【作者】 赵磊；

【导师】 冯吉才； 张丽霞；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2010， 博士

【摘要】 SiO_2f/SiO₂复合材料(Quartz fibers reinforced silica composite,简称SiO_2f/SiO₂,限本文使用)具有良好的透波性能和耐高温烧蚀性能,已在航天工业领域逐渐得到应用。目前,该材料是以胶接的方法和Invar合金实现连接。然而,在工程应用中,胶接接头较低的耐热性能和老化问题已成为制约其发展的技术瓶颈。因此,本课题将实现SiO_2f/SiO₂与Invar合金的高性能连接作为研究目标,以获得可靠的连接接头。文中提出了一种环氧树脂作用下的钎焊连接方法（Epoxy resin assisted brazing,简称ERAB,限本文使用）,即通过环氧树脂的粘附力改善材料的界面特性,并在钎焊过程中实现接头的冶金反应连接。本文深入研究了SiO_2f/SiO₂与Invar的ERAB接头界面组织结构及形成机理,揭示了接头形成过程中界面的动力学行为。采用ERAB方法对SiO_2f/SiO₂和Invar合金进行连接试验,通过界面组织观察及物相分析,确定了接头的典型界面结构为:SiO_2f/SiO₂复合材料/TiO+Si+ Cu（s,s）+Ag（s,s）+TiC/Cu（s,s）+Ag（s,s）+Fe2Ti/Invar。在钎焊温度为850℃、保温时间为15min条件时,SiO_2f/SiO₂与Invar接头的抗剪强度达到最高值44MPa(约为SiO_2f/SiO₂母材强度的4倍),这主要是由于铺展润湿的钎料对界面处的SiO_2f/SiO₂起到了金属化增强的作用,此时接头断裂在SiO_2f/SiO₂未被钎料包覆增强的母材上。研究表明:此ERAB方法可实现Al2O3陶瓷或Cf/SiC复合材料与Invar合金的可靠连接。不同参数条件下的连接工艺试验结果表明,SiO_2f/SiO₂与Invar的ERAB接头界面中的物相种类基本保持不变,Cu（s,s）的形态及分布、Fe2Ti化合物的数量及分布、SiO_2f/SiO₂侧TiOx+Si界面反应层的厚度受到钎焊工艺参数的影响较大。钎焊温度的升高或保温时间的延长,都会促进Fe2Ti化合物相的增多和TiOx+Si反应层的增厚,弥散分布的Fe2Ti相逐渐聚集并在界面中心到Invar的区域内呈现链状分布;Cu（s,s）先随钎焊温度的升高或保温时间的延长逐渐向细小条状转变,但钎焊温度过高（950℃）或保温时间过长（35min）,Cu（s,s）呈大块状分布。通过界面组织观察和热力学分析,揭示了SiO_2f/SiO₂与Invar接头的界面形成过程,即:界面粘接、活性中间层的热解后界面处的物理接触及TiH2的诱导热解,TiH2的热解及高纯Ti在界面的初步反应,钎料的熔化、SiO_2f/SiO₂侧反应层开始形成（TiOx化合物）、Invar侧发生原子扩散反应,SiO_2f/SiO₂侧反应层厚度增加、扩散到界面中心区的Fe原子与Ti发生反应,固溶体组织开始形成、SiO_2f/SiO₂侧的界面反应结束、Invar侧的扩散反应停止,焊缝中心区固溶体、金属间化合物的凝固及接头的最终形成。通过活性中间层热解动力学和接头形成过程中反应相成长的动力学行为分析,获得了接头粘接阶段活性中间层的热解机理函数、活化能及热解动力学方程和钎焊阶段界面反应层TiOx+Si的成长动力学方程及相关动力学参数。通过有限元模拟对SiO_2f/SiO₂与Invar套接构件进行残余应力分析,得出采用减薄和等分Invar合金环的方法可有效降低套接结构的残余应力,并采用ERAB方法实现了SiO_2f/SiO₂与Invar工程构件的致密连接。更多还原

【Abstract】 Based on ther properties of well wave transmissivity and heat protection, Quartz fibers reinforced silica composites (QFSC, tell SiO_2f/SiO₂ for short) received wide application in aerospace industry. At present, the bad high temperature resistence and heat ageing resistance of adhesive-banded joint is the technical bottleneck in the application. Therefore, brazing of SiO_2f/SiO₂ and Invar alloy is expected in the present work to realize reliable joining. Direct and indirect brazing of SiO_2f/SiO₂ and Invar were experimented, one kind of new process named as epoxy resin assisted brazing （ERAB） was introduced under the base of above. High quality of SiO_2f/SiO₂ and Invar joint is successfully realized by ERAB. Microstructure, bonding mechanism and reaction kinetic equation of joint were identified. In addition, ERAB process can be applied in bonding of Al2O3 and Cf/SiC, respectively.SiO_2f/SiO₂ composite was brazed to Invar using active interlayer composing epoxy resin and TiH2 powder, Ag-Cu eutectic and pure copper as interlayer. After interfacial analysis through SEM, EDS and XRD, the typical interface structure was identified as SiO_2f/SiO₂ composite /TiO+Si+Cu（s,s）+Ag（s,s）+TiC/Cu（s,s）+Ag（s,s）+ Fe2Ti/Invar. When the brazing temperature is 850℃and holding time is 15min, the largest shear strength 44MPa of joint was reached, which is about 4 times the shear strength of SiO_2f/SiO₂. The spreading and wetting of solder reinforced the base of SiO_2f/SiO₂ near junction. The fracture of joint occurred at the base of SiO_2f/SiO₂ without solder coated.From the brazing experiments with various parameters, it can be identified that the kind of interfacial phases in the SiO_2f/SiO₂ and Invar joint was stable, amount and distribution of Cu（s,s） and Fe2Ti, thickness of reaction layer TiOx+Si were influenced obviously by the brazing parameters. With rising of brazing temperature and increasing of holding time, amount of Fe2Ti and thickness of reaction layer TiOx+Si increased, the diffuse spots of Fe2Ti aggregated gradually from Invar to the center of junction. The shape of Cu（s,s） changed into small and thin strip when brazing temperature and holding time increased at first, and aggregated into massive structure when brazing temperature reached 950℃or holding time was over 35min.Based on the thermal analysis and interface structure observation, formation of SiO_2f/SiO₂ and Invar joint was divided into six stages as follows: adhesive bonding, physical contact after thermal decomposition of active interlayer and induced decomposition of TiH2; decomposition of TiH2 powders and initial reaction of pure Ti in the interface; melting of Ag-Cu alloy, diffusion and reaction at the interfaces of both sides; increase of thickness of reaction layer near SiO_2f/SiO₂ and formation of Fe2Ti; formation of solid solution and stop of interfacial reactions; freezing of solid solutions, intermetallic componds and formation of joint. Under the base of thermal decomposition kinetics of active interlayer and reaction layer growth kinetics during the formation of joint, the kinetic behavior of interface in the joining formation was analysed. Thermal decomposition mechanism function, kinetics equation and activation energy of active interlayer in the adhesive bonding stage, growth kinetics equation and corresponding parameters of reaction layer TiOx+Si were calculated.Thinning and dividation of Invar ring can effective reduce residual stress in the sleeving structure of SiO_2f/SiO₂ and Invar. Joined component of SiO_2f/SiO₂ and Invar can be obtained by ERAB in appropriate structure.更多还原