Research On Interface And Connection Performance Of C/C Composite Brazed Joint

C/C,as a typical composite material with high temperature resistance,has been widely used in engineering.This paper aims at the requirements of C/C connection in aerospace and other fields.It is proposed to use nickel-based brazing filler metal and a composite brazing filler metal to braze C/C itself,and the interface structure of the brazing seam is analyzed by EDS,SEM and XRD.The effects of different brazing parameters on the microstructure and shear strength of the joint were studied,and the fracture mechanism of the joint was expounded.The finite element model of the joint welded by nickel-based brazing filler metal was established,and the residual stress was analyzed,which provided relevant experimental basis for C/C connection.The foil BNi2 solder is used to bond C/C,which provides a theoretical basis for the subsequent use of paste BNi-1a solder.C/C bonding can be realized when BNi-1a solder is used.The change of brazing process parameters affects the microscopic state of brazed joints,and the process parameters are low,and the bonding strength of interface reaction layer is low high process parameters lead to defects in brazing seam.The types of products in the brazing joint do not change with the change of brazing process parameters,and the microstructure of the brazing joint is C/C/Ni(s.s)+Cr₃C₂+M-type compound/Ni(s.s)+Cr₃C₂+M-type compound/C/C.The process parameters of the joint were optimized.When the temperature is T=1120? and the time is t=60min,the interface reaction state in the brazing seam was the best and the residual stress was the lowest,which made the shear test show that the shear strength was the highest at 24.13MPa under this process parameter.Below or above this parameter,the intensity will decrease.Fracture analysis shows that there are three typical fracture areas of the joint under the best process parameters,and C/C fracture appears under the different parameters.The residual stress distribution characteristics of the joint formed by brazing C/C with BNi-1a were simulated by finite element method.The residual stress has a large value near the center of the joint and the joint surface between the joint and C/C.Combined with the previous fracture analysis,the stress distribution characteristics have their own representativeness for judging the dangerous areas of connecting parts.Combine BNi2 foil solder and Ag Cu Ti solder,and the composite solder formed by the two is used for brazing C/C.Except the influence of few elements,the components with the highest specific gravity in the brazing seam are Ag(s.s)and the compound formed by solid solution of Ni and Cu.The main organizational structure of the joint is C/C/Ti C(Cr₃C₂)/Ag(s.s)+Ni(s.s)+Cu(s.s)/Ti C(Cr₃C₂)/C/C.The addition of BNi2 filler metal can fill the loss of Ag Cu Ti filler metal at high temperature,at the same time,the solid solution formed by the cooperation of Ni element and Cu element can gain the brazing seam.And the influence of different parameters on the interface and mechanical function of the joint is also analyzed.Under the parameters of temperature is T=1060? and time is t=30min,the best shear strength of the joint is18.83MPa.By observing the shear morphology under different process parameters,C/C fracture appears in the fracture.Under lower and higher process parameters,the fracture occurs in the interface reaction layer,but the reaction state is different and the shear morphology is different.Under proper process parameters,the fracture occurred and penetrated the C/C matrix,interface reaction layer and the center of brazing seam.