Thermal expansion and mechanical properties of middle reinforcement content SiCp/Al composites fabricated by PM technology

Middle reinforcement content SiCp/Al composites(Vp=30%, 35% and 40%) for precision optical systems applications were fabricated by powder metallurgy technology. The composites were free of porosity and SiC particles distributed uniformly in the composites. The mean linear coefficients of thermal expansion(20-100 ℃) of SiCp/Al composites ranged from 11.6×10-6 to 13.3×10-6 K-1 and decreased with an increase in volume fraction of SiC content. The experimental coeffi cients of thermal expansion agreed well with predicted values based on Kerner's model. The Brinell hardness increased from 116 to 147, and the modulus increased from 99 to 112 GPa for the corresponding composites. The tensile strengths were higher than 320 MPa, but no signifi cant increasing trend between tensile strength and SiC content was observed.     

Aluminum matrix composites reinforced by molybdenum-coated carbon nanotubes

To extend the application of carbon nanotubes (CNTs) and explore novel aluminum matrix composites,CNTs were coated by molybdenum layers using metal organic chemical vapor deposition,and then Mo-coated CNT (Mo-CNT)/Al composites were prepared by the combination processes of powder mixing and spark plasma sintering.The influences of powder mixing and Mo-CNT content on the mechanical properties and electrical conductivity of the composites were investigated.The results show that magnetic stirring is better tha...     

改性碳纳米管/高密度聚乙烯复合材料正温度系数性能

以高密度聚乙烯(HDPE)为基体,改性的碳纳米管(CNTs)为导电填料,采用熔融法制备正温度系数(positive temperature coefficient,PTC)复合材料。通过扫描电子显微镜和热敏电阻曲线测试仪以及冲击试验机等,观察CNTs/HDPE复合材料的微观形貌,研究PTC效应随CNTs含量变化规律及对力学性能的影响。结果表明:CNTs在HDPE基体中分散性较好;当CNTS含量在体积分数为9%时,CNTs/HDPE复合材料的室温电阻率为102?·cm,PTC强度达4个数量级;HDPE基体中加入经过表面修饰过的CNTs后,复合材料的力学性能明显提高。当CNTs的体积含量在8%时,复合材料的冲击性能较纯HDPE提高了93%。     

制备工艺对CNTs/EP复合材料性能的影响

采用溶液共混法制备碳纳米管(CNTs)/环氧树脂(EP)复合材料,主要研究丙酮用量、混合方式、超声时间、CNTs含量等制备工艺对复合材料的热性能和导电性能的影响.通过用SEM、DSC,TGA以及万用表对复合材料进行分析表征,结果表明,丙酮的加入量越多,超声时间越长,CNTs/EP的复合材料的导电性越好,CNTs在复合材料中分散性也好,而随着CNTs含量增加,复合材料的导电性按照逾渗理论的规律提高,且逾渗闶值出现在0.5 0A～1%范围内.利用超声处理伴随着搅拌这种混合方式所得复合材料的导电性最好,加入碳纳米管的复合材料玻璃转化温度Tg和热稳定性能较纯EP有显著提高.     

Evaluation and Characterization of Mechanical, Electrical, and Thermal Properties of Polymer Nanocomposites Reinforced with Different Allotropes of Carbon

The present work aims to present the results based on the processing of nanocomposites, which consist of matrix materials like epoxy and filler materials such as conjugated nanomaterials/allotropes of carbon, namely, carbon black, graphite, and multiwalled carbon nanotube (MWCNT) used for targeted applications. To improve the physical and chemical properties and to facilitate a better interfacial interface between the polymer and nanotube, functional MWCNT is used during the preparation of the composite. The prime objective of the study is to establish the thermal, mechanical, and electrical properties of nanocomposites using experimental methods. It has been observed from the experimental results that carbon nanotube (CNT) based composite exhibits higher mechanical (tensile and hardness) and thermal properties as compared with the others. The electrical properties are found to be better in a graphite-based composite. Although CNT has superior mechanical and thermal properties, the exorbitant price limits its use. Hence, the allotropes of carbon may be used judiciously considering both the cost and property requirements of the targeted application. The work also studies the dispersion state of nanofibers through scanning electron microscopy (SEM).     

