Volume Fraction of Graphene Platelets in Copper-Graphene Composites

Copper-graphene composite films were deposited on copper foil using electrochemical deposition. Four electrolyte solutions that each consist of 250 mL of graphene oxide suspension in distilled water and increasing volume of 0.2 M solution of CuSO₄ in steps of 250 mL were used to deposit the composite films with and without a magnetic stirrer. Graphene oxide in the films was reduced to graphene by hydrogen treatment for 6 hours at 673 K (400 °C). The samples were characterized by X-ray diffraction for identification of phases, scanning electron microscopy for distribution of graphene, energy dispersive spectrometry for evaluation of elemental composition, electrical resistivity and temperature coefficient of electrical resistance and thermal conductivity. Effective mean field analysis (EMA) was used to determine the volume fraction and electrical conductivity of graphene and interfacial thermal conductance between graphene and copper. The electrical resistivity was reduced from 2.031 to 1.966 ???? cm and the thermal conductivity was improved from 3.8 to 5.0 W/cm K upon addition of graphene platelets to electrolytic copper. The use of stirrer during deposition of the films increased the average size and the thickness of the graphene platelets and as a result the improvement in electrical conductivity was lower compared to the values obtained without the stirrer. Using the EMA, the volume fraction of graphene platelets that was responsible for the improvement in the electrical conductivity was found to be lower than that for the improvement in the thermal conductivity. The results of the analysis are used to determine the volume fraction of the thinner and the thicker graphene platelets in the composite films.     

The Effects of Composition and Microstructure on the Thermal Conductivity of Liquid-Phase-Sintered W-Cu

Liquid-phase sintering of high-purity, submicron, co-reduced W-15Cu powders at temperatures of 1463 to 1623 K (1190 to 1350 °C) produces W grain sizes ranging from 0.6 to 1.2 μm while maintaining less than 2 pct porosity. Measured thermal conductivities of 185 to 221 W/(m·K) are related to the grain size and contiguity, which ranged from 0.51 to 0.62. The effects of composition and microstructure on thermal conductivity are further investigated with a model based on a computational cell that allows adjustment of the grain shape to produce selected matrix volume fractions and contiguities. The model considers porosity, the effects of transition metal impurities on the thermal conductivities of the W and Cu phases, and the role of an interfacial resistance between W grains. The effects of grain size and contiguity on thermal conductivity are shown for thermal boundary conductances ranging from 0 to 1.7 × 10¹⁰ W/(m²·K). Comparison of the model predictions with those of prior models, the experimental results, and previously reported thermal conductivities shows that impurities are highly detrimental to the thermal conductivity, but the thermal boundary conductance is a significant factor for high-purity W-Cu.     

Mechanical and Thermal Properties of Hot-Pressed ZrB2-SiC Composites

ZrB₂-SiC composites were hot pressed at 2473 K (2200 °C) with graded amounts (5 to 20 wt pct) of SiC and the effect of the SiC addition on mechanical properties like hardness, fracture toughness, scratch and wear resistances, and thermal conductivity were studied. Addition of submicron-sized SiC particles in ZrB₂ matrices enhanced mechanical properties like hardness (15.6 to 19.1 GPa at 1 kgf), fracture toughness (2 to 3.6 MPa(m)^1/2) by second phase dispersion toughening mechanism, and also improved scratch and wear resistances. Thermal conductivity of ZrB₂-SiC (5 wt pct) composite was higher [121 to 93 W/m K from 373 K to 1273 K (100 °C to 1000 °C)] and decreased slowly upto 1273 K (1000 °C) in comparison to monolithic ZrB₂ providing better resistance to thermal fluctuation of the composite and improved service life in UHTC applications. At higher loading of SiC (15 wt pct and above), increased thermal barrier at the grain boundaries probably reduced the thermal conductivity of the composite.     

金刚石表面改性及基体合金化对金刚石/铜复合材料导热性能的影响

以Pr₆O₁₁为刻蚀剂表面粗糙化处理金刚石颗粒,采用放电等离子烧结技术制备了金刚石/铜（硼）复合材料（金刚石体积分数为60.0%,硼体积分数为0.3%）,通过试验、热流密度模拟和声子谱计算研究了金刚石表面改性及基体硼合金化对金刚石/铜复合材料导热性能的影响。结果表明,粗糙化的金刚石界面增加了接触面积;在基体中添加硼元素,复合材料在烧结后出现B₄C相,B₄C相的形成改善了金刚石–铜两相界面结合状态。金刚石粗糙化与基体合金化两者的共同作用有效减少了界面热阻,优化了热通量传递的效率,提高了复合材料的导热性能。金刚石/铜复合材料热导率从421 W·m?1·K?1提高到了598 W·m?1·K?1,提升了近42%。     

