旋转CVI快速沉积热解碳基体

采用一种新的CVI工艺(旋转CVI)进行了二维碳布沉积热解碳基体的实验研究.通过实验优化工艺参数,在低压(5 kPa)、高温(1 100 ℃)、体积分数为62.5%的C3H6与3.5 mm.min-1的碳布旋转线速度条件下,获得了微观孔隙中0.25 μm.h-1的热解碳沉积速度、约7%的C3H6转化率与理想的热解碳基体形貌.分析了旋转CVI工艺中沉积温度和C3H6浓度等分别对沉积速度、热解碳基体形貌及C3H6转化率的影响.     

沉积温度对微波热解CVI制备碳/碳复合材料密度及组织结构的影响

以碳毡为预制体,N2为稀释气体,甲烷为碳源前驱体,其分压为10 kPa,滞留时间为0.15 s的工艺条件下,研究了不同沉积温度对微波热解化学气相渗透(chemical vapor infiltration,CVI)工艺制备碳/碳复合材料的致密化速率、样品的体积密度及其密度均匀性的影响,并对其组织结构进行了观察.分析了沉积温度对微波热解CVI工艺制备碳/碳复合材料的密度与组织结构的变化规律.结果表明:在微波热解CVI工艺中,随着沉积温度的降低,碳毡预制体的致密化速率及最终体积密度呈现先升后降,1100 ℃沉积制备复合材料的密度均匀性最好,并呈现从内到外逐步沉积的规律.热解碳的织构主要为中等织构.     

碳化硅CVI工艺沉积动力学模拟研究

化学气相渗透(CVI)工艺被广泛应用于制备碳基及碳化硅(SiC)基复合材料，CVI工艺是实现制备高纯度和高晶粒度SiC基体的SiC_f/SiC复合材料最佳方案。为了优化CVI制备SiC基体的工艺参数，本文主要研究了CVI工艺沉积SiC的动力学机理及数值模拟。对于CVI工艺SiC沉积的动力学，本文提出了SiC沉积过程的反应动力学机理模型，并通过耦合反应器内的流场和浓度场，模拟了甲基三氯硅烷(MTS)在CVI过程中的SiC沉积实验。通过对样品在CVI致密化过程中孔隙率的实验结果与模拟结果比较，表明该SiC沉积动力学模型的合理性。通过模拟获得了在反应器内的速度场和各组分(MTS, CH₃,SiCl₃)的浓度场分布情况，以及预制体致密化过程的密度分布情况。以上SiC的CVI工艺动力学模拟，对未来优化SiC_f/SiC复合材料CVI工艺具有重要的指导意义。     

快速液相气化法制备碳/碳复合材料研究进展

快速液相气化沉积是目前高温复合材料制备工艺中致密化效率最快的一种方法，比传统等温CVI技术要快2个数量级以上，可大幅度降低制备成本。文中介绍了这一快速致密化技术的基本原理，方法特点，分析了该技术快速致密化的根本原因；概述及探讨了国内外对该技术在工艺及模拟方面的研究现状及存在的问题；最后展望了液相气化致密技术的应用前景。     

碳/碳复合材料力学性能的研究进展

本文综述了碳/碳复合材料力学性能的研究进展,包括碳纤维、基体炭、界面性能、制备工艺及工艺参数等对碳/碳复合材料力学性能的影响。同时简单介绍了当今单向碳/碳复合材料力学性能的表征手段。希望对碳/碳复合材料力学性能的研究及应用提供帮助。     

碳/碳复合材料表面软复合磷酸钙层

为改进碳／碳复合材料的生物活性，发展了表面软复合磷酸钙层的制备工艺。首先在碳／碳复合材料表面通过离子束辅助沉积技术形成的钛镀层，然后经浓碱液处理后呈多孔网状，该网状结构可在模拟体液（SBF）中诱导沉积出生理磷灰石层，从而在碳／碳复合材料表面形成软复合磷酸钙层。所获得的软复合磷酸钙层厚度约为8μm ，结晶结构为羟基磷灰石，但其Ca,P摩尔比n(Ca)/n(P)低于1．67。     

石墨化处理对高压浸渍碳化碳/碳复合材料抗氧化性能的影响

用超高压液相浸渍和碳化,经石墨化处理制备了毡基碳／碳复合材料。采用等温氧化实验,系统研究了所得试样在不同温度(773～1 173 K)条件下的氧化动力学行为;用X射线衍射和扫描电子显微镜检验观察了石墨化处理前后毡基碳／碳复合材料的氧化形貌和微观结构。结果表明：石墨化处理可明显的提高毡基碳／碳复合材料的抗氧化性能;毡基碳／碳复合材料的基体在氧化反应中优先氧化,氧化反应速率随温度的升高而增大;在高于或低于临界温度973 K时,毡基碳／碳复合材料的氧化反应分别受2种不同的机制控制,其反应活化能E,在石墨化前分别为7.91×10~4 J／mol和2.80×10~4J／mol,石墨化后分别为1.08×10~5J／mol和4.42×10~4J／mol。     

