Effects of boron on the microstructure and thermal properties of Cu/diamond composites prepared by pressure infiltration

Diamond reinforced copper (Cu/diamond) composites were prepared by pressure infiltration for their application in thermal management where both high thermal conductivity and low coefficient of thermal expansion (CTE) are important. They were characterized by the microstructure and thermal properties as a function of boron content, which is used for matrix-alloying to increase the interfacial bonding between the diamond and copper. The obtained composites show high thermal conductivity (>660 W/(m·K)) and low CET (<7.4×10-6 K-1) due to the formation of the B₁₃C₂ layer at the diamond-copper interface, which greatly strengthens the interfacial bonding. Thermal property measurements indicate that in the Cu-B/diamond composites, the thermal conductivity and the CTE show a different variation trend as a function of boron content, which is attributed to the thickness and distribution of the interfacial carbide layer. The CTE behavior of the present composites can be well described by Kerner’s model, especially for the composites with 0.5wt% B.     

SiC颗粒特性对无压熔渗SiCp/Al复合材料热物理性能的影响

采用粉末注射成形-无压熔渗相结合技术制备出了电子封装用高体积分数SiCp/Al复合材料. 重点研究了SiC粒径、体积分数以及粒径大小等颗粒特性对所制备复合材料热物理性能的影响规律. 研究结果表明,SiCp/Al复合材料的热导率随SiC粒径的增大和体积分数的增加而增加;SiC粒径的大小对复合材料的热膨胀系数(CTE)没有显著的影响,而其体积分数对CTE的影响较大. CTE随着SiC颗粒体积分数的增加而减小,CTE实验值与基于Turner模型的预测值比较接近. 通过对不同粒径的SiC粉末进行级配,可以实现体积分数在53%～68%、CTE(20～100℃)在7.8×10-6～5.4×10-6K-1、热导率在140～190W·m·K-1范围内变化.     

机械合金化法制备的Cu/SiC纳米复合材料的组织、热性能和力学性能评估

Nano-sized silicon carbide (SiC: 0wt%, 1wt%, 2wt%, 4wt%, and 8wt%) reinforced copper (Cu) matrix nanocomposites were manufactured, pressed, and sintered at 775 and 875°C in an argon atmosphere. X-ray diffraction (XRD) and scanning electron microscopy were performed to characterize the microstructural evolution. The density, thermal expansion, mechanical, and electrical properties were studied. XRD analyses showed that with increasing SiC content, the microstrain and dislocation density increased, while the crystal size decreased. The coefficient of thermal expansion (CTE) of the nanocomposites was less than that of the Cu matrix. The improvement in the CTE with increasing sintering temperature may be because of densification of the microstructure. Moreover, the mechanical properties of these nanocomposites showed noticeable enhancements with the addition of SiC and sintering temperatures, where the microhardness and apparent strengthening efficiency of nanocomposites containing 8wt% SiC and sintered at 875°C were 958.7 MPa and 1.07 vol%?1, respectively. The electrical conductivity of the sample slightly decreased with additional SiC and increased with sintering temperature. The prepared Cu/SiC nanocomposites possessed good electrical conductivity, high thermal stability, and excellent mechanical properties.     

双掺杂钙钛矿型复合氧化物La_(0.7)Sr_(0.3)Co_(1-x)M_xO_3的电性能研究

以开发新型激光器阴极材料和固体氧化物燃料电池阴极材料为目的 ,合成一系列钙钛矿型复合氧化物 La0 .7Sr0 .3 Co1- x Mx O3 ( M:过渡族金属元素 ) ,并对 Co位掺杂过渡族元素后样品的高温电阻率和热电动势进行研究 ,发现 Co位掺杂不同元素显著影响材料的电导率和导电类型 ,并对其相应的物理机制进行探讨 .     