SPS法制备SiC_P/Cu复合材料的研究

为了开发高导热低成本电子封装材料与器件,采用SPS方法制备了SiC/Cu复合材料,研究了SiC的粒径和体积分数对材料致密度和热导率的影响.结果表明:随着SiC体积分数的减少(从70%到50%),材料致密度逐渐提高;随着SiC粒径从40μm变化到14μm,材料的致密度提高.在材料未达到完全致密的情况下,材料的热导率主要受致密度的影响,SiC粒径的减小和体积分数的适宜降低对材料热导率的提高有利.此外,研究了对SiC进行化学镀铜对复合材料的影响.SiC化学镀铜改善了复合材料两相界面的润湿性,与未镀铜SiC相比,使样品相对密度提高了3%,热扩散系数提高了60%,热导率为167 W/(m·K).     

镀层对金刚石/玻璃复合材料性能的影响

为满足现代电子工业日益增长的散热需求,急需研究和开发新型高导热陶瓷（玻璃）基复合材料,而改善复合材料中增强相与基体的界面结合状况是提高复合材料热导率的重要途径.本文在对金刚石和镀Cr金刚石进行镀Cu和控制氧化的基础上,利用放电等离子烧结方法制备了不同的金刚石增强玻璃基复合材料,并观察了其微观形貌和界面结合状况,测定了复合材料的热导率.实验结果表明:复合材料中金刚石颗粒均匀分布于玻璃基体中,Cu/金刚石界面和Cr/Cu界面分别是两种复合材料中结合最弱的界面;复合材料的热导率随着金刚石体积分数的增加而增加;金刚石/玻璃复合材料的热导率随着镀Cu层厚度的增加而降低,由于镀Cr层实现了与金刚石的化学结合以及Cr在Cu层中的扩散,镀Cr金刚石/玻璃复合材料的热导率随着镀Cu层厚度的增加而增加.当金刚石粒径为100μm、体积分数为70%及镀Cu层厚度为约1.59μm时,复合材料的热导率最高达到约91.0 W·m-1·K-1.      

Effects of Processing Parameters on the Fabrication of Copper Cladding Aluminum Rods by Horizontal Core-Filling Continuous Casting

Copper cladding aluminum (CCA) rods with a diameter of 30 mm and a sheath thickness of 3 mm were fabricated by horizontal core-filling continuous casting (HCFC) technology. The effects of key processing parameters, such as the length of the mandrel tube of composite mold, aluminum casting temperature, flux of the secondary cooling water, and mean withdrawing speed were optimized based on some quality criteria, including the uniformity of the sheath thickness, integrality of the rods, and thickness of the interface. The causes of internal flaws formation of CCA rods were also discussed. The results showed that the continuity of the liquid aluminum core-filling process and the interface reaction control between solid copper and liquid aluminum were two key problems that strongly affected the stability of the casting process and the product quality. Our research indicated that for the CCA rod with the previously mentioned size, the optimal length of mandrel tube was 210 mm. A shorter mandrel tube allowed of easier erosion at the interface, which led to a nonuniform sheath thickness. Conversely, it tended to result in a discontinuous filling process of liquid aluminum, which causes shrinkage or cold shuts. The optimal casting temperatures of copper and aluminum were 1503 K (1230 °C) and 1043 K to 1123 K (770 °C to 850 °C), respectively. When the casting temperature of aluminum was below 1043 K (770 °C), the casting process would be discontinuous, resulting in shrinkages or cold shuts. Nevertheless, when the casting temperature of aluminum was higher than 1123 K (850 °C), a severe interface reaction between solid copper and liquid aluminum would occur. The proper flux of the secondary cooling water and the mean withdrawing speed were determined as 600 to 800 L/h and 60 to 87 mm/min, respectively. In the previously mentioned proper ranges of processing parameters, the interfacial shear strengths of CCA rods were 40.5 to 67.9 MPa.     

