前驱体对C/C复合材料的致密化和性能的影响

研究了分别以甲烷和丙烯为前驱体对制备C/C复合材料的新型ICVI工艺致密化速率及组织结构和力学性能的影响.考察了密度与致密化时间之间的变化规律和密度分布,采用偏光显微镜和扫描电镜观察材料的组织结构和试样的断口形貌,利用三点弯曲实验测定材料的弯曲强度.实验结果表明:在致密化时间100h前,以甲烷为前驱体,C/C复合材料的致密化速率比丙烯为前驱体时低,100h后致密化速率发生逆转;以甲烷为前驱体所得C/C复合材料的密度梯度小,组织结构为粗糙层,弯曲强度为250.87MPa,模量为29.29GPa;而以丙烯为前驱体所得C/C复合材料的密度梯度大,组织结构为光滑层,弯曲强度为102.75MPa,模量为11.42GPa.因此,相对而言甲烷作为制备C/C复合材料的前驱体优于丙烯.     

正丙醇ICVI制备C/C复合材料的组织结构及力学性能

以正丙醇为前驱体,N2为载气和稀释气体,采用等温化学气相渗透(ICVI)工艺,沉积温度为1050、1100、1150℃,压力为6kPa,对初始密度为0.43g/cm3的2D针刺炭毡进行致密化,沉积96h制备出表观密度分别为1.64、1.68和1.69/cm3的C/C复合材料.考察了密度随沉积时间的变化规律,利用三点弯曲测试了材料的弯曲强度,采用偏光显微镜、扫描电子显微镜观察了材料的组织结构和断口形貌.结果表明:以正丙醇为前驱体,采用ICVI工艺在1050和1150℃下制备的试样组织为高织构和中织构的混合组织,1100℃制备的试样基体组织为均一的高织构,其弯曲强度可达199.24MPa.在本实验条件下,并未发现正丙醇中的氧元素在高温下对炭纤维的腐蚀作用,正丙醇可以作为前驱体制备高性能C/C复合材料.     

ICVI法制备C/SiC复合材料构件的数值模拟

根据C/ SiC 复合材料的结构特点及等温化学气相浸渗法的工艺特点, 建立了C/ SiC 复合材料ICVI 致密化过程的数学模型, 并将该模型应用于C/ SiC 复合材料构件制备过程的数值模拟中。利用有限单元法, 对航空发动机用C/ SiC 复合材料小喉衬的ICVI 致密化行为进行了数值计算和分析。为了验证计算结果, 设计并进行了相应的对比实验, 对致密化后的喉衬构件进行了密度测量和CT 断层扫描无损检测。实验结果与模拟结果呈现出相同的变化规律并且两者之间偏差较小, 表明本文作者所建立的模型可以很好地描述C/ SiC 复合材料的ICVI 过程。利用该数学模型, 计算了ICVI 过程中喉衬构件的密度分布及其演变规律, 为ICVI 法制备C/ SiC 复合材料构件的进一步研究打下基础, 对ICVI 工艺的优化具有一定的指导意义。      

预制体孔隙结构对炭/炭复合材料ICVI制备工艺的影响

研究了预制体孔隙结构对ICVI工艺致密化过程及基体热解炭微观结构的影响。结果表明：2D针刺炭毡致密化速度高于炭布叠层预制体，1K炭布叠层预制体的致密化速度高于3K炭布叠层；在致密化过程中，热解炭均匀沉积在纤维表面，预制体AS／VR比值变化是导致热解炭微观结构发生改变的根本原因。     

ICVI法制备Si3N4P/ Si3N4 复合材料致密化行为数值模拟

根据Si₃N₄ 颗粒增强体的结构特点及等温化学气相法( ICVI) 的工艺特点, 对Si₃N₄ 颗粒增强Si₃N₄ 复合材料的致密化过程进行了数值模拟。用球形孔隙模型表征Si₃N₄ 颗粒增强体的结构特征, 用传质连续方程表征先驱体在预制体中的浓度分布。为了检验模型的准确性和适用性, 进行了相应的实验验证。模拟结果与实验结果具有相似的致密化规律, 预测的渗透时间和孔隙率与实验结果均十分接近, 表明本文中建立的数学模型可以较好地表征Si₃N₄P / Si₃N₄ 复合材料的ICVI 过程。     

The Infiltration Process and Texture Transition of 2D C/C Composites

2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. The porosity and the variations of the cumulative pore volume were determined by mercury porosimetry. The texture of matrix carbon was studied under a polarized light microscope. The results show that the relative mass gain of the sample increases directly as the infiltration time at the initial stage until 20 h, and subsequently the increasing rate of the relative mass gain decreases gradually with the prolonging of infiltration time. Three layers of pyrocarbon were formed around fibers. Low-textured pyrocarbon was obtained at the initial stage. With the densification going on, high-textured pyrocarbon was formed on the surface of low-textured pyrocarbon. Then, low-textured pyrocarbon was produced again during the final stage of densification. The texture transition is ascribed to the variation of the ratio of cumulative inner surface area to volume of pores and the gas partial pressure in pores.     

Thermo-mechanical characterization of carbon fiber reinforced silicon carbide composites having boron nitride as an interphase material

The carbon fiber reinforced silicon carbide composites were prepared by an isothermal chemical vapour infiltration process. In order to achieve the required density, the carbon fiber preforms in the form of rectangular panels were infiltrated by silicon carbide (SiC) matrix. Prior to the matrix infiltration, a thin coating of boron nitride, as an interphase, was applied on the fiber preform. The test samples were subjected to seal coating of silicon carbide by chemical vapour deposition process. The effect of protective SiC seal coating was examined by testing (3-point bend test) the uncoated and the seal coated samples at different temperatures. Higher value of the flexural strength was observed for the seal coated samples as compared to the uncoated samples, when got tested at high temperature (up to 1400?°C). The detailed analysis of the fractured surfaces of the tested samples was carried out.     

ICVI工艺参数对碳/碳复合材料快速均匀致密化的影响

为了研究碳/碳(C/C)复合材料的快速均匀致密化工艺,参考工业天然气的成分,以92％甲烷(CH4)、5％乙烷(C2H6)、3％丙烷(C3H6)组成的混合气作为前驱体,在沉积温度为1075℃时,采用等温化学气相渗透(ICVI)工艺,在不同系统压力和滞留时间下对16和26 mm两种厚度的碳纤维针刺预制体进行120 h致密化...     

等温化学气相渗透制备碳化硅复合材料的工艺研究

通过研究等温化学气相渗透(ICVI)工艺的主要影响因素,如渗透温度、前驱气体组分比与流速等,对制件密度的影响规律,为 ICVI 制备碳化硅复合材料提供了优化的工艺参数.实验表明:渗透温度为 1050℃,炉压为6666.2Pa (50乇),反应气体配比Ar/CH3SiCl3(iTS)约为 10,仅渗透 3h 表面的渗透厚度便接近 20μm,密度略有增加,渗透效果较好.     

Modeling of CVI process in fabrication of carbon/carbon composites by an artificial neural network

C/C composites maintain unique intensity features at temperatures as high as 2600℃. Be-cause of their superior thermal and mechanical properties, which can persist at ultra-high tem-peratures, C/C composites are used in many areas including national defense, aviation aerospace, etc. At present, high performance C/C composites are mainly fabricated by using CVI proc-esses[1,2]. But it should be pointed out that the CVI process is controlled by many factors such as the infiltration temperat…