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Properties and microstructure of nickel-coated graphite flakes/copper composites fabricated by spark plasma sintering

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Abstract

Copper (Cu) matrix composites reinforced with graphite flakes (GFs) were fabricated by spark plasma sintering, and electroless nickel plating was introduced to improve the interfacial bonding between GFs and Cu matrix. The microstructures and morphology of the composites were characterized by scanning electron microscopy and X-ray diffraction, and three-point bending test was performed to obtain the bending strength of the composites. The results showed obvious improvement in the bending properties and coefficient of thermal expansion (CTE) because of the introduction of Ni-P transition layer, and an ultralow negative CTE of −3.85 ppm K⁻¹ for metal matrix composites was obtained for the first time. The volume shrinkage of GFs along c-axis direction under uniaxial compression stress as well as good interfacial bonding were considered to be the key reasons for the counterintuitive CTE of metal matrix composite with graphite inclusion. Furthermore, the obtained CTEs are in excellent agreement with the values reported by using the theoretical models. The ultralow CTE in Z direction, together with good mechanical properties make the composite fabricated in this study an appropriate candidate for electronic packaging material with two-dimensional heat dissipation function.

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... Ces méthodes privilégient donc l'homogénéité du mélange aux propriétés intrinsèques des GFs et nécessitent un contrôle précis des conditions expérimentales pour ne pas trop détériorer les GFs. Dans le but de diminuer le temps de broyage (et donc la dégradation des renforts) sans générer de pollution, une faible proportion d'éthanol (~ 5% vol ) est parfois ajoutée aux poudres [115]. Les alternatives à l'utilisation des broyeurs sont les mélangeurs tridimensionnels de type Turbula® [116], [103] et le mélange par agitation en voie liquide (majoritairement dans l'éthanol) [117], [118], qui permettent de préserver les propriétés des renforts mais qui peuvent conduire à des inhomogénéités dans le matériau final [101], [103], [116]. ...
... Ils constatent que ces matériaux ne suivent pas les prévisions apportées par les modèles de Turner [89] et Kerner [146] et attribuent ce phénomène à une dégradation des renforts au niveau de l'interface Al/GF [145], sans apporter de valeur de CTE selon l'axe Z du matériau. D'autres auteurs rapportent par la suite les mêmes observations sur des matériaux composites à matrice Al, Mg et Cu, mais observent de plus une importante diminution du CTE selon la direction Z du matériau [82], [108], [115] (cf. Figure Firkowka et al. [82] proposèrent un modèle théorique basé sur la théorie élastique permettant d'expliquer ce phénomène (cf. Figure I-24.b). Ce modèle prend en compte la structure lamellaire des matériaux composites et explique la chute du CTE en Z par l'action des contraintes internes générée par la différence de CTE entre matrice et renfort (combinée à la forte dépendance du coefficient de Poisson du graphite à la température). ...
... Si ce modèle permet une bonne corrélation entre valeurs théoriques et expérimentales [82], [110], [115], Oddone et al. [110] montrèrent en 2019 en mesurant le CTE des GFs dans des matrices variées (Al, Cu et alliages) par diffraction des neutrons, que le CTE en Z du graphite contraint dans la matrice était compris entre 27 ppm.K -1 et 31 ppm.K -1 (27,5 ppm.K -1 à l'état libre). Ils en conclurent que si ce modèle échoue dans la description du CTE à l'échelle microscopique, il constitue une approche qualitative du CTE macroscopique des matériaux composites. ...
Thesis
Du fait leur conductivité thermique élevée, les matériaux composites à matrice métallique et renfort carbone possèdent un fort potentiel d’application pour la gestion thermique en électronique. Ces travaux présentent le développement d’un nouveau procédé pour la synthèse de matériaux composites Ag/rGO (argent / « reduced Graphene Oxide ») et Ag/GF (argent / « Graphite Flakes ») par métallurgie des poudres. Ce procédé, inspiré des méthodes de « molecular level mixing », permet d’obtenir des poudres composites Ag/rGO dans lesquelles les nano-renforts sont individualisés jusqu’à une concentration volumique de 1 %. Lorsqu’il est appliqué à la synthèse de matériaux composites Ag/GF, ce dernier permet l’élaboration de matériaux composites denses avec une concentration volumique en graphite jusqu’à 70 % et une conductivité thermique jusqu’à 675 W.m-1.K-1 (426 W.m-1.K-1 pour l’argent pur). En outre, il a été montré que le procédé d’élaboration des poudres composites Ag/GF a une forte influence sur l’anisotropie structurale des matériaux massifs ainsi que sur la résistance thermique d’interface extrinsèque Ag-graphite. Le procédé d’élaboration développé dans ces travaux permet ainsi d’obtenir des matériaux ayant une conductivité thermique jusqu’à 19 % supérieure à celle des matériaux obtenus par un procédé de mélange conventionnel. Néanmoins, comme la plupart des matériaux composites métal/GF (à matrice Cu, Al, Mg et Fe), la dilatation thermique des matériaux composites Ag/GF présente des « anomalies ». En effet, l’anisotropie de leur coefficient d’expansion thermique (CTE) est opposée à leur anisotropie structurale, leur CTE a une dépendance anormalement élevée vis-à-vis de la température et ces matériaux présentent une instabilité dimensionnelle en cyclage thermique. S’il est communément admis dans la littérature que ces anomalies sont la conséquence des contraintes internes générées lors de l’élaboration des matériaux (du fait de la différence de CTE entre matrice et renfort), ce phénomène reste mal compris et difficile à maitriser. Une part importante de ces travaux est consacrée à l’étude de ces « anomalies » et en particulier à l’étude de l’influence des propriétés mécaniques de la matrice d’argent sur la dilation thermique des matériaux composites. Grâce à la combinaison des caractérisations d’EBSD, de DRX, de microdureté instrumentée et de microscopie, des phénomènes clés responsables des propriétés thermomécaniques des matériaux composites Ag/GF ont pu être identifiés. En particulier, il a été montré qu’une part importante des contraintes internes est relaxée via la déformation plastique de la matrice d’argent et la déformation pseudo plastique du graphite lors du refroidissement post-densification des matériaux composites. Ainsi, le contrôle des propriétés mécaniques de la matrice métallique (en particulier de sa limite d’élasticité) permet d’atténuer les anomalies en CTE et confère une meilleure stabilité dimensionnelle aux matériaux composites Ag/GF lors d’un cycle thermique. L’addition de rGO dans la matrice d’argent des matériaux composites Ag/GF a également permis de réduire l’instabilité dimensionnel des matériaux jusqu’à 50 % grâce aux propriétés d’amortissement du rGO.
... With increasing power density and continuing miniaturization in semiconductor devices, heat removal has become a crucial issue for continuing progress in the electronic industry. Thermal management of the next generation of integrated circuits requires a heat sink material with high thermal conductivity (TC) [1][2][3]. Current high-TC materials mainly used for heat spreaders and heat sinks are composed of metal matrix composites reinforced with appropriate reinforcement, such as SiC, diamond, and graphite [4][5][6][7][8][9]. Among various candidate reinforcements, graphite flakes (GFs) exhibit good comprehensive properties, with a theoretical TC above 2000 W m −1 K −1 in the (002) crystal plane (basal plane), low mass, affordability and ease of machinability. ...
... One example of this is from SB Ren et al who fabricated GF/copper composites with Ni coating on the surface of GF. The TC of composites with 20 vol%-60 vol% GF ranged from 466-532 W m −1 K −1 [1]. Bai et al prepared GF/copper composites with a Si coating on GF to improve the mechanical properties. ...
... When compared with diamond reinforced copper composites, the interfacial thermal resistances of the graphite in the c-axis (R 33 ) are within the same order of magnitude (∼10 −8 m 2 K W −1 ), whereas the graphite in the a-axis (R 11 ) exhibit a lower interfacial thermal resistance (∼10 −9 m 2 K W −1 ). In order to further analyze the influence of interfacial thermal resistance, we set the orientation factor q á ñ cos 2 to 0 in the equation (1). Then, we can obtain the theoretical estimates for the TC in the X-Y plane of the composites with 60 vol% GF as a function of the interfacial thermal resistance, as is shown in figure 11. ...
Article
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Graphite flake/Cu composites with Cu or TiC coatings on the graphite surface were fabricated via a powder metallurgy method. The effect of the flake’s surface coating on the microstructure and thermal conductivities of the graphite flake/Cu composites was studied. The results show that a good contact interfacial structure is established when the TiC or Cu coating is introduced. The thermal conductivity of the TiC- and Cu-coated composites with a 60 vol% flake reached 668 W m⁻¹ K⁻¹ and 612 W m⁻¹ K⁻¹, respectively. A modified Diffuse Mismatch Model for anisotropic graphite was established to estimate the interfacial thermal resistance, and the Effective Medium Approach was used to analyze the thermal conductivity behavior of composites. The results show that both coated composites exhibit low interfacial thermal resistance, resulting in high thermal conductivity in the X-Y plane. The thermal conductivity may be further enhanced if a preferable alignment control is used.
... Therefore, a suitable bonding interface is very important for improving the properties of the composite. The interfacial bonding modes of composite mainly include mechanical bonding [27,54,75,97], infiltration bonding [88,[98][99][100] and reaction bonding [101][102][103][104]. Fig. 6 illustrates some information about various interfaces in literatures. ...
... Although carbon materials and some metals are difficult to diffuse, in the preparation of nano-carbon reinforced metal matrix composites, sometimes the interface bonding strength between nano-carbon and metal matrix is improved by adding alloying elements or a special method to form a diffusion transition layer at the interface (As shown in Fig. 8b-e) [76,98,100]. As shown in Fig. 6c, Cr elements will diffuse to Fig. 7. (a) The poor wettability between two phases with a wetting Angle (θ) more than 90°; (b-d) Schematics of mechanical interface formation; (e) The interface mainly bonded by Van der Waals' force and frictional force [67,86]. ...
... The good wettability between two phases with a wetting Angle (θ) smaller than 90°; (b) A transition layer exists between CNT and matrix to form an infiltration interface; (c-e) Schematic of the formation of an infiltration interface though the method for depositing metal layer on the surface of nano-carbon by metal ions [60,98,112]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) the interface zone to form an interfacial layer with good wettability during the sintering process, so as to improve the interface bonding strength [76]. ...
