Low-temperature heat conduction characteristics of diamond/Cu composite by pressure infiltration method

In this paper,diamond/CuCr and diamond/CuB composites were prepared using the pressure infiltration method.The physical property measurement system(PPMS)was adopted to evaluate the thermal conductivity of diamond/Cu and MoCu composites within the range of100–350 K,and a scanning electron microscope(SEM)was utilized to analyze the microstructure and fracture appearance of the materials.The research indicates that the thermal conductivity of diamond/Cu composite within the range of100–350 K is 2.5–3.0 times that of the existing MoCu material,and the low-temperature thermal conductivity of diamond/Cu composite presents an exponential relationship with the temperature.If B element was added to a Cu matrix and a low-temperature binder was used for prefabricated elements,favorable interfacial adhesion,relatively high interfacial thermal conductivity,and favorable low-temperature heat conduction characteristics would be apparent.

Effect of sintering parameters on the microstructure and thermal conductivity of diamond/Cu composites prepared by high pressure and high temperature infiltration

Pure Cu composites reinforced with diamond particles were fabricated by a high pressure and high temperature （HPHT） infiltration technique. Their microstructural evolution and thermal conductivity were presented as a function of sintering parameters （temperature, pressure, and time）. The improvement in interfacial bonding strength and the maximum thermM conductivity of 750 W/（m.K） were achieved at the optimal sintering parameters of 1200℃, 6 GPa and 10 min. It is found that the thermal conductivity of the composites depends strongly on sintering pressure. When the sintering pressure is above 6 GPa, the diamond skeleton is detected, which greatly contributes to the excellent thermal conductivity.

Effect of sintering on the relative density of Cr-coated diamond/Cu composites prepared by spark plasma sintering

Cr-coated diamond/Cu composites were prepared by spark plasma sintering. The effects of sintering pressure, sintering temperature, sintering duration, and Cu powder particle size on the relative density and thermal conductivity of the composites were investigated in this paper. The influence of these parameters on the properties and microstructures of the composites was also discussed. The results show that the relative density of Cr-coated diamond/Cu reaches ~100% when the composite is gradually compressed to 30 MPa during the heating process. The densification temperature increases from 880 to 915℃ when the diamond content is increased from 45vol% to 60vol%. The densification temperature does not increase further when the content reaches 65vol%. Cu powder particles in larger size are beneficial for increasing the relative density of the composite.

Thermal Physical Properties of Al-coated Diamond/Cu Composites

To acquire a well bonded interface between the copper and the diamond particles in diamondcopper matrix composites, an available process to apply a vapor deposited aluminum（Al） coating onto diamond particles was used to solve this interfacial problem. The diamond-copper matrix composites were prepared by spark plasma sintering（SPS） process and the effect of Al-coated diamond particles was demonstrated. The experimental results showed that the densification, interfacial bonding and thermal conductivity of Al-coated composites were evidently improved compared to those of the uncoated composites. A maximum thermal conductivity（TC） of 565 W/（m·K） was obtained in the coated composite containing 50vol% diamond particles sintered at 1163 K. Additionally, the experimental data of thermal conductivity and coefficient of thermal expansion（CTE） were compared with the predictions from several theoretical models.

Effects of diamond particle size on microstructure and properties of diamond/Al-12Si composites prepared by vacuum-assisted pressure infiltration

Diamond/aluminium composites have attracted attention in the field of thermal management of electronic packaging for their excellent properties.In order to solve the interfacial problem between diamond and aluminium,a novel process combining pressure infiltration with vacuum-assisted technology was proposed to prepare diamond/aluminum composites.The effect of diamond particle size on the microstructure and properties of the diamond/Al-12Si composites was investigated.The results show that the diamond/Al-12Si composites exhibit high relative density and a uniform microstructure.Both thermal conductivity and coefficient of thermal expansion increase with increasing particle size,while the bending strength exhibits the opposite trend.When the average diamond particle size increases from 45μm to 425μm,the thermal conductivity of the composites increases from 455 W·m^(-1)·K^(-1)to 713 W·m^(-1)·K^(-1)and the coefficient of thermal expansion increases from 4.97×10^(-6)K^(-1)to 6.72×10^(-6)K^(-1),while the bending strength decreases from 353 MPa to 246 MPa.This research demonstrates that high-quality composites can be prepared by the vacuum-assisted pressure infiltration process and the thermal conductivity of the composites can be effectively improved by increasing the diamond particle size.

