炭／炭复合材料导热系数影响因素的研究

研究了影响炭／炭复合材料导热系数的主要因素：炭纤维取向，热处理温度和CVD热解炭的结构，结果表明，在炭／炭复合材料中，影响炭／炭复合材料导热系数的主要因素是CVD热解炭结构；以RL结构为主的CVD热解炭，导热系数高，热处理温度对材料导热系数的影响不及CVD热解炭的微观结构对其的影响。     

DK4缸体冒口优化研究

通过DK4缸体毛坯气孔种类鉴别,分析气孔形成的基本原理,发现气孔多发的根本原因是浇注时型腔内气体压强大于铁液总压强。通过增加冒口数量和高度,缓解型腔内气体压强的同时提高了液体表面压强,使两者大小关系发生逆转,减轻了气孔缺陷。结果表明,生产出组织致密、形状完整、性能优良、各项指标达到用户要求的缸体毛坯。     

炭/炭复合材料制动过程中温度场的仿真

利用有限元热分析软件ANSYS建立炭／炭复合材料制动过程三维有限元模型,确定相关热载荷计算方法和关键参数,仿真制动过程瞬态温度场。计算结果表明：在试环轴向存在明显温度梯度,而径向温度梯度微小,摩擦表面在t=12．7S时达到最高温度662℃,且最高温度出现在靠近试环外径处,与实验结果基本相符,证实了仿真计算结果的正确性。     

ICT技术测试炭/炭复合材料内部密度分布

利用工业计算机辅助层析成像技术(ICT)对不同尺寸的炭/炭复合材料进行了断层摄像试验,发现该技术能真实地反映材料内部的实际密实情况.利用ICT图像给出的相关数据,经过一系列计算,得出材料内部各处的密度值,该方法比传统的排水法所得的结果精确,而且无需从制品中取样,节省了材料和时间.ICT技术有望用于其它复合材料的密度测试.     

带凸缘高盒形件毛坯尺寸计算方法

基于简单盒形件毛坯计算方法,研究食品罐类带凸缘高盒形件毛坯尺寸的理论计算方法,用该理论方法和计算机模拟方法分别计算某食品罐毛坯尺寸,理论计算与计算机模拟结果一致,按照理论计算的结果进行落料试冲,成形的食品罐符合要求,表明该理论计算方法具有一定的指导意义。     

电磁场辅助CVD沉积倒锥状热解炭的微结构及形成机理(英文)

采用电磁场辅助CVD法,在650～750°C的温度下制备出具有中空结构的倒锥状热解炭。此类倒锥状热解炭生长在C/C复合材料中热解炭的表面。采用高分辨率透射电镜对倒锥状热解炭的内部结构进行精细表征。结果表明,倒锥状热解炭的内部织构呈现出从根部杂乱的缠绕织构直接到其紧邻茎部有序的高织构的变化趋势,而从其茎部至锥尾部区域,炭微晶结构有序化程度逐渐降低。倒锥状热解炭的形成机理可推测为是一种在强电磁场作用下的极化诱导效应和击穿放电作用下的颗粒填充效应的综合作用。     

沉积条件对低温各向同性热解炭微观结构的影响

采用不同浓度的丙烷通过准稳态流化床化学气相沉积(FBCVD)工艺在1250~1450℃的沉积温度下产生低温各向同性热解炭(LTIC),利用SEM和TEM研究沉积温度和丙烷浓度对LTIC微观结构的影响。结果表明:沉积温度和丙烷气体浓度对低温各向同性热解炭的形貌结构有较大的影响。随着沉积温度或丙烷气体浓度的升高,各向同性热解炭形貌结构由片层状向类球形颗粒状转变,密度和织构降低,而这些变化与芳香碳平面的弯曲度发生变化有关。增大密度和提高形核率是获得性能优异各向同性热解炭的一个重要途径,沉积温度选择1350℃,丙烷浓度保持在25%~40%之间,所获得的热解炭结构和性能较为优异。     

超声波钎焊原理

<正>超声波通过液体时,由于交变声压的作用,会产生稀疏和压密区域。当为负压强时,液体中出现数量多、体积极小的空腔,这种现象称为"空化效应"。空腔产生后,随即在短暂的时间内,在声压的作用下闭合。空腔在闭合时,会产生高达几百或几千个大气压的局部瞬时高压,从而产生冲击波。该冲击压力作用到固体时,能破坏固     

渗硼提高炭材料抗氧化性研究进展

综述了气体渗硼、液体渗硼和固体渗硼三种主要渗硼方式、各自优缺点及适用范围,分析了微波对炭材料渗硼的促进作用,给出了渗硼提高炭材料抗氧化性的机理,对渗硼技术的今后发展进行了展望。     

浅盒形板壳件毛坯展开的算法研究

在浅盒形板壳件毛坯几何算法的基础上,分析了盒形板壳件拉深过程中的变形与网格变化,阐述了盒形板壳件的设计特点及冲压成形条件,基于Bézier曲线构建,对盒形板壳件直边上的毛坯展开给出了解析计算,其计算结果所得到的毛坯展开图形与几何算法所得到的毛坯展开图形结果基本一致,两者的展开图形的面积也非常接近.该方法求解具有一定的应用价值.     