Analytical model of elastic modulus and coefficient of thermal expansion for 2.5D C/SiC composite

To make better use of 2.5D C/SiC composites in industry, it is necessary to understand the mechanical properties. A finite element model of 2.5D composites is established, by considering the fiber undulation and the porosity in 2.5D C/SiC composites. The fiber direction of warp is defined by cosine function to simulate the undulation of warp, and based on uniform strain assumption, analytical model of the elastic modulus and coefficient of thermal expansion (CTE) for 2.5D C/SiC composites were established by using dualscale model. The result is found to correlate reasonably well with the predicted results and experimental results. The parametric study also demonstrates the effects of the fiber volume fraction, distance of warp yarn, and porosity in micro-scale on the mechanical properties and the coefficients of thermal expansion.     

向列相液晶聚合物接枝碳纳米管制备及其性能

为了制备碳纳米管/液晶复合材料,合成了液晶单体1,4-苯二甲酸二-(4-羧基苯)酯,采用原位聚合法将其与1,6-己二酸、1,4-联苯酚、碳纳米管进行共聚,制备了不同配比的碳纳米管/液晶复合材料.利用红外光谱(FT-IR),差式扫描量热仪(DSC)、偏光显微镜(POM)、扫描电子显微镜(SEM)等研究了碳纳米管在液晶基体中的分散以及复合材料的液晶性.结果表明,少量的碳纳米管可以在液晶中分散良好;液晶复合材料的液晶区间变窄,但没有改变液晶复合材料的液晶类型.     

Mechanical properties and microstructure of sulfur aluminate cement composites reinforced by multi-walled carbon nanotubes

The effect of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and microstructure of sulfur aluminate cement (SAC) composites was investigated. The dispersed MWCNTs were added into SAC in various weight contents.The results of mechanical properties of the MWCNTs/SAC composites indicated that the addition of 0.08 wt% MWCNTs can improve the SAC compressive strength, flexural strength, and bend-press ratio by 15.54%, 52.38%, and 31.30% at maximum, respectively. The degree of SAC hydration and porosity and pore size distribution of the matrix were measured by X-ray diffraction (XRD), thermal analysis (TG/DTG), and mercury intrusion porosimetry (MIP). Results show that the addition of MWCNTs in SAC composites can promote the hydration of SAC and the formation of C-S-H gel, reduce the porosity and refine the pore size distribution of the matrix. The microstructure was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the MWCNTs have been dispersed homogeneously between the hydration products of SAC paste and act as bridges and networks between cracks and voids, which prevents the development of the cracks and transfers the load.     

Microstructure and properties of electronic packaging shell with high silicon carbide aluminum-base composites by semi-solid thixoforming

The electronic packaging shell with high silicon carbide aluminum-base composites was prepared by semi-solid thixoforming technique. The flow characteristic of the Si C particulate was analyzed. The microstructures of different parts of the shell were observed by scanning electron microscopy and optical microscopy, and the thermophysical and mechanical properties of the shell were tested. The results show that there exists the segregation phenomenon between the Si C particulate and the liquid phase during thixoforming, the liquid phase flows from the shell, and the Si C particles accumulate at the bottom of the shell. The volume fraction of Si C decreases gradually from the bottom to the walls. Accordingly, the thermal conductivities of bottom center and walls are 178 and 164 W·m-1·K-1, the coefficients of thermal expansion（CTE） are 8.2×10-6 and 12.6×10-6 K-1, respectively. The flexural strength decreases slightly from 437 to 347 MPa. The microstructures and properties of the shell show gradient distribution.     