Article
Natural materials usually have excellent performance for their special structures. Learning from the nature may catalyze the creation of artificial composites with unprecedented performance and functionalities. To realize this bio-inspired design idea on nano-carbon reinforced metal matrix composites, it is indispensable to understand and quantify the design principles of natural materials and consider the inherent characteristics of artificial materials and conditions of engineering applications. In this paper, recent researches of the bio-inspired nano-carbon reinforced metal matrix composites are reviewed to highlight the scientific and technological questions to obtain the bio-inspired structure artificial composites. These include the fabrication methods for solving the dispersion problem of nano-carbon and achieving the bio-inspired structure, characterization of microstructure and properties of bio-inspired composites. The interface and reinforcement mechanisms are emphatically investigated and discussed, in this way to help unveil natural design principles and provide reference for the future research of bio-inspired composites.
... Graphite materials used as thermally conductive fillers commonly include graphite fiber, flake graphite (FG), and graphite film [4][5][6][12][13][14][15][16][17]. Flake graphite/copper (FG/Cu) composites have good TC (397 W·m −1 ·K −1 ) and mechanical properties of Cu, as well as ultra-high TC (1500 W·m −1 ·K −1 ), low density, low CTE (−1.0 × 10 −6 K −1 [18]), and good workability of FG [19,20]. Graphite can be used for devices or materials that require directional heat conduction in special cases because of the anisotropy. ...
... It can be found that the pressure sintering is commonly chosen to prepare FG/Cu composites, owing to its ability to obtain the tightly integrated Cu-FG interface. Higher TC acquired in this study should give the credit to the high alignment of FGs in the matrix acquired by a special process [7,10,18,36,37]. CTE in this study has wider adjustment range when TC is not prominent [9]. ...
Article
Full-text available
Highly-aligned flake graphite (FG) reinforced Cu matrix composites with high thermal conductivity and adaptive coefficient of thermal expansion were successfully prepared via the collaborative process of tape-casting and hot-pressing sintering. To overcome the problem of fragile interface, Zr-Cu alloy powder was introduced instead of pure Zr powder to enhance the interfacial strength, ascribed to the physical-chemical bonding at the Cu-FG interface. The results indicate that the synthetic ZrC as interfacial phase affects the properties of FG/Cu composites. The thermal conductivity reaches the maximum value of 608.7 W/m∙K (52% higher than pure Cu) with 0.5 wt % Zr. Surprisingly, the negative coefficient of thermal expansion (CTE) in the Z direction is acquired from −7.61 × 10−6 to −1.1 × 10−6/K with 0 to 2 wt % Zr due to the physical mechanism of strain-engineering of the thermal expansion. Moreover, the CTE in X-Y plane with Zr addition is 8~10 × 10−6/K, meeting the requirements of semiconductor materials. Furthermore, the bending strength of the FG/Cu-2 wt % Zr composite is 42% higher than the FG/Cu composite. Combining excellent thermal conductivity with ultralow thermal expansion make the FG/Cu-Zr composites be a highly promising candidate in the electronic packaging field.
... These thick layers, in turn, are agglomerated with other thick layers forming thick blocks, giving rise to a collapsed structure between 30 and 60 μm with a lateral dimension of 600 × 700 μm. Chen, Ren, He and Qu (2017) in addition to observing that the surface of this type of graphite is exceptionally smooth and bright, it is also observed by microscopy that the natural graphite flakes have a size distribution in which some agglomerated particles can reach up to 1000 μm being able to be observed even by an optical microscope [33]. ...
Article
Studies on graphite flakes with a lateral size greater than 50 μm, having a large number of stacked collapse blocks, are neglected and replaced by graphene nanosheets or by powdered graphite, which can be obtained from graphite through chemical or physical exfoliation, as filler in polymer composites. Besides, the production of graphene nanosheets or the purification of powdered graphite uses a high concentration of strong and toxic acids that pollutes the environment. These processes are extremely time-consuming and generate an expensive product. Composites of poly(vinylidene fluoride) (PVDF) were prepared via extrusion with graphite flakes with up to 60 μm thick and 700 μm lateral size, in the range from 0.1 to 5% m/m. The quality of graphite flakes was analyzed by thermogravimetric analysis, x-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The increase in the graphite content in the PVDF matrix improved thermal resistance while showed an increase in the degree of crystallinity up to 25% by XRD and 43% by differential scanning calorimetry, approximately. Although the graphite acted as a nucleating agent, the content of the PVDF beta phase did not change. In the composites with up to 2.0% of graphite, a significant increase in mechanical properties, 13% modulus, and 36% in the storage modulus, evaluated by thermodynamic-mechanical analysis and tensile tests. In the analyses of time-domain nuclear magnetic resonance and oscillatory rheology in parallel plates, it was noticed that the increase of mechanical properties is due to the reinforcing effect along with the lubricant protection of stacked graphene sheets, attenuating the stress and friction between the polymer chains. Therefore, even though graphite flakes are inexpensive, that filler without any treatment at low contents are capable of significantly improving the performance of PVDF. This work suggests that these composites could be employed in applications such as electrical insulator with less energy dissipation, and also in oil pipelines, specifically to replace PVDF-based terpolymers or mixtures thereof, and polyamide-11 in flexible risers as a barrier layer, improving their performance.
... However, even stopping for 30 min after every 1 h of milling, these copper powders would be oxidized after 5 h [11]. The ethanol is always used as the liquid medium to avoid the heat creation as much as possible during milling [12][13][14][15]. For the powders in the liquid medium, the ultrasonic and magnetic stirring can provide the energy to move from one position to another. ...
Article
Full-text available
The microstructure and properties of Copper-Graphite Composites (CGC) prepared by spark plasma sintering (SPS) based on two-step mixing and wet milling were investigated. The results showed that Cu powders were rolled into Cu flakes during milling, and their size significantly decreased from 23.2 to 10.9 μm when the graphite content increased from 1.0 wt.% to 2.5 wt.%. The oxidation of Cu powder was avoided during two-step mixing and wet milling. After spark plasma sintering, the graphite powders of the composites were mainly distributed at Cu grain boundaries in granular and flake shapes. The mean size of Cu grains was 9.4 um for 1.0 wt.% graphite content and reduced slightly with the increasing of graphite content. Compared with other conventional methods, the composite prepared by two-step mixing and SPS achieved higher relative density, electrical conductivity, and micro-hardness, which, respectively, reduced from 98.78%, 89.7% IACS (International annealed copper standard), and 64 HV (Vickers-hardness) to 96.56%, 81.3% IACS, and 55 HV when the graphite content increased from 1.0 wt.% to 2.5 wt.%. As the graphite content increases, the friction coefficient and wear rate of the composite decreases. When the graphite content of CGC is 1.0 wt.%, the main wear mechanism was plastic deformation, delamination, adhesive, and fatigue wear. The adhesive and fatigue wear disappeared gradually with the increasing of graphite content.
... Electroless plating has been widely used to fabricate composite coated powders in the powder metallurgy fields. Chen et al. [18] have fabricated graphite-Cu composites with strong interface bonding by pre-electroless plating Ni on graphite. W powders could be fully coated with Cu phase to improve the interface wettability during the sintering process, meanwhile, the traditional sintering mode of the sintering between W and Cu can be transformed to the sintering between Cu and Cu [21]. ...
Article
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Dense and homogeneous W–Cu composites with high strength were successfully prepared from Cu-coated W powders by hot pressure sintering (800 °C) with Sn as activated additives. The relative density, microstructure and properties of W–Cu composites with Sn additives were studied. The results have indicated that the addition of Sn additives could significantly promote the densification of W–Cu composites. When Sn was added as additives, the sintering process is mainly the sintering between Cu–Cu and Cu–Sn, and the better mobility of Cu–Sn solid solution is help to eliminate pores and promote low-temperature densification. The relative density of sintered composites has reached 99.2% with 2 wt.% Sn additives. Stacking faults and Twin structure can be distinctly observed in the Cu matrix when 2 wt.% Sn was added as additives. With adding of Sn additives,the Vickers hardness has increased to 263.5 HV. The addition of Sn can lead to the strengthening of interface bonding of sintered composites, and the fracture microstructure with the ductile fracture of Cu matrix and the trans-granular fracture of W phase has been observed in the sintered composites with Sn additives. The bending strength of sintered composites has increased to 993.1 MPa due to the transform of fracture mechanism of sintered composites. The coefficient of thermal expansion of sintered composites has reduced to the minimum value of 7.56 × 10⁻⁶/K with the 1.5 wt.% Sn additives.
... Efficient thermal conductivity of composite materials an important parameter for many practical applications. Its theoretical simulation is a significant problem for basic investigations [1][2][3][4]. ...
Article
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A method of measurement of the thermal performances of composite materials on the base of the porous aluminium oxide is described. The method takes into account the heat inhomogeneity, the material inhomogeneity and anisotropy as well as specimen’s surface radiation. Investigations of the thermophysics properties of the porous substrate fabricated with using of the electrochemical aluminium oxide technology vs. temperature and long staying in a climate chamber were fulfilled. The tests demonstrated that the climatic impact does not influence on the high thermophysics properties of the aluminium oxide material that have extremely high thermal conductivity > 120 W/(m·K).
... Graphite/copper composites have a series of advantages, such as high strength, excellent electrical conductivity and thermal conductivity, and good wear resistance and corrosion resistance [1][2][3][4][5], and are widely used in the thermal management applications of electronic packaging and semiconductor industry [6][7][8][9][10][11]. Graphite/copper composites can be prepared by conventional powder metallurgy methods [12,13], such as cold pressing sintering, hot pressing sintering, hot isostatic pressing, and mechanical alloying [13][14][15][16][17]. ...
Article
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In this study, graphite/copper composites were prepared by microwave sintering. The microstructure and properties of the composites were characterized. The effects of different sintering temperatures on the properties of the composites were studied, and the differences between microwave sintering and conventional sintering composites were compared. The results show that after microwave sintering, the grain size of the copper matrix is refined and the graphite/copper interface is improved, and the distribution of graphite over the matrix becomes more uniform. Compared with conventional sintering, the properties of microwave-sintered samples have been further improved. Besides, with the increase in sintering temperature, the density, hardness, electrical conductivity and thermal conductivity of the composite have been improved, and some properties have become anisotropic obviously. Thus, the electrical conductivity and thermal conductivity along the direction of graphite sheet are higher than those perpendicular to the sheet.
