| In order to meet the need of the application of C/C composites and GH99 nickel-base superalloy in aerospace and nuclear industries as high-temperature structure materials, vacuum brazing of C/C composite to GH99 Ni-base superalloy was carried out using BNi2 brazing filler metal and BNi2+TiH2brazing powder respectively. Accompanying the experimental investigation with theoretical analysis, the affection from the brazing parameters to the microstructure of the joints was studied, the thermodynamics and mechanism of the generation of the interface were found out; at the mean time, affection from brazing parameters to the properties of the joints was analyzed, the fracture mechanism of the joints was found out, and the technology of brazing was optimized.The microstructure of the C/C/BNi2/GH99 joints is: C/C composites/Ni(s,s)+ Cr7C3+MC/Ni(s,s)+Cr7C3+MC+(Cr,Mo,W)xNiySiz+Ni3Si/Ni(s,s)+Cr7C3+MC/GH99 Ni-base superalloy. With the increasing of the brazing temperature and the extending of the holding time, the content of carbide in the joints increased. The interface reaction mechanism of C/C/BNi2/GH99 joints was studied, the reaction process was: physical contact while the temperature was increasing; dissolution and diffusion of the elements and the generation of the carbides after the melting of the brazing filler metal; the precipitation of Cr7C3 while the temperature was decreasing. Evaluate the mechanical properties of the joints using shear strength as the measurement, and the results showed that, with the increasing of brazing temperature and the extending of holding time, the shear strength of the joints increased and then decreased. When the brazing temperature is 1170℃and the holding time is 60min, the maximum environment temperature and high temperature shear strength of the C/C/BNi2/GH99 joints are 35.4MPa, 15.3MPa (800℃) and 8.6MPa respectively. The fracture of the joints all took place in the C/C composites without any affection of the brazing parameters. But when using BNi2 filler metal, sound joints could only obtained when the brazing parameters were strong, that could do bad to the GH99 base metal.Base on the study of properties and fracture of BNi2 brazing joints, BNi2+TiH2brazing powder were used for brazing C/C composites and GH99 Ni-base superalloy, the ideal composition of brazing powder is BNi2+5wt.%TiH2.The microstructure of C/C/BNi2+TiH2/GH99 joints is: C/C composites/Ni(s,s)+ Cr7C3+MC/(M+C)/Ni(s,s)+(MC,Cr7C3)+Cr7C3+MC+(Cr,Mo,W)xNiySiz+Ni3Si/Ni(s,s)+Cr7C3+MC/GH99 Ni-base superalloy. Reaction mechanism of the joints were study and the model of interface reaction were built. Evaluate the mechanical properties of the joints using shear strength as the measurement, and the results showed that, with the increasing of brazing temperature and the extending of holding time, the shear strength of the joints increased and then decreased. When the brazing temperature is 1170℃and the holding time is 60min, the maximum environment temperature and high temperature shear strength of the C/C/BNi2+TiH2/GH99 joints are 37.8MPa, 16.0MPa (800℃) and 8.7MPa (1000℃) respectively. The fracture of the joints all took place in the C/C composites. While using BNi2+TiH2brazing powder, sound joints could be obtained even if the brazing temperature was lower and the holding time was shorter, which was significant to this study.
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