形状因子对微观定向结构Cu-W复合材料触头的力学和电学性能的影响

设计了三种微观定向结构的Cu-W复合电触头材料,用差异显著的形状因子对其表征,研究了形状因子对其导电性能和力学性能的影响。基于有效介质方程(GEM)和导电通道理论并结合仿真计算,得到不同骨架结构复合材料的电流密度分布及其与形状因子的关系。结果表明,形状因子F越接近1导电通道越容易形成团簇,导电性能越好;基于Mises屈服准则计算力学性能,仿真分析了不同结构复合材料的形变特性,提出其力学性能与形状因子的关系,即随着形状因子圆形度的增大力传导微元的稳定性随之提高;形状因子的圆形度越大,力传导微元越不易发生变形,机械性能越好。根据Cu-W复合电触头材料的导电性能和力学特性,可进一步优化其综合性能。     

真空烧结制备电触头Cu-W/Al2O3合金组织和侵蚀性能分析北大核心CSCD

选择真空烧结方法制得组成为Cu-33.6W/Al2O3与Cu-26.8W/Al2O3的两种合金,并对电导率、组织致密度以及表面硬度进行分析,表征了经过电弧侵蚀得到的微观形貌及其熔焊性能。研究结果表明:以真空烧结方式制得的Cu-W/Al2O3触头达到了高于97%的致密度,随着W含量的提高,试样电阻率减小,硬度增加。在铜基体中出现了弥散态的Al2O3颗粒,实现弥散增强效果,显著提升合金耐高温能力。对阳极与阴极触头进行每次电接触测试时都发生了质量减小。采用DC(30 V,30 A)参数对触头阳极与阴极进行侵蚀,形成了长条状、液滴形以及凹凸变化的微观侵蚀形貌。施加10 A电流时,在最初测试阶段形成了大幅波动的熔焊力,随着合金内的W比例从26.8%提高到33.6%的过程中,材料获得了更强的抗熔焊性能。     

真空烧结制备电触头Cu-W/Al_2O_3合金组织和侵蚀性能分析

选择真空烧结方法制得组成为Cu-33.6W/Al_2O_3与Cu-26.8W/Al_2O_3的两种合金,并对电导率、组织致密度以及表面硬度进行分析,表征了经过电弧侵蚀得到的微观形貌及其熔焊性能。研究结果表明:以真空烧结方式制得的Cu-W/Al_2O_3触头达到了高于97%的致密度,随着W含量的提高,试样电阻率减小,硬度增加。在铜基体中出现了弥散态的Al_2O_3颗粒,实现弥散增强效果,显著提升合金耐高温能力。对阳极与阴极触头进行每次电接触测试时都发生了质量减小。采用DC(30 V,30 A)参数对触头阳极与阴极进行侵蚀,形成了长条状、液滴形以及凹凸变化的微观侵蚀形貌。施加10 A电流时,在最初测试阶段形成了大幅波动的熔焊力,随着合金内的W比例从26.8%提高到33.6%的过程中,材料获得了更强的抗熔焊性能。     

C/C多孔体的高温热处理对C/C-SiC复合材料摩擦磨损行为的影响

低密度C/C多孔体的结构与性能调控是制备具有优异摩擦磨损性能的C/C-SiC复合材料的关键。本研究采用化学气相渗积法制备了C/C多孔体,并对其进行2100℃高温热处理,再通过反应熔渗法制备了C/C-SiC复合材料,研究了C/C多孔体高温热处理对C/C-SiC复合材料微观结构、导热性能和摩擦磨损性能的影响。结果表明,经2100℃热处理的C/C多孔体孔隙率和石墨化程度增加,用其制备的C/C-SiC复合材料比C/C多孔体未经热处理的密度更大(2.22 g/cm3),孔隙率由5.1%降低至3.4%, SiC陶瓷相含量比热处理前提高11.9%。石墨化程度越高,声子的平均自由程越大,因此其室温的导热率提升到3.1倍, 1200℃导热率提升到1.2倍。经过热处理的热解炭更软,摩擦面易形成连续且稳定的摩擦膜,因此摩擦系数更稳定,并且在测试载荷为3、6和9 N下磨损率均显著降低,下降幅度达到47.8%、41.9%和11.7%,平均摩擦系数分别为0.47、0.38和0.39。综上所述,对C/C多孔体进行高温热处理可使C/C-SiC复合材料的导热性能提升,更耐磨并且表现出更稳定的摩擦系数。     

SnO2添加剂对AgCuOIn2O3复合材料电接触性能的影响

采用反应合成法结合塑性变形工艺制备了不同SnO2含量的AgCuOIn2O3SnO2电触头材料,在JF04C触点材料测试机上对不同SnO2含量的电触头材料进行电接触实验,研究了该材料的接触电阻、抗熔焊性和材料转移特性,并通过扫描电镜对试样阴/阳表面电侵蚀下的微观形貌进行了分析.结果表明AgCuOIn2O3SnO2触头材料...     

