multiscale diamond dispersions is proposed for the production of this type of materials: a Cu-nDiamond composite produced by high-energy milling is used as a nanostructured matrix for further dispersion of micrometer sized diamond. The former offers strength and microstructural thermal stability while the latter provides high thermal conductivity. A series of Cu-nDiamond mixtures have been milled to define the minimum nanodiamond fraction suitable for matrix refinement and thermal stabilization. A refined matrix with homogenously dispersed nanoparticles could be obtained with 4 at.% nanodiamond for posterior mixture with mDiamond and subsequent consolidation. In order to define optimal processing parameters, consolidation by hot extrusion has been carried out for a Cu-nDiamond composite and, in parallel, for a mixture of pure copper and mDiamond. The materials produced were characterized by X-ray diffraction, scanning and transmission electron microscopy and microhardness measurements.

Influence of interfacial carbide layer characteristics on thermal properties of copper–diamond composites

Copper–diamond composites are increasingly being considered for thermal management applications because of their attractive combination of properties, such as high thermal conductivity (λ) and low coefficient of thermal expansion (CTE). In this research, thermal properties of Cu–diamond composites with two different types of interfacial carbides (Cr3C2 and SiC) were studied. The interface thermal conductance (h c) was calculated with Maxwell mean-field and differential effective medium schemes, wherein experimentally measured λ was entered as an input parameter. The λ and h c of both the Cu–Cr3C2–diamond and Cu–SiC–diamond composites are higher than those reported in previous studies for Cu–diamond composites with no interfacial carbides. The value of h c is intimately related to the morphology and thickness of the interface carbide layer, with the highest h c being associated with a thin and continuous interface carbide layer. A lower h c resulting from a thicker Cr3C2 layer can provide an alternate explanation for a previously reported trend in λ of Cu–Cr3C2–diamond composites with different Cr-contents. The experimentally measured CTE was compared with the Turner and Kerner model predictions. The CTE of both the Cu–Cr3C2–diamond and Cu–SiC–diamond composites is lower and better matches the model predictions than the previously reported CTE of Cu–diamond composite with no interfacial carbides. The CTE of Cu–Cr3C2–diamond composites agrees better with the Kerner model than the Turner model, which suggests that deformation during temperature excursions involves shear.

Alloy development for highly conductive thermal management materials using copper-diamond composites fabricated by field assisted sintering technology

Improving thermal management materials is critical to many industries including the microelectronics where smaller components lead to larger heat densities. Performance of thermal management materials are largely governed by the thermal conductivity of the material. Commercial diamond particles have a very high thermal conductivity, but their inclusion into conductive metals such as copper is challenging due to a lack of compatibility which creates a poor interface between materials. This study uses a powder metallurgy approach employing an alloyed powder blend to act as an agent to improve the interface leading to improved thermal properties. Results show that minor additions of zirconium to the copper matrix is successful in improving the interface and allows for improvement of thermal conductivity up to a maximum of 533 W/m K with 40 vol.% diamond. Energy-dispersive X-ray spectroscopy mapping analysis shows that additions of zirconium are vastly better than chromium for improvement of interface. It is shown that caution must be taken when adding alloying elements because small additions result in a rapid decrease in conductivity of the alloy before diamonds are added.

Effect of Diamond on the Thermal Conductivities of Diamond-Copper Composites Prepared by Spark Plasma Sintering

Diamond-copper composites are fabricated by spark plasma sintering (SPS). The effects of particle size, original properties and coatings of diamond on the thermal conductivity (TC) of diamond-copper composites have been investigated, respectively. The results indicate that thermal conductivity of composites enhances with an increase in particle size and original properties of diamond. Composites with Cr, Ti or Ni coatings on diamond surface appear remarkably higher TC than that which without any coatings. The improvements of TC of diamond/copper composites are mainly due to the large particle size diamond decreasing the interfacial area in composites, the high original properties diamond possessing higher original TC, and coatings on diamond surface declining the interfacial thermal resistance and improving the wetting properties between diamond and copper.

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.

Dry Sliding Wear Behavior of Sintered Copper-Diamond Composite Fabricated by Powder Metallurgy

Copper matrix composites with 3wt% diamond particles were fabricated by powder metallurgy method. Sliding wear behavior of the copper-diamond composites was carried out by using a pin-on-disk wear tester under dry sliding conditions at a constant sliding speed of 100 m/s. The results showed that the wear rate of the composites was significantly lower than that of pure copper. The addition of diamond particles can markedly increase hardness and wear resistance of the copper-diamond composites. For determination of the wear mechanisms of the copper-diamond composites, a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) was employed to observe the microstructure and analyze the chemical compositions of the worn surface. It is found that the main wear mechanisms of the sintered copper-diamond composites were abrasive wear and adhesive wear.