C/C复合材料正压CVI工艺的实验探索

研究了沉积温度、反应气浓度等因素对沉积过程的影响,并对所得试样的微观组织结构及其内部孔隙的分布规律进行了分析。研究表明,当沉积温度低于900℃时,可以避免或减少沉积过程中炭黑的生成,在该前提下,正压CVI工艺可在较短时间内制备出具有合理微观组织结构的C／C复合材料制作,因此提高了反应气体的利用率,正压CVI工艺是一种低成本的C／C复合材料制备工艺。     

化学气相沉积碳/碳复合材料结构与性能的研究

一、序言 碳/碳复合材料由于有良好的热物理和力学性能,因而在宇航方面的应用无与伦比。化学气相沉积的碳/碳复合材料性能变化复杂,影响因素也很多,但其最主要的要受材料内部沉积碳微结构的影响,而微结构又是由工艺参数所决定的。笔者以前报导了工艺部分,采用热梯度法,以碳毡为基,不同工艺参数得出不同沉积碳微结构,指出控     

碳毡自加热热解沉积致密化工艺初探

本文通过对不同尺寸、叠层层数,密度,形状和孔洞的碳毡进行自加热研究,探究了不同物性参数碳毡预制体的自加热规律,并进一步进行了自加热热解沉积制备C／C复合材料的可行性研究。研究发现：预制体在加热中能维持高温,并能在预制体中形成一定的逆向温度梯度,在自加热的工艺条件下,热解沉积制备C／C复合材料工艺是完全可行的。     

镍催化制备炭/炭复合材料

利用催化化学气相沉积法制备炭／炭复合材料，研究了反应温度、前驱体气体含量、催化剂含量和时间对所制备的炭／炭复合材料密度的影响，采用扫描电镜观察分析了基体碳的形貌。结果表明，利用催化剂镍可制取密度达1．594g／cm^3的炭／炭复合材料，并有晶须状基体碳生成。在各种工艺参数中，对炭／炭复合材料的密度影响最大的是温度和前驱体气体，其次为催化剂含量，最后是时间。     

结构炭/炭复合材料力学性能及微观结构研究

采用四向编织、快速化学气相渗透致密化新工艺制备了炭／炭复合材料,其弯曲强度达３２０ＭＰａ。分析研究了这种材料的力学性能特征。利用ＳＥＭ和高分辨ＴＥＭ分析了基体炭、炭纤维／基体灰界面的精细结构,发现炭纤维呈单根被基体炭包围,基体现灰呈层片状,为二维有序的乱层石墨结构;在炭纤维与基体炭之间存在着过渡相,这一过渡相厚度的约几十纳米,随着与炭纤维之间距离的增大,它们之间形成的夹角由小变大,这一过渡相即为炭     

生命周期评价法在炭/炭复合材料制备中的应用研究

生命周期评价法(LCA)是指用数学物理方法结合实验分析对某一过程、产品或事件的资源、能源消耗，以及废物排放、环境吸收和消化能力等环境负担性能进行评价，以定量确定该过程、产品或事件的环境合理性及环境负荷量大小的一种新型研究方法。输入／输出法是LCA中的一种重要方法，本研究利用该方法对炭／炭(C／C)复合材料两种制备工艺(等温和热梯度化学气相渗透)中的资源、能源消耗以及污染物排放进行了定量评估。结果表明，与热梯度工艺相比，等温化学气相渗透法消耗了更多的资源、能源，给环境造成了严重的负荷，等温化学气相渗透法需改进，热梯度化学气相渗透工艺有广阔的应用前景。     

新型炭纤维/泡沫炭预制体的制备及致密化研究

由炭纤维/酚醛树脂经过发泡、固化和炭化制备出4种不同炭纤维含量(3%,7%,10%和15%)的泡沫炭作为制备炭/炭复合材料新型预制体,通过等温化学气相沉积对预制体进行致密化处理。研究了炭纤维含量对预制体微观结构、致密化过程及力学性能的影响。结果表明:炭纤维含量增加,使预制体产生更多的微裂纹,并有更多的炭纤维裸露在泡沫炭韧带外,有助于提高化学气相沉积的沉积速率。炭纤维/泡沫炭预制体炭/炭复合材料压缩强度随着预制体中炭纤维含量的增加而增加,当炭纤维体积分数为10%时,压缩强度达到峰值,为43MPa。     

Oxidation behavior and protection of carbon/carbon composites prepared using rapid directional diffused CVI techniques