... Because of the poor wettability between graphite phase and copper phase [9] ,each phase of the composites can only be connected by mechanical bounding and physical bonding,resulting in the poor binding effect between the two phases and there are voids existing in the composites [10] ,which seriously affects the mechanical properties and wear-resisting property of the composites.To improve the bonding strength and enhance the properties of the composites,some measures such as the addition of alloying elements which are prone to form carbides [11] ,the addition of new carbon material reinforcing agents and the modi cation of the graphite surface have been taken [12] .Many scholars have improved the mechanical properties and friction properties of composites by adding appropriate new high-performance materials such as carbon nanotubes(CNTs) [13] ,carbon bers(CF) [1] and graphene [14,15] .However,the nanomaterials are prone to agglomeration due to the high surface activity [16] ,which limits the amount and application elds of nano-materials.Metal coating on the surface of carbon material is a feasible method to improve the bonding strength [17] .Numerous studies show that the copper,nickel [18] and silver coating on the surface of carbon materials can availably improve the bonding strength between the strengthened graphite and metal phases.After a lot of research and exploration,the technology of preparing metalcoated graphite has become mature,the preparation cost of the composites have also been reduced,which can be effectively applied in industrial preparation.Wear resistance is an important property that affects the use of G/Cu composite materials [19] .A large number of scholars have studied the friction and wear performance of C/Cu composites and the reinforcement materials in different conditions from macro perspective [20,21] ,the friction mechanisms are derived by observing the friction coe cient,wear rate and SEM diagrams [22] .But few studies have observed the morphology,structure and crystal changes before and after the friction experiment from the micro perspective. ...
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The ring-block tribological behavior of the graphite/Cu(G/Cu) composites and copper-coated graphite-graphite/Cu(CCG-G/Cu) were studied by observing the friction coefficient,wear rate,microstructure and morphogoly of the composites after friction experiments.SEM and TEM were used to character the micro-morphology and micro-structure of debris,friction surface and friction cross section of the composites.The results show that adding 20wt% copper-coated graphite could reduced the friction coefficient and wear rate of the composites.The micro-morphology and micro-structure show that the copper phase are undergo oxidation and plastic deformation under cyclic stress,results in abundant deformation area in copper-rich zones.Interlaminar shedding and intramolecular tearing occurs in graphite phase,and then laid flat on the friction surface,forming a friction film with higher integrity and reducing the friction coefficient of the composites.The TEM images of the friction cross section show that deformation zone is mainly composed of accumulation zone,drag zone and carbon film.The simulation of the friction process shows that the initial stage is mainly dominated by abrasive wear and adhesive wear.With the progress of the experiment,the exposed copper phase is oxidized and oxidative wear occurs,graphite is shed and transferred to the contact surface.In the later stage of the experiment,a complete friction film with high graphite content is formed on the contact surface,which is mainly dominated by fatigue wear.
... They would have high in-plane TC, and they can be attached to the chips to dissipate the heat generated from the chips by quickly diffusing the heat along the in-plane directions, which can strongly improve the heat dissipation efficiency [7]. In a previous study, Chen et al. used the spark plasma sintering (SPS) process to prepare graphite/Cu composites and observed many gaps at the interface between Cu and graphite, which was considered as a major cause for the lower TC of these composites [23]. Tao et al. investigated the wettability and interface thermal resistance of copper/ graphite (Cu/Gr) system by adding chromium (Cr) elements. ...
Article
Effective thermal management of electronic integrated devices with high powder density has become a serious issue, which requires materials with high thermal conductivity (TC). In order to solve the problem of weak bonding between graphite and Cu, a novel Cu/graphite film/Cu sandwich composite (Cu/GF/Cu composite) with ultrahigh TC was fabricated by electro-deposition. The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electro-deposition. TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated. The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content, and the strong texture orientation of deposited Cu resulted in high TC. Under the optimizing preparing condition, the highest in-plane TC reached 824.3 W·m−1K−1, while the ultimate tensile strength of this composite was about four times higher than that of the graphite film.
... Among metallic materials, copper (Cu) has excellent electrical and thermal conductivity, high mechanical strength and good corrosion resistance, which has been selected as the matrix to prepare high performance electronic packaging materials [4] . Carbon materials as ideal reinforcement materials for metal matrix composites have become a hot research topic owing to their outstanding thermal properties, mechanical properties, corrosion resistant and low density [5] , such as carbon fibers [6] , carbon nanotubes [7] , diamond [8] , graphene [9], [10] and graphite. However, the high price of carbon fibers and carbon nanotubes, poor machinability of metal/diamond composites, and nonuniform distribution and uncontrollable orientation of graphene [11] severely limit their commercial applications. ...
Article
Graphite flake (average lateral size of 292 μm and average thickness of 13 μm)/copper composites with high volume fractions (72.08%-93.34 %) of graphite flake were produced by a vacuum hot pressing method. Results show that the composites are anisotropic due to the alignment of the surface plane of graphite flake perpendicular to the pressing direction. With increasing the volume fraction of graphite flake, the density of the composites decreases from 4.07 to 2.63 g cm⁻³, the relative density decreases apparently when the volume fraction of graphite flake are more than 82.6%, the in-plane electrical conductivity decreases from 14.71% to 2.45% of the international annealed copper standard, the in-plane coefficient of thermal expansion decreases from 6.6 to 2.2×10⁻⁶ /K, the in-plane bending strength decreases from 42.48 to 14.63 MPa, the in-plane compressive strength decreases 45.75 to 20.46 MPa while the in-plane thermal conductivity exhibits a maximum of 663.73 W m⁻¹ K⁻¹ at the volume fraction of GF 82.6%. The maximum in-plane thermal conductivity is caused by inter-flake pores that are not fully infiltrated by Cu. The in-plane and out-of-plane thermal conductivity agree well with the modified layers-in-parallel model and modified layers-in-series, respectively.
... Consequently, the porosity of the prepared graphite-Cu composites decreased from 34.5 to 2.9% and the TC increased from 209.1 to 323 W m À1 K À1 . Chen et al. [12] prepared GFs/Cu composites by spark plasma sintering, and improved the interfacial bonding by electroless nickel (Ni) plating on the surface of graphite. Owing to the introduction of NieP transition layer, the bending properties and CTE were improved. ...
Article
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.
... The P element, which takes part in the coating processes and is reduced by the reducing agent hypophosphite, forms the Ni-P layer by wrapping it on the Ni ions. Similar implications are emphasized in the literature according to this phenomenon [48]. The carbon element, which has an 8% count density, shows the porosities between Ni-P layers and is due to the substrate material of the EG paper. ...
Article
In this study, electroless nickel-phosphorus(Ni-P) coating is applied on expanded graphite(EG) papers with excellent electrochemical performances and served as supercapacitor electrodes in alkaline electrolytes. The porosities of Ni-P/EG electrode, measured by mercury intrusion, are compared to expanded graphite papers. It is noticed that the as-prepared ultra-thin, binder-free, eco-friendly, and low-cost Ni-P/EG electrodes can be precisely used as an electrode for supercapacitors and show outstanding performance, including a high specific capacitance of 625 F/g at 1A/g. This material is attained an excellent energy density of 81 Wh/kg at a power density of 1005 W/kg, superior durability with 100,2% retention after 5,000 cycles. The results show that the Ni-P/EG electrode can be used as next-generation advanced metal phosphides for applications in portable electronics, supercapacitors, and wearable energy storage.
... However, the B 4 C layers also increased the phonon scattering at the Cu-graphite interface, and slightly brought down the TC of composite. Chen et al. [35] studied the effects of the nickel coatings on the GFs on the thermal expansion behaviors of the GF/ Cu composites. The Cu-GF interfacial bonding had been significantly enhanced owing to the introduction of NieP plating layer on GFs, contributing to the better thermal properties. ...
... Dislocations are also found in Cu matrix in Figure 3(g-1) (region g-1 in Figure 3b) ('T' symbol), where the dislocation density is higher than that in B-MWCNTs/Cu composite. These dislocations are partly due to the compressive stress and shear strain produced by severe deformation during hot extrusion and drawing, partly due to the lattice distortion caused by the different lattice parameters of Cu2O and Cu, and some are due to the different thermal expansion coefficients of MWCNTs and Cu [40,41]. During the cooling process after high temperature treatment such as sintering and hot extrusion, dislocations were generated at the interface [42]. ...
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The effects of electroless coatings on the microstructure and composition of the interface between multi-walled carbon nanotubes (MWCNTs) and a Cu matrix and the mechanical properties and wear behavior of the resulting copper matrix composites were investigated. Ni and Cu coatings were electrolessly plated on MWCNTs and mixed subsequently with copper powder. Then copper matrix composites were prepared by sintering, hot extrusion and cold drawing processes. The results showed that MWCNTs were straight, long, uniformly dispersed and aligned in the composites. The Ni coating is more continuous, dense and complete than a Cu coating. The tensile strength, compressive strength, microhardness and tribological properties of Ni@MWCNTs/Cu composite along the drawing direction were enhanced most. The ultimate tensile strength and compressive strength were 381 MPa and 463 MPa, respectively. The friction coefficient and wear rate were reduced by 59% and 77%, respectively, compared with pure Cu samples. This study provides a new insight into the regulation of tribological properties of composites by their interface.
... Metal coating on the surface of carbon material is a feasible method for improving the bonding strength. 17 Numerous studies show that copper, nickel, 18 and silver coatings on the surface of carbon materials can improve the bonding strength between strengthened graphite and metal phases. The process of electroless copper plating on the graphite surface is mature, the preparation cost is low, and the surface metal coating effect is good. ...
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To improve the combination of graphite and copper, the friction and wear of a graphite/copper composite with a high content of graphite (50 wt %), copper-coated graphite were used to modify it. To observe the distribution law of each phase in the material and the change of composite surface structure after the friction and wear experiment, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the micro-structure, friction film, debris, and friction cross section of the composites. The results show that the large particle size of copper-coated graphite is anisotropic in the material, which helps to form a friction film with a high graphite content on the contact surface. TEM images of the friction film and debris directly reflect the structure changes of graphite and copper during friction; under normal load and shear force, interlamellar detachment and interlamellar fracture of graphite occur, and its edge is folded and crimped, resulting in the loss of an ordered state in some regions, which results in the instability of crystal lattice and the transition from an ordered to disordered state of graphite, resulting in the (002) halo ring in FFT results. Severe plastic deformation and oxidation reactions occur in copper, and copper oxides are formed, forming a high-strength and smooth oxide film in the metal-rich area and improving the wear resistance of the material. TEM images of the friction section directly show that an inverted triangular deformation zone is formed on the surface of the sample after friction and wear experiments. The edge of the deformation zone is stepped, consisting of a drag zone and an accumulation zone, and the surface of the contact zone is covered by a carbon film.
... The results indicated that electroless plating facilitated uniform dispersion of CNTs and strengthened the chemical bond between CNTs and copper, thereby significantly improving the mechanical properties. Ren et al. [32] fabricated graphite flakes/ copper composites by electroless nickel plating and SPS to significantly improve the interface bonding between graphene and copper base. The results showed an obvious improvement in the bending properties and coefficient of thermal expansion because of the introduction of NieP transition layer. ...
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In this study, we prepared nickel and phosphorus decorated graphene nanoflakes ([email protected]) as a reinforcement in Ti-6Al-4V (TC4) alloy matrix by an electroless plating method. It can enhance the interface bonding force between GNFs and TC4 matrix, and facilitate uniform dispersion of the GNFs in the TC4 matrix. This in turn relieve severe interface reactions between the metal and the carbon nanomaterial. The [email protected]/TC4 composites with different GNFs content (0, 0.25, 0.5, 0.75, 1, 1.5 wt.%) were fabricated via short-term ball milling and spark plasma sintering (SPS). The effects of reinforcement content on microstructures and mechanical properties of [email protected]/TC4 composites were studied while the sintered composites were characterized by X-Ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicated that the mechanical properties of [email protected]/TC4 composites were dramatically improved due to the homogeneous dispersion of GNFs in the TC4 matrix. The compressive strength of 0.5 wt.% [email protected]/TC4 composite reaches 1133 MPa: this was an increase of 30.6% versus TC4 (867 MPa) while maintaining 34.2% ductility. The strengthening mechanism of the mechanical properties of the composites are discussed.
... The load transfer effect accounted for 72.29% of the total in Ni@CNTs/Cu composite. There was thermal expansion coefficient (CTE) mismatch between MWCNTs and the Cu matrix (CNTs is 2.1 × 10 −5 k −1 [68], Cu is 1.7 × 10 −6 k −1 [69]). Many new dislocations were produced during sintering, hot extrusion, and drawing. ...
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Graphite flake/Cu composite has attracted tremendous attention as a promising heat sinks materials owing to its easy machinability and superior thermal properties. However, its preparation process still faces several technological limitations including complex, time-consuming and costly synthetic approaches. In this work, a facile and scalable intermittently electroplated method is applied to prepare Cu-coated graphite flake composite powders, which are subsequently sintered into dense composite bulks. The results show that the graphite flake is successfully coated with a uniform and compact Cu shell, which effectively inhibits the segregation accumulation of graphite flakes and contributes to homogeneous distribution of graphite in the sintered graphite flake/Cu composites. The as-sintered composites exhibit an excellent thermal conductivity of 710 W·m⁻¹·K⁻¹ and an outstanding bending strength of 93 MPa. Such performance, together with the simple, efficient powder-preparation process, suggests that the present strategy may open up opportunities for the development of thermal management materials.
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A self-developed pressureless sintering and subsequent thermo-mechanical treatment process was employed to fabricate 1-5 wt% graphite nanoflakes (GNFs)/Cu matrix composites. The distribution of GNFs and GNFs/Cu interface structure, as well as mechanical and thermal properties of the composites were investigated. The results showed that the thermo-mechanical treatment can significantly improve the GNFs/Cu interface structure, as well as the densities and properties of the composites. However, the distribution orientation of the GNFs and the anisotropy of properties of the composites increase in the process. After pressureless sintering and thermo-mechanical treatment, the relative densities of the 1-5 wt% GNFs/Cu matrix composites can rise as high as 99.4%. As the amount of the GNFs is increased from 1 wt% to 5 wt%, the thermal conductivities of the composites change from 380.4 W/(m·K) to 244.4 W/(m·K) in rolling direction and from 179.3 W/(m·K) to 51.9 W/(m·K) in normal direction. The tensile strengths and the coefficients of thermal expansion of the composites change form 153 MPa to 56 MPa and from 13.5 × 10⁻⁶/K to 11.9 × 10⁻⁶/K respectively. This fully satisfies the application requirements of electronic packaging materials.
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Tungsten carbide (WC) reinforced highly oriented graphite flake composites were obtained using a combined process of surface-coating and spark plasma sintering techniques. Uniform and continuous three-dimensional WC skeleton was formed in the samples with WC concentration higher than 7 vol%, rendering the resulting dense composites light, mechanical strong, high thermal conductive and with low thermal expansion. The skeleton architecture played a role of thermal expansion constraint which remarkably reduced the thermal expansion from 28 × 10⁻⁶ K⁻¹ for highly oriented graphite matrix to ~5 × 10⁻⁶ K⁻¹ for the composite with 26 vol% WC in the direction parallel to the sintering pressure. Concurrently, the composite with 26 vol% WC exhibited bending strength up to ~95 MPa, thermal conductivity up to ~381 W·m⁻¹·K⁻¹ in direction perpendicular to the sintering pressure. The created highly oriented graphite-based composites with uniform 3D ceramic reinforcement are expected to be applied in thermal management of current demanding situation.
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Graphite flake/Al composites are promising thermal management materials due to their lightweight and excellent thermal properties. The interface structure is a key factor that impacts the thermophysical properties. In this work, a prediction model based on the Hatta-Taya model and an extended diffusion mismatch model was developed to evaluate the effect of the interface structure on the interfacial thermal conductance (ITC) and thermal conductivity (TC) of graphite flake/Al composites. Although the model only approximates the ITC rather than precisely calculates it, the model can effectively predict the TC. The theoretical ITC between graphite and various materials can reach 10⁸ W/m²K. The TCs of graphite/Al composites with different interlayers decrease with increasing interlayer thickness but at different rates. Interface layers with high TCs, such as Cu, W, SiC, Si and WC, have good TC performance, regardless of their thickness. Among them, W layers are considered to be the most promising candidate to improve the TC of graphite/Al composites.
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The copper–graphite metal matrix composites were prepared by powder metallurgy method using cuprous oxide and graphite as the raw materials. Their microstructure, relative density, hardness, electrical resistivity and the compressive strength of the cuprous oxide–graphite (Cu2O-Gr) composites were studied. This composite when compared with copper–graphite (Cu-Gr) composites using copper powder and graphite demonstrated that the new composite had finer microstructures with increased to the higher compression strength value. The Brinell hardness is about 1.5-1.6 times higher than the original material and the compressive strength increased by 50-100 MPa. The good parameters can be attributed to the redox reaction that occurs at the interface between cuprous oxide and graphite particles, resulting in uniform distribution of the reinforcements in matrix and strong interfacial bonding between the copper matrix and the graphite particles.
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The effect of graphite surface modification on the thermal conductivity (TC) and bending strength of graphite flakes /Al composites (Gf/Al) prepared by gas pressure infiltration were investigated. Al3Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm−1·K−1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.
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Dual-layer (Cu and Ni coated W) coated powders were successfully prepared by electroless plating to fabricate high-density W-Cu composites with excellent mechanical properties. Field emission scanning electron microscope, transmission electron microscope and X-ray diffraction were used to analyze the microstructure and phase of sintered composites. Vickers hardness and bending strength of sintered composites were investigated. The results show that W powders were coated by Ni layer with a dense and uniform cell structure, the thickness of the Ni layer increased with the increasing of the content of Ni. Then Ni coated W composite powders were covered by Cu layer to prepare dual-layer composite coated powders (Cu and Ni coated W) with uniform and dense structure. W-Cu composites prepared from dual-layer composite coated powders with 2.48 wt.% content of Ni can achieve high densification and strong mechanical strength due to the transformation of sintering mode and the formation of Ni3P phase. Vickers hardness and bending strength can achieve to 257.9 HV and 953.80 MPa, respectively.
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A controlled alignment of micro-/nano-fillers with anisotropic morphology and properties in a composite matrix will allow developing materials with tailored properties, but which still remains challenging. Here, alignment of graphite plates in Cu matrix was well controlled in a wide range with fine steps by elaborately designed morphologies of copper powders. Polarized Raman scattering demonstrated that a record-high orientation degree could be obtained as assisted by Cu micro-flakes. Furthermore, owing to the improvements on intrinsic thermal conductivity of graphite by hot-pressing and graphite/Cu interface wettability by using in-situ graphene as interlayer, high-performance thermally conductive (~600 W/mK) and light-weight (4.9 g/cm³) graphite/graphene-interlayer/Cu matrix composites were successfully fabricated.
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To investigate the effect of the dispersion and alignment of the graphite fibers (GFs) on the thermal expansion induced fracture of GF/copper composites, composite test specimens were fabricated by the mechanical mixing, wet powder mixing, and chemical mixing (CM) methods at various GF volume fractions. The coefficient of thermal expansion (CTE) and mechanical properties of the fabricated composites were measured in the in-plane and through-plane directions, and their variations were investigated as functions of the dispersion and alignment of the GFs, which are key to reinforcement. From the measured CTE and the mechanical properties, the maximum temperature that the composite can withstand without fracture due to thermal expansion (i.e., fracture temperature) was estimated. The highest fracture temperature was observed in the in-plane direction of the composite fabricated by the CM method. Furthermore, with increasing GF volume fraction, the fracture temperature increased even though the maximum compressive strength decreased, because of the very small CTE of the composite.
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Thermal management materials with high thermal conductivity (TC), adjustable coefficient of thermal expansion (CTE) and excellent mechanical properties have promising applications in the electronic packaging and high-power density equipment fields. In this work, we have developed a novel strategy for tungsten-copper coated graphite flakes and aluminum nitride nanoparticles reinforced copper matrix composites (GFs(W–Cu)/AlN/Cu composites) fabricated by vacuum hot-pressing sintering. Herein, tungsten-copper coated graphite flakes (GFs(W–Cu)) were prepared by impregnation reduction and ultrasonic-assisted electroless plating, in which W–Cu coating improved interfacial bonding and realized metallurgical-physical synergy. Meanwhile, the AlN nanoparticles reinforced Cu flakes (AlN/Cu) were prepared by high energy ball milling, where AlN nanoparticles were evenly dispersed in the Cu matrix and played the role of pinning boundary and refining grain. Effects of nano-AlN with different volume fractions on the mechanical and thermal properties of GFs(W–Cu)/AlN/Cu composites were studied as well. As for the mechanical properties, the in-plane, through-plane flexural strength and tensile strength of GFs(W–Cu)/1.5AlN/Cu composite reached 276.7 ± 4.5, 390.6 ± 4.5 and 136.1 ± 3.0 MPa respectively, which increased by 96.8%, 283.7% and 120.7% than those of the GFs(W–Cu)/Cu composites. In terms of the thermal properties, the in-plane TC of GFs(W–Cu)/1.5AlN/Cu composite is 617.8 ± 12 Wm⁻¹K⁻¹, while the through-plane CTE ranging 25–200 °C is 4.9 ± 0.2 ppmK⁻¹. In conclusion, the GFs(W–Cu)/AlN/Cu composites provide a huge potential for design and application in the thermal management materials.