C/C复合材料表面原位生长SiC_w的工艺

以三氯甲基硅烷(CH3SiCl3,MTS)为先驱体原料,采用化学气相沉积法在C/C复合材料基体上原位生长碳化硅晶须,研究稀释气体流量、催化剂以及沉积温度对碳化硅晶须生长的影响。结果表明:有催化剂存在时可以制备具有较高长径比的SiCw,无催化剂制备的SiC主要以短棒状或球状SiC为主;随着稀释气体流量或者沉积温度的增加,SiCw的产率是先增加、后减少,在1 100℃、载气和稀释气体流量均为100 mL/min时,制备的碳化硅晶须的产率最高,晶须质量最好。     

Rhenium Oxidation by Steam at High Temperatures

The kinetics of rhenium oxidation were studied under flowing steam+argon mixtures, at atmospheric total pressure and steam partial pressure in the range 24–74 kPa, and at temperatures from 1600°C up to 2200°C. No regime change was observed in the temperature dependence of the oxidation rate, which shows that the same chemical regime extends up to the highest temperature investigated. Moreover, at high temperature, the results showed a dependence of the oxidation rate on the gas velocity and the steam partial pressure, in good agreement with a gas-phase mass-transfer correlation for laminar flow, revealing that, for the conditions used, mass-transport processes in the gas phase also act as a limiting factor. It was assumed that the mass-transport limiting factor is the steam diffusion through a volatile oxides gaseous layer above the rhenium surface. A comparison of these results with rhenium oxidation rates reported for air leads us to propose the dissociative adsorption of the H₂O molecule as the limiting chemical stage of the oxidation process.     

预制体对C／C复合材料热膨胀系数的影响

以天然气为前驱气体,整体碳毡和2D针刺碳毡为预制体,采用热悌度化学气相渗积技术制备了两种C／C复合材料,其表观密度均为1．74g／cm^3。借助光学显微镜和扫描电子显微镜观察了热解碳基体的生长特征和微观形貌,采用热膨胀仪测量了两种材料的热膨胀系数（CTE）,研究了由不同预制体增强C／C复合材料的CTE,解释了造成材料不同方向CTE差异的主要原因。结果表明,随着温度升高,材料A和B的CTE是逐渐升高的,且Z向CTE值均大于XY向。当两种材料在Z向的纤维体积分数接近时,随着XY方向纤维体积分数增大,材料在Z向的CTE增大,在XY向的CTE降低,两种材料存XY和Z向的CTE旱如下分布：αB—z〉dAz〉αA—xy〉αBxY-C／C复合材料的CTE主要取决于纤维体积分数和排市、碳基体及材料中的孔隙分布情况,前者起决定作用。     

Rapid chemical vapor infiltration of C/C composites

With liquid petrol gas (LPG) as carbon source, carbon felt as porous perform and hydrogen as diluent, C/C composites were fast fabricated by using a multi-physics field chemical vapor infiltration (MFCVI) process in a self-made furnace. A set of orthogonal experiments were carried out to optimize parameters in terms of indices of density and graphitization degree. The results show the optimal indices can be achieved under the conditions of temperature 650 °C, LPG concentration 80%, gas flux 60 mL/s, total pressure 20 kPa, infiltration time 15 h. The verification experiment proves the effectiveness of the orthogonal experiments. Under the optimal conditions, the graphitization degree of 75% and bulk density of 1.69 g/cm are achieved with a uniform density distribution. At the same time, a new structure is obtained.     

