Brazing Joint Study Of Si 3 N 4 Ceramics And Nickel-based Alloys

Si₃N₄ ceramics are inorganic non-metallic strong covalent bond compounds,it has the advantages of high specific strength,high specific mold,high temperature resistance,oxidation resistance and wear resistance and high thermal shock resistance,and in the high temperature,high speed,strong corrosive media work environment,has a special value.Si₃N₄ ceramic is currently one of the leading materials at home and abroad missile radome.GH4169 nickel-based alloys have high yield strength,plasticity,fatigue resistance and long-lasting performance under high temperature conditions,and are widely used in some key components of aeroengine.Using?AgCu28?95.5Ti4.5 solder brazing connection Si₃N₄ ceramic and nickel-based alloy,the effects of brazing temperature on the microstructure and mechanical properties of the interface were studiedand the typical structure of the joint is Si₃N₄ ceramic/Ti N/Ag?s,s?+Cu?s,s?+?Ag,Cu?+Fe2Ti+Al Ni2Ti/nickel based alloy.The brazing temperature mainly affects the behavior of the intermetallic compound in the joint and the thickness of the ceramic side reaction layer.With the increase of brazing temperature,the intermetallic compound size increases,the ceramic side reaction layer becomes thicker,and the shear strength of the joint increases firstly and then decreases.In the scope of this study,the optimum brazing temperature of Si₃N₄/nickel-based alