Joining Process And Mechanism On Brazing AlON And H-BN/Si₃N₄ Ceramics With CuTi Based Active Filler Metal

?-AlON transparent ceramic possessing excellent optical properties,such as dielectric properties and thermal shock resistance,is an ideal material for high temperature infrared windows.Si₃N₄ ceramic is an ideal material for preparing missile radome,but its dielectric constant is high.When introducing h-BN in it,its dielectric properties can be significantly improved.Besides,h-BN/Si₃N₄ composite ceramic has better wave transmission performance compared with other ceramic types.Therefore,the key point to the preparation of infrared guided missiles is to achieve the effective connection of?-AlON ceramics and h-BN/Si₃N₄ composite ceramics.Joining of?-AlON ceramics and h-BN/Si₃N₄ composite ceramics,carried out using CuTiand Cu Ni Ti.The wetting and spreading behaviors of the two kinds of active solders on?-AlON and h-BN/Si₃N₄ surfaces were analyzed.The microstructure and composition of the joints were studied as well as the effects of brazing temperature,holding time,and the thickness of the solder layer on the microstructure and properties of the joints.The high-temperature mechanical properties of the joints were evaluated and the joint formation mechanism was analyzed.Sessile Drop experiments indicated that the wetting angle of Cu75Ti25?at.%?active solder on?-AlON and h-BN/Si₃N₄ can reach 20°and 18°,respectively.The typical microstructure of?-AlON and h-BN/Si₃N₄ joints brazed with Cu75Ti25 solder is:?-AlON ceramics/?Cu,Al?₂Ti₄O+Ti₅Si₃ reaction layers/Cu?s.s?+CuTiintermetallic compound/reaction layer Ti₅Si₃+TiB+TiN/h-BN/Si₃N₄ ceramics.Brazing temperature,holding time and thickness of the solder layer mainly affect the width of the weld,the thickness of the reaction layer and the intermetallic compound in the joint,which affects the performance of the joint.As the brazing temperature increases,the holding time is prolonged and the thickness of the solder foil increases,the shear strength of the joint first rises and then decreases.The shear strength of the joint reach the maximum value of 57 MPa at room temperature,64 MPa at 400?,and 70 MPa at600?,when the joints were brazed at 1060? for 10 minutes with the solder in the thickness of 400?m.The connection mechanism of the joint is as follows:when the temperature reaches the melting point of the solder,the solder begins to melt,and the active element Tiin the liquid solder diffused enriched close to the ceramic matrix and generated a reaction layer at the two interfaces,the liquid solder in the cooling chamber solidifies to generate Cu?s.s?and the CuTicompound eventually form a stable linker.The?-AlON and h-BN/Si₃N₄ ceramics were brazed with Cu70Ni10Ti20?at.%?active solder.The wetting angles of Cu70Ni10Ti20 on?-AlON and h-BN/Si₃N₄ceramics 60°and 18°,respectively.Typical microstructure is:?-AlON ceramics/Al₂O_3-x·TiO+?Cu,Ni?₂Ti₄O reaction layers/Cu?s.s?+Cu Ni Ti+?Cu,Ni?Ti₂ Intermetallic Compound/reaction Layer Ti₅Si₃+TiB+TiN/?h-BN/Si₃N₄ Composite Ceramics?.With the increase of brazing temperature,the holding time and thickness of brazing sheet,the shear strength of the joint increases first and then decreases.The shear strength reached up to 65 MPa at room temperature,69 MPa at 400? and 75 MPa at 600? when brazed at 1100? for 15 min using solder foil thickness of 400?m.The connection mechanism of the joint is:when the temperature reaches the melting point of the solder,the solder begins to melt,the active element Tiin the liquid solder forms enrichment and generates a reaction layer at the interface between the two welds;the liquid solder in the cooling chamber solidifies to generate Cu?s.s?and the?Cu,Ni?_x Ti_y compound phase eventually form a stable linker.