Cu含量及纯度对Mo-Cu合金热物理性能的影响

研究了不同Cu含量及纯度对Mo-Cu合金热物理性能的影响规律。结果表明:随着Cu含量的增加,合金的热导率呈较为明显的增加趋势,且实测值均比理论值偏低,Cu含量不同偏差的比值也不同,这主要是由Cu含量的不同影响合金的烧结过程从而影响烧结体的致密度,Cu相纯度是Mo-Cu合金热导率的高敏感因素,当Cu纯度仅在99.8%～97%之间变动时,其热导率显著下降;随Cu含量的增加,合金的热膨胀系数也相应的增加,而Cu纯度对其热膨胀性能影响较小,随Cu纯度的下降只呈略微的上升波动趋势,但其值均在10×10-6/K以下,可达到热沉基片所封接的热匹配系数要求。     

Chemical,mechanical, and thermal expansion properties of a carbon nanotube-reinforced aluminum nanocomposite

In the present study, the chemical and mechanical properties and the thermal expansion of a carbon nanotube (CNT)-based crystalline nano-aluminum (nano Al) composite were reported. The properties of nanocomposites were tailored by incorporating CNTs into the nano Al matrix using a physical mixing method. The elastic moduli and the coefficient of thermal expansion (CTE) of the nanocomposites were also estimated to understand the effects of CNT reinforcement in the Al matrix. Microstructural characterization of the nanocomposite reveals that the CNTs are dispersed and embedded in the Al matrix. The experimental results indicate that the incorporation of CNTs into the nano Al matrix results in the increase in hardness and elastic modulus along with a concomitant decrease in the coefficient of thermal expansion. The hardness and elastic modulus of the nanocomposite increase by 21% and 20%, respectively, upon CNT addition. The CTE of CNT/Al nanocomposite decreases to 70% compared with that of nano Al.     

氧化物材料负热膨胀机理

氧化物的负热膨胀性（ＮＴＥ）是由于在其开放式的骨架结构中,有二配位的桥氧键产一横向热运动,以及引起的多面体热摆动和耦合作用使非键合Ｍ－Ｍ１键距变短,导致单胞体积缩小;各向同性ＮＴＥ氧化物在复合材料及其相关技术领域具有更广泛的应用价值。     

Fabrication and thermal conductivity of copper matrix composites reinforced by tungsten-coated carbon nanotubes

Carbon nanotubes (CNTs) were coated by tungsten using metal organic chemical vapor deposition. Magnetic stirring was employed to disperse the W-coated CNTs (W-CNTs) in a Cu matrix, and then, the mixed powders were consolidated by spark plasma sintering. The W-CNTs obtained a uniform dispersion within the Cu matrix when the W-CNT content was less than 5.0vol%, but high content of W-CNTs (10vol%) resulted in the presence of clusters. The W-CNT/Cu composites containing low content of W-CNTs (<5.0vol%) exhibited a higher thermal conductivity than the sintered pure Cu, while the CNT/Cu composites exhibited no increase in thermal conductivity after the incorporation of uncoated CNTs. The W-CNT content was found to play a crucial role in determining the thermal conductivity of the W-CNT/Cu composites. The thermal conductivity of the W-CNT/Cu composites increased first and then decreased with the W-CNT content increasing. When the W-CNT content was 2.5vol%, the W-CNT/Cu composite obtained the maximum value of thermal conductivity. The thermal resistance of the (W-CNT)-Cu interface was predicted in terms of Maxwell-Garnett effective medium approximation, and its calculated value was about 3.0×10-9 m2·K·W-1.     

Review of metal matrix composites with high thermal conductivity for thermal management applications

Metal matrix composites with high thermal conductivity and tailorable coefficient of thermal expansion are found widespread applications in electronic package and thermal management.The latest advances in manufacturing process,thermal properties and brazing technology of SiC/metal,carbon/metal and diamond/metal composites were presented.Key factors controlling the thermo-physical properties were discussed in detail.The problems involved in the fabrication and the brazing of these composites were elucidat...     

