压力梯度CVI工艺制备2D炭/炭复合材料的弯曲断裂行为

采用三点弯曲方法测试了压力梯度化学气相浸渗法(CVI)工艺制备的2D炭／炭复合材料的性能，借助于扫描电镜研究了断口和界面形貌，分析了密度和纤维基体界面对材料力学性能的影响。结果表明，随试样密度增加，2D炭／炭复合材料的断裂模式从剪切断裂、层问分离向拉伸断裂转变。材料密度对弯曲强度和模量影响很大，但对弯曲挠度基本没有影响。揭示了影响2D炭／炭复合材料弯曲挠度的关键因素是纤维与热解炭基体界面的结合情况。     

C/C-ZrC复合材料的微观结构和力学性能研究

采用ZrOCl₂溶液浸渍法把锆化合物引入碳纤维预制体, 经热处理、热梯度化学气相渗透致密化和高温石墨化工艺制备了C/C-ZrC复合材料。性能测试结果表明, C/C复合材料的弯曲强度和模量随ZrC含量的增加而增大, ZrC含量为12.08wt%时, 其强度和模量分别为42.5 MPa 和9.6 GPa, 比未改性试样分别提高了70.0%和43.3%。基体中结合较弱的微米级ZrC颗粒的存在不利于碳基体强度的提高, 但其对材料最终性能的影响是次要的, 碳基体中亚微米/纳米级ZrC颗粒的存在和良好的ZrC-C界面结合, 提高了碳基体的强度和模量, 进而提高了复合材料的最终性能。     

3DC/C复合材料的弯曲行为

采用三点弯曲方法测试了化学气相浸渗法(CVI)工艺制备的三维编织碳/碳复合材料(3DC/C复合材料)的性能,借助于偏光显微镜和扫描电镜研究了材料的组织结构和断口形貌,分析了密度及编织结构对材料性能和断裂模式的影响.结果表明:材料密度对弯曲强度、模量影响很大,并随试样密度的增加,3DC/C复合材料的材料的破坏模式从"假塑性"向"脆性"模式转化,"假塑性"破坏模式表现出纤维束间的剪切破坏,"脆性"破坏模式表现出纤维束的拉伸断裂.     

2.5D浅交直联C_f/Al复合材料的显微组织及弯曲和剪切性能

采用真空压力浸渗法制备体积分数为50%的2.5D浅交直联C_f/Al复合材料,研究复合材料的显微组织以及室温、高温下弯曲和剪切性能,分析复合材料弯曲和剪切性能的破坏失效机理。结果表明:2.5D浅交直联C_f/Al复合材料经向、纬向显微组织均存在一定的微孔、纤维丝偏聚等缺陷。室温的弯曲强度、弯曲模量、剪切强度分别为268.4 MPa,75.2 GPa和41.0 MPa,350℃的弯曲强度、弯曲模量、剪切强度分别为139 MPa,70.9 GPa和39.2 MPa,400℃的弯曲强度、弯曲模量、剪切强度分别为97.6 MPa,68.5 GPa和29.9 MPa;其中,弯曲失效主要由于内侧面受压导致经向纤维束在压应力作用下被压断,纬向纤维束产生挤压变形;外侧面受拉处随测试温度升高复合材料拉伸破坏现象不明显;而剪切破坏首先出现在基体与纤维束界面损伤处,室温下纤维束被拔出,断口不平齐,350,400℃时纤维束断口呈现45°破坏;经向纤维束屈曲与纬向纤维束挤压变形程度随测试温度升高越来越严重。     

叠层缝合结构碳纤维/Al复合材料微观特征与高温弯曲性能

将M40J碳纤维(C_f)以叠层缝合结构编织成预制体,采用真空气压浸渗工艺制备成C_f/Al复合材料。在高温环境(350℃、400℃)下进行三点弯曲测试试验,通过SEM、TEM、EDS和XRD对材料的元素分布、物相组成、微观组织和界面特征进行观察分析,研究其高温弯曲性能,探讨该种材料在高温环境下弯曲失效机制。结果表明,制备的C_f/Al复合材料基体与增强体界面轮廓清晰且结合紧密,材料内部基体受残余拉应力。C_f/Al复合材料在350℃时的弯曲强度和模量分别为175.2 MPa和90.1 GPa,在400℃时为160.8 MPa和87.5 GPa;温度升高时叠层缝合结构C_f/Al复合材料的弯曲强度未出现大比例下降,其高温稳定性较其他编织结构更好。C_f/Al复合材料在高温环境下弯曲失效时受拉伸、压缩共同作用,其失效方式是基体开裂及部分纤维断裂,主导因素为基体在高温下软化和材料界面结合强度下降。      

