Research On Processing And Mechanismof Brazing C/SiC Composite And GH99

C/Si C composites is a new generation of composite material in the modern aerospace industry, which has the advantages of high strength, high temperature resistance, corrosion resistance, wear resistance and thermal shock resistance. Nickel-base alloy can withstand high mechanical stress in high temperature, so it is meaningful to connect GH99 with C/Si C composites. To successfully gain the brazing joint, the following two questions needs to be solved: the control of the reaction level between parent materials; the residual stress caused by the mismatch of CET will weaken the joint strength.It is found that the dissolution of Ni from GH99 will change the interface reaction products and intensify the reaction seriously in the brazing process.Besides, the Ni-Si products cannot stop the continous diffusion of Ni atoms, so the interface reaction products are massive. According to this, this dissertation design a new brazing structure, adding the Nb interlayer, to obstruct the interaction between parent materials.When using Ni Cr Nb alloy to braze GH99 with C/Si C, the interafial microstructure of C/Si C/Nb was: Ni2 Si + Ni Si/Nb C+ CrxCy/Nb Cr2(HT) + Ni3Nb/(Nb, Cr, Ni) s.s.. The highest joint shear strength was 32 MPa, obtained when brazing temperature is 1190 ℃ and holding time is 10 min. Ni2 Si is the main interface reaction product, and Ni Si is formed between Ni2 Si and Si C interface in the cooling stage. The growth of Ni2 Si depend on Ni rapid diffusion in the grain boundary, the square of its thickness values is propotional to the diffusion time.When using the Ti-Co alloy in brazing C/Si C and GH99, the interafial microstructure of C/Si C/Nb was: C/Si C/Ti C+Nb C/Ti2Co+(αTi,Nb)/(αTi,Nb) /Nb. In the liquid Ti-Co alloy, the activity of Co is low, so the main products is Ti C; while in the Ni-Cr-Nb alloy, the activity of Ni reach 0.285, which promote the reaction of Ni and Si. The shear strength reach 68 MPa when brazing temperature is 1160℃ and holding time is 10 min.Mesh-interlayer was designed to relieve the residual stress in the joint. The dissolution of Nb causes the forming of products with irregular morphology. The dissoulution amounts vary much in interlayers with different porosity. The highest shear strength is 83 MPa when porosity is 9%. The residual stress was calculated with mathematical models, the results show the residual stress of joints without and with mesh-interlayer are 463 MPa and 327 MPa respectively.