Research On Processing And Mechanismof Brazing ZSC Ceramic And GH99 Alloy

As a novel thermal protection material, Zr B2-Si C-C ceramic(ZSC) possesses superior elevated temperature properties. Achieving the brazing of ZSC and GH99 nickel base superalloy(GH99), can be applied for fabricating composite component in hypersonic vehicle, such as the nose cone. However, the mismatch of the coefficients of thermal extension(CTE) between ZSC and GH99 leads the high residual stress concentration in the brazed joint, and severely deteriorates the brazing properties. In order to achieve the CTE gradient transition of the matrix materials, Si C-Ag Cu Ti composite material is proposed in this study. The brazing of ZSC and GH99 is conducted using Si C-Ag Cu Ti interlayer and Ti/Si C-Ag Cu Ti composite interlayer, and the sound joints are obtained. With the combination of experimental researches and the Finite Element Analysis(FEA), the interfacial microstructure as well as the mechanical properties of the brazed joints is determined, and the residual stresses in different interlayer joints were analyzed.The Si C-Ag Cu Ti composite interlayer was fabricated by the Pressureless Infiltration technology. When the infiltration parameter is T=860℃, t=10min, the porous Si C ceramic can be entirely infiltrated by liquid Ag Cu Ti, and Ti3 Si C2, Ti C, Ti Cu2, Ti5Si3 forms by the interfacial reactions. The CTE of the interlayer is examined, and the results show that it is between the CTEs of ZSC and GH99.The sound brazing is conducted using Si C-Ag Cu Ti interlayer. The interfacial microstructure of the joint is: ZSC /Ti3 Si C2+ Ti5Si3+Ag Cu eutectic structure /Ti5Si3+Ti C+Si C+Ti5Si3+Ti C +Ag Cu eutectic structure /Ti Cu2+Ti Al Ni2 +Ti Cu Ni2 +Ag Cu eutectic structure /GH99. When the interlayer thickness is 250μm, the brazing temperature is 870℃ and the dwelling time is 10 min, the shear strength reaches 102 MPa.Accordingly, Ti/Si C-Ag Cu Ti composite interlayer was proposed to enhance the residual stress reducing. Moreover, the interlayer supplies Ti in the braze seam and promotes the interfacial reactions of ZSC. The interfacial microstructure of the joint is: ZSC/Ti5Si3+Ti C+Ag Cu eutectic structure +Ti3Cu4/Ti Cu+(α-Ti+Ti2Cu)+ α-Ti+remaining Ti foil+α-Ti+(α-Ti+Ti2Cu)+Ti Cu/Ag Cu eutectic structure +Si C-Ag Cu Ti/Ti Cu Ni2+ Ti Al Ni2+ Ag Cu eutectic structure /GH99. When the brazing temperature is 850℃ and the dwelling time is 10 min, the shear strength reaches 112 MPa.The process parameters of geting high strength were wide. The fracture surface of the joint transformed from ZSC ceramic matrix to the interface of ZSC and the brazing seam.The FEA analysis is utilized to evaluate the residual stress in the brazed joints with interlayers. The results show that, the maximum stress is in the ZSC and adjacent the ZSC/filler interface. The maximum residual stresses of the Si C-Ag Cu Ti interlayer and the Ti/Si C-Ag Cu Ti composite interlayer joints are 280 MPa and 258 MPa, respectively. Which are 64 MPa and 87 MPa lower than the joint brazed with no interlayer applied.