2.5D浅交直联Cf/Al复合材料的显微组织及弯曲和剪切性能EI北大核心CSCD

采用真空压力浸渗法制备体积分数为50% 的2.5D浅交直联Cf/Al复合材料,研究复合材料的显微组织以及室温、高温下弯曲和剪切性能,分析复合材料弯曲和剪切性能的破坏失效机理.结果表明:2.5D浅交直联Cf/Al复合材料经向、纬向显微组织均存在一定的微孔、纤维丝偏聚等缺陷.室温的弯曲强度、弯曲模量、剪切强度分别为268.4 M Pa,75.2 GPa和41.0 M Pa,350℃的弯曲强度、弯曲模量、剪切强度分别为139 M Pa,70.9 GPa和39.2 M Pa,400℃的弯曲强度、弯曲模量、剪切强度分别为97.6 M Pa,68.5 GPa和29.9 M Pa;其中,弯曲失效主要由于内侧面受压导致经向纤维束在压应力作用下被压断,纬向纤维束产生挤压变形;外侧面受拉处随测试温度升高复合材料拉伸破坏现象不明显;而剪切破坏首先出现在基体与纤维束界面损伤处,室温下纤维束被拔出,断口不平齐,350,400℃时纤维束断口呈现45°破坏;经向纤维束屈曲与纬向纤维束挤压变形程度随测试温度升高越来越严重.     

弯曲疲劳后4D-C/C复合材料的抗弯强度及热膨胀性能(英文)

采用液相浸渍炭化技术,在压力为75MPa下制备出4D-C/C复合材料,并进行高温热处理。研究静态和动态加载条件下,材料沿厚度方向的弯曲性能及断裂行为。结果表明,循环次数达到10×105次、频率为10 Hz时,材料的临界弯曲疲劳极限是静态弯曲强度的80%。静态弯曲加载情况下,C/C复合材料失效机制取决于试样底层炭纤维的取向。循环疲劳载荷作用下,其失效机制包括基体开裂、纤维-基体界面弱化及纤维断裂。复合材料在循环加载过程中界面结合强度降低,并释放内应力,故增强了纤维拔出以及复合材料的假塑性,疲劳加载后其剩余弯曲强度增加10%左右,而模量降低。疲劳载荷引起材料基体缺陷和裂纹数量的增加及纤维断裂,削弱了长度方向上的热膨胀,使材料热膨胀系数降低。     

基体含量对2D炭/炭复合材料性能影响的研究

研究了 2 D炭 /炭毛坯 -炭 /酚醛 (C/ P)的基体含量对 2 D-C/ C层间剪切性能的影响和防分层作用。结果表明 ,炭化后 2 D-C/ C、致密 2 D-C/ C的层剪强度都随 C/ P基体含量的增大而线性增加 ,而拉伸性能不受此影响。C/ P基体含量影响 2 D-C/ C的分层 ,基体含量低 ,ILSS低 ,难以抵抗热应力而发生分层。最终 2 D-C/ C的 ILSS在 1 3— 1 6MPa之间 ,拉伸强度在 1 3 0— 1 80 MPa之间 ,拉伸模量在 68— 93 GPa之间。     

