【作者】 刘多；

【导师】 冯吉才； 何鹏；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2010， 博士

【摘要】 SiO₂玻璃陶瓷具有耐热、抗震且多孔、热膨胀性能可调、耐腐蚀、热稳定性能好、较大的高温粘性等特点,在宇航工业中可将SiO₂玻璃陶瓷与TC4合金（即Ti-6Al-4V）连接应用于发动机隔舱上。目前,陶瓷隔舱是在外径处通过机械连接方式实现与燃烧室的连接,消极质量较重,因此本课题要实现SiO₂陶瓷隔舱与TC4钛合金结构件的可靠连接。解决消极质量重的问题,同时提高构件连接的气密性。本文采用钎焊的方法解决SiO₂玻璃陶瓷与TC4合金的连接问题,深入探讨连接机理,确定最佳工艺,得到性能符合要求的构件。采用AgCu/Ni复合中间层进行了SiO₂陶瓷与TC4钛合金的钎焊连接,通过多种分析测试方法确定了钎焊接头典型的界面结构为:TC4钛合金/针状α-Ti/ Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu）过共析组织/Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu）过共晶组织/Ti₂（Ni,Cu）+Ti₂（Cu,Ni）化合物/Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu）过共晶组织/ Ti₄O₇+TiSi₂/SiO₂陶瓷。钎焊温度为970℃,保温时间为10min的接头抗剪强度最高,平均值达到110MPa,此时接头断裂发生在陶瓷母材上,接头界面中各层强度较高,使接头强度高于母材。多种工艺参数下的钎焊试验表明:钎焊温度对界面产物种类影响不大,但对陶瓷侧Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu）过共晶组织的分布有一定影响。钎焊温度较低时,焊缝中部有少量该组织呈岛状分布。当钎焊温度达到970℃时,该组织已呈带状近连续分布于靠近陶瓷侧反应层的区域。钎焊温度升高至980℃,陶瓷侧连续的Ti（s.s） + Ti₂（Cu, Ni） + Ti₂（Ni, Cu）过共晶组织明显增厚。钎焊温度对陶瓷侧Ti₄O₇+TiSi₂反应层厚度影响不大。保温时间对陶瓷侧岛状Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu）过共晶组织的分布与钎焊温度的影响类似,但对陶瓷侧Ti₄O₇+TiSi₂反应层生长的影响却不同,保温时间的延长,导致Ti₄O₇+TiSi₂反应层厚度增加明显。根据所观察到的接头界面结构,确定了界面形成过程具体分为以下几个阶段:中间层与两待焊母材的物理接触;AgCu钎料箔片的熔化以及液态AgCu与Ni箔片、钛合金母材的相互作用;共晶液相大量出现、钎料中Ti、Cu、Ni、Ag原子共存、陶瓷侧反应层开始形成;钎焊温度下钎料液相对钛合金母材继续溶解、焊缝中液相成分均匀化、陶瓷侧反应层厚度增加;钎料对钛合金母材溶解的停止、陶瓷侧反应层反应的终止以及过共析组织的形成;Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu）过共晶组织的形成;焊缝中心金属间化合物的凝固。分析了焊缝中Ag、Cu、Ti、Ni各元素的作用机理,其中,来自于TC4母材的Ti元素是该连接过程中不可或缺的重要组元,Ti与中间层合金通过共晶接触反应作用形成了对SiO₂陶瓷润湿性极好的液态钎料,Ti原子进入焊缝后,迅速扩散到陶瓷侧与陶瓷形成反应层,实现钎料与陶瓷之间的良好冶金结合。通过分析钎料在钛合金母材侧的冶金反应,发现共晶液相倾向于在钛合金一侧产生,这主要是由于Ni向Ti中的扩散系数比Ti向Ni中的扩散系数大很多。得到了钎焊温度恒定的情况下,保温一段时间后焊缝中Ti在液态钎料中的浓度表达式,并以此为切入点得到了焊后TC4钛合金母材的溶解厚度表达式,这对有效控制钛合金母材溶解量,防止发生溶蚀具有重要意义。研究了钎焊过程中钎料液相在SiO₂陶瓷侧的铺展行为及界面反应行为。以活性元素Ti的行为特征为主线,获得了陶瓷侧反应层的生长动力学方程,通过钎焊温度和保温时间两个中间变量实现了对陶瓷侧反应层成长的微观调控。更多还原