Fabrication,microstructures and properties of 50 vol.-% SiCp/6061Al composites via a pressureless sintering technique

Commercial F500 SiC powder and 6061 Al powder were chosen to fabricate the 50?vol.-% SiCp/6061Al composites via pressureless sintering. Effects of pre-treatment of the SiC powder and sintering temperature on the microstructures and properties of the composites were studied. Densification mechanism and interfacial reaction of the composites were also investigated. The results show that the composites have a high sintering ability and a low interfacial reaction activity. The density, bending strength and thermal conductivity of the composites are all sensitive to the sintering temperature. The composites sintered at 680°C are nearly fully dense and have the following optimal properties: the relative density of 98.5%, the bending strength of 495?MPa, the TC of 153?W/(m?K) and the coefficient of thermal expansion of 8.1?×?10^?6/°C (50–100°C), which are superior to most of the SiCp/Al composites of the similar composition reported previously.     

镀钛金刚石增强玻璃基复合材料的性能

现代电子封装迫切需要开发新型高导热陶瓷（玻璃）基复合材料.本文在对镀钛金刚石进行镀铜和控制氧化的基础上,利用放电等离子烧结方法制备了金刚石增强玻璃基复合材料,并观察了其微观形貌和界面结合情况,测定了复合材料的热导率和热膨胀系数.实验结果表明:复合材料微观组织均匀,Ti/金刚石界面是复合材料中结合最弱的界面,复合材料的热导率随着金刚石粒径和含量的增大而增加,而热膨胀系数随着金刚石含量的增加而降低.当金刚石粒径为100 μm、体积分数为70%时,复合材料热导率最高达到了40.2 W·m-1·K-1,热膨胀系数为3.3×10-6K-1,满足电子封装材料的要求.      

石墨烯化学镀铜及其对石墨烯/铜基复合材料组织性能的影响

以还原氧化石墨烯（reduced graphene oxide,RGO）和CuSO₄·5H₂O为主要原料,通过化学镀法得到铜包覆RGO复合粉体,再与铜粉混合得到含有不同质量分数RGO（0.2%、0.4%、0.6%、0.8%）的RGO/Cu粉末混合料,经压制及烧结得到RGO/Cu复合材料。通过X射线衍射仪（X-ray diffraction,XRD）、拉曼光谱仪（Raman spectroscopy,RS）和场发射扫描电镜（field emission scanning electron microscope,FESEM）等对RGO/Cu复合材料的微观组织和相关性能进行测试分析,并与由未镀铜处理的RGO所制备的RGO/Cu复合材料的组织性能进行对比。结果表明,经化学镀处理的RGO在RGO/Cu复合材料中分布较均匀,而未镀铜处理的RGO在基体中发生明显的团聚。RGO/Cu复合材料的导电导热性随石墨烯加入量的增加有所下降,但石墨烯的加入可有效提高RGO/Cu复合材料的力学性能,且由镀铜RGO所制备的RGO/Cu复合材料的性能要优于由未处理RGO所制备的RGO/Cu复合材料的性能。此外,RGO加入量对复合材料性能也有明显影响,当添加RGO质量分数为0.4%时,由镀铜RGO所制备的RGO/Cu复合材料的综合性能达到最好,其电导率达95.01% IACS,热导率达415.5W·（m·K）-1,而压缩屈服强度和抗拉强度分别为156.73 MPa和268.62 MPa,较相同工艺条件制备的纯铜的屈服强度（75 MPa）和抗拉强度（234.64 MPa）提升了109%和14.48%。     

Thermal conductivity and thermal expansion of graphite fiber-reinforced copper matrix composites

The high specific conductivity of graphite fiber/copper matrix (Gr/Cu) composites offers great potential for high heat flux structures operating at elevated temperatures. To determine the feasibility of applying Gr/Cu composites to high heat flux structures, composite plates were fabricated using unidirectional and cross-plied pitch-based P-100 graphite fibers in a pure copper matrix. Thermal conductivity of the composites was measured from room temperature to 1073 K, and thermal expansion was measured from room temperature to 1050 K. The longitudinal thermal conductivity, parallel to the fiber direction, was comparable to pure copper. The transverse thermal conductivity, normal to the fiber direction, was less than that of pure copper and decreased with increasing fiber content. The longitudinal thermal expansion decreased with increasing fiber content. The transverse thermal expansion was greater than pure copper and nearly independent of fiber content. formerly with NASA Lewis Research Center, is retired David L. McDanels, This article is based on a presentation made in the symposium “High Performance Copper-Base Materials” as part of the 1991 TMS Annual Meeting, February 17–21, 1991, New Orleans, LA, under the auspices of the TMS Structural Materials Committee.     