The oxidation kinetics of carbon/carbon (C/C) composites prepared using a rapid directional diffused (RDD) CVI process were studied. The results showed that the Arrhenius curve for the RDD CVI C/C composites consists of two straight lines, the intercept of which is at about 700 °C at the linear oxidation stage. The oxidation rates are controlled by the surface reaction at 600-700 °C, and the corresponding activation energy is 121 kJ/mol. Between 700 and 800 °C, the oxidation rates are dominated by chemical reaction and diffusion, and the relevant activation energy is 80 kJ/mol. SEM investigation showed that the oxidation starts with original pores on the C/C composite surface with the carbon fiber and matrix oxidized simultaneously. An inexpensive and easily pasted coating containing epoxy organic silicon resin, borates, refractory particulates, etc. was developed. After isothermal temperature, thermal cycle and immersion water oxidation tests, the coating was demonstrated to exhibit good oxidation-resistance properties. The oxidation-resistant mechanism of the coating is discussed.     

Friction performance of C/C composites prepared using rapid directional diffused chemical vapor infiltration processes

A technology used to prepare C/C composites using a rapid directional diffused (RDD) chemical vapor infiltration process has been investigated. General RDD technologies were explored, and optimal parameters were determined. The friction and wear properties of this material were researched. The results showed that in the RDD process, propylene and nitrogen were rapidly and directionally diffused into the carbon preforms enabling carbon deposition to occur from the inside of the preform to the outside. This method prevents the formation of an outer crust on the surface of preforms and facilitates uniformity of densification. With the RDD process no surface machining was required between chemical vapor infiltration (CVI) cycles thereby enabling continuous densification and reducing the CVI cycle times. The optimum processing conditions for RDD CVI were as follows; furnace temperature 950 °C; and furnace pressure 6.7 kPa. The C/C composites produced using RDD CVI processing exhibited good friction performance. Their curves of the brake moment with the velocity are stable under dry conditions, and their wet brake moment is greatly reduced. The average thickness wear is decreased to 9.5×10⁻⁴ mm/surface/stop.     

Microstructure and tribological behaviors of C/C–BN composites fabricated by chemical vapor infiltration

In this paper carbon fiber reinforced carbon–boron nitride binary matrix composites (C/C–BN) were prepared by chemical vapor infiltration (CVI). The infiltration of BN in the CVI process was controlled by the diffusion of BCl₃, and BN matrix was distributed homogeneously in the porous carbon fiber reinforced carbon matrix composites (C/C) due to the good infiltration ability of BN. The as-received C/C–BN composites were composed of 92 vol% C and 8 vol% BN. Both the friction coefficient and wear rate of C/C composites decreased significantly by the incorporation of BN. After heat-treated at 1600 °C, the interlayer spacing of CVI BN decreased to 3.36 Å, and CVI BN with high crystalline degree displayed the excellent lubricating effect, leading to the decrease of friction coefficient and wear rate. The improvement of the tribological properties also was partially attributed to the improved oxidation resistance and the formation of friction film by the incorporation of BN matrix.     

C/C复合材料的高温抗氧化研究进展

以设计思路的发展演化为线索,结合国内外近年的研究报道,从选材的性能要求、组成、抗氧化机理、成功范例及制备工艺的角度出发,分别对抗氧化涂层技术以及抗氧化基体改性技术进行了介绍。特别选取了近年在碳／碳复合材料抗氧化研究中报道较少的制备技术进行详细介绍,其中包括涂层技术中的超临界态流体工艺、溶胶－凝胶法、熔浆法、PACVD法以及基体改性技术的快速致密化工艺。这一领域内的中外研究也进行了对比,并在文章最后提出了对于碳／碳复合材料高温氧化保护研究方向的一些看法。     

Effect of Carbon and Silicon Carbide/Carbon Interlayers on the Mechanical Behavior of Tyranno-SA-Fiber-Reinforced Silicon Carbide-Matrix Composites

Several CVI-SiC/SiC composites were fabricated and the mechanical properties were investigated using unloading–reloading tensile tests. The composites were reinforced with a new Tyranno-SA fiber (2-D, plain-woven). Various carbon and SiC/C layers were deposited as fiber/matrix interlayers by the isothermal CVI process. The Tyranno-SA/SiC composites exhibited high proportional limit stress (∼120 MPa) and relatively small strain-to-failure. The tensile stress/strain curves exhibited features corresponding to strong interfacial shear and sliding resistance, and indicated failures of all the composites before matrix-cracking saturation was achieved. Fiber/matrix debonding and relatively short fiber pullouts were observed on the fracture surfaces. The ultimate tensile strength displayed an increasing trend with increasing carbon layer thickness up to 100 nm. Further improvement of the mechanical properties of Tyranno-SA/SiC composites is expected with more suitable interlayer structures.