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.     

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.     

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.     

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.     

The desirable dielectric properties and high thermal conductivity of epoxy composites with the cobweb-structured SiCnw–SiO2–NH2 hybrids

We report the preparation of epoxy-based composites by intercalating low loading of core–shell silicon carbide nanowire-silica-amino (named as SiCnw–SiO₂–NH₂) hybrids, exhibiting simultaneously high permittivity and thermal conductivity (TC) and maintaining rather low dielectric loss. More interestingly, the epoxy composites with the cobweb-structured SiCnw–SiO₂–NH₂ hybrids exhibited high thermal conductivity at low filler loading due to space micro-structures and hydrogen bond interaction. Specifically, permittivity of the sample with 3.0 vol% SiCnw–SiO₂–NH₂ hybrids reaches 61.9 under 0.1 Hz, while its dielectric loss is only 0.012, and possessing a high TC of 1.59 W/m K, respectively.

     

Computational analysis of the thermal conductivity of the carbon–carbon composite materials

Experimental data for carbon–carbon constituent materials are combined with a three-dimensional stationary heat-transfer finite element analysis to compute the average transverse and longitudinal thermal conductivities in carbon–carbon composites. Particular attention is given in elucidating the roles of various micro-structural defects such as de-bonded fiber/matrix interfaces, cracks and voids on thermal conductivity in these materials. In addition, the effect of the fiber precursor material is explored by analyzing PAN-based and pitch-based carbon fibers, both in the same type pitch-based carbon matrix. The finite element analysis is carried out at two distinct length scales: (a) a micro scale comparable with the diameter of carbon fibers and (b) a macro scale comparable with the thickness of carbon–carbon composite structures used in the thermal protection systems for space vehicles. The results obtain at room temperature are quite consistent with their experimental counterparts. At high temperatures, the model predicts that the contributions of gas-phase conduction and radiation within the micro-structural defects can significantly increase the transverse thermal conductivity of the carbon–carbon composites.     

Experimental study on capillary and mechanical properties of a porous nickel–copper composite

A novel porous nickel–copper composite was designed and fabricated by sintering a mixture of a high-porosity open-cell copper foam plate and fine nickel powder. The microstructure of the porous nickel–copper composite was characterised by the scanning electron microscope. The effects of sintering temperature and dwelling time on the sintering shrinkage, sintered porosity, capillary performance and mechanical properties of the porous composite and monoporous sintered nickel powder were investigated experimentally. The nickel–copper composite presented significant lower sintering shrinkage, higher porosity, lower tensile strength and better capillary performance than the sintered nickel powder under all sintering conditions. The sintering temperature has more influence than the dwelling time on both the capillary performance and tensile strength of the sintered composite.     

Mechanical properties and microstructure of ZrO2–SiO2 composite

ZrO2–SiO2 composite powder has been prepared by a wet chemical route using zirconyl chloride and fumed silica as starting materials and subsequently sintered by the hot-pressing method to obtain a ZrO2–SiO2 ceramic. The mechanical properties of the silica matrix have been much increased by the addition of 20 vol% zirconia. The microstructural features of the composite are observed by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The stabilibity of tetragonal zirconia in the matrix is attributed to the particle-size effect, and to the constraint effect of the silica matrix and that of the interphasic reaction layer. The increase in mechanical properties is discussed in relation to the residual stress and the enhanced elastic modulus caused by the incorporated ZrO2 particles.     

Mechanical alloying process and mechanical properties of Cu–SiCp composite

Abstract

A composite of copper powder and SiC particle reinforcement was prepared by mechanical ball milling and subsequent sintering. Proper choice of processing parameters ensured a homogenous distribution of SiC particles in the copper matrix. Microstructure, powder morphology and mechanical properties of the composite were investigated as a function of milling time. With increasing milling time, the dentritic copper powder became flattened, which subsequently became spherical shaped. Mechanical properties of the composites change with the distribution of SiC.     

