Effect of tungsten addition on thermal conductivity of graphite/copper composites

Graphite/copper composites with high thermal conductivity were fabricated by tungsten addition, which formed a thin tungsten carbide layer at the interface. The microstructure and thermal conductivity of the composite material were studied. The results indicated that the insertion of tungsten carbide layer obviously suppressed spheroidization of copper coating on the graphite particles during the sintering process, and decreased the interfacial thermal resistance of the composites. Compared with the graphite/copper composites without tungsten, the thermal conductivity of the obtained composites was increased by 43.6%.     

烧结温度对Cf/SiC复合材料结构及性能的影响

以碳纤维为增强体, 热压烧结制备了C_f/SiC复合材料, 研究了烧结温度对C_f/SiC复合材料密度、结构及性能的影响. 研究发现: 提高烧结温度能够促进C_f/SiC复合材料的致密度; 当烧结温度低于1850℃时, 升高烧结温度, 复合材料的强度和断裂韧性也随之提高. 当烧结温度为1850℃时, 复合材料的性能最优, 弯曲强度达500.1MPa, 断裂韧性为16.9MPa·m ^1/2. 当烧结温度达到1880℃时, 复合材料性能反而下降.     

炭/炭复合材料表面C/SiC/Si-Mo-Cr多层复合防氧化涂层研究(英文)

为提高炭/炭(C/C)复合材料的高温抗氧化性能,采用料浆涂刷法首先在C/C复合材料表面制备了预炭层,然后以Si粉及石墨粉(Si粉与石墨粉的质量配比为:60～80:10～25)为原材料采用包埋法经高温热处理获得C/SiC内涂层,最后在涂有C/SiC内涂层的C/C复合材料表面采用包埋法制备Si-Mo-Cr外涂层。借助扫描电镜、X射线衍射、电子能谱等分析测试手段对涂层试样的微观结构进行了分析,研究了涂层C/C复合材料在1 873 K和1 973 K下的氧化行为。结果表明:由于涂层氧化过程中表面生成了SiO2和Cr2O3复合玻璃层,其在1 873 K温度下表现出优异的防氧化性能,可以有效保护C/C复合材料达135 h。当氧化温度提高至1 973 K并氧化30 h后,该复合涂层氧化过程玻璃层完整性被破坏,涂层失效。     

电解铜粉和雾化铜粉对SPS过程中显微组织演变的影响

以电解铜粉和雾化铜粉为SPS烧结原材料,对它们在SPS烧结过程中的烧结曲线、烧结体显微组织的演变过程,以及烧结温度对烧结体相对密度的影响进行了分析、比较,并分析了其中的原因。得到电解铜粉和雾化铜粉在SPS烧结过程中显微组织演变特征和规律不同的结论。     

炭/炭复合材料表面预炭层的制备及其性能研究

为在炭/炭复合材料表面制备C/SiC浓度梯度高温抗氧化涂层,预先用料浆涂刷-高温处理工艺在其表面制备了预炭层.借助XRD、Raman和SEM等测试手段对所制备预炭层的组织结构和微观形貌进行了表征,讨论了不同的原料配比和炭化温度对预炭层结构的影响,并对预炭层与基体的结合性能进行了测定.研究结果表明：制备的预炭层结构致密,与基体具有较好的结合性能,其结合强度可达10.95MPa.不同的原料配比和炭化温度影响了炭层序态结构的形成,最终形成了不同结构的预炭层.     

Cf/ZrC-ZrB2-SiC-C超高温陶瓷复合材料的显微结构表征

利用X-射线衍射、扫描电子显微镜和透射电子显微镜对Cf/ZrC-ZrB2-SiC-C超高温陶瓷复合材料的相组成、纤维/热解碳层的界面特征和超高温陶瓷基体的显微结构特征进行了表征。在碳纤维表面有一层厚度为2～3μm石墨化程度较高的热解碳界面层,该界面层可以避免采用PIP工艺制备超高温陶瓷基体时可能对碳纤维造成的损伤。热解碳层与碳纤维之间为弱机械结合,其界面间分布着20～30 nm的ZrC纳米颗粒。Cf/ZrC-ZrB2-SiC-C超高温陶瓷复合材料基体主要由ZrC,ZrB2,SiC和石墨相(Cg)组成。基体中石墨的(002)面沿着ZrC,ZrB2或SiC的表面生长。在石墨与ZrB2和石墨与SiC的界面没有观察到取向关系,界面处既没有反应层也没有非晶相存在。在石墨与ZrC之间存在ZrC(111)∥Cg(002),ZrC[110]∥Cg[010]的取向关系。ZrB2和SiC之间也没有界面反应和非晶层存在。     