Investigation on the Novel High-performance Copper/Graphene Composite Conductor for High Power Density Motor

High-performance Cu/Graphene composite wire synergistically strengthened by nano Cr_(3)C_(2) phase was directly synthesized via hot press sintering followed by severe cold plastic deformation, using liquid paraffin and CuCr alloy powder as the raw materials. Since graphene is in situ formed under the catalysis of copper powder during the sintering process, the problem that graphene is easy to agglomerate and difficult to disperse uniformly in the copper matrix has been solved. The nano Cr_(3)C_(2)-particles nailed at the interface favor to improve the interface bonding. The Cu/Graphene composite possesses high electrical conductivity, hardness, and plasticity. The composite wire exhibits high electrical conductivity of 96.93% IACS, great tensile strength of 488MPa, and excellent resistance to softening. Even after annealing at 400℃ for 1 h, the tensile strength can still reach 268 MPa with a conductivity of about 99.14% IACS.The wire's temperature coefficient of resistance(TCR) is largely reduced to 0.0035/℃ due to the complex structure,which leads the wire to present low resistivity at higher temperatures. Such Cu/Graphene composite wire with excellent comprehensive performance has a good application prospect in high-power density motors.

Selective interfacial bonding and thermal conductivity of diamond/Cu-alloy composites prepared by HPHT technique

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature （HPHT） sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, 13, and Ti. The thermal conductivity （TC） oh- mined exhibited as high as 688 W.m-1.K-1, but also as low as 325 W.m-1.K-l. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification.

Pressure infiltrated Cu/diamond composites for LED applications

Diamond reinforced copper （Cu/diamond） composites were prepared by a pressure infilla＇ation technique. The composites show a super high conductivity of 713 W.m-1.K-1 in combination with an extremely low coefficient of thermal expansion （CTE） of 7.72 × 10-6 K-1 （25-100℃）, which are achieved by modifying the copper matrix with adding 0.3 wt.% of boron to get a good thermal contact between the matrix and the diamond particles. By adopting a series of postmachining techniques the composites were made into near-net-shape parts, and an electroless silver coating was also successfully plated on the composites. Finally, their potential applications in the thermal management of fight emitting diodes （LED） were illustrated via prototype examples.

Effect of carbide formers on microstructure and thermal conductivity of diamond-Cu composites for heat sink materials

Diamond-copper composites were prepared by powder metallurgy,in which the diamond particles were pre-coated by magnetic sputtering with copper alloy containing a small amount of carbide forming elements(including B,Cr,Ti,and Si).The influence of the carbide forming element additives on the microstructure and thermal conductivity of diamond composites was investigated.It is found that the composites fabricated with Cu-0.5B coated diamond particles has a relatively higher density and its thermal conductivity approaches 300 W/(m·K).Addition of 0.5%B improves the interfacial bonding and decreases thermal boundary resistance between diamond and Cu,while addition of 1%Cr makes the interfacial layer break away from diamond surface.The actual interfacial thermal conductivity of the composites with Cu-0.5B alloy coated on diamond is much higher than that of the Cu-1Cr layer,which suggests that the intrinsic thermal conductivity of the interfacial layer is an important factor for improving the thermal conductivity of the diamond composites.

Thermodynamic and kinetic study on interfacial reaction and diamond graphitization of Cu Fe-based diamond composite

Cu-Fe based diamond composites used for saw-blade segments are directly fabricated by vacuum and pressureassisted sintering. The carbide forming elements Cr and Ti are added to improve interfacial bonding between diamond and the Cu-Fe matrix. The interfacial reactions between diamond/graphite and Cr or Ti, and diamond graphitization are investigated by thermodynamics/kinetics analyses and experimental methods. The results show that interfacial reactions and graphitization of diamond can automatically proceed thermodynamically. The Cr3C2, Cr7C3, Cr23C6, and TiC are formed at the interfaces of composites by reactions between diamond and Cr or Ti; diamond graphitization does not occur because of the kinetic difficulty at 1093 K under the pressure of 13 MPa.

Effect of Boron Addition on the Thermal Properties of Diamond-Particle-Dispersed Cu-Matrix Composites Fabricated by SPS

Diamond particle dispersed copper (Cu) matrix composites were fabricated from the powder mixture composed of diamond, pure-Cu and boron (B) by spark plasma sintering (SPS). The composites were consolidated at 1173 K for 600 s by SPS. The reaction between the diamond particle and the Cu matrix in the composite was not confirmed by SEM observation and X-ray diffraction (XRD) analysis. The relative packing density of the Cu/diamond composites increased with B addition and attained 93.2% - 95.8% at the B content range between 1.8 vol.% and 13.8 vol.%. The thermal conductivity of the diamond-dispersed Cu composite drastically increased with B addition and reached the maximum value of 689 W/mK at 7.2 vol% B. Numerous transgranular fractures of diamond particles were observed on bending fracture surfaces of Cu-B/diamond composites. This indicates strong bonding between the diamond particle and the Cu matrix in the composite. The coefficient of thermal expansion of the composite falls in the upper line of Kerner’s model.

