| 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. |
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