碳纤维含量对碳纤维／中铜石墨复合材料减摩耐磨性能的影响

在干磨擦条件下，对不同碳纤维含量的碳纤维／中铜石墨复合材料，进行了５０ｈ的摩擦磨损试验并借助扫描电镜观察了综们的磨面，结果表明，随碳纤维 增加，碳纤维．中铜石墨复合材料的摩擦系数和磨损量均明显减少。     

几种喉衬材料断裂韧性的比较

测试了几种石墨、毡基C／C、多维编织C／C及石墨渗铜材料的断裂韧性，定性地比较了它们之间的抗断裂能力，并对材料的微观结构和断裂机理作了简要的分析。石墨渗铜材料的断裂韧性与高强石墨相比基本相当，主要是由于铜相与石墨结合强度低而未能发挥铜相增韧的作用。毡基C／C材料的断裂韧性明显优于石墨渗铜材料和石墨，以两种不同基体炭为基体的毡基C／C的KIC值基本相同。多维编织C／C材料中纤维含量及分布与材料的断裂性能密切相关。     

Fabrication,Microstructure and Mechanical Properties of TiC/Ti_2AlC/TiAl_3 in situ Composite

This paper described a process for synthesizing a new multiphase TiC/Ti2AlC/TiAl3 composite,in which Ti,Al4C3 and graphite powders were utilized as raw materials,and in situ spark plasma sintering-reactive sintering(SPS-RS) methods were involved.The intermediate phases of Ti3Al and TiAl were found during the reactive sintering process and the reactions for the phase’s formation were proposed.The microstructure and mechanical properties of the composites were investigated.The high-resolution transmission electron microscopy(HRTEM) image of the interface showed that no amorphous phases were detected along the grain boundary.The orientation relationships between the Ti2AlC and the TiC were shown to be(0001)Ti2AlC||(111)TiC and [110]Ti2AlC||[110]TiC.The average hardness,fracture toughness,Young’s modulus and bending strength of the composite were 15.1±0.8 GPa,4.9±0.3 MPa·m 1/2,261±13 GPa and 776±18 MPa,respectively.The toughening mechanism was also discussed.     

Processing, microstructure and mechanical properties of hot-pressed SiC continuous fibre/SiC composites

SiC (SCS-6TM) continuous fibre/SiC composites were fabricated by hot-pressing at 1700°C in vacuum using an Al sintering additive. Analytical transmission electron microscopy was used to investigate the microstructure of the composites. The room-temperature mechanical and high-temperature creep properties of the composites were investigated by four-point bending. The SiC powders used were sintered at a relatively low sintering temperature to high density (97% of theoretical density) with the addition of the Al sintering additive. It is believed that the Al additive is very efficient for the densification of SiC. The SiC fibres maintained their original form and microstructure during fabrication. The SiC matrix reacted with the outermost carbon sublayer in the fibre, forming a thin (1.8–4.8m) interfacial layer, which was composed of Al4C3, Si–Al–C, and Si–Al–O phases. The incorporation of SiC fibre into a dense SiC matrix significantly increased the room-temperature failure strain and improved the high-temperature creep properties. In addition, the incorporation of SiC fibre into a porous SiC matrix increased the room-temperature failure strain, but did not contribute to the high-temperature creep properties.     

三维针刺C/SiC复合材料显微结构演变分析

以三维针刺碳毡作为预制体,采用树脂浸渍-热解工艺制备C/C多孔体,然后采用反应熔体浸渍法(Reactive melt infiltration,RMI)对C/C多孔体分别浸渗Si和Si-Mo合金制备C/SiC复合材料。首先研究了C/C多孔体制备过程中的显微结构演变。结果表明,浸渍过程中树脂主要填充在纤维束内小孔隙中,热解后裂纹增多,生成网格状C/C亚结构单元;高温热处理使C/C复合材料裂纹进一步扩展,石墨化度提高,束内闭气孔打开,从而为RMI渗Si提供通道。然后对C/C多孔体分别渗Si和Si-Mo合金所得材料的物相组成和显微结构进行对比分析。发现纯Si浸渗得到的复合材料残余Si较多,束内纤维受损严重;而浸渗Si-Mo合金可以减少残余Si含量,束内纤维受损轻微,仍保持着完整的C/C亚结构单元。     