Evolution of thermo-physical properties of diamond/Cu composite materials under thermal shock load

In this paper, the two-flume method was used to study the change laws of the thermal conductivity and thermal expansion coefficient of diamond/Cu composite materials with 100, 300, and 500 cycle numbers, under the action of thermal shock load between-196 and 85 °C; the X-ray diffraction method（XRD） was used to study the change of the residual stress in the thermal shock process of the diamond/Cu composite materials; and the evolution of the fracture microstructure with different thermal shock cycle numbers was observed through scanning electron microscopy（SEM）. The results of the study show that the increase of the binder residue at the interface reduces the thermal shock stability of the diamond/Cu composite materials. In addition, under the thermal shock load between-196 and 85 °C, the residual stress of the diamond/Cu composite materials increases continuously with the increase of the cycle numbers, the increase of residual stress leads to a small amount of interface debonding, an increase of the interfacial thermal resistances, and a decrease of the constraints of low-expansion component on material deformation, thus the thermal conductivity decreases slightly and the thermal expansion coefficient increases slightly.

Cu-Diamond复合材料的多次电弧烧蚀性能研究

采用真空热压烧结法制得金刚石分布均匀,且与铜基结合良好的Cu-Diamond复合材料(金刚石体积分数为5%)。在空气气氛中对Cu-5vol.%Diamond复合材料进行多次电弧烧蚀,通过场发射扫描电子显微镜(SEM)和三维激光共聚焦显微镜(3D LSCM)对烧蚀表面进行观察分析,利用能谱仪(EDS)和X射线光电子能谱仪(XPS)对烧蚀后的成分进行分析,结果表明,经过100次9 kV高电压电弧烧蚀后,复合材料烧蚀区域中的铜基体出现熔化和溅射,并被氧化成了CuO和Cu_(2)O,同时金刚石颗粒较大幅度提高了该复合材料的抗电弧烧蚀能力。

Si调控Cu-20Sn-15Ti钎料显微组织与性能的演变行为

为通过成分调控改善Cu-Sn-Ti钎料的显微组织及性能,采用扫描电子显微镜、X射线衍射仪及EDS能谱分析等设备,研究了Si对Cu-20Sn-15Ti钎料显微组织与性能的影响规律。结果表明:Cu-20Sn-15Ti钎料的显微组织为大尺寸多边形状CuSn_(3)Ti_(5)相、共晶组织和α-Cu相。添加少量的Si(质量分数≤2.0%)可细化钎料中多边形状CuSn_(3)Ti_(5)相,并生成小尺寸Si_(3)Ti_(5)相,较多的Si(质量分数≥3.0%)会造成多边形状CuSn_(3)Ti_(5)相分化离散、共晶组织粗化减少,Si_(3)Ti_(5)相含量增加且粗化,当Si含量增至5.0%时,钎料不再生成多边形状CuSn_(3)Ti_(5)相和共晶组织,Ti主要用于生成Ti_(5)Si_(3)相,显微组织主要为Ti_(5)Si_(3)相、α-Cu相、Cu41Sn11相和少量条状CuSn_(3)Ti_(5)相;与Cu、Sn相比,Si与Ti具有更强的化学亲和力,Si优先与Ti反应生成Ti_(5)Si_(3)相;Ti_(5)Si_(3)相的三维组织形貌为棱柱状,且呈团聚附生特征,粗条状Ti_(5)Si_(3)相具有中心或侧面孔洞缺陷,孔洞的形成主要与其生长机制有关;随着Si含量的增加,钎料的剪切强度呈“升高-降低-升高”的趋势,断口形貌由准解理断裂和解理断裂的混合形态向解理断裂转变;CuSn_(3)Ti_(5)相易破碎开裂成为起裂源,不同粗大状态CuSn_(3)Ti_(5)相的存在均在一定程度上恶化钎料剪切强度。

