【作者】 李伟；

【导师】 陈振华；

【作者基本信息】 湖南大学 ， 材料加工工程， 2009， 博士

【摘要】 炭纤维/炭(Cf/C)复合材料具有高比强度、高比模量、材料结构可设计性、高温下强度保持率高等优异的性能,它广泛应用于军事、航空航天等领域。Cf/C复合材料抗氧化涂层研制成功后,在氧化气氛下可以多次重复使用,使它成为一种极好的耐烧蚀材料,也是一种耐高温热结构材料,成为当今先进复合材料研究和开发的重点。但是Cf/C复合材料也存在一些问题限制了它的应用,目前主要的问题是各种常用的致密化方法和浸渍剂性能不尽如人意。探索一种全新的粉末涂层快速制备Cf/C复合材料途径,并通过沥青浸渍-炭化和萘原位浸渍聚合-炭化的复合致密化工艺,来达到减少致密化周期、降低材料成本。本文主要研究炭纤维处理、硼改性酚醛树脂(BPR)粉末涂层、预制体的成型及炭化、Cf/C复合材料的致密化和抗氧化涂层等对试样性能的影响,其中炭纤维开纤和BPR粉末涂层对Cf/C复合材料的性能研究十分重要,采用空气梳对炭纤维进行气流开纤和BPR粉末涂层可以制备柔韧性优良的丝束,该丝束不仅可以直接成型,而且还可以编织、纺织成一定的形状后成型。Cf/C复合材料的致密化对其性能提高有非常明显的效果,集中探讨了三种致密化方法对Cf/C复合材料性能的影响。针对炭纤维表面惰性不易被浸润的特性,使用浓硝酸氧化法对炭纤维进行表面改性,采用扫描电镜(SEM)、红外光谱(FT-IR)和动态接触角法等研究了炭纤维的形态、特征基团和表面浸润性能的改变。首次利用空气梳开纤和粉末涂层的方法制备柔韧预浸炭纤维丝束,空气梳对炭纤维进行开纤时,考察气流压力和炭纤维处理速度对开纤幅度和稳定性的影响;该方法充分克服炭纤维开纤困难的难题,如采用常规的罗拉法开纤,分丝效果不太理想,并且对炭纤维产生巨大的破坏作用。比较系统地研究开纤幅度、处理速度、树脂粉末的粒径和加热温度等对BPR粉末在炭纤维丝束上的涂层效果。采用热压成型工艺对BPR粉末涂层炭纤维进行成型,并对预制体的成型工艺和性能进行研究,成功地制备高体积分数炭纤维的预制体,为降低Cf/C复合材料的成本提出了新思路。通过达西定律、粉末涂层炭纤维热压成型的特点和BPR的性能首次建立热压成型的浸渍模型,并成功地将其运用于预制体成型过程中的工艺参数调整。在合理控制炭化工艺的前提下,将预制体热解制备Cf/C复合材料。研究不同致密化方法对Cf/C复合材料性能的影响。通过沥青浸渍-炭化(PIC)、原位浸渍聚合-炭化(IsIPC)和硼改性酚醛树脂浸渍-炭化(BPR-IC)对Cf/C复合材料进行致密化,研究不同致密化方法对Cf/C复合材料的密度、开口气孔率和形态结构等的影响。首次提出PIC和IsIPC复合致密化方法,并对萘原位浸渍聚合的浸渍机理、聚合机理和聚合最佳条件进行研究,通过复合致密化方法处理的Cf/C复合材料的性能有较大幅度的提高。采用X-射线衍射(XRD)分析不同致密化方法对Cf/C复合材料的石墨化度的影响,并由导热机理探讨了不同致密化方法对Cf/C复合材料导热性能的影响。比较粉末涂层工艺和致密化方法对Cf/C复合材料高温热失重的变化,从而研究Cf/C复合材料基体制备工艺对高温抗氧化性能的影响。由于Cf/C复合材料本身的抗氧化性能较差,必须对其进行抗氧化处理才得以应用。对Cf/C复合材料采用包埋法制备SiC/MoSi2复合涂层,并对其界面性能和抗氧化性能进行初步的探讨。对涂层Cf/C复合材料在1500℃下进行等温氧化和1500℃至室温条件的抗热震研究,分析涂层对高温抗氧化性能的影响。更多还原