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Carbon/copper composites are widely used in collector brushes, pantograph sliders, collector shoes and other fields due to their excellent mechanical friction, wear, thermal conductivity and electrical conductivity. However, the interfacial bonding force of composites is weak because of the natural non-wetting of copper and carbon graphite matrix, which restricts its comprehensive mechanical and electrical properties. In this paper, the nickel element was doped and introduced in the preparation process of the carbon graphite matrix, and the carbon/copper composites were further prepared by the pressure impregnation method. The results showed that the modified carbon matrix doped with nickel was denser, and the nickel element could evenly distribute in the carbon matrix. The porosity of the modified carbon/copper composites was significantly reduced and the interfacial bonding method was changed from the original simple mechanical interlock to solid solution bonding so that the interfacial state was obviously improved. The effect of nickel content on the mechanical and electrical properties of composites was systematically studied. It was found that when the nickel content was 3 wt%, the compressive strength and flexural strength were increased by nearly 52% and 58%, and the electrical conductivity was increased by nearly 35%.
Article
Copper matrix composites reinforced with graphene nanoplatelets (GNPs) were fabricated using an electroless plating method, and the effects of the GNP content on the thermal conductivity (TC), coefficient of thermal expansion (CTE), and mechanical properties of the composites were studied. The TC, CTE, and strength of the composites were measured in the in-plane and through-plane directions and compared. Increasing the GNP content in the GNP/Cu composite was effective in reducing the CTE and increasing the compressive yield strength of the composite. The compressive yield strength was higher in the through-plane direction, but the maximum compressive strength was higher in the in-plane direction. In the case of compressive deformation in the in-plane direction, a single shear fracture with one fracture direction occurred. The compressive deformation in the through-plane direction of the composite with high GNP content (15% and 20%) exhibited a duplex shear fracture with two fracture directions. The significant findings of the present study are that it is possible to fabricate GNP/Cu composites with uniformly dispersed GNPs and low porosity by electroless plating. In addition, the failure mechanism of GNP/Cu composites was revealed for the first time.
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The focus of this study is to fabricate thermal management materials integrating thermal and electrical structural and functional materials by preparing graphene film reinforced Cu laminated composites. Strengthening the interface is a core scientific issue. Graphene is considered a good reinforcement phase because of its excellent electrical and thermal conductivity. The production route includes electroless Cu coating on graphene film and ball milling Cu powder into Cu flake. Due to the particularity of the film and the Cu flake through vacuum hot pressing sintering, laminated composite materials can be obtained. The transfer of electrons and internal energy within a material determines the electrical and thermal conductivity of the material. With the increase of content of graphene films, electrical properties of laminated composites and thermal conductivity on the plane direction increase, while the thermal conductivity on thickness direction decreases. The best thermal conductivity and electric conductivity can reach 457 W m⁻¹ K⁻¹ and 175 MS/m, respectively. However, when the graphene films contents exceed 30 vol.%, the thermal conductivity in the plane direction decreases due to the severe interfacial cracks. In summary, copper coating on the graphene films surfaces can generally improve the interfacial bonding and thermal properties of laminated composites. It provides an effective method to perform the development of novel thermal management structures and functional materials.
Article
In order to improve the interfacial bonding between copper and graphite, copper was coated on the graphite by electroless plating. Copper/graphite composites with copper‐coated graphite were fabricated by spark plasma sintering. The effects of copper‐coated graphite on the density, electrical conductivity, mechanical properties, friction and wear properties of copper/graphite composites were studied. The results show that: copper plating on the graphite surface can improve the wettability of graphite and copper, and the interface between them is well bonded. Compared with pure copper, the microstructure of the composites was significantly refined after adding copper‐coated graphite. The mechanical properties of the composites were significantly improved, with yield compressive strength and elastic modulus increasing by 220 % and 240 %, respectively. With the increase of copper‐coated graphite contents, the density and the conductivity of the composites gradually decreased. The friction coefficient and wear rate of the composites were significantly reduced. The friction and wear mechanisms of the composites are mainly oxidation wear, fatigue wear and adhesive wear. The interfacial bonding between copper and graphite was significantly improved owing to the pre‐coated copper on the surface of graphite. Copper/graphite composites were prepared by spark plasma sintering. Copper/graphite composites own low friction coefficient and good electrical conductivity, which can be used to fabricate conductive lubricating materials.
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With the rapid development of the miniaturization and high-integration of electronic devices, conventional thermal conductive materials cannot ensure the safety and reliability of the high-power devices in working environments. It is urgent to develop thermal management materials with excellent thermophysical and mechanical properties. In this work, the tungsten-coated graphite flakes (GFs(W)) were prepared by the immersion reduction, and the GFs(W) reinforced copper matrix composites (GFs(W)/Cu composites) were prepared by the vacuum hot-pressing sintering. Based on the microstructure and surface analysis, the W coating obtained at 900 °C and 200 g/L AMT appears the excellent surface structure and interfacial adhesion, which transfer the interfacial bonding from mechanical combination to mechanical-metallurgical synergy between the GFs and Cu. In addition, the volume fraction of W coating has a threshold to improve properties of the GFs(W)/Cu composites, in which the GFs(6 W)/Cu composites show the outstanding comprehensive performance: the in-plane thermal conductivity and flexural strength are 879.0 ± 10.0 Wm⁻¹K⁻¹ and 166.9 ± 3.4 MPa respectively, which are improved by 22.3% and 356.0%, and the lowest coefficient of thermal expansion is 4.3 ± 0.5 ppmK⁻¹. To sum up, it provides an effective way to develop novel structural and functional integrated graphite/copper composites for thermal management.
Article
Carbon materials reinforced copper matrix composites with excellent mechanical properties, high thermal conductivity (TC) and suitable coefficient of thermal expansion (CTE) are expected to meet the urgent need for the thermal management materials with structural stability and efficient heat dissipation in civil and military fields. In this work, the tungsten-copper (W-Cu) composite coating was deposited on the graphite flakes (GFs) by the impregnation-reduction and ultrasonic-assisted electroless plating. Meanwhile, the W-Cu coated GFs reinforced Cu matrix composites (GFs(W-Cu)/Cu) were also prepared by the vacuum hot-pressing sintering. Based on the microstructure and surface analysis, the interfacial bonding has changed from the simple mechanical connection to the mechanical-metallurgical synergy. As for the three-point bending and uniaxial tensile tests, the largest in-plane, through-plane flexural strength and tensile strength of the GFs(W-Cu)/Cu composite can achieve the values of 189.6 ± 3.8, 172.3 ± 4.2 and 91.9 ± 2.6 MPa, respectively. Among the GFs(W-Cu)/Cu composites, the ultrahigh in-plane TC and lowest through-plane CTE can reach 929.8 ± 5.0 Wm⁻¹K⁻¹ and 6.3 ± 0.2 ppmK⁻¹ respectively, and the better thermal response rate can be 0.67 °C·s⁻¹. In conclusion, an effective way to develop the structural and functional integrated carbon-based thermal management materials can be provided.
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Combining short-process reduction and vacuum hot pressing, copper matrix composites with the graphite volume fraction of 55% and 70% were prepared by cuprous oxide and spherical graphite (Cu2O-Gr composites). Transmission electron microscopic (TEM) results show that some graphite particles in Cu2O-Gr composites change from spherical to finer flocculent or acicular shape, and the interface between the matrix and graphite is partially coherent. The reaction enhances interface bonding and modifies the interface morphology of graphite, leading to the good mechanical performance of the composites. Compared with the Cu-Gr composites prepared by conventional hot pressing, the Cu2O-Gr composites present higher density and strength and lower friction coefficients and wear rates. In the current-carrying friction experiments, the wear rate of the Cu2O-55Gr is nearly 25% lower than that of the Cu-55Gr. The short-process reduction contributes to better self-lubricating behaviors of the Cu2O-Gr composites, reducing the adhesive wear and abrasion wear.
Article
Copper–graphite sandwich composites are new functional composites with excellent tribological and mechanical properties. More and more researchers prepare the sandwich composites by accumulative roll-bonding processes due to severe plasticity deformation. The microstructure and properties of copper–graphite sandwich composites prepared by continual annealing and accumulative roll-bonding processes for eight rolling cycles were investigated. The results showed that with the increase of rolling cycles, the dispersion of graphite particles between two copper layers along a rolling direction became more uniform, the pores at the interface between graphite particles and the Cu matrix gradually disappeared, and the hardness of copper–graphite composites gradually increased. After eight rolling cycles, the Vickers hardness of the composites increased by 140.8% as compared with that of annealed pure copper. During friction, the steel balls can meet some graphite particles in the composites rolled by four cycles. The friction coefficient and wear loss of copper–graphite composites gradually decreased with the increase of rolling cycles. Compared with the composites rolled by one cycle, the friction coefficient and wear loss of the composites rolled by eight cycles were reduced by 32.5 and 49.0%, respectively. The main wear mechanism gradually evolved from fatigue wear and abrasive wear to adhesive wear, and then to fatigue wear.
Article
The interface doping with transition metal elements (TM = Ti, Cr, Co, Ni) has been experimentally proved to be an effective pathway to improve the weak interface bonding of graphene/copper (Gr/Cu) composites. In this paper, the microscopic influencing mechanism of TM doping on the interface interaction and mechanical properties of Gr/Cu was investigated by the first-principles calculations. The sandwich model with graphene embedded in Cu matrix was adopted here to simulate the TM-doped interfaces. It is revealed that the introduction of TM doping elements can significantly improve the work of separation, which relates to the electronegativity difference between TM and Cu elements based on the analysis of the interface electronic structure. Then, the mechanical properties of the clean and TM-doped interfaces were studied by the rigid stretching and the relaxed stretching. We found that, in rigid case, the theoretical tensile strengths of different interfaces are positively correlated with the work of separation, and the electronegativity is also a main factor affecting the mechanical properties. Furthermore, a fitting function containing the element electronegativity was applied to get the stress–strain relationship curve, and the quantitative relationship between the interface bonding and mechanical properties determined in this work can be served as a favorable support for the experimental design of Gr/Cu composites.