【Abstract】 Due to the properties of heat and vibration-resisting, multi-micropore, adjustable thermal expansion property, corrosion-resisting, excellent thermal stability and large high-temperature viscosity, SiO₂ glass ceramic is bonded to TC4 alloy （Ti-6Al-4V） to manufacture engine bay in aerospace fields. So far, ceramic bay is mechanically bonded to the combustor at external diameter, resulting in large negative mass. Therefore, reliable joining of SiO₂ glass ceramic to TC4 alloy is expected in the present work to decrease the negative mass and improve the gas impermeability at the same time. High quality joining of SiO₂ glass ceramic to TC4 alloy is successfully realized by brazing, and the optimal brazing parameters are identified as well as the bonding mechanism.SiO₂ glass ceramic was brazed to TC4 alloy using AgCu/Ni composite interlayer. According to several testing methods, the typical interface structure was identified to be TC4 alloy/acicularα-Ti/Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu） hypereutectoid structure/ Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu） hypereutectic structure/Ti₂（Ni,Cu）+Ti₂（Cu,Ni） compounds/Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu） hypereutectic structure/Ti₄O₇+TiSi₂/SiO₂ ceramic when the joint was brazed at 970℃for 10min. Under this condition, the largest shear strength 110MPa was reached. The fracture occurred on SiO₂ glass ceramic because of its lower strength than that of each interfacial layer.Based on the brazing experiments under different parameters, species of the interface products were hardly influenced by the brazing temperature, but it was not the condition for the hypereutectic structure near SiO₂ /braze interface. When the brazing temperature was low, island-like Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu） hypereutectic structures were distributed at SiO₂ glass ceramic side. As the temperature rised to 970℃, these structures had distributed continuously near the reaction layer at ceramic side, and they were thickened as the temperature increased to 980℃. Ti₄O₇+TiSi₂ layer was hardly influenced by the brazing temperature. The effect of holding time on Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu） hypereutectic structures was similar to that of temperature, however, effect of time on Ti₄O₇+TiSi₂ layer was quite different, the holding time longer, the reaction layer thicker.According to the observed interfacial microstructure, joint formation was divided into the following seven stages: physical contact of the brazed surfaces; melting of AgCu and interaction between liquid AgCu and Ni foil, TC4 alloy; formation of eutectic liquid, coexistence of Ti, Cu, Ni, Ag, and appearance of reaction products at ceramic side; dissolution of TC4 alloy, homogeneousness of liquid filler and width increase of reaction layer at ceramic side; stop of dissolution of TC4 alloy and reaction at ceramic side, formation of hypereutectoid microstructure; formation of hypereutectic microstructure Ti（s.s）+Ti₂（Cu,Ni）+Ti₂（Ni,Cu）; solidification of intermetallic compounds on joint center. Effect mechanisms of element Ag, Cu, Ti and Ni on joint formation were studied. Among these elements, Ti is the most important. Ti dissolved from Ti alloy by eutectic reaction and diffused to ceramic side, resulting in the reaction layer formation and excellent spreading of liquid filler on SiO₂ glass ceramic.Metallurgy reaction at Ti alloy side was researched. The result was that eutectic liquid tended to appear at Ti alloy side instead of Ni filler side, because diffusion coefficient of Ni to Ti is much larger than that of Ti to Ni. Concentration of Ti in the liquid filler after dwelling was obtained. Dissolution thickness X of TC4 alloy after brazing was calculated based on the concentration of Ti, and this is meaningful to control the dissolution of Ti alloy and prevent the erosion of base material.Spreading and interface reaction of liquid filler on SiO₂ glass ceramic were investigated. Growth kinetics equation of reaction layer at SiO₂ side was attained according to the process property of active element Ti, realizing the micro-controlling of reaction layer growth via the brazing temperature and dwelling time.更多还原