【Abstract】 Compared with conventional composites, Cf/C composites possess good qualities such as higher specific strength, higher specific modulus, programmabler material structure and better retentive ratio of strength at high temperature. So Cf/C composites have been widely used in the military, aerospace and other fields. After Cf/C composites anti-oxidation coated are successfully developed, Cf/C composites can be reusable under the condition of oxidized ambience. This makes it possible to become an exellent ablative resistant material and also a high temperature thermal structure material, as today’s focus on advanced composite research and development. But some problems limited the application of Cf/C composites. At present the main problem is that commonly-used methods for densification and the property of the impregnant are not satisfactory. This essay explored a new rapid way for preparing Cf/C composites with the powder coated carbon fiber tows, and through the multiple densification process of the pitch impregnation-carbonization and naphthalene in-situ impregnation polymerization-carbonization, few densification cycles and material costs were realized.This article has mainly studied the performance of the samples under the influence of the carbon fiber disposed, BPR powder coating, the formation technology and carbonization of the preforms, the densification and the oxidation protective coating and so on. The spreading of carbon fiber and the coating of BPR powder are the very important aspects to study the performance of Cf/C composites. The carbon fiber dispersed by air-comb and BPR powder coated the carbon fiber results to the flexible towpreg carbon fiber tows. These carbon fiber tows may not only carry on the formation in a direct way, but also product a very flexible towpreg suitable for weaving, braiding, and so on. The densification of Cf/C composites has a very significant effect on its performance, so we focus on three densification methods of Cf/C composites.Due to the inertia feature on the surface, the carbon fiber was hard to be fully soaked, nitric acid oxidized treatment scheme was put forward. The surface treatment of carbon fiber influencing the performance of the composites was deeply explored. The surface shapes, the characteristic groups and surface wettability of surface treated carbon fiber were analyzed by SEM, FT-IR and dynamic contact angle as well. Air-comb spread carbon fiber tows and the powder coating process are firstly introduced to prepare the flexible towpreg carbon fiber tows. When the carbon fiber was spread by the air-comb, the scope and the stability of the spread carbon fiber tow was studied under the gas pressure of air-comb and the processing speed of the carbon fiber, thus the difficulty of the spread carbon fiber tow was overcome. If the routine Roller spreading carbon fiber tow was adopted, the effect was not perfect and it also had the immense breakage to carbon fiber. This essay systematically investigated that the scope of the spread carbon fiber tow, the processing speed, the resin powder particle size and the heating temperature have the influence on the effect of the powder coating. Secondly, the research in boron modified phenolic resin powder coating on the spread carbon fiber tows, focused the powder coating influence on the scope of the spread carbon fiber tow, the processing speed, the resin powder particle size and the heating temperature.The formation technology and the performance relations of the preforms were studied by hot pressing with BPR powder coated carbon fiber tows, and simultaneously the mechanical properties of the preforms and the appearance of cross section were researched in details, finally the preforms with high volume fraction of carbon fiber were triumphantly prepared, which put forward a new train of thought in reducing the cost of Cf/C composites. The BPR impregnation experiment model was established on the basic of Darcy’s law, the hot pressing of the powder coated carbon fiber tows and the property of BPR. In addition, it was successfully applied in adjusting parameter in the hot pressing process of the preforms. Cf/C composites were formed after the preforms were carbonized with a reasonable carbonization technology.This article analyzed how the densification methods influenced the performance of Cf/C composites. The PIC, IsIPC and BPR-IC were adopted to densify Cf/C composites, and meanwhile the influence from the densification cycle to the density and open porosity of Cf/C composites was detailedly analyzed. The PIC and IsIPC multiple treatments were used to densify Cf/C composites. The impregnation mechanism, polymerization mechanism and the best conditions of in-situ impregnation polymerization were investigated. The properties of Cf/C composites increased at a certain rate after multiple densifications. The degree of graphitization of Cf/C composites with different densifications have been earnestly analyzed by XRD. The thermal conductivity of Cf/C composites with different densifications were discussed on the thermal conductivity mechanism.In order to study the technology of preparation Cf /C composites to the high temperature oxidation properties resistance, the techniques of powder coating and the methods of densification to Cf/C composites had been researched by the weight loss of Cf/C composites. As a result, poor oxidation resistance of Cf/C composites, Cf/C composites must be treated with oxidation resistance before their application. The SiC/MoSi2 compound coating was prepared by pack cementation technology on Cf/C composites, and the preliminary discussion to its boundary performance and the oxidation resistance performance were explored. The coated Cf/C composites were studied on isothermal oxidation at 1500℃, the research on the thermal shock was done at 1500℃on the condition of the room temperature, and the influence on oxidation resistance at high temperature was analyzed.更多还原