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In order to increase the radial thermal conductivity (TC) of UO2 pellets, highly-oriented graphite flakes (GFs) were first introduced to UO2 pellets by spark plasma sintering. The radial TC of GFs/UO2 agreed well with Hatta-Taya model, which was closely related to the well-bonded interface and highly-oriented structure. Compared with UO2, the radial TC of GFs/UO2 was greatly improved by about 200 % within a wide temperature range, higher than all the other reported value until now. Such enhancement in TC would significantly improve the safety of UO2 fuel pellets.
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The addition of graphene is expected to improve the properties of solder and graphene reinforced Sn–Ag–Cu (GNSs/SAC) is considered to be able to adapt to harsh service environment. However, it is difficult to realize homogeneous dispersion of reinforcement and the metallurgical bonding between graphene and Sn–Ag–Cu alloys. In this study, composite solders with various dispersion of graphene have been prepared by different ball milling method. The microstructure characterization shows that incoherent interface and amorphous interface have been produced between graphene and Sn. The results of Energy Dispersive Spectrometer (EDS) and X-ray diffraction (XRD) indicate that the interstitial solid solution of carbon atoms in β-Sn is the cause of metallurgical bonding. The relative amount of the two types of interfaces and the dispersion of graphene were evaluated. The incoherent interface of composites tends to form at lower milling speed, and its thermal expansion response indicates that the interface has more effective load transfer, while the amorphous interface is opposite. Besides, the {101} fiber texture was also confirmed to be formed during ball milling and sintering. Finally, the nano indentation test verified the metallurgical bond, and the mechanical properties of the GNSs/SAC composites are determined by the interface type and graphene dispersion.
Article
The robust interface adhesion between matrix and reinforcement is the guarantee for enhancing mechanical performance of the metal matrix composites (MMCs). Unfortunately, the low strengthening efficiency and drastically reduced elongation have always been the cases for MMCs due to the difficulties for architecting tightly-bonded and effective interface structure. Herein, a new strategy is proposed to construct interfacial interlocking structure in the Al matrix composites reinforced by graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni [email protected]), which were in-situ synthesized by using assembled NaCl particles as templates. The hybrid particle of Al3Ni and Ni serves as an interface interlocking factor to fasten the bonding of Al and GNS, thus the outstanding load transfer and dislocation accumulation capability are adequately achieved at the interfaces. Besides, experiments and first-principles calculations disclosed that the robust covalent bonding between Ni NPs and GNS with few defects and lower oxygen level synthesized in this work facilitates a tortuous crack propagation path before fracture. Hence, the as-obtained composites exhibited an excellent strengthening efficiency while preserving a good ductility. It is evidenced that the construction of interfacial interlocking structure can pave a promising path to produce strong, tough and lightweight MMCs for wide applications.
Article
Copper/nickel coated graphite film/copper sandwich composite foils were fabricated by electro-deposition and subsequent vacuum hot pressing treatment. Intermediate nickel layers with different volume faction (5%, 10%, 15%, and 20%), which was calculated corresponds to the proportion between graphite film and Ni coating, were introduced to modify the interfacial bonding between graphite film and deposited copper. The effect of the vacuum hot pressing (VHP) parameters on the in-plane thermal conductivity (TC) was investigated systemically. The results showed that the existence of intermediate nickel layer could improve the interfacial bonding between graphite and copper, thus enhance the thermal conductivity of the fabricated composite foils. The maximum TC value of the composite foil (graphite volume fraction of 50 vol% with 10 vol% intermediate nickel layers) reached up to 1042.4 W·m⁻¹·K⁻¹ after VHP treatment at the optimal process parameters (800℃, 60 min and 40 MPa). These composites possess higher in-plane thermal conductivities than graphite flake/copper composites due to well-controlled graphite/copper interfacial bonding and fabrication parameters.
Article
In the trend of integration of structure and function, novel thermal management materials are urgent to be developed owning good mechanical properties as well as excellent thermal properties. In this work, a complete and dense copper (Cu) coating with a thickness of 400 nm was deposited on the surfaces of graphite films (GFs) by ultrasonic-assisted electroless plating, which can improve the surface roughness of GFs and interfacial bonding between GFs and Cu foils. Cu-coated and uncoated GFs reinforced copper matrix laminated composites (noted as GFs(Cu)/Cu and GFs/Cu) were fabricated by optimized vacuum hot-pressing sintering. Based on the scratch test and microstructures of GFs(Cu) and GFs(Cu)/Cu composites, addition of Cu coating can improve the interfacial adhesion and element diffusion behavior, and intuitively explains the mechanical interlocking effect at the C–Cu interface. On basis of the nanoindentation mechanical properties across GFs(Cu)/Cu and GFs/Cu interfaces, the interfacial transition region with Cu coating of ∼3 μm is three times of that without Cu coating. Flexural strength of 27.6 vol.% GFs(Cu)/Cu laminated composite is 45.9 MPa, which is 56% higher than that of the corresponding GFs/Cu laminated composite. In-plane thermal conductivity (TC) and out-of-plane coefficient of thermal expansion (CTE) of 69.4 vol. % GFs(Cu)/Cu laminated composite are 1177.8 W/m·K and −2.5 ppm/K respectively, which could be explained on the theoretical calculations and interfacial structures. In conclusion, the Cu coating on surfaces of GFs can generally improve the interfacial bonding, mechanical properties and thermal properties of GFs(Cu)/Cu laminated composites. It provides an effective way to develop novel structural and functional materials for thermal management.
Article
As an ideal reinforcing phase, nano-carbon has been widely used to improve the properties of composites. In this paper, Mo-Cu-Zr ternary composites were reinforced with various types and contents of nano-carbon to find the optimal composition and the microstructure and mechanical properties of the composites were systematically characterized and analyzed. The composites were fabricated via a powder metallurgy method to achieve high compactness and structural uniformity. The analysis results show that the increase of nano-carbon may cause a serious agglomeration and subsequent decrease of the composite compactness, while the synergetic effect of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) can improve their dispersion. The 0.8C+0.2G-MCZ3 composite showed the best comprehensive properties, which achieved a relative density, hardness and compressive strength of 99.7%, 343.6 HV and 953.5 MPa, respectively. Moreover, the component Zr mainly formed solid solution and compound particles with Cu or C through in-situ chemical reactions. It played an important role in solid solution strengthening and dispersion strengthening, and the in-situ synthesized ZrC nanoparticles on nano-carbon surfaces can pin interfaces and improve the effect of load transfer. The synergetic effects and multiple strengthening mechanisms result in the improvement of the microstructure and properties of the composites.
Article
In this work, graphene nanoplates(GNPs) reinforced CuCr composite coatings were prepared by mechanical alloying(MA) method. In order to further improve the thermal performance, the coatings with different GNPs contents were annealed at 700 °C for 1 h. Raman, XRD and SEM were employed to characterize the defect of graphene, the phase transformation and the element distribution of coatings. Consequently, GNPs were detected to be well dispersed in the composite coatings. Moreover, the distributions of Cu and Cr were more homogeneous after annealing. In addition, chromium carbides formed in the coating during the annealing process, and the interfacial bonding in the coating would be further strengthened. Although the defects of GNPs increased during MA process, the thermal properties of as-synthesized samples were still greatly improved compared with Cu substrate.With the increase of GNPs content, the thermal conductivity of as-fabricated samples enhanced initially and then decreased. When the content of GNPs increased to 1.12 vol%, the highest thermal conductivity reached 424.210 W m⁻¹ K⁻¹. This remarkable result might provide a new idea for GNPs reinforced thermal conductive materials.
Article
Copper/graphite composites and copper/graphite/Ti2SnC composites were fabricated through the process of ball-milling, pressing and sintering. The effects of Ti2SnC as the second lubrication component on the mechanical properties, wear resistance and lubrication properties of copper/graphite composites were studied in this paper. The results showed that copper/graphite/Ti2SnC composites had better hardness, impact toughness, wear resistance and lubrication performance than copper/graphite composites. The optimum values of hardness, impact toughness, friction coefficient and wear rate of copper/graphite/Ti2SnC composites were, respectively, 56 HSD, 1.8J/cm², 0.15, 9.126×10⁻⁶ mm³/N·m, while these were only 45 HSD, 1.2 J/cm², 0.17, 3.534×10⁻⁴ mm³/N·m of copper/graphite composites.
Chapter
This chapter attempts to make a review of electroless metal deposition over various non-conducting substrates like for its application in the field of medical research, electrical and electronics units, household aesthetics, automobile and textile industries. Electroless coating of metals over conducting substrates have been developed, critically reviewed, and proven its worth by showing excellent desired properties over the years. This review aims to discuss the techniques that have been applied by the researchers to overcome the difficulties of coating on these materials, their influence in their physical and mechanical properties, and their prospects of use in the industries. With the discussion of the underlying coating fundamentals and its historical backgrounds, the emphasis was put into the coating deposition with sensitizations and activations of various substrates, electroless baths, and the characteristically changed properties of the materials observed in the analysis.
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Cu/graphite composites with 30 and 50 vol.% of graphite were prepared. Copper coated graphite particles enabled to prepare more homogeneous structure at 50 vol.% of graphite as simple powder mixture. In the case of 30 vol.% of graphite, composite prepared from mixture of coated graphite and copper powders is more heterogeneous as simple powder mixture. Measured CTE of coated composites was significantly smaller at both compositions. It is the result of the different area of copper-graphite interface that is established only by mechanical clamping. For coated composites the area of interface increases significantly due to avoiding graphite clustering. Simple model was proposed to predict this behaviour on the basis of anisotropy of graphite CTE. Further, the model can be used for calculation of the thermal expansion coefficient of the graphite reinforcement.
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A method to fabricate one dimensional nanoscale composite based on coating of carbon nanotube with metal is proposed and demonstrated in this letter. Carbon nanotubes have been coated with a layer of nickel by electroless plating. It was found that the nickel coating had a tendency to form as nanoparticles on the surface of carbon nanotube and on the net of carbon nanotubes. High density active sites and low deposition rate were found to be critical for getting better coating.