聚酰亚胺辅助制备高定向石墨烯基全炭泡沫及其在导热聚合物复合材料中的应用（英文）

石墨烯及其衍生物具有高纵横比的二维层状结构,在加工过程中通常倾向于水平排列。因此,石墨烯基复合热界面材料虽然具有较高的面内热导率,但其表现出的低面外热导率难以满足实际应用需求。本文通过定向冷冻策略制备了竖直排列的聚酰亚胺/石墨纳米片(PG)导热骨架以提高聚合物复合材料的面外热导率,其中石墨纳米片(GNs)为高导热石墨烯薄膜的粉体边角料。在该过程中,采用水溶性聚酰胺盐溶液直接分散疏水的GNs,热亚胺化后获得的聚酰亚胺在辅助GNs定向排列的同时经石墨化处理转变为人造石墨。同时,GNs的引入提高了PG骨架的有序度和密度,进一步提高了聚二甲基硅氧烷(PDMS)基复合材料的强度和导热性能。结果表明,所制备的PDMS/PG复合材料(PG:21.1%)的面外热导率达14.56 W·m^-1·K^-1,是纯PDMS的81倍。这种简便的聚酰亚胺辅助二维疏水填料定向排列的方法为各向异性热界面材料的规模制备提供了思路,同时实现了石墨烯薄膜边角料的再利用。     

基于RTM技术的碳纤维/聚酰亚胺复合材料舵面一体化制备与验证

设计了一种碳纤维/聚酰亚胺复合材料舵面结构,采用PAM-RTM软件模拟了舵面在注胶过程中的树脂流动,根据模拟结果设计了成型模具,并通过树脂传递模塑(RTM)工艺制备了耐高温碳纤维/聚酰亚胺复合材料舵面,对其进行了力学试验,并将三维有限元分析结果与试验结果对比。试验结果表明,碳纤维/聚酰亚胺复合材料舵面在150%的使用载荷下保持了结构的完整性,骨架的最大应变为2 408×10–6,复合材料蒙皮的最大应变为2 371×10–6。有限元分析结果表明,金属骨架的最大应力出现在舵轴根部圆弧过渡区,而碳纤维/聚酰亚胺复合材料蒙皮的最大应力出现在与垫片外圆弧接触处;碳纤维/聚酰亚胺复合材料舵面的初始破坏为蒙皮单向带横向拉伸失效。      

银靶电流及溅射偏压对溅射沉积Cu/Ag薄膜导电性能的影响研究

磁控溅射技术制备有望作为电接触材料的Cu-Ag薄膜的工艺探索。利用方块电阻仪测试薄膜电阻,借助白光干涉仪和扫描电镜分析不同电流和不同偏压下粗糙度、薄膜厚度、Ag含量及微观结构对薄膜电阻影响规律。结果表明:不同银靶溅射电流下,Ag含量及微观结构为影响薄膜面电阻的主要因素,Ag含量低于18.13%(原子比)时膜中Cu-Ag固溶体相占比增大,这可能是引起薄膜面电阻增大的主要原因,柱状晶的贯穿程度越高电阻越小。不同偏压下,薄膜致密性和粗糙度对面电阻的影响较为明显,薄膜致密性越好,缺陷越少,电阻越小,而致密性相差不大时薄膜表面越光滑面电阻越小。     

骨架增强复合材料的微观结构和性能

从骨架增强复合材料的微观结构特点出发,揭示出在相同结构参数时骨架增强复合材料相比颗粒增强复合材料具有更高的增强体体积分数∫和更多的界面Ａ;并从理论上证明在∫相同时,骨架增强复合材料的强度为颗粒增强复合材料的强度和单纯骨架材料强度的和。     