Zero thermal expansion in YbGaGe due to an electronic valence transition

Most materials expand upon heating. Although rare, some materials expand on cooling, and are said to exhibit negative thermal expansion (NTE); but the property is exhibited in only one crystallographic direction. Such materials include silicon and germanium at very low temperature (<100 K) and, at room temperature, glasses in the titania-silica family, Kevlar, carbon fibres, anisotropic Invar Fe-Ni alloys, ZrW2O3 (ref. 4) and certain molecular networks. NTE materials can be combined with materials demonstrating a positive thermal expansion coefficient to fabricate composites exhibiting an overall zero thermal expansion (ZTE). ZTE materials are useful because they do not undergo thermal shock on rapid heating or cooling. The need for such composites could be avoided if ZTE materials were available in a pure form. Here we show that an electrically conductive intermetallic compound, YbGaGe, can exhibit nearly ZTE--that is, negligible volume change between 100 and 400 K. We suggest that this response is due to a temperature-induced valence transition in the Yb atoms. ZTE materials are desirable to prevent or reduce resulting strain or internal stresses in systems subject to large temperature fluctuations, such as in space applications and thermomechanical actuators.     

La(ClO_4)_3·3H_2O与18C6在乙醇中配合行为的研究

采用改进的半微量相平衡方法研究了La(ClO_4)_3·3H_2o—18c6—C_2H_5OH三元体系在25℃时的溶解度,测定了各饱和液相的检光率,结果表明有了三种化学计量的配合物(4La(ClO_4)_3·3(18C6)·12H_2O·9C_2H_5OH;La(ClO_4)_3·18C6·3H_2O·2C_2H_sOH和La(ClO_4)_3·2(18C6)·3H_2O·C_2H_5OH)生成。分离制备了两种配合物,经化学分析测定,确定了配合物的组成为La(ClO_4)_3·18C6·3H_2O与La(ClO_4)_3·2(18C6)·3H_2O;用IR,TG,DTG及电导对配合物进行了研究。     

Si对无压浸渗SiCp/Al复合材料显微组织与热导率的影响

研究了Al-8Mg基体中添加Si对无压浸渗SiCp/Al复合材料显微组织和热导率的影响.结果表明,Si能够改善Al与SiC的润湿性,减少复合材料孔隙度,抑制界面反应,提高相对密度.不含Si时,Al与SiC界面反应严重,并且润湿性较差,导致复合材料的热导率和相对密度较低;当基体中添加质量分数12%的Si时,界面反应受到完全抑制,热导率取得最大值;进一步提高基体中Si含量,由于铝基体的热导率随Si含量的增加而降低,导致复合材料的热导率也随之降低.     

电热式化学镀铜地热地板的表面化学结构与导热性

用X射线光电子能谱及激光导热性能测试仪测试化学镀铜杨木单板的表面化学结构及其复合后地热地板的导热性.结果表明:镀铜后杨木单板的Cu元素与其复合后的地热地板导热率呈正相关关系;镀层中Cu元素以Cu~(2+)的形式存在,随着施镀时间的增加,Cu~+的歧化反应更加完全,CuOH与Cu_2O逐渐还原为金属Cu;在相同含水率条件下,镀铜地热地板复合材料的导热率比全素复合材料的导热率高2倍多,且随着施镀时间的增加,其导热率也随之增大.     

Dielectric AlN/epoxy and SiC/epoxy composites with enhanced thermal and dynamic mechanical properties at low temperatures

In a superconducting magnet, the thermal properties of the insulating material at low temperatures is an important technical index to ensure the normal operation of a superconducting coil. Herein, a low-temperature thermal conductivity testing device with a tiny uncertainty was developed to measure the composites. Furthermore, SiC/epoxy and AlN/epoxy composites were prepared and their properties were tested at low temperatures. The results showed that the composites have a better thermal conductivity at low temperatures than pure epoxy. In addition, the AlN/epoxy and SiC/epoxy composites have excellent dynamic mechanical properties and low coefficient of thermal expansion. Due to the fair thermal and dynamic mechanical properties, the composites will have potential application in the superconducting magnet.     