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A study has been made of microstructures and crystallization of the electroless Ni-P deposits containing 11.3 to 23.0 at% P obtained from acidic nickel sulphate baths with sodium hypophosphite as a reducing agent by means of differential scanning calorimetry, X-ray diffractometry and hot stage transmission electron microscopy. The deposits containing low phosphorus content of 11.3 at% could be represented as an fcc Ni-P solid solution of 5 to 10 nm microcrystallites, whereas the deposits containing high phosphorus content were amorphous. The crystallization process of amorphous Ni-P solution involved more than one intermediate phases; precrystallized nickel or off-stoichiometric Ni3(P, Ni) or Ni5(P, Ni)2 phase in which some phosphorus sites are replaced by nickel atoms. The final equilibrium phases were bct Ni3P and fcc nickel crystals regardless of phosphorus content. The amorphous phase containing 20 to 22 at% phosphorus was the most stable among the amorphous Ni-P alloys.
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Diamond-based metal matrix composites have been made based on pure Al and eutectic Ag-3Si alloy by gas pressure infiltration into diamond powder beds with the aim to maximize thermal conductivity and to explore the range of coefficient of thermal expansion (CTE) that can be covered. The resulting composites covered roughly the range between 60 and 75 vol-% of diamond content. For the Al-based composites a maximum thermal conductivity at room temperature of 7.6 W/cmK is found while for the Ag-3Si based composites an unprecedented value of 9.7 W/cmK was achieved. The CTE at room temperature varied as a function of the diamond volume fraction between 3.3 and 7.0 ppm/K and 3.1 and 5.7 ppm/K for the Al-based and the Ag-3Si-based composites, respectively. The CTE was further found to vary quite significantly with temperature for the Al-based composites while the variation with temperature was less pronounced for the Ag-3Si-based composites. The results are compared with prediction by analytical modeling using the differential effective medium scheme for thermal conductivity and the Schapery bounds for the CTE. For the thermal conductivity good agreement is found while for the CTE a transition of the increases. While the thermophysical properties are quite satisfactory, there is a trade-off to be made in these materials between high thermal conductivity and low CTE on the one side and surface quality and machinability on the other.
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Electroless Ni-7.4 to 10% P deposits obtained from acidic nickel sulphate baths with sodium hypophosphite as a reducing agent were analysed by transmission electron microscopy, X-ray diffraction and thermal analysis. The deposits could be represented better by a microcrystalline structure composed of 4 to 5 nm fcc Ni-P solid-solution grains rather than an amorphous structure. The deposits also had the (111) texture, which persisted in nickel grains even after phase separation of nickel and Ni3P by heating in the case of the low nickel content, whereas the texture approached the random orientation with increasing phosphorus content. The phase transformation temperature was independent of the phosphorus content.
Article
The pore structure of exfoliated graphite was discussed on the basis of exfoliation volume, and size determination of pores among and inside the worm-like particles. In order to evaluate pore structures, new techniques were developed, which included a paraffin impregnation method for filling large spaces between the particles and fracturing across the worm-like particles for pores inside the particles, both being assisted by an image processing technique. In the first pan of the present review, the pore structure of a commercially available exfoliated graphite was determined. In the second and third parts, the effects of exfoliation temperature and intercalate content are respectively discussed.
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A modified semi-powder method was adopted to fabricate graphene nanoplatelets (GNPs)-copper composites in the present study. Electroless Cu and Ni plating were firstly performed on the surface of GNPs before semi-powder mixing to improve wettability of GNPs. The main structure of GNPs was maintained after the plating process. Microstructure studies showed both of 0.5 vol.% copper-plated and nickel-plated GNPs (Cu-GNPs and Ni-GNPs) were uniformly distributed and well bonded with the Cu matrix. The electroless plating improved the mutual disperse of GNPs and the Cu matrix. Compared with pure Cu, the composite with addition of 0.5% Cu-GNPs exhibited an increase of 49.1% in yield strength. Benefiting from better dispersion and stronger interfacial bonding, the increase of 64.5% in yield strength was obtained in the 0.5% Ni-GNPs/Cu composite. The strengthening mechanisms, including grain refinement, thermal mismatch and load transfer were carefully discussed.
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Diamond particles dispersed Zr-alloyed Cu matrix composites were produced by a gas pressure infiltration route. The thermal conductivity first increased and then decreased with increasing Zr content in the range of 0.0–1.0 wt.%, yielding a maximum thermal conductivity of 930 W/mK at 0.5 wt.% Zr. The high thermal conductivity is attributed to the optimized thickness of interfacial ZrC layer formed between Cu and diamond. The interfacial layer thickness is crucial to the thermal conductivity enhancement in the Cu/diamond composites.
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We developed a nanocomposite with highly aligned graphite platelets in a copper matrix. Spark plasma sintering ensured an excellent copper-graphite interface for transmitting heat and stress. The resulting composite has superior thermal conductivity (500 W m(-1) K(-1), 140% of copper), which is in excellent agreement with modeling based on the effective medium approximation. The thermal expansion perpendicular to the graphite platelets drops dramatically from ∼20 ppm K(-1) for graphite and copper separately to 2 ppm K(-1) for the combined structure. We show that this originates from the layered, highly anisotropic structure of graphite combined with residual stress under ambient conditions, that is, strain-engineering of the thermal expansion. Combining excellent thermal conductivity with ultralow thermal expansion results in ideal materials for heat sinks and other devices for thermal management.
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Ultra-high temperature ceramics (UHTCs) composed of ZrC and SiC were fabricated via pyrolysis of hybrid polymeric precursors comprising of polycarbosilane (PCS) and polyzirconobutanediol (PZC). Phase separation in these polymers blends during different removal methods of toluene solution by freezing drying, vacuum drying and rotary evaporation was studied. Elements and phase distribution as well as molecular aggregation state in the hybrid polymeric precursors and the pyrolyzed composite ceramics were characterized with AFM and SEM. It was found that macromolecules of pre-ceramic polymers aggregated spontaneously in the hybrid precursor solution and formed molecular clusters within dozens of nanometers, and the resultant phase separation during removal of toluene solution exhibits strongly impact on the microstructure of the derived UHTCs after being pyrolyzed at temperature above 1000 °C, which was controlled by solvent removing time.
Article
a b s t r a c t Highly thermally conductive graphite flakes (G f)/Si/Al composites have been fabricated using G f , Si pow-der and an AlSi 7 Mg 0.3 alloy by an optimized pressure infiltration process for thermal management appli-cations. In the composites, the layers of G f were spaced apart by Si particles and oriented perpendicular to the pressing direction, which offered the opportunity to tailor the thermal conductivity (TC) and coeffi-cient of thermal expansion (CTE) of the composites. Microstructural characterization revealed that the formation of a clean and tightly-adhered interface at the nanoscale between the side surface of the G f and Al matrix, devoid of a detrimental Al 4 C 3 phase and a reacted amorphous Al–Si–O–C layer, contributed to excellent thermal performance along the alignment direction. With increasing volume fraction of G f from 13.7 to 71.1 vol.%, the longitudinal (i.e. parallel to the graphite layers) TC of the composites increased from 179 to 526 W/m K, while the longitudinal CTE decreased from 12.1 to 7.3 ppm/K (match-ing the values of electronic components). Furthermore, the modified layers-in-parallel model better fitted the longitudinal TC data than the layers-in-parallel model and confirmed that the clean and tightly-adhered interface is favorable for the enhanced longitudinal TC.
Article
In order to obtain high thermal conductivity materials for efficient heat sink applications, diamond particles dispersed CuB alloy matrix composites (CuB/diamond composites) containing diamond as high as 90 vol.% were produced by a high temperature–high pressure infiltration method. The thermal conductivity of the Cu–0.3 wt.%B/diamond composite was measured to be 731 W m−1 K−1. The presence of B4C on the surface of diamond was identified by Raman scattering. The influence of B addition on interface microstructure was clarified to interpret the thermal conductivity enhancement. The results show that B addition can improve the thermal conductivity of Cu/diamond composites produced by high temperature–high pressure infiltration method.
Article
A new family of high thermal conductivity composites, produced through infiltration of a metallic alloy into preforms of mixtures of graphite flakes and either ceramic or carbon materials (in the form of particles or short fibers), has been recently developed. Composites microstructure roughly consists of alternating layers of flakes and metal-particles composite. The present work focuses on graphite flakes–SiC particles/Al–12 wt%Si composites. The effects that the relative amounts of the components, as well as the average diameter of SiC particles (varied over the range 13–170 μm), have on the thermal conductivity are investigated. The experimental results are analyzed by means of two model microstructures: (i) alternating layers of flakes and metal-particle composite, and, (ii) oriented discs (graphite flakes) randomly distributed in a metal-particle composite matrix. Fitting experimental data by means of these model microstructures leads to reasonable values of the thermal conductivity of graphite flakes along the transversal and longitudinal directions.
Article
Cu matrix composites reinforced with Ti-coated diamond particles were consolidated by spark plasma sintering. A layered structure of TiC/transition layer was formed uniformly on the diamond particle surface, with a total thickness of ∼285 nm. A high thermal conductivity of 493 W m−1 K−1 was achieved in the Cu/Ti-coated diamond composites. The greatly enhanced thermal conductivity is ascribed to the 285 nm thick Ti coating. Ti coating on diamond particles is therefore an effective way to enhance the thermal conductivity of Cu/diamond composites.
Article
Carbon-based/metal composites are materials showing excellent thermal performance. Graphite flakes are attractive carbon-based reinforcements in terms of thermal properties, price and machinability. However, their packed preforms pose insurmountable difficulties to metal infiltration. Here a novel fabrication process is discussed which consists of using mixtures of graphite flakes and other material with different morphology. Preforms of such mixtures can be easily infiltrated with a variety of metals and alloys. The thermal properties of the resulting composites are also reported.
Article
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.
Article
By taking advantage of the redox potential differences between substrate and the metal ions (Mm+/M), and the excellent conductivity of graphene sheets, a versatile platform, electroless deposition, is used for the synthesis of metal (M)-graphene hybrid materials (MAg, Au, Pd, Pt and Cu) by immersing graphene sheets coated on metal (Cu or Zn) foils into solutions containing the corresponding precursors, which have higher redox potentials than that of Cu or Zn foil. The size and density of the metal nanoparticles on the graphene sheet surface can be controlled by rationally designing of the experiments. Stacks of metal-decorated graphenes were obtained by repeating the processes of graphene-coating and metal-depositing. Pt-graphene hybrid materials have shown good electrocatalytic activity toward methanol oxidation.