纤维体积分数对K3D/MCPA复合材料力学性能的影响

本文研究了纤维体积分数对三维编织芳纶纤维增强铸性尼龙(简称K3D／MCPA)复合材料力学性能的影响。研究表明，K3D／MCPA复合材料有优异的抗冲击性能，冲击强度比三维编织芳纶纤维增强铸性尼龙(简称C3D／MCPA)和纯基体均有大幅度的提高，且随着纤维体积的提高而升高。K3D／MCPA复合材料剪切强度随纤维体积比的增大而增大，其纵向剪切强度低于纯基体和C3D／MCPA复合材料，但其横向剪切强度高于它们。K3D／MCPA复合材料弯曲强度与弯曲模量随纤维体积比的提高而提高，但与相同体积比的C3D／MCPA相比，K3D／MCPA的弯曲强度与弯曲模量均较低。     

面向3D打印的连续碳纤维上浆工艺及其对复合材料性能的影响

对连续纤维增强热塑性复合材料(CFRTPCs)进行3D打印能够实现无模具快速制造,扩展增材制造的实际应用。为进一步提高3D打印连续碳纤维增强复合材料制件的性能,采用热塑性上浆剂对干碳纤维进行上浆处理,以尼龙6(PA6)为基体打印连续碳纤维增强复合材料,对比了上浆前后碳纤维表面性质及复合材料力学和界面性能。结果表明,上浆后碳纤维表面极性官能团增加,纤维与树脂浸润性改善;纤维表面粗糙度增加,纤维与树脂的机械结合力增强;上浆后碳纤维增强PA6复合材料较原始碳纤维增强PA6复合材料层间剪切强度提高42. 2%,层间结合增强,弯曲强度提高了82%,弯曲模量提高2. 46倍; 3D打印的上浆后碳纤维增强PA6复合材料试样断面上有明显纤维拔出现象,界面性能显著改善。     

短切炭纤维增强沥青基C/C复合材料的组织特征

利用新型、高效的模压半炭化成型工艺，在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料制品，并借助光学显做镜和扫描电镜对其微观组织和断口形貌进行了观察。通过分析，解释了短切炭纤维增强沥青基C／C复合材料中炭纤维损伤的形成机制，提出了作为增强体相的短切炭纤维和焦炭颗粒与基体炭之间独特的界而结构模型。研究还表明：复合材料中明显存在着基体相和颗粒相一基体相的显微结构不仅呈层片状，而且层片状的结构好像数层桔子皮，将颗粒相包裹起来，这种“桔皮包裹”式的结构与炭纤维表面的POG结构基本相似。     

短切炭纤维增强沥青基C/C复合材料的力学性能

利用模压半炭化成型工艺在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料（简称SCFRC）。研究了短切炭纤维的体积分数对SCFRC材料的体积密度和力学性能的影响规律。借助光学显微镜和扫描电镜对其微观组织和断口形貌进行了观察，分析了短切炭纤维对SCFRC材料的增强机制。结果表明，当短切炭纤维的体积分数由0％增大到11．8％时，SCFRC材料的力学性能随之呈线性增加；短切炭纤维增强SCFRC材料的机制主要有裂纹偏转效应、桥联效应以及脱粘和拔出效应。     

Kinetics of chemical vapor infiltration of carbon nanofiber-reinforced carbon/carbon composites

Preforms containing 0, 5, 10, 15 and 20 wt.% carbon nanofibers (CNFs) were fabricated by spreading layers of carbon cloth, and infiltrated by using the technique of isothermal chemical vapor infiltration (ICVI) at the temperature of 1100 °C under the total pressure of 1 kPa and with the flow of the mixture of propane/nitrogen in a ratio of 13:1. The infiltration rates increased with the rising of CNF content, and after 580 h of infiltration, the achievable degree of pore filling was the highest when the CNF content was 5 wt.%, but the composite could not be densified efficiently as the CNF content ranged from 10 to 20 wt.%. An analysis of the results, based on the effective diffusion coefficient and on the in-pore deposition rates, shows that the CNFs, due to their higher aspect ratio, accelerate overgrowth at pore entrances and thus lead to incomplete pore filling.     