ZCNTs/EP 复合材料的制备及其介电、导热性能

以环氧树脂 (epoxy resin, EP) 作为基体, 在多壁碳纳米管 (multi-walled carbon nanotubes, MWCNTs) 表面通过原位生长 2-甲基咪唑锌盐 (ZIF-8), 得到 ZIF-8/MWCNTs (ZCNTs) 复合材料。通过改变 EP 基体中 ZCNTs 含量, 制备 ZCNTs/EP 系列复合材料, 并对其介电、导热性能进行研究。研究结果表明, 当填料 ZCNTs 质量分数为 0.3%,频率为 10² Hz 时, ZCNTs/EP 复合材料的介电常数为 8.19; 频率为 10² ～ 10⁷ Hz 时介电损耗始终低于 0.025。同时,ZCNTs/EP 的导热系数达到 0.467 W/(m·K), 比纯 EP 的导热系数提高了 116%, 显著提升了 ZCNTs/EP 复合材料的导热性能。     

Wear behavior of Cu matrix composites reinforced with mixture of carbon and carbon nanotubes

In order to improve wear resistance and decrease the cost, carbon and carbon nanotubes reinforced copper matrix composites were fabricated by the power metallurgy method. The effects of carbon (carbon and carbon nanotubes) volume fraction and applied load on the friction coefficient and wear rate under dry sliding of the composites were investigated at room temperature. By scanning electron microscopy (SEM), the worn surfaces and debris were observed, and wear mechanism was also analyzed and discussed. The experimental wear process consists of the run-in, steady wear and severe wear process with the increasing of sliding distance. Both the friction coefficient and wear rate of the composites first decrease and then increase with the increasing of carbon volume fraction. The minimum friction coefficient and wear rate are obtained when carbon is 4.0vol%. The wear mechanisms of the composites change from the adhesive wear and delamination wear to abrasive wear with the increasing of carbon volume fraction. Funded by the National Natural Science Foundation of China (50873047) and the Natural Science Foundation of Gansu Province (3ZS061-A25-039)     

Effect of microstructure on the mechanical,thermal, and electronic property measurement ofceramic coatings

Ceramic materials were investigated as thermal barrier coatings and electrolytes. Electrophoretic deposition（EPD） and physical vapor deposition（PVD） were employed to fabricate samples, and the mechanical properties and microstructure were examined by nanoindentation and microscopy, respectively. Yttria-stabilized zirconia/alumina（YSZ/Al2O3） composite coatings, a candidate for thermal barrier coatings, yield a kinky, rather than smooth, load–displacement curve. Scanning electron microscope（SEM） examination reveals that the kinky curve is because of the porous microstructure and cracks are caused by the compression of the indenter. Li0.34La0.51 Ti O2.94（LLTO） on Si/Sr Ru O3（Si/SRO） substrates, an ionic conductor in nature, demonstrates electronic performance. Although SEM images show a continuous and smooth microstructure, a close examination of the microstructure by transmission electron microscopy（TEM） reveals that the observed spikes indicate electronic performance. Therefore, we can conclude that ceramic coatings could serve multiple purposes but their properties are microstructure-dependent.     

碳纳米管/铝基复合材料的制备及摩擦性能研究

采用无压渗透法制备了碳纳米管增强铝基复合材料，并对其摩擦性能进行了研究。利用扫描电镜（SEM）观察了复合材料断面的形貌，通过复合材料硬度测量和摩擦磨损实验，研究了不同碳纳米管体积分数对复合材料的硬度及摩擦磨损性能的影响。实验结果表明，碳纳米管均匀地分散于复合材料中，且与铝基体结合良好；碳纳米管的加入增大了复合材料的硬度，且其摩擦系数和磨损率随着碳纳米管体积分数的增大而减小。由于碳纳米管本身具有自润滑和增强作用，碳纳米管的加入极大地改善了铝合金材料的摩擦性能。     

Properties and Structure of Magnesium Matrix Composite Reinforced with CNTs

By using high pure Magnesium (99.9 wt% ) as matrix and multi-walled bended carbon nanotubes ( CNTs ) as reinforced phase, carbon nanotubes/magnesium matrix composite was prepared to the foundry method under the argon gas protection, and its mechanical properties were tested. The interface structure and component of plating and un-plating carbon nanotubes were analyzed by TEM and EDS , and the action mechanism was discussed. The experiment results show that the CNTs con strengthen mechanical properties of the nano-tube-reinforced Mg matrix composite, the tensile strength and elongation ratio are greatly improved. Furthermore, the plating CNTs are better than un-plating CNTs in strengthening effects. The tensile strength is inereased by 150% and the elongation ratio is increased by 30% than that of matrix when content of CNTs is 0.67 wt%.     