Mechanical properties of type IIb synthetic diamond at a temperature of 900°C

Mechanical properties of a type IIb synthetic diamond produced by the temperature gradient method have been studied at 900°C using indenters having different angles between the pyramid axis and face. The strain-strain curve has been constructed in the stress-total strain coordinates. It has been shown that in the diamond deformation the strain hardening with a linear dependence of flow stress on the plastic strain degree occurs. It has been found that the microhardness and fracture toughness of the tested synthetic diamond and natural diamond and the mechanism of their deformation do not differ essentially.     

Pullulan–nanofibrillated cellulose composite films with improved thermal and mechanical properties

Novel bionanocomposite films with improved thermal and mechanical properties, were prepared by casting water-based suspensions of pullulan and nanofibrillated cellulose. The effect of the addition of glycerol, as a plasticizer, on the properties of the materials was also evaluated. The ensuing materials were characterized in terms of morphology, thermal stability, crystalline structure and mechanical properties. All bionanocomposites were very homogeneous, translucent and showed considerable improvements in thermal stability (increments of up to 20 °C in the degradation temperature) and mechanical properties (increments of up to 5500% and 8000% in the Young’s modulus and tensile strength, respectively, for films plasticized with glycerol) when compared to the unfilled pullulan films. Additionally, these novel bionanocomposite could be labeled as sustainable materials since they were prepared entirely from renewable resources and through a green approach.     

Mechanical properties of a laminin–apatite composite layer formed on an ethylene–vinyl alcohol copolymer

A polymeric material with a laminin–apatite composite (L–Ap) layer on its surface would be useful as a material for percutaneous devices with improved cell-adhesion properties and good biocompatibility. Such a laminin–apatite-polymer composite can be prepared using a liquid phase coating process. In this study, the mechanical properties of an L–Ap layer formed on an ethylene–vinyl alcohol copolymer (EVOH) plate were evaluated and compared with those of an apatite (Ap) layer. The laminin immobilized in the L–Ap layer increased the layer's shear strength under wet conditions. However, under dry conditions, there was no advantage of the laminin immobilization on the layer's shear strength and adhesive strength to an EVOH plate. The adhesive strength of the layer to an EVOH plate improved as the thickness of the L–Ap layer decreased from 10 to 3 µm. From these results, it is suggested that a 3 µm thick L–Ap layer is better than a 10 µm thick L–Ap layer on an EVOH surface, and the resulting laminin–apatite–EVOH composite should not be dried when used as a material for percutaneous devices, to avoid any possible adverse effect of drying on the mechanical properties.     

Thermomechanical behaviour of a copper–chromium in situ composite

Abstract

The mechanical response of an in situ copper–chromium composite was investigated over a range of temperatures by means of tensile and isothermal creep tests. Scanning electron microscopy was used to characterise the extent, type, and distribution of damage. It was found that the failure mechanisms fell into distinct regimes. At cryogenic temperatures damage tended to occur in the form of reinforcement fracture. Around room temperature, very little damage was observed in the composite. At temperatures of about 400°C, extensive damage was again observed in the form of reinforcement failure and cavitation. Further increase in the test temperature resulted in a transition from a local to a global load sharing, with damage distribution becoming more homogeneous. These experimental observations were rationalised by considering the relative extent of deformation within the two phases as a function of temperature.     

Structure–property relationships for high thermal conductivity carbon fibers

Previous work at Clemson University has shown that ribbon-shaped mesophase pitch-based carbon fibers graphitized at only 2400°C can develop thermal conductivities comparable with those of commercial round-shaped pitch-based carbon fibers graphitized at temperatures above 3000°C. The thermal and electronic transport properties (i.e. thermal conductivity and electrical resistivity) of ribbon-shaped carbon fibers produced at Clemson University are being studied. In addition, the structure of these fibers is being analyzed by electron microscopy and X-ray diffraction techniques. This paper will discuss the relationships between processing conditions, fiber structure and fiber properties.     

