【作者】 杨振文；

【导师】 何鹏；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2010， 硕士

【摘要】 C/SiC复合材料和TiAl合金的密度低,具有良好的高温力学性能和抗氧化性能,将两者连接制成应用于航空航天领域的耐高温构件,可减轻结构重量,获得满意的高温性能。但是,C/SiC复合材料和TiAl合金的可靠连接不仅要解决两者热膨胀系数差异导致的接头残余应力,而且还要考虑TiAl合金的扩散溶解对接头界面组织和性能的影响。针对以上两点,本文在使用AgCu钎料分析两种母材钎焊性的基础上,提出了原位反应辅助钎焊TiAl合金和C/SiC复合材料。通过Ti-Ni-B高温钎料的设计,实现了接头热膨胀系数的梯度过渡,研究了界面反应机理,初步揭示了TiAl合金在液态钎料中的溶解现象和规律。C/SiC复合材料/AgCu/TiAl合金钎焊接头界面组织和性能分析表明,TiAl合金的扩散溶解量是接头界面组织的主要控制因素。TiAl合金溶解量增加,钎缝中Al-Cu-Ti化合物增多,Ag基固溶体所占比例减小;复合材料侧TiC反应层变厚。TiC反应层过厚导致接头残余应力增加,弱化接头性能。这些结论对原位反应中间层的设计和优化具有指导意义。确定了由Ti-Ni-B组成的中间层体系,采用细观力学夹杂理论和试验相结合的方法优化中间层的成分为(Ti-66Ni)1-xBBx(x=2.3~4.0wt.%)。采用粉末机械合金化和电弧熔炼两种方法制备了B含量为3.2wt.%的钎料作为研究对象,两种形式的钎料钎焊接头的界面结构相似,从TiAl到C/SiC侧依次为β/β+τ3/β+τ3+TiB/τ3/TiC。但是,钎缝中TiB的形成机理不同。钎焊过程中,电弧熔炼合金钎料中B源是以块状TiB2的形式参与反应形成长条状TiB相,试验表明,TiB2向TiB的转化是伴随着TiAl合金的溶解逐步发生的。钎焊温度为1180°C,保温10min时,优化的粉末钎料钎焊接头的室温抗剪强度和600°C高温抗剪强度最大,平均值分别为99MPa和63MPa。室温剪切后,接头的断裂主要发生在TiC反应层以及复合材料基体,复合材料的破坏形式是C纤维被剪断后沿SiC基体形成台阶状断裂面。600°C高温剪切后,接头的断裂主要发生在复合材料侧τ3反应层。建立了TiAl向液态钎料中溶解厚度的数学模型,设计了平行等间隙试验装置,实现了钎缝间隙的可调节性。采用两种方法测量TiAl合金的溶解厚度,提高了TiAl合金溶解厚度测量的精确性。试验验证结果表明,溶解厚度数学模型可用于研究高温钎焊条件下母材的溶解特性及评价钎料对母材的溶蚀。更多还原

【Abstract】 Both of C/SiC composites and TiAl alloy possess lower density, excellent high-temperature mechanical properties as well as oxidation resistance. Therefore, the preparation of the high-temperature resistant components using the two materials will have a good future of applications in the territory of aerospace due to its lightweight and satisfactory high-temperature properties. However, in order to successfully join the two materials, not only thermal stress caused by the high mismatches of thermal expansion coefficient between TiAl alloy and C/SiC composites, but also the dissolution of the TiAl alloy should be paid attention. AgCu filler metal was used to study the brazing behavior of TiAl and C/SiC. According to the results, the in situ reaction assisted brazing method was used to join TiAl and C/SiC. A novel Ti-Ni-B filler metal was designed to achieve a gradient thermal expansion coefficient of the joint. The interfacial reaction mechanism of the joint and the dissolution of TiAl alloy were also studied in this paper.The analysis of the microstructure and mechanical properties of the C/SiC composite/AgCu/TiAl joint shows that the dissolution of the TiAl alloy is the main controlling factor pertains to the microstructure evolution of the joint interface. With the increase of the dissolution of the TiAl, Al-Cu-Ti compounds increased, the proportion of Ag base solid solution decreased and TiC reaction layer thickened. The thickness of TiC layer plays an important role on the shear strength of the joint. These results are significance for the design and optimize of the high temperature filler metal.The ternary system Ti-Ni-B with the optimized components of (Ti-66Ni)1-xBBx (x=2.3-4.0wt.%) was designed as the filler metal. The filler metal was prepared by mechanical alloying and conventional tungsten vacuum arc melting respectively. The similar joint interfacial structure of the two filler metal isβ/β+τ3/β+τ3+TiB/τ3/TiC from TiAl side to C/SiC side. However, the formation mechanism of TiB in the brazing seam was different. The B resource from the filler metal prepared by vacuum arc remelt was TiB2 blocks which react with active elements Ti to form TiB strips during the brazing process.The maximum shear strength of the joint using the optimized filler metal power is 99MPa at room temperature and 63MPa at 600°C respectively, with the corresponding brazing temperature 1180°C for 10 min. After shear tests at room temperature, the fracture path mainly occurs along the TiC layer and the matrix of the composite. After the C fiber was pulling up, a step-like fracture surface was formed along the SiC matrix. When shear test at 600°C, the brazing seam adjacent to C/SiC composite become the weak area of the joint. A mathematic model was set up to evaluate the base metal dissolution thickness. In order to achieve an adjustable brazing gap, the parallel test model was designed. Meanwhile, two kinds of dissolution thickness measurement methods were used to improve the measurement accuracy. According to the experimental results, the dissolution thickness model has good accuracy and reliability, it can be used to evaluate the dissolution characteristics of TiAl base metal and estimate the corrosion of brazing filler metals, which is very important for the utility of TiAl alloy brazed joint.更多还原