Thermal-Treated Pitches as Binders for TiB2/C Composite Cathodes

The effect of thermal treatment on the microstructure and properties of pitches and thermal-treated, pitch-based TiB₂/C composite cathodes were investigated. Thermal treatments were performed at 473 K, 523 K, 573 K, 623 K, and 673 K (200 °C, 250 °C, 300 °C, 350 °C, and 400 °C), respectively. The results show that the aromaticity of the treated pitches increases with an increasing thermal treatment temperature, and subsequently, the coking value and quinoline-insoluble (QI) content increase from 60.62 wt pct to 79.09 wt. pct and from 8.97 wt pct to 32.54 wt pct when the treatment temperature increases from 473 K to 623 K (200 °C to 350 °C). The volume fraction of coalesced mesophase in semicoke decreases with an increasing thermal treatment temperature, and after 673 K (400 °C) is reached, the coalesced mesophase is almost invisible. The bulk density and compressive strength of modified pitch-based cathodes increase with an increasing thermal treatment temperature from 2.24 g cm⁻³ to 2.39 g cm⁻³ and from 24.21 MPa to 54.85 MPa, whereas open porosity decreases from 34.62 pct to 27.06 pct. Both electrical resistivity and electrolysis expansion ratio first decrease and then increase with an increasing thermal treatment temperature, and the lowest values (45.63 μΩ m and 0.65 pct) are achieved at 573 K (300 °C). Compared with those of the parent pitch-based cathode, the properties of the modified pitch-based cathodes had improved significantly. The mechanisms of the improvements are discussed in the text.     

Mechanical and Thermal Properties of Pulsed Electric Current Sintered (PECS) Cu-Diamond Compacts

In this work, dispersion strengthening of copper by diamonds is explored. In particular, the influence of 50- and 250-nm diamonds at contents of 3 and 6 vol. pct on the mechanical and thermal properties of pulsed electric current sintered (PECS) Cu composites is studied. The composite powders were prepared by mechanical alloying in argon atmosphere using a high-energy vibratory ball mill. The PECS compacts prepared had high density (>97 pct of T.D.) with quite evenly distributed diamonds. The effectiveness of dispersoids in increasing the microhardness was more pronounced at a smaller particle size and larger volume fraction, explained by Hall–Petch and Orowan strengthening models. The microhardness of Cu with 6 and 3 vol. pct nanodiamonds and pure sm-Cu (submicron-sized Cu) was 1.77, 1.46, and 1.02 GPa, respectively. In annealing experiments at 623 K to 873 K (350 °C to 600 °C), the composites with 6 vol. pct dispersoids retained their hardness better than those with less dispersoids or sm-Cu. The coefficient of thermal expansion was lowered when diamonds were added, being the lowest at about 14 × 10^?6 K^?1 between 473 K and 573 K (200 °C and 300 °C). Good bonding between the copper and diamond was qualitatively demonstrated by nanoindentation. In conclusion, high-quality Cu-diamond composites can be produced by PECS with improved strength and better thermal stability than for sm-Cu.     

Al2O3含量对放电等离子烧结Al2O3/Cu复合材料组织与性能的影响

以微米级Cu粉为基体相,纳米Al₂O₃颗粒为绝缘相,采用机械球磨和放电等离子烧结工艺相结合的方法制备Al₂O₃/Cu复合材料,研究Al₂O₃含量对复合材料微观结构、电阻率和热导率的影响。结果表明,Al₂O₃/Cu复合材料为核?壳结构,随Al₂O₃含量增加,Al₂O₃包覆层对Cu基体的包覆效果逐渐提升;当w(Al₂O₃)为5%时,Al₂O₃/Cu复合材料的热导率较高,为85.92 W/(m·K),但电阻率偏低,仅为12.6 mΩ·cm。当w(Al₂O₃)增加至15%时,虽然Al₂O₃/Cu复合材料的密度降至6.69 g/cm³,孔隙率较高,但电阻率显著提高至2.09×10⁸ mΩ·cm,约为Cu电阻率的10¹¹倍,且热导率为7.6 W/(m·K),明显高于传统金属基板的热导率。     

Influence of Microstructure on Microhardness of Fe81Si4B13C2 Amorphous Alloy after Thermal Treatment

The influence of microstructure, and its changes, on microhardness of the amorphous Fe₈₁Si₄B₁₃C₂ alloy after thermal treatment at different temperatures from 298 K to 973 K (25 °C to 700 °C) was studied. The as-prepared alloy ribbon containing a small amount of crystalline phases, as well as domains of short-range crystalline ordering embedded in the amorphous matrix, exhibits unexpectedly high microhardness, mostly due to its composition. After thermal treatment above 723 K (450 °C), the alloy samples begin to crystallize, creating a nanocomposite structure involving nanocrystals embedded in an amorphous matrix, leading to an increase in microhardness. Further growth of the nanocrystals, as the heating temperature was increased to 973 K (700 °C), caused the change from nanocomposite structure into a more granulated and porous structure, with a dominant type of interface changing from amorphous/crystal to crystal/crystal, leading to a decrease in microhardness.     

