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Diamond/Cu composites with excellent thermal performance were fabricated by a novel method which coated diamond particles with tungsten as the inner layer through salt-bath plating and then deposited copper as the outer layer through electroless plating. After ultra-high cold pressing and vacuum sintering, these double-layer particles directly formed diamond/Cu composites without addition of copper powders. The thermal conductivity of 60 vol.% diamond/Cu composite reached maximum at 661 W m-1 K-1. The outstanding performance can be ascribed to strong interface bonding in the double-layer particles and uniform distribution of diamond particles in the composites when electroless plating was used to replace copper powder addition.

Nickel-coated graphite flakes/copper (GN/Cu) composites were fabricated by spark plasma sintering with the surface of graphite flakes (GFs) being modified by Ni–P electroless plating. The effects of the phase transition of the amorphous Ni–P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity (TC) of the GN/Cu composites were systematically investigated. The introduction of Ni–P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650°C and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20vol%–30vol% graphite flakes. However, when the graphite flake content was greater than 30vol%, the TC of the GF/Cu composites decreased with the introduction of Ni–P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.

A new method was proposed to fabricate diamond/Cu composites. Double-layer diamond particles were directly compressed at ultra-high pressure to prepare the preform and then sintered in a vacuum equipment for densification. The raw diamond particles were coated with zirconium carbide by magnetron sputtering for the inner layer and then deposited with copper by chemical method for the outer layer. Prepared with these particles, the composites had good interface bonding and homogeneously distributed particles in the copper matrix. The thermal conductivity of 65 vol% diamond/Cu composite was as high as 720 W m−1 K−1. When the diamond content increased to 70 vol%, the coefficient of thermal expansion was extremely low (4.33 × 10−6/K). With superb thermal–physical performance, diamond/Cu composites are potentially applicable to electronic packaging.

Copper matrix composites reinforced with graphite flakes (GFs/Cu) were fabricated by powder hot pressing method and the alloying chromium (Cr) element in powdered form was directly added into the Cu matrix powder to enhance the interfacial bonding between GFs and Cu matrix. Effects of addition of Cr on thermal conductivity (TC), coefficient of thermal expansion (CTE), and bending strength of GFs/Cu composites in X Y (basal plane of GF) and Z directions were investigated in this study. The results showed that in X Y direction, the TC of 50 vol% GFs/Cu composites increased from 560 to 628 W m−1 K−1 after adding 2.0 wt% Cr, and the bending strength nearly doubled from 53.8 (GF/Cu) to 93 MPa. The CTE in Z direction could be obviously reduced with Cr addition, which dropped gradually from 9.4 to 3.2 ppm K−1 at 150 °C with the increase in content of Cr from 0 to 5.0 wt%. This improvement in TC, bending strength, and CTE is attributed to the formation of carbide transition layer at the interface between Cu and graphite. The detailed influence of carbide layer on the properties of the composites was thoroughly studied by corresponding evolution of interfacial microstructure with increasing Cr content.

The wetting mechanism of AgCuTi reactive alloy on copper, diamond films and Diamond/Cu composites surfaces is investigated. It is found that the AgCuTi/Cu and AgCuTi/Diamond wetting systems belong to dissolutive wetting and compound forming systems, respectively. The coexistence and interaction of dissolutive wetting and compounding forming wetting in AgCuTi/composites system play a crucial role in the wetting behavior, including the spreading time, wetting kinetics, driving force, final contact angle ( θ f ), and final configuration of triple line. The initial wetting stage on composites surface is mainly controlled by the non-reactive wetting and dissolutive wetting, and the later stage is governed by the diffusion-limited compound forming wetting. The spreading of AgCuTi alloy on composites surface proceeds in the way that it spreads on Cu phase and diamond phase alternately. Wetting on composites surface exhibits the highest θ f and medium length of spreading time among the three substrates. The θ f of AgCuTi alloy on Diamond/Cu composites surfaces increases with the increase of diamond volume fraction.