聚乳酸/石墨/多壁碳纳米管复合材料的制备及性能

通过共溶剂法制备了由石墨(GN)和多壁碳纳米管(MWCNTs)掺杂的聚乳酸(PLA)纳米复合材料,借助扫描电镜等手段,研究了MWCNTs用量对复合材料微观结构、热稳定性、导热和导热性能及介电性能的影响。结果显示,MWC-NTs和GN在PLA基体中形成了稳定的导电和导热网络结构,从而导致复合材料具有较低的导电和导热逾渗阈值,其值约为MWCNTs/GN=0.5/1。MWCNTs和GN均匀分散和协同增强效应促使复合材料热稳定性、导热和导电性能明显提高。与纯PLA相比,填料在逾渗阈值附近的复合材料的初始分解温度提高了近16℃,导热系数提高了1倍,体积电阻降低了109数量级。     

多壁碳纳米管/聚亚苯基苯并二噁唑复合材料的微结构与性能

以甲基磺酸(MSA)为溶剂通过溶液共混法制备了不同多壁碳纳米管(MWNTs)含量的多壁碳纳米管/聚亚苯基苯并二噁唑(MWNTs/PBO)复合材料, 用扫描电镜(SEM)对热处理前后复合材料的微结构进行了分析, 并对其导电、力学和耐热性能进行了研究。结果表明: MWNTs能均匀地分散在聚合物基体中, 并能形成一定的网络结构, 热处理后的复合材料较热处理前的结构更致密, 导电性能和力学性能都有所改善, 其中MWNTs质量分数为10％的热处理后复合材料与纯PBO聚合物相比, 体积电阻率降低约9个数量级, 而拉伸强度和拉伸模量分别提高了95％和53％, 耐热性能也有一定的提高。      

鳞片石墨取向对鳞片石墨/聚丙烯、鳞片石墨/尼龙66复合材料导热性能的影响

为了研究鳞片石墨在基体中的取向对复合材料导热性能特别是不同方向导热性能的影响,通过双螺杆挤出混合及注射成型制备了鳞片石墨/聚丙烯（PP）、鳞片石墨/尼龙66（PA66）导热复合材料,并利用扫描电子显微镜和超声波测试对制备的样品进行了分析。结果表明：鳞片石墨的粒径越小,平面取向度越高,平面与垂直方向的热导率差值越大。加工中双螺杆挤出机的过度剪切会破坏鳞片石墨的片层结构,影响鳞片石墨导热网络的形成,降低复合材料的热导率,但提高了材料导热的各向均匀性。适度的剪切可以打开鳞片石墨的片层结构,提高复合材料的热导率,注射成型更多影响到制品导热的各向异性。     

Bounds on the effective thermal conductivity of composites with imperfect interface

A new model is developed to bound the effective thermal conductivity of composites with thermal contact resistance between spherical inclusions and matrix. To construct the trial temperature and heat flux fields which satisfy the necessary interface conditions, the transition layer for each spherical inclusion is introduced. For the upper bound, the trial temperature field needs to satisfy the thermal contact resistance conditions between spherical inclusions and transition layers and the continuous interface conditions between transition layers and remnant matrix. For the lower bound, the trial heat flux field needs to satisfy the continuous interface conditions between different regions. It should be pointed out that the continuous interface conditions mentioned above are absolutely necessary for the application of variational principles, and the thermal contact resistance conditions between spherical inclusions and transition layers are suggested by the author. According to the principles of minimum potential energy and minimum complementary energy, the bounds of the effective thermal conductivity of composites with imperfect interfaces are rigorously derived. The effects of the size and distribution of spherical inclusions on the bounds of the effective thermal conductivity of composites are analyzed. It should be shown that the present method is simple and does not need to calculate the complex integrals of multi-point correlation functions. Meanwhile, the present method provides an entirely different way to bound the effective thermal conductivity of composites with imperfect interface, which can be developed to obtain a series of bounds by taking different trial temperature and heat flux fields. In addition, the present upper and lower bounds are finite when the thermal conductivity of spherical inclusions tends to ∞ and 0, respectively.     

Relationships between the properties and microstructure of Mo–Cu composites prepared by infiltrating copper into flame-sprayed porous Mo skeleton

In this paper, the porous Mo skeleton was fabricated through deposition of semi-molten Mo particles by flame spraying. The Mo–Cu composites with different Cu contents up to 68% were produced by infiltrating molten copper into porous Mo skeleton in vacuum. The microstructures of both the as-sprayed porous Mo skeletons and the as-infiltrated Mo–Cu composites were characterized. The physical and mechanical properties of Mo–Cu composite materials with different Mo constituents were investigated. The results indicate that the excellent connecting pore structure feature of sprayed Mo skeleton is beneficial to the copper infiltration and the resultant Mo–Cu composite materials exhibit high density and microhardness. Moreover, there exists a hardness gradient at the interface region between the large Mo particle and Cu matrix. The results showed that the coefficient of thermal expansion (CTE) and thermal conductivity (TC) of Mo–Cu composites increase with the copper content of the composites and the temperature. The TC data of the composites are close to the results calculated by the finite differential method by taking account of the interface structure. Moreover, the observed CTEs are in good agreement with the theoretical values calculated based on Kerner's model.     