Improved properties of carbon fiber paper as electrode for fuel cell by coating pyrocarbon via CVD method

The fabrication of a pyrocarbon coated carbon paper and its application to the gas diffusion lay (GDL) of proton exchange membrane (PEM) fuel cell were described. This carbon paper was fabricated by using conventional carbon paper as the precursor, and coating it with pyrocarbon by pyrolyzing propylene via the chemical vapor deposition (CVD) method. For comparison, conventional carbon paper composites were also prepared by using PAN-based carbon fiber felt as the precursor followed by impregnation with resin, molding and heat-treatment. SEM characterization indicates that pyrocarbon is uniformly deposited on the surface of the fiber in the pyrocarbon coated carbon paper and made the fibers of carbon felt bind more tightly. In contrast, there are cracks in matrix and debonding of fibers due to carbonization shrinkage in the conventional carbon paper. Property measurements show that the former has much better conductivity and gas permeability than the latter. In addition, current density-voltage performance tests also reveal that the pyrocarbon coating can improve the properties of carbon paper used for electrode materials of fuel cell.     

Microstructure of carbon fiber preform and distribution of pyrolytic carbon by chemical vapor infiltration

The carbon/carbon composites were made by chemical vapor infiltration(CVI) with needled felt preform. The distribution of the pyrolytic carbon in the carbon fiber preform was studied by polarized light microscope (PLM) and scanning electronic microscope(SEM). The experimental results indicate that the amount of pyrolytic carbon deposited on the surface of chopped carbon fiber is more than that on the surface of long carbon fiber. The reason is the different porosity between the layer of chopped carbon fiber and long carbon fiber. The carbon precursor gas which passes through the part of chopped carbon fibers decomposes and deposits on the surface of chopped carbon fiber. The pyrolytic carbon on the surface of long carbon fibers is produced by the carbon precursor gas diffusing from the chopped fiber and the Z-d fiber. Uniform pore distribution and porosity in preform are necessary for producing C/C composites with high properties.     

C／C复合材料等温CVI工艺模糊神经网络建模

C／C复合材料等温CVI工艺影响因素繁多，而效率极低，造成C／C复合材料的生产周期极长、制造成本极高。基于模糊神经网络技术及遗传算法，以有限元数值模拟结果作为网络训练的虚拟样本，建立了C／C复合材料等温CVI工艺预测系统，利用该系统挖掘得到了等温CVI工艺主要影响因素，如沉积温度，前驱气体组份比与流速等，对制件密度的作用规律，为CVI工艺的综合设计与优化提供了理论依据，提高了CVI工艺的设计水平，以期达到降低C／C复合材料制造成本的目的。     

Microstructure characteristic and formation mechanism of crackfree TaC coating on C/C composite

The microstructure characteristic and formation mechanism of the crackfree and ablation-resistant TaC coating deposited on the C/C composite by Chemical Vapour Deposition（CVD） were investigated, using the reaction system of TaCl5-C3 H6-H2-Ar. The results show that the nanosized pore structure formed in the TaC coating interior during CVD process is the main factor to reduce the hardness, elastic modulus, linear expansibility and inner thermal stress. Then crackfree coatings can be prepared and their thermal shock resistance can be enhanced. To obtain the dense and homogeneous matrix surface is necessary for the crackfree and low stress coating. The TaC coating structure that distributes from the dense matrix towards loose coating surface will result in the thick crackfree coating with good thermal shock resistance.     

多孔体制备工艺对C/C-SiC复合材料弯曲性能的影响

以针刺整体炭毡为坯体,采用CVD和树脂浸渍／炭化混合法增密制备了4种C／C多孔体,然后熔硅浸渗C／C多孔体制备了C／C-SiC复合材料;研究了不同炭涂层、高温热处理对C／C-SiC复合材料弯曲强度和断裂方式的影响。结果表明：热解炭涂层可减少制备过程中炭纤维的损伤,具有适中的界面结合强度,使复合材料的弯曲强度达到161．5MPa,表现出良好的“假塑性”;适当选择高温热处理工艺可制备弯曲性能较高,具有一定“假塑性”的C／C-SiC复合材料。     

Production and characterization of wear resistant Ti(C,N) coatings manufactured by modified chemical vapor deposition process

Wear resistant Ti(C,N) coatings were produced by changing the heating rate during the chemical vapor deposition process (CVD). The modification of the CVD process led to the formation of Ti(C,N) coatings with a particulate grain architecture consisting of two different crystallites (star-shaped and lenticular-like morphologies) co-existing in the coating layer. The microstructure formation of the Ti(C,N) layer was investigated by interrupting the CVD process at different temperatures. Depending on the deposition temperature, rounded, star-shaped and/or lenticular-like crystallites formed. The overall C/N ratio of the Ti(C,N) layer was 0.16/0.84, as determined by x-ray diffraction. TEM/EELS investigations of Ti(C,N) crystallites revealed an inhomogeneous distribution of carbon and nitrogen in the grains. Cutting tests showed outstanding wear resistance of the Ti(C,N) layers produced by the modified CVD process.