中间相沥青基碳纤维石墨化度对Cf/Al界面损伤的影响

以不同石墨化度的中间相沥青基碳纤维为基底磁控溅射构筑Cf/Al界面,研究了不同石墨化度Cf/Al界面微观结构的演变,并与聚丙烯腈碳纤维比较揭示了Cf/Al界面的损伤机制。结果表明：随着石墨化处理温度的提高中间相沥青基碳纤维的石墨微晶尺寸增大、取向度和石墨化度提高,Cf/Al界面的反应程度降低和碳纤维损伤减少。不同石墨化度Cf/Al界面的损伤决定于初始缺陷的数量和后续裂纹在碳纤维内部的增殖和扩展。在2400℃和2700℃石墨化处理使裂纹更容易在中间相沥青基碳纤维石墨微晶片层间扩展,去除镀层后纤维损伤比聚丙烯腈碳纤维分别高5.19%和3.70%;在3000℃石墨化处理后,化学惰性较大的中间相沥青碳纤维使界面反应产生的缺陷数量大幅度减小,去除镀层后纤维的损伤比聚丙烯腈碳纤维低1.85%。     

C/C复合材料层间裂纹扩展研究

作为一种耐高温高性能复合材料,Ｃ／Ｃ复合材料具优异的高温力学性能,但是材料本身的脆性是其弱点之一,其中,对于二维碳碳复合材料而言,层间裂纹扩展是其主要损伤机理,本文针对Ⅰ型和Ⅱ型层间裂纹扩展进行实验研究,深入分析了不同密度及加入填充剂填充的二维碳／碳复合材料的层间裂纹扩展方式,测试了Ⅰ型和Ⅱ型层间裂纹扩展能,发现裂纹扩展能随密度的增大而增大,加入石墨粉或热解炭粉可以有效提高材料的裂纹扩展能．     

Microstructure evolution and densification behavior of TiC/316L composite powders during cold/warm die compaction and solid-state sintering: 3D particulate scale numerical modelling and experimental validation

To identify the microstructure evolution and densification behavior of TiC/316L composites in powder metallurgy (PM) process, 3D particulate scale numerical simulations were conducted to reproduce the cold/warm compaction and solid-state sintering of TiC/316L composite powders with corresponding physical experiments being carried out for model validation. The effects of compaction parameters and sintering temperature on the densification behavior of TiC/316L composite powders were systemically investigated. The particle deformation and morphology, stress/strain and microstructure evolutions, and grain size distribution in the whole process were characterized and compared to further illustrate the densification behavior and the underlying dynamics/mechanisms. The results show that compared with the cold compaction, the warm compaction can not only achieve higher relative density, smaller and more uniform equivalent stress, and weaker spring back effect, but also improve the friction condition among powder particles. The plastic deformation of 316L particles is the main densification mechanism during compaction. In the solid-state sintering of TiC/316L compacts, the densification is mainly indicated by shrinkage and vanishing of large residual pores along with the growth of the sintering necks, accompanied by the particle movement and growth along the boundary regions. Meanwhile, the particle displacement and grain size distribution are more uniform in the warm compacted TiC/316L component. Moreover, the equivalent (von Mises) stress in 316L particles is smaller than that in TiC particles.     

Thermal conductivity of wood-derived graphite and copper–graphite composites produced via electrodeposition

The thermal conductivity of wood-derived graphite and graphite/copper composites was studied both experimentally and using finite element analysis. The unique, naturally-derived, anisotropic porosity inherent to wood-derived carbon makes standard porosity-based approximations for thermal conductivity poor estimators. For this reason, a finite element technique which uses sample microstructure as model input was utilized to determine the conductivity of the carbon phase independent of porosity. Similar modeling techniques were also applied to carbon/copper composite microstructures and predicted conductivities compared well to those determined via experiment.     