Article
Electroless Ni–P coatings are recognized for their excellent properties. In the present investigation electroless Ni–P nano-crystalline coatings were prepared. X-ray diffraction technique (XRD), scanning electron microscopy (SEM), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were utilized to study prior and post-deposition vacuum heat treatment effects on corrosion resistance together with the physical properties of the applied coatings.X-ray diffraction (XRD) results indicated that the As-plated had nano-crystalline structure. Heat treatment of the coatings produced a mixture of polycrystalline phases. The highest micro-hardness was achieved for the samples annealed at 600°C for 15min due to the formation of an inter-diffusional layer at the substrate/coating interface.Lower corrosion current density values were obtained for the coatings heat treated at 400°C for 1h. EIS results showed that proper heat treatments also enhanced the corrosion resistance, which was attributed to the coatings’ structure improvement.
Article
Crystallisation process in electroless nickel phosphorus (Ni–P) platings during continuous heating was investigated using X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC). X-ray line broadening technique was used to estimate the grain size and microstrain, with the aid of PROFIT software to separate the reflections of crystalline nickel from the amorphous phase. Results showed that in the as-deposited condition, platings with 3–5 wt.% (NiP4), 5–8 wt.% (NiP65), and 6–9 wt.% (NiP75) phosphorus are a mixture of amorphous and microcrystalline materials, whereas the plating with 10–14 wt.% (NiP12) phosphorus is fully amorphous. In all the platings after continuous heating the grain size increases sharply when the temperature increases above 400°C. The microstrain in the platings decreases with increasing temperature. The crystalline nickel formed is largely randomly orientated. It was also shown that the NiP4 specimen heated up to the termination point of the major exothermal DSC peak at 40°C/min has larger grain size and microstrain than that heated at 5°C/min. The amount of Ni3P phase formed at this point is about the same, which indicates that the major DSC peak in the NiP4 plating corresponds to similar transition processes regardless of the heating rate. The processes that contribute to the major exothermal peak in the DSC curve are discussed.
Article
Various composites with metals such as aluminum and copper, and carbons such as pitch based carbon fiber and carbon nanotube, and scale-like graphite have been prepared to realize high thermal conductive materials utilizing pulsed electric current sintering method. The composites have high thermal conductivity and one- or two-dimensional low thermal expansion coefficient.
Article
Interstitial solid solutions could be formed at the matrix–fibre interface in the processing of metal matrix composites. Typically these solutions are of small concentrations and the solubility is usually diffusion-controled. To calculate the diffusivity, a model of the interstitial solid solution is used which gives the possibility of choosing whether octahedral or tetrahedral interstitial positions are occupied by the fibre atoms dissolved in the matrix. Analysis of Ag–C and Cu–C solid solutions allow a comparison of the occupation of the interstitial positions and its temperature dependences. The results obtained on the basis of non-empirical calculations predict the preferable occupation of octahedral positions up to T ~ 1200 K. This confirms the structure of the interstitial solid solution. In the framework of this model we calculate the heights of diffusion barriers and the temperature dependences of carbon diffusion in silver and copper hosts.
Article
Copper/carbon nanofibre composites containing titanium varying from 0.3wt.% to 5wt.% were made, and their thermal conductivities measured using the laser flash technique. The measured thermal conductivities were much lower than predicted. The difference between measured and predicted values has often been attributed to limited heat flow across the interface. A study has been made of the composite microstructure using X-ray diffraction, transmission electron microscopy and Raman spectroscopy. It is shown in these materials, that the low composite thermal conductivity arises primarily because the highly graphitic carbon nanofibre structure transforms into amorphous carbon during the fabrication process.
Article
Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements were performed on an electroless plated Ni-P amorphous alloy to study the influence of different heat-treatments (linear heating and isothermal annealing). The phases formed after crystallization and the average grain size of the crystallization products were determined from XRD line broadening, and the heat evolved during the structural transformations were established from DSC measurements. A detailed study of the transformation products obtained along different heating routes was performed. From these studies, a scheme of the structural transformations and their energetics was constructed. The grain boundary energies in the different nanocrystalline states were also estimated. © 2001 The Electrochemical Society. All rights reserved.
Article
The variation with temperature of the a and c unti-cell dimensions of hexagonal Ceylon graphite has been measured over the temperature range 15°-800°c. by the X-ray powder method. At 14°6c., a=2.4562±0.0001 kx. c=6.6943±0.0007 kx. The carbon-carbon bond length, C-C=1.4210±0.0001a. The a dimension shows a slight contraction up to about 400°c., a small expansion occurring above this temperature. The thermal expansion in the c direction is large; the average value for a over the temperature range is 28.3 × 10-6. The complex nature of the expansion in both directions is discussed qualitatively.
Article
Between 30 and 290 K the thermal expansion of vitreous silica is shown to be particularly sensitive to thermal history. Values given for the linear coefficient α were determined relative to copper, and existing reference data for copper are discussed. α for silicon has also been measured relative to copper from 55 K to room temperature. Values of α at 283 K are reported for a number of samples of copper, and for Ag, Au, Al, Pt, Pd, MgO, NaCl and CaF2.
Article
A new expansion cell for the three-terminal capacitance method is developed. Length changes in the order of 10−9 cm can be measured at samples of only 4 mm. At first the expansion coefficient of silicon (reference material) is investigated in detail from 20 to 300 °K. The work is completed by interferometric measurements up to 800 °K. The temperature dependence of the expansion coefficient is discussed using the thermal equation of state. Furthermore conclusions are drawn concerning the contributions of different phonon branches and compared to calculations on the basis of well-known models. Zur Messung der thermischen Ausdehnung an kleinen Einkristallen wurde eine neue Meßzelle für die kapazitive Dreipunktmethode entwickelt. Damit können Längenänderungen von 10−9 cm an nur 4 mm langen Proben gemessen werden. Zunächst wurde der Ausdehnungskoeffizient von dem als Referenzmaterial verwendeten Silizium zwischen 20 und 300 °K eingehend untersucht. Die Ergebnisse wurden vervollständigt durch interferometrische Messungen bis zu 800 °K. Der Temperaturverlauf des Ausdehnungskoeffizienten wird an Hand der thermischen Zustandsgleichung ausgewertet. Ferner wurden die Beiträge verschiedener Phononen-Zweige untersucht und die Resultate mit Rechnungen auf der Grundlage bekannter Modelle verglichen.
Article
Amorphous alloy is thermodynamically unstable, and it crystallizes after heat treatment. Considering ordered clusters as crystalline nuclei in amorphous electroless nickel–phosphorus alloy, crystallization thermodynamics and growth controlled by diffusion of nuclei were studied in detail. Crystallization temperature is determined when the size of nuclei is equal to the critical grain size at a heating rate. The simulated crystallization temperatures of alloys with various phosphorus contents are examined by experiment and other investigations under like conditions.
Article
Tribological properties of carbon-nanotube-reinforced copper composites were investigated using a pin-on-disk test rig under dry conditions. The composites containing 4–16 vol% carbon nanotubes (CNTs) were fabricated by a powder-metallurgy technique. The tests were carried out at normal loads between 10 and 50 N, and the effect of volume fraction of CNTs on tribological behavior of the composites was examined. The composites revealed a low coefficient of friction compared with the copper matrix alloy. Due to the effects of the reinforcement and reduced friction, the wear rate of the composites decreased with increasing volume fraction of CNTs at low and intermediate loads. The composites with a high volume fraction of CNTs exhibited high porosity and their wear resistance decreased under high-load conditions.
Article
Epoxy composites based on vapor grown carbon fiber (VGCF) were fabricated and analyzed for room temperature thermophysical properties. An unprecedented high thermal conductivity of 695 W/m K for polymer matrix composites was obtained. The densities of all the composites are lower than 1.5 g/cc. In addition the high value of coefficient of thermal expansion (CTE) of the polymer material was largely reduced by the incorporation of VGCF. Also, unlike metal matrix composite (MMC), the epoxy composite has an electrically insulating surface. Based on the composite thermal conductivities, the room temperature thermal conductivity of VGCF, heat-treated at 2600°C, was estimated to be 1260 W/m K. Furthermore, the longitudinal CTE of the heat-treated VGCF was determined, for the first time, to be −1.5 ppm/K.
Article
The evolution of the thermal conductivity and the coefficient of thermal expansion as a function of the alloying content of boron and chromium in the copper matrix in Cu-X/diamond composites is presented. In both systems a transition from weak matrix/diamond bonding to strong bonding is observed, the latter leading concomitantly to high thermal conductivity (> 600 W m(-1) K-1) and a low coefficient of thermal expansion (< 10 ppm K-1). (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Article
Electroless plating has been successfully applied for nickel coatings on multiwall carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD). The samples before and after coating were checked using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that the coating process can be divided into two steps: nickel was first deposited as nanoparticles at the activated sites on the pre-treated surface of carbon nanotubes in the initial stage; it was then thickened later, as the reaction time increased and eventually formed a continuous layer. Finally a uniform Ni-layer on individual tubes with thickness of 20–40 nm can be obtained after coating. A simple model for the mechanism of the coating is also discussed.
Article
While sandwich construction offers well-known advantages for high stiffness with light weight, the problem of designing the sandwich structure to withstand localized loading, such as from accidental impact, remains an important problem. This problem is more difficult with lower stiffness cores, such as expanded foam. In the present study, experiments have been carried out on foam core sandwich beams with carbon/epoxy faces, under conditions of concentrated loading. The variables considered were the density of the foam and the relative thickness of the core. The common failure modes of sandwich structures were observed, including core failure in compression and shear, delamination, and fiber failure in the faces. These failure modes were systematically related to the test variables by means of a detailed stress analysis of the specimen, and a consideration of the failure properties of the constituent materials. The loading is characterized by localized high stress and strain concentrations that are not predicted in first-order shear deformation sandwich beam theory. The three-dimensional elasticity solution of Pagano was used to obtain the stress distributions. The strength prediction requires a detailed consideration of the localized nature of the loading, including the effects of strain gradients in the faces. The results show that failure modes and load levels can be predicted for sandwich structures under concentrated loading, but that accurate predictions require a consideration of the details of the concentrated loading. The results have a direct application in predicting the ability of sandwich structures to withstand localized loading such as from accidental impact.
  • K Chu
  • C C Jia
  • H Guo
  • W S Li
K. Chu, C.C. Jia, H. Guo, W.S. Li, On the thermal conductivity of Cu-Zr/diamond composites, Mater. Des. 45 (45) (2013) 36e42.
Nanocrystallization studies of an electroless plated Ni-P amorphous alloy
  • J Lendvai
  • J Or Anth
  • I Bakonyi
A. R ev esz, J. Lendvai, J. L or anth, J. P ad ar, I. Bakonyi, Nanocrystallization studies of an electroless plated Ni-P amorphous alloy, J. Electrochem. Soc. 148 (11) (2001) C715eC720.