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 thermal 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.     

颗粒增强复合材料热性能的数值模拟研究

利用C语言编写了能生成随机分布的颗粒增强复合材料几何模型的程序,结合MSC商用有限元软件分析了颗粒的体积分数、大小以及分布形态对颗粒增强复合材料热学性能的影响。结果表明:颗粒的分布形态对材料的热膨胀变形及热传导无明显影响,但对热应力有很大影响;颗粒的大小对材料的热膨胀有一定影响;颗粒体积分数的影响和利用混合律的预测结果基本一致。     

La_(0.8)M_(0.2)Fe_(1-x)Cu_xO_3钙钛矿型氧化物的制备及催化性能研究

采用溶胶-凝胶法制备了一系列钙钛矿复合氧化物La0.8M0.2Fe1-xCuxO3(M为Sr、Ba和Ce).催化性能测定结果发现,800℃焙烧所制得的La0.8Ce0.2Fe0.7Cu0.3O3具有良好的三效催化性能,在该催化剂上C3H6、CO和NO的起燃温度较低,分别为225℃、200℃和280℃,并且在温度达到325℃之前都能得到完全转化.扫描电子显微镜和X射线衍射测试分析表明,La0.8Ce0.2Fe0.7Cu0.3O3具有良好的钙钛矿型晶体结构,晶粒为纳米级,团聚不严重,这可能是其三效催化性能良好的主要因素.     

Fe-C-MoS2/CuSn合金基复合材料的研究

应用粉末冶金技术制备了烧结Fe-C-MoS2/CuSn合金基减摩复合材料,对其组织结构和机械物理性能进行了研究.结果表明以CuSn合金为基体保证了材料的导电性.CuSn合金的强度大于混合同种金属元素烧结材料的强度.CuSn合金与Fe润湿性好,促进了烧结合金化,因而大幅度提高了材料的强度、硬度、冲击韧性.C以游离状态存在于基体中,其膨胀系数大于基体材料,起到了减摩作用.MoS2均匀分布在基体中,明显地起到了高温减摩作用.其中当Fe(质量分数)增加到15%时,冲击韧性达20.6 J/cm2,抗拉伸强度为163.2 MPa,布氏硬度为53.8,达到和超过了TB/T1842.1-2002电力机车粉末冶...     

Cu0.5Zr2(PO4)3:Cu2+中心g因子研究

由于Cu0．5Zr2(PO4)3晶体具有良好的离子传导能力、催化特性、较低的热膨胀性，对它的研究引起了广泛的关注．本文引入平均共价因子N，并结合晶体结构数据给出了3d^9离子在晶场D4h下的g因子公式，利用该公式并结合Cu0．5Zr2(PO4)3晶体的具体结构数据对Cu0．5Zr2(PO4)3晶体中CU^2 中心的EPRg因子进行了理论分析计算，所得到的结果与实验值基本吻合．     

Glass-forming ability,phase formation and mechanical properties of glass-forming Cu-Hf-Zr alloys

The influence of Hf additions on the glass-forming ability(GFA),phase formation and mechanical properties of Cu_(50)Hf_xZr_(50-x)(x=2,5,10,20 at.%)alloys has been systematically investigated.We report on a distinct correlation between phase formation and GFA of Cu_(50)Zr_(50)-based alloys.Increasing additions of Hf reduce the thermal stability of the high-temperature B2Cu(Hf,Zr)phase,while the thermal stability of the corresponding undercooled melt is enhanced.The GFA of these alloy series gradually raises up to 10 at.%Hf,whereas at 20 at.%Hf,the GFA is drastically lowered,since the B2Cu(Hf,Zr)phase becomes unstable and the precipitation of the lowtemperature equilibrium phases is favoured.This interrelation determines the microstructure and results in the formation of Cu-Hf-Zr-based bulk metallic glass composites.These composites not only show appreciable macroscopic plastic strain,but also high yield strength.