高体积分数的 SiCp/Al复合材料的 SPS致密化机理研究

运用放电等离子烧结（SPS）技术制备出体积分数达60％，致密度达99％的SiCp／Al复合材料．从烧结工艺的控制及电场的影响两方面对SPS烧结SiC，／Al复合材料的机理进行了研究，认为SPS烧结SiCp／Al复合材料的致密化过程主要依靠烧结温度、压力及升温速率的合理搭配，使Al熔融粘结SiC颗粒，而又不溢出模具；烧结过程中未发现明显的放电现象，可能由于电场太弱不足以引发放电．     

Fe/Al2O3复合材料的制备和性能

用石墨埋烧方法制备Fe/Al₂O₃复合材料,对其力学性能和微观结构进行了分析。结果表明:Fe/Al₂O₃复合材料的弯曲强度与断裂韧性均随Al₂O₃含量的升高先升高后降低,当Al₂O₃含量（质量分数）为70%时,其弯曲强度与断裂韧性分别达到602.49 MPa和9.33 MPa·m¹/2,其硬度随Al₂O₃含量先降低后升高。在烧结过程中在Fe颗粒周围形成一种成分为FeO与FeAl₂O₄的壳体,在壳体与Fe颗粒之间存在微裂纹缺陷。壳体的形成和壳体与金属颗粒间的微裂纹钝化了外部应力,从而提高了复合材料的韧性。     

热处理对炭/炭-铜复合材料载流磨损行为的影响

为探明炭/炭(C/C)多孔体热处理对炭/炭-铜(C/C-Cu)复合材料载流磨损行为的影响,采用化学气相渗透法(CVI)增密的C/C多孔体,再通过压力熔渗法制备C/C-Cu复合材料.采用载流动态磨损试验机测试C/C-Cu复合材料载流磨损行为,利用数字式三维视频显微镜和扫描电子显微镜观察复合材料磨损前后的表面形貌,研究了C/C多孔体经过2 000℃热处理对C/C-Cu复合材料载流磨损行为的影响.结果表明:C/C-Cu复合材料的质量磨损率和线磨损率比C/C多孔体未经热处理的复合材料分别降低了34.42%和17.84%;C/C多孔体经过2 000℃热处理,石墨化度提高,片层劈裂阻力减小,在载荷的作用下石墨片层易于劈裂形成细小的石墨微晶碎片,迅速填充修复表面缺陷,形成具有一定润滑作用、平整的摩擦膜,有效抑制了局部非均匀磨损的扩大,减弱了磨粒磨损和电弧放电引起的烧蚀、粘着、氧化磨损之间的循环交替磨损,载流磨损性能提高.     

Three dimensional simulation of microstructure evolution for ceramic tool materials

The observation and scientific quantitative characterization of three dimensional microstructure evolution during sintering process of ceramic tool materials is important to investigate the influence of nano-particles on mechanical properties. The relationship between microstructure and mechanical properties of ceramic tool materials can be established to direct the development of nano-composite ceramic tool materials by the research of the grain growth, grain boundary migration, distribution of nano-particles and microstructure densification at the different sintering temperature and pressure. In this paper, a 3D Monte Carlo model of three-phase nano-composite ceramic tool material is built and applied to simulate the microstructure evolution during sintering process. In this model, the grain boundary energy of each phase and interfacial energy between two phases are taken into consideration as the driving forces for grain growth. The sintering temperature and pressure are successfully coupled into the Monte Carlo simulation model. The microstructure evolution of defect free three-phase nano-composite ceramic tool materials is successfully simulated at different sintering temperature and pressure. The simulation results show that the higher the sintering temperature is, the faster the grain growth. However, the sintering pressure has little effect on the grain growth.     

钼铜复合粉末的致密化及性能

对微波辅助法制备的钼铜复合粉末进行压制烧结,研究其致密化行为及复合材料性能。结果表明:烧结温度是控制钼铜复合材料成分、微观组织及综合性能的关键因素。1100℃下烧结的钼铜复合材料Cu含量最接近设计含量,过高的烧结温度将引起铜的损耗。在较低的烧结温度下(≤1100℃),复合材料的力学性能和物理性能随温度的升高而升高,但是过高的烧结温度(1200℃)会引起铜相的大量损失及颗粒异常长大,从而导致复合材料密度、硬度、导电率及导热率的降低。通过优化实验参数,1100℃下的复合材料具有理想的微观结构,铜相损失较少,复合材料成分接近设计成分,钼铜两相分散较为均匀,力学性能及物理性能优异,复合材料的密度、硬度、抗弯强度、电导率及热导率分别为9.79g/cm^3,229.1HV,837.76MPa,24.97×10~6S·m^-1和176.57W·m^-1·K^-1。