Boron (B) powder was added directly into the copper (Cu) matrix by powder metallurgy method, and then the contents were mixed with graphite flakes (GFs) to fabricate GFs/Cu composites by vacuum hot pressing. The effects of B content (0–2.5 wt%) on the thermal conductivity (TC) and coefficient of thermal expansion (CTE) of GFs/Cu composites in X–Y (basal plane of GF) and Z directions were investigated in this study. The results showed that in X–Y direction, the TC of 50 vol% GFs/Cu composites increased significantly from 563.00 to 634.87 W m−1 K−1 when B content was 0.4 wt%; however, it dropped gradually with the further increase in B content. The CTE of 50 vol% GFs/Cu composites in Z direction decreased gradually from 9.50 to 3.63 ppm K−1 with the increase in B content from 0 to 2.5 wt%. This improvement in TC and CTE is attributed to changes in interface structure. The fluidity of the Cu matrix and the wettability of interface between GFs and Cu were improved due to the addition of B, which was found to be conducive for the Cu matrix to spread on the rough GFs surface and thus filling the gaps and microvoids caused by the insufficient filling of the Cu matrix. As a result, the interfacial thermal resistance between GFs and Cu reduced and the TC of the composites increased significantly.

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 658 W m− 1 K− 1. Significant reduction in coefficient of thermal expansion of the composite compared with that of pure copper was obtained.

This study focuses on the fabrication of thermal management material for power electronics applications using graphite flake reinforced copper composites. The effects of mixing, die-filling, and particle size of copper on microstructure and thermal conductivity of the composites were investigated. The results indicate that the process, especially die-filling, affects the distribution and orientation of graphite flake and then affects the relative density and thermal conductivity of the composites. The graphite flake/copper composites with 20–50 vol. % flakes have relatively high density of over 98%. The composites show a strong anisotropy in thermal conductivity and have a value of 528 W·m−1·K−1 with 40 vol. % graphite flakes at room temperature in the direction perpendicular to the pressing direction, which exhibit excellent thermo-physical properties to meet the heat dispersion and matching requirements of power electronic devices to the packaging materials.

This study focuses on the fabrication of thermal management material for power electronics applications using graphite flake reinforced copper composites. The manufacturing route involved electroless plating of copper on the graphite flake and further spark plasma sintering of composite powders. The relative density of the composites with 44–71 vol.% flakes achieved up to 98%. Measured thermal conductivities and coefficients of thermal expansion of composites ranged from 455–565 W m � 1 K

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.

The Ti-coated diamond/copper composites with near-net-shape are manufactured by pressurelessly infiltrating liquid copper into porous Ti-coated diamond preforms. The contact angle between diamond and copper, relative density, thermal conductivity (TC), coefficient of thermal expansion (CTE), leak rate and microstructure are evaluated and characterized. In addition, the numerical analysis of the pressureless infiltration kinetics is also discussed. The results indicate that the relative density, TC and CTE of composites are 99.3%, 385 Wm−1 k−1 and 3–8 × 10−6 K−1, respectively. It can meet heat-sink package requirement of high-power electronic devices as LED, insulated gate bipolar transistor (IGBT), etc. The liquid copper exhibits a turbulent flow with the Reynolds number in the range of 27.83–49.7. The porosity ϕ and the pressure drop Δp are the main influence factors controlling the velocity of liquid copper. Moreover, under vacuum condition of 8.7 × 10−3 Pa, the maximum theoretical infiltration length Lmax of Ti-coated diamond/copper composites is found to be 552 mm.

As a carbide forming additive, molybdenum gets maximum benefit of high thermal conductivities of diamond and copper. Coating Mo on the diamond surface can promote the interfacial bonding in diamond/Cu composites. A Mo coated diamond/Cu composite with high thermal conductivity of 726 W/mK is obtained, which is achieved by a thin nano-sized Mo 2 C layer. Mo coated diamond or un-coated diamond reinforced copper composites have been made by pressure assisted liquid copper infiltration method. The interfacial configuration, the bulk thermal conductivity and the evolution of interfacial thermal resistance are presented, indicating that the good adhesion at the interface can decrease the thermal boundary resistance and thus increase the thermal conductivity of the composites.

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.