软硬混编预制体增强沥青基4D-C/C材料的拉伸破坏行为

以X-Y平面依次铺设炭纤维束、Z向穿插炭棒的4D软硬混编为预制体,采用沥青液相常压、高压浸渍/炭化-石墨化循环致密工艺制备4D-C/C复合材料。通过该材料Z向(炭棒方向)的拉伸实验,测定其拉伸性能和力学行为,并采用SEM分析试样表面及断口形貌。结果表明:宏观上拉伸试样以炭棒整体拔出的形式破坏;细观尺度上,试样表面形成了与载荷方向垂直的贯穿性裂纹,裂纹以2 mm左右的距离呈等间距分布;材料进一步的破坏过程中,基体裂纹在X-Y向纤维束中呈线性扩展,快速分割了基体材料,使4D-C/C复合材料的拉伸破坏演变为1D-C/C复合材料的破坏模式,由于炭棒与基体炭界面结合弱,炭棒以拔出方式失效和破坏。     

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.     

Diamond formation on carbon/carbon composite

A carbon/carbon composite was used as substrate for low-pressure diamond deposition. To enhanced diamond nucleation on carbon/carbon composites, a total of ten surface preparation methods have been investigated. These methods involved the use of atomic hydrogen etching, mechanical polishing, sonication, or coating. Diamond nucleation was found to occur on either the defects of the carbon/carbon composite substrates or diamond particulate left on the substrates. The defects were created primarily by atomic hydrogen etching during the coating process. Seeding with diamond powders was performed by dip coating, sonication, or spray-coating processes. It was found that these seeding processes resulted in excellent nucleation of diamond.     

Graphitization behaviour of carbon fibre-glassy carbon composites

Carbon fibre-carbon composites were fabricated by aligning PAN-based carbon fibre unidirectionally in furfuryl alcohol resin char. The graphitization behaviour was investigated by an X-ray diffraction technique and by the measurement of magnetoresistance. The time-temperature superimposition study for interlayer spacing resulted in an activation energy of 242±35 kcal mol⁻¹. The kinetic study on magnetoresistance agreed with the result of X-ray measurement. The activation energy is that for the graphitization of the layer structure formed in the glassy carbon matrix of the composites. The graphitization mechanism of the layer structure is the same as that of soft carbons.     

Mesoscale evolution of non-graphitizing pyrolytic carbon in aligned carbon nanotube carbon matrix nanocomposites

Polymer-derived pyrolytic carbons (PyCs) are highly desirable building blocks for high-strength low-density ceramic meta-materials, and reinforcement with nanofibers is of interest to address brittleness and tailor multi-functional properties. The properties of carbon nanotubes (CNTs) make them leading candidates for nanocomposite reinforcement, but how CNT confinement influences the structural evolution of the PyC matrix is unknown. Here, the influence of aligned CNT proximity interactions on nano- and mesoscale structural evolution of phenol-formaldehyde-derived PyCs is established as a function of pyrolysis temperature (\(T_{\mathrm {p}}\)) using X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. Aligned CNT PyC matrix nanocomposites are found to evolve faster at the mesoscale by plateauing in crystallite size at \(T_{\mathrm {p}}\) \(\sim\)800 \(^{\circ }\hbox {C}\), which is more than \(200\,\,^{\circ }\hbox {C}\) below that of unconfined PyCs. Since the aligned CNTs used here exhibit \(\sim\)80 nm average separations and \(\sim\)8 nm diameters, confinement effects are surprisingly not found to influence PyC structure on the atomic-scale at \(T_{\mathrm {p}}\) \(\le \)1400 \(^{\circ }\hbox {C}\). Since CNT confinement could lead to anisotropic crystallite growth in PyCs synthesized below \(\sim\)1000 \(^{\circ }\hbox {C}\), and recent modeling indicates that more slender crystallites increase PyC hardness, these results inform fabrication of PyC-based meta-materials with unrivaled specific mechanical properties.     

Co-synthesis of single-walled carbon nanotubes and carbon fibers

A new vertical floating catalytic technique is developed and used to prepare both single-walled carbon nanotubes (SWNTs) and carbon fibers (CFs). Scanning electron microscopy (SEM) observation shows a clear separation of these two materials. Thin films of SWNTs can be peeled easily from the CF substrate which just acts as a catalyst support for the SWNT growth. The production process is also semicontinuous, resulting in a yield of ∼1.0 g h⁻¹ of SWNTs film with high purity. Structure and vibrational properties of these materials are investigated by electron microscopy and Raman spectroscopy, respectively.