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm⁻¹, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.     

Failure Analysis of Welded Radiant Tubes Made of Cast Heat-Resisting Steel

Radiant tubes made of cast heat-resisting steels were cracked after 4 years of operation at 1020 °C temperature in hydrocarbon cracking furnace. Optical microscopy of the tubes showed that there was extensive precipitation and intermetallic compound formation especially as brittle networks with progressive reduction in toughness and resistance to thermal and mechanical stresses. SEM and EDS analysis proved both decarburization and oxidation on interior and exterior surfaces. Apart from cracking due to long-term heating, the tubes experienced high temperature creep. HAZ cracking after welding of cracked and/or creeped tubes due to formation of brittle carbide networks was overcome by localized solution heat treatment followed by fast dry air cooling. Localized dissolution of carbide networks and intermetallic compounds resulted in lower strain microstructures and enhanced resistance of parts to thermal and mechanical stresses during repair welding. It is evident that localized solution heat treating other than lowering strains can cause the precipitates to be more uniformly and finely distributed. Fast dry air cooling rate after solution heat treating and similar cooling after welding can help to control precipitation of carbides. Detailed non-destructive testing after welding along with tensile testing proved that post-weld cracking was controlled.     

不同压力下聚四氟乙烯复合材料的磨损行为

对炭纤维等无机填料增强的聚四氟乙烯(PTFE)复合材料在低、中、高压下的摩擦磨损行为进行了研究。利用扫描电子显微镜分析了材料的磨损状况,利用差热扫描量热分析仅、X射线衍射仪对材料的热性能及结晶性能进行了分析,并与材料的摩擦、磨损性能相联系．研究结果表明．高压摩擦环境中,蠕变的发生是加速PTFE复合材料磨损、恶化材料性能的主要原因;高比表面填料的加入会提高复合材料的熔化热,有助于降低材料的磨损率;结晶度的提高对增强复合材料的耐蠕变性有明显的效果。     

Low-velocity impact and static behaviors of high-resilience thermal-bonding inter/intra-ply hybrid composites

This study prepared inter/intra-ply hybrid composites reinforced with sandwich-structure recycled Kevlar nonwoven/glass woven compound fabric. Negative-depth needle punching and thermal bonding were applied to strengthen the structure with two compound cover plies and a fluffy cushioning center ply. The effects of center ply areal density, needle punching depth, and fiber blending ratio on the static and dynamic impact resistance behaviors of the composites were investigated. The results indicated that areal density significantly influenced the static and dynamic impact behaviors, which were both enhanced by the promotion of thermal-bonding points. As the needle punching deepened, the static and dynamic puncture resistances represented opposite tendencies because of different failure mechanisms. Static friction was the dominant factor for static puncture resistance, whereas kinetic friction was the dominant factor for dynamic puncture resistance. A similar phenomenon was observed when fiber blending ratio was varied. In terms of the non-penetrating dynamic cushioning test, areal density was the most distinct influence factor on cushioning behavior and the hybrid composites sample with an areal density of 700 g/m² could eliminate up to 66.5% of the incident force. Therefore, the inter/intra-ply hybrid composites showed high impact resistance and excellent dynamic cushioning property.     

Continuous resistance welding of thermoplastic composites: Modelling of heat generation and heat transfer

A process model composed of electrical and heat transfer models was developed to simulate continuous resistance welding of thermoplastic composites. Glass fabric reinforced polyphenylenesulfide welded in a lap-shear configuration with a stainless steel mesh as the heating element was considered for modelling and experimental validation of the numerical results. The welding temperatures predicted by the model showed good agreement with the experimental results. Welding input power and welding speed were found to be the two most important parameters influencing the welding temperature. The contact quality between the electrical connectors and the heating element was found to influence the distribution of the welding temperature transverse to the welding direction. Moreover, the size of the electrical connectors was found to influence the achievable welding speed and required power input for a certain welding temperature.