三维互穿结构Cu-W触头抗熔焊机理

触头闭合回跳电弧引起的开关电器动熔焊问题,直接影响大功率接触器的电寿命和可靠性。为此设计了2种三维互穿有序结构的四边形和菱形十二面体的Cu-W复合材料触头,围绕触头动熔焊过程中的电弧、熔池、液滴溅射及凝固相变降温等问题,建立触头熔池流体动力学模型和冷凝降温数学模型,研究了2种有序结构和商用无序结构的触头阳极在闭合回跳电弧作用下熔化温度分布、熔池喷溅形貌和接触区域金属凝固过程,通过模拟熔焊实验平台进行了熔焊力验证。结果表明,通过调节三维互穿有序W骨架结构,能够有效抑制熔池扩散和液态金属喷溅,并降低熔焊力,从而提高Cu-W复合材料的抗熔焊性能。

晶粒尺寸对界面含Cr-O-C防黏层Cu/Ni复合体拉伸性能的影响

通过分子动力学方法研究含Cr-O-C防黏层的具有不同晶粒尺寸的Cu/Ni复合体的拉伸变形。结果表明:当Cu/Ni复合体的晶粒尺寸大于12 nm时,不论界面不含Cr、O和C原子或含有定量Cr、O和C原子,复合体的屈服强度随着晶粒尺寸的减小呈现增大趋势,符合细晶强化规律,晶粒塑性变形主要受晶体内部的位错滑移控制,最大应力增加9.52%;当晶粒尺寸小于12 nm时,由于晶界所占比例的增加,拉伸过程的塑性变形更多受晶界变形控制,屈服强度下降。Cr-O-C界面弱化了Cu/Ni复合体的强度,随着界面上Cr、O和C原子数量的增加,Cu/Ni复合体的抗拉强度随之降低,最大应力下降56.40%,Cu/Ni复合体内部的位错数量也随之降低,转移到Ni表面的Cu原子数量随之减少。

Lightweight diamond/Cu interface tuning for outstanding heat conduction

With rapid developments in the field of very large-scale integrated circuits,heat dissipation has emerged as a significant factor that restricts the high-density integration of chips.Due to their high thermal conductivity and low thermal expansion coefficient,diamond/Cu composites have attracted considerable attention as a promising thermal management material.In this study,a surface tungsten carbide gradient layer coating of diamond particles has been realized using comprehensive magnetron sputtering technology and a heat treatment process.Diamond/Cu composites were prepared using high-temperature and high-pressure technology.The results show that,by adjusting the heat treatment process,tungsten carbide and di-tungsten carbide are generated by an in situ reaction at the tungsten–diamond interface,and W–WC–W_(2)C gradient layer-coated diamond particles were obtained.The diamond/Cu composites were sintered by high-temperature and high-pressure technology,and the density of surface-modified diamond/Cu composites was less than 4 g cm^(-3).The W–WC–W_(2)C@diamond/Cu composites have a thermal diffusivity as high as 331 mm^(2)s^(-1),and their thermal expansion coefficient is as low as 1.76×10^(-6)K^(-1).The interface coherent structure of the gradient layer-coated diamond/copper composite can effectively improve the interface heat transport efficiency.

Preparation of nanosized W/Cu composite powder by sol-gel technique

Cu(NO3)(2) and (NH4)(6)H(2)W(12)O(40)center dot 4H(2)O were used to prepare W/Cu nanosized composite powder by sol-gel technique. The influences of heat treatment process, pH value of the solution and the amount of an addition agent on particle size were investigated by DSC, XRD and TEM. The results show that, at a certain heat treatment temperature, the W/Cu nanoparticle size increases with the pH value or the amount of the addition agent increasing.

Predicted interfacial thermal conductance and thermal conductivity of diamond/Al composites with various interfacial coatings

The interfacial thermal conductance （ITC） and thermal conductivity （TC） of diamond/Al composites with various coatings were theoretically studied and discussed. A series of predictions and numerical analyses were performed to investigate the effect of thickness, sound velocity, and other parameters of coating layers on the ITC and TC. It is found that both the ITC and TC decline with increasing coating thickness, especially for the coatings with relatively low thermal conductivity. Nevertheless, if the coating thickness is close to zero, or quite a small value, the ITC and TC are mainly determined by the constants of the coating material. Under this condition, coatings such as Ni, TiC, Mo 2 C, SiC, and Si can significantly improve the ITC and TC of diamond/Al composites. By contrast, coatings like Ag will exert the negative effect. Taking the optimization of interfacial bonding into account, conductive carbides such as TiC or Mo 2 C with low thickness can be the most suitable coatings for diamond/Al composites.