The wetting behavior of copper alloys on SiC substrates was studied by a sessile drop technique. The microstructure of SiCp/Cu composites and the pressureless infiltration mechanism were analyzed. The results indicate that Ti and Cr are effective elements to improve the wettability, while Ni, Fe, and Al have minor influence on the improvement of wettability. Non-wetting to wetting transition occurs at 1210 and 1190°C for Cu-3Al-3Ni-9Si and Cu-3Si-2Al-1Ti, respectively. All the copper alloys react with SiC at the interface forming a reaction layer except for Cu-3Al-3Ni-9Si. High Si content favors the suppression of interfacial reaction. The infiltration mechanism during pressureless infiltration is attributed to the decomposition of SiC. The beneficial effect of Fe, Ni, and Al is to favor the dissolution of SiC. The real active element during pressureless infiltration is Si.

SiCp/Cu composites with high reinforcement content (56–65 vol.-%) were fabricated by spontaneously infiltrating copper alloy into porous SiC preform obtained by powder injection moulding. The main influencing factors of the preparation of the preform and the infiltration behaviour of various preforms were studied. The results indicate that the viscosity increases with an increase in powder loading or decreases with an increase in particle size. The feedstocks with bimodal mixture exhibit low viscosity due to the improvement in packing efficiency. When small particles or bimodal mixture with large size ratio were used, the preforms were difficult to be fully infiltrated. The preforms debound in air exhibit lower infiltration rate than the ones debound in vacuum due to the reduction of porosity and the poor wettability between the oxidised layer and copper alloy. Kinetic analysis on the infiltration curves yielded activation energies of 253 kJ mol–1.

High-performance mesophase pitch-based graphite fiber reinforced metal matrix composites offer a good thermal conductivity and tailorable coefficient of thermal expansion. These composites are regarded as a promising heat dissipation materials for electronic packaging application. It is reported that short graphite fiber/Al composites were fabricated by vacuum pressure infiltration, which is a suitable procedure for the fabrication of complex shaped components at high production rates and low cost. The thermal conductivity of short fiber/Al composites is lower than 230 W m−1 K−1. It is expected that the composites using copper as the matrix, which has a higher thermal conductivity and lower coefficient of thermal expansion than aluminum, may have a better thermal properties. However, there is few investigation on fabrication of graphite fiber/Cu composites since copper does not wet graphite. This work focuses on the fabrication of short graphite fiber/Cu composites for thermal management application by vacuum pressure infiltration technique. A Mo 2 C coating was synthesized on the surface of graphite fiber through molten salts method for improving the wetting between graphite fibers and copper. Certain Grfs reacted with molybdenum oxides powders in a molten salts mixture composed of NaCl-KCl at 1000 °C for 30 min under a flowing argon atmosphere. The obtained coating is compact and homogenous with the thickness of 0.3 μm. Copper was infiltrated into Mo 2 C-coated graphite preform at 1150 °C with low pressure and Cu matrix composites with 20 vol%–40 vol% fibers were fabricated. Due to the unidirectional compression in the perform and infiltration process, the fibers were uniform distribution in the plane perpendicular to the press direction (X-Y plane) and showed a two dimensional orientation. The interface of composites was examined by EDS line-scan. Results show that there was copper infiltrated into the Mo 2 C interlayer. A good adhesion was observed in composites in which the Mo 2 C interlayer tightly adhered to both fiber and Cu matrix. The obtained composites present high relative density above 99.5%. With increasing volume fraction of fiber from 20% to 40%, the thermal conductivity of composites in X-Y plane slightly decreased from 356 W m−1 K−1 to 311 W m−1 K−1. The coefficient of thermal expansion in X-Y plane decreased from 14× 10−6 to 7 × 10−6 K−1. The experimental values of thermal conductivities of composites were compared with the theoretical calculation. With the introduction of Mo 2 C interlayer, the interface thermal conductance of graphite fiber/Mo 2 C interlayer/copper matrix had to be taken into consideration. So the effective thermal conductivity of coated fiber was firstly calculated by using the acoustic mismatch model (AMM). Then, a model of Maxwell-Garnett effective medium approach on the anisotropic short fiber reinforcement was used to estimate the thermal conductivity of composites. The result showed that the theoretical predictions are in good agreement with the experimental values. The thermal conductivity of composites could be further improved if perform with single axile orientation fiber was infiltrated.