Cosintering of Powder Injection Molding Parts Made from Ultrafine WC-Co and 316L Stainless Steel Powders for Fabrication of Novel Composite Structures

Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (>4 pct) is developed in the temperature range of 1080 °C to 1350 °C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the mismatch strain to <2 pct. Meanwhile, WC is decomposed at the contact area and the diffusion of C and Co into the iron lattice results in the formation of a liquid and MC and M₆C carbides at 1220 °C. Spreading of the liquid accelerates the reaction, affecting the dimensional stability of the PIM parts. To prevent the reaction, surface oxidation of the cemented carbide followed by hydrogen reduction during sintering was examined. Although the amount of mismatch strain increased, formation of a metallic interface consisting of a W-Co alloy (45 to 50 at. pct Co) and a Co-rich iron alloy (18 at. pct Co) prevented the decomposition of WC and melt formation. It is also shown that the deposition of a thin Ni layer after thermal debinding decreases the mismatch stresses through melt formation, although interlayer diffusion causes pore-band formation close to the steel part.     

Effects of Aging Temperature on Electrical Conductivity and Hardness of Cu-3 at. pct Ti Alloy Aged in a Hydrogen Atmosphere

To improve the balance of the electrical conductivity and mechanical strength for dilute Cu-Ti alloys by aging in a hydrogen atmosphere, the influence of aging temperature ranging from 673 K to 773 K (400 °C to 500 °C) on the properties of Cu-3 at. pct Ti alloy was studied. The Vickers hardness increases steadily with aging time and starts to fall at 3 hours at 773 K (500 °C), 10 hours at 723 K (450 °C), or over 620 hours at 673 K (400 °C), which is the same as the case of conventional aging in vacuum. The maximum hardness increases from 220 to 236 with the decrease of aging temperature, which is slightly lower than aging at the same temperature in vacuum. The electrical conductivity at the maximum hardness also increases from 18 to 32 pct of pure copper with the decrease of the temperature, which is enhanced by a factor of 1.3 to 1.5 in comparison to aging in vacuum. Thus, aging at 673 K (400 °C) in a hydrogen atmosphere renders fairly good balance of strength and conductivity, although it takes nearly a month to achieve. The microstructural changes during aging were examined by transmission electron microscopy (TEM) and atom-probe tomography (APT), and it was confirmed that precipitation of the Cu₄Ti phase occurs first and then particles of TiH₂ form as the third phase, thereby efficiently removing the Ti solutes in the matrix.     

Copper alloy-impregnated carbon-carbon hybrid composites for electronic packaging applications

Porous carbon-carbon preforms, based on three-dimensional networks of PAN (Polyacrylonitrile)-based carbon fibers and various volume fractions of chemical vapor-deposited (CVD) carbon, were impregnated by oxygen-free, high-conductivity (OFHC) Cu, Cu-6Si-0.9Cr, and Cu-0.3Si-0.3Cr (wt pct) alloys by pressure infiltration casting. The obtained composites were characterized for their coefficient of thermal expansion (CTE) and thermal conductivity (K) along the through-thickness and two in-plane directions. One composite, with a 28 vol pct Cu-0.3Si-0.3Cr alloy, showed outstanding potential for thermal management applications in electronic applications. This composite exhibited approximately isotropic thermal expansion properties (CTE=4 to 6.5 ppm/K) and thermal conductivities (k≥260 W/m K).     

The Influence of a TiN Film on the Electronic Contribution to the Thermal Conductivity of a TiC Film in a TiN-TiC Layer System

TiC and TiN films were deposited by reactive magnetron sputtering on Si substrates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization of the microstructure and interface structure have been carried out and the stoichiometric composition of TiC is determined. Thermal conductivity and interface thermal conductance between different layers in the films are evaluated by the transient thermo reflectance (TTR) and three-omega (3-ω) methods. The results showed that the thermal conductivity of the TiC films increased with temperature. The thermal conductivity of TiC in the absence of TiN is dominated by phonon contribution. The electronic contribution to the thermal conductivity of TiC in the presence of TiN is found to be more significant. The interface thermal conductance of the TiC/TiN interface is much larger than that of interfaces at Au/TiC, TiC/Si, or TiN/Si. The interface thermal conductance between TiC and TiN is reduced by the layer formed as a result of interdiffusion.