加捻纤维复合材料固化界面应力分析

含有加捻纤维束的复合材料由于固化而产生的热残余应力问题,可以用能量法获得解答。这种热残余应力可以表示为纤维、基体材料性质以及纤维束几何参数的函数。分析结果表明:加捻纤维束构成的复合材料,由于纤维适当加捻,可以大大减弱纤维与基体各具不同的热膨胀系数而产生的固化残余应力。     

UMTE复合材料的制备及其介电、导热性能

面对超大规模集成电路的发展和严苛的应用环境, 从市场需求入手, 通过原位生长的方法, 将二维杂化材料 MOFs (UIO-66) 包覆在多羟基碳纳米管表面, 制备出UMT 纳米材料, 并掺入环氧基体(EP) 中, 制得UMTE 复合材 料。研究表明, 相比于纯EP, 0.5% UMTE 复合材料介电常数下降了8.7%, 介电损耗始终低于0.035 (100~10⁷ Hz), 纳 米填料含量达到2% 时, UMTE 复合材料热导率提高了233%, 具有良好的电绝缘性、导热性。这类低介电常数、低 介电损耗、高导热的复合材料为设计微电子行业所需的环氧树脂材料提出了新的研究思路。     

改性MWNTs/纳米HA/PLA骨修复材料的制备

采用气相氧化法及液相氧化法制备了带有羧基的多壁碳纳米管(MWNTs—COOH)。在超声波辅助下,通过原位合成法将纳米羟基磷灰石(nano-HA)包覆在MWNTs—COOH上,得到纳米复合材料(MWNTs—COO/nano-HA),该纳米复合材料与聚乳酸(PLA)熔融共混成功制备出MWNTs—COO/nano-HA/PLA骨修复材料。经过FT-IR、XRD、TEM和电子拉力等分析表明,MWNTs—COOH完全被nano-HA包覆,MWNTs—COO/nano-HA复合材料颗粒完全达到纳米级。实验考察了复合材料中不同含量的MWNTs—COOH和MWNTs—COO/nano-HA对力学性能的影响,确定了MWNTs—COOH和MWNT—COO/nano-HA在材料中的最佳比例。     

纳米复合材料超声波焊接制备下剪切强度及组织研究

采用超声波焊接方法制备碳纳米管增强铝基复合材料,研究试件表面处理状态、焊接时间和焊接压力等工艺参数对焊接接头剪切强度的影响规律。试验结果表明:碳纳米管的加入具有较好的增强效果,提高了复合材料的力学性能;试件表面加乙醇处理、焊接时间120 ms及焊接压力17.5 MPa时,复合材料的接头剪切强度最高为11.12 MPa,相比基体材料提高28.6%;通过金相观察、扫描电镜(SEM)分析,发现碳纳米管很好地嵌入到了铝合金基体中,起到增强效果。     

Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-in situ reaction

Carbon fibre reinforced carbon and silicon carbide dual matrix composites(C/C-SiC) were fabricated by the warm compacted-in situ reaction.The microstructure,mechanical properties,tribological properties,and wear mechanism of C/C-SiC composites at different brake speeds were investigated.The results indicate that the composites are composed of 58wt%C,37wt%SiC,and 5wt%Si.The density and open porosity are 2.0 g.cm~(-3) and 10%,respectively.The C/C-SiC brake composites exhibit good mechanical properties.The ...     

Mn3(Cu0.6Si0.15Ge0.25)N/Ag复合材料的负热膨胀与物理性能

采用机械球磨加固相烧结法合成Mn3(Cu0.6Si0.15Ge0.25)N/Ag复合材料。在77K-300K温度范围内,分别研究了Mn3(Cu0.6Si0.15Ge0.25)N/Ag复合材料的热膨胀性能,电导性能和热导性能。当含Ag量分别为1,5,10和20 wt%时,所有样品在有效的温度区间205K-275K表现出负热膨胀。随着Ag含量的增加,有效温度区间向室温方向移动。另外,和Mn3(Cu0.6Si0.15Ge0.25)N材料相比,Mn3(Cu0.6Si0.15Ge0.25)N/Ag复合材料具有更高的电导率1?0-6（Ohm.m）-1和热导率10.5W/(mK)。