Mechanical and tribological properties of “substrate–material” multifunctional composite with shape memory effect

The properties of steel–TiNi, TiNiCu, NiAl alloy multifunctional composite with shape memory effect are studied. The system is obtained under high-energy exposure (argon arc and laser surfacing, plasma and high-rate gas flame sputtering) with the formation of a structure with fine-grained to nanoscale dispersity. The experimental studies reveal the efficiency of the elaborated technique of the synthesis of composites to increase the wear resistance, fatigue strength, and endurance at frictionally cyclic low-cycle loading of material. The increase in fatigue and wear characteristics are explained by the processes caused by the combined cyclic loading and reverse friction. As is shown, the friction and mechanical fatigue in a surface-modified layer of the material undergoing the shape memory effect in the friction domain causes an increase in temperature that favors the martensite–austenite transformation, whereas the pressure arising in friction induces the transformation plasticity effect owing to the formation of stress martensite.     

Mechanical properties of aluminium–copper–lithium alloy AA2195 at cryogenic temperatures

Tensile testing was performed on a 4 mm thick sheet of the aluminum–lithium alloy AA2195 in T87 (solution treatment + water quenching + 7% cold work + peak aging) temper which was subjected to 7% cold working by combination of cold rolling and stretching, over a temperature range from ambient to liquid hydrogen (20 K) conditions. Properties were evaluated in longitudinal as well as transverse directions to characterize anisotropy with respect to strength and ductility. Strength and ductility were compared to the conventional aluminum alloy AA2219-T87, developed for similar cryogenic applications. Decreases in test temperature led to higher strengths with little or no change in ductility. As the temperature decreases, the differences between ultimate tensile strength as well as yield strength for two different combinations of cold roll and stretch studied in the present work, narrows down and become equal at 20 K.     

Mechanical and thermal characteristics of high density polyethylene–fly ash Cenospheres composites

Fly ash Cenospheres was used as reinforcing filler in High density polyethylene (HDPE) to develop lightweight composites. Cenospheres are inert hollow silicate spheres. Cenospheres are a naturally occurring by-product of the burning process at coal-fired power plants, and they have most of the same properties as manufactured hollow-sphere products. Cenospheres are primarily used to reduce the weight of plastics, rubbers, resins, cements, etc. used extensively as filler lubricants in oil drilling operations under high heat and high stress conditions down the hole. Also used as oil well cementing, mud putty and similar applications. Cenospheres were first used in the United States as an extender for plastic compounds, as they are compatible with plastisols thermoplastics, Latex, Polyesters, Epoxies, Phenolic resins and urethanes. The compatibility of Cenospheres with special cements and adhesives coating and composites have been well identified. Cenospheres are widely used in a variety of products, including sports equipments, insulation, automobile bodies, marine craft bodies, paints, and fire and heat protection devices. Typically applied in gypsum board jointing compounds, veneering plasters, stuccos, sealants, coating and cast resins. Providing the advantages of reduces weight, increased filler loadings, better flow characteristics, less shrinkage and warping and reduces water absorption. In order to improve the interaction between the inorganic filler and the organic matrix, the Cenospheres were surface treated with silane coupling agent and HDPE-g-dibutyl maleate was used as compatibilizer. The tensile and thermal properties of the composites were measured according to ASTM methods. The results reveal that, both surface modification of Cenospheres accompanied by compatibilization led to the substantial improvement to mechanical properties and thermal stability of the composites.     

Relationship between composition,structure, and mechanical properties of a condensed composite of copper–tungsten system

For a copper–tungsten microlayered composite material for electrical contact applications, which is prepared by electron-beam evaporation-condensation, the changes in its structure, conductivity, hardness, and mechanical properties in tension at room temperature and elevated temperatures are studied versus the tungsten content and heat treatment conditions. New morphological features of the condensed composite and the related changes in the material properties have been revealed. The conditions for the formation of structural defects and their influence on mechanical properties and fracture behavior of the material in tensile tests have been investigated. A relationship has been established between the tungsten content of the composite, its structure, strength, and hardness.