C/C复合材料SiC涂层的研究

【作者】 刘兴昉；

【导师】 黄启忠；

【作者基本信息】 中南大学 ， 材料学， 2004， 硕士

【摘要】 C／C复合材料具有质轻、耐高温等一系列优点，但是抗氧化性差，耐冲刷能力较低，这些固有缺陷限制了它在高温场合下的实际应用。对C／C复合材料进行涂层防护是一种重要的解决方案。SiC涂层具有高的硬度、较好的高温强度、良好的导热性能和热稳定性等，且SiC涂层与炭石墨基体化学相容性好。因此，对C／C复合材料表面进行SiC涂层的研究，具有十分重要的现实意义。 本研究由不同的涂层制备方法（刷涂法、浸涂法、气相反应法）在C／C复合材料、石墨基体表面制备了SiC涂层。 刷涂和浸涂是湿式工艺中较为通用的方法。制备出合适的浆料是其关键技术之一，它要具有悬浮稳定性和流变性。通过调节浆料酸碱度、比重等因素可获得较满意的悬浮稳定性和流变性。由硅溶胶和Si粉配备的简单浆料经高温热处理工艺可以在C／C复合材料上用刷涂法制备最优涂层。浸涂工艺控制参数较多，在时间一定的情况下，浸涂量与浆料比重、基体种类有关，可以通过控制浸涂量来控制涂层的厚度。所用浆料的最优参数是PH=9，密度为1.62 gcm^-3。 气相反应法工艺较复杂，它是以工业用Si和辅助剂（SiO₂）为原料，在高温、惰性环境中反应产生SiO蒸汽，将其引入反应室与C／C复合材料在不同温度下进行气相反应，从而在试样表面生成SiC涂层。所得涂层致密性好，可达一定的厚度，SiC的生成主要是SiO蒸气通过扩散进入C／C复合材料并与之反应生成的。得出了获得最优涂层的高温热处理工艺为（室温～1700℃／2hr→1700℃／1hr→1700℃～1900℃／1hr→1900℃／1hr），这个工艺制度不仅可以获得较好的梯度分布，有效地消除涂层制备中产生的裂纹，并使SiC组织趋于连续、均匀，获得较理想的SiC涂层，它还能在涂层中制备SiC晶须。通过在基体材料中引入Fe、Co、Ni，在涂层中制备出了长径比更大的SiC纳米晶须。 用抗热震和抗氧化综合考查了SiC涂层的性能。结果表明，气相反应法涂层热震性最好。涂层中的SiC纳米晶须和SiC颗粒共同影响了涂层材料的抗弯强度，进而影响了其热震性能。纳米晶须的瓦解会削弱抗弯强度，而SiC颗粒重结晶可以增强抗弯强度。含SiC纳米晶须丰富的涂层在急冷或缓冷条件下抗热震性都优于其它涂层材料，而中南大学硕士学位论文摘要SIC纳米晶须较少的涂层在急冷条件下抗热震性优越。气相反应法涂层随工艺不同抗氧化性各异。在氧化初期，不含SIC纳米晶须的涂层抗氧化性能最好;而在氧化后期，不经催化处理得到纳米晶须的涂层抗氧化性最好。浸涂法涂层和气相反应法涂层在抗氧化过程中的氧化失重率相差比较大，在氧化初期，前者有一个重量增加的过程，表明其抗氧化性最好;而后者在氧化的各个阶段都是一个失重的过程。更多还原

【Abstract】 Although C/C composites and graphites have a series of excellent properties such as low density,high temperature resistance,etc.,they are limited to be used in high temperature situation for their poor oxidation resistance and weak erosion resistance.Coating protection is regard as one of the most important resolution schemes.Because SiC coating has high rigidity preferable high temperature intensity, favourable heat conductance , thermal stability and good chemical compatibility with C/C,it is very important in practice to launch research on SiC coating for C/C composites and graphites.In this paper,SiC coating was prepared by different methods（paste coating,dip coating and vapor reaction coating） on the surfaces of C/C composites and graphites.Paste coating and dip coating are both ordinary methods in wet technics,whose key technology is to make suitable slurry with appropriate floating stability and rheology,which can be obtained by adjust its PH value and density. The best coating prepared by paste method can coat C/C through high temperature heat treatment with simple slurry which was made of silica sol and Si powder. There are more control parameters in dip coating technics,and the SiC coating thickness can be foresaw via controlled dip weight because dip weight was relative with slurry density and varieties of C/C in a given period of time.The best parameters of slurry for dip coating were PH=9 and density of 1.62 gcm-3.Vapor reaction coating （VR coating） is a more complex technology. The compact coatings by vapor reaction （VR） were gained on the surface of C/C at different temperature by introducing SiO vapor ,which generated by Si and auxiliary SiO₂ at high temperature in inertial atmosphere, into reaction chamber, where it occurred VR with C/C through diffusion. The best VR coating was obtained by the following technics: room temperature- 1700/℃2hr→1700℃/lhr→1700℃-1900 ℃/lhr→1900℃/lhr , which is thought of a kind of perfect coating not only because of its continuous distribution and uniformity of SiC tissues and eliminating cracks produced during period of preparing process by better graded distrubution,but also because of the SiC whiskers preparedaccompanyly in the coating.In a further investigation,SiC whiskers with much larger slenderness ratio were also prepared in the VR coating by soaking C/C composites and graphites,the parent materials,in Sol of Fe3+ or Co2+ or Ni2+ for a preset time .The performance of these coatings was comprehensively checked by heat shock resistance （HSR） and oxidation resistance（OR）.It showed that the VR coating has a best HSR.The HSR is affected by SiC whiskers and grains of coating together because of their affecting the flexural strength of coating materials?the collapse of SiC whiskers weakened the flexural strength while recrystallization of grains swelled it. The HSR of coating with rich SiC whiskers was more excellent than any other ones either in rapid or slow cooling HSR condition,while those with poor SiC whiskers showed its high HSR only in rapid cooling condition. The OR of VR coatings is defferent due to technics,the VR coatings without SiC whiskers have the best OR in the initial stage while those with SiC whiskers which were not obtained by catalytic reaction have the best OR in the final stage.The mass loss ratios of dip and VR coating were different from each other during process of oxidation resistance,the former underwent a period of mass increase which indicating a best OR in the initial stage while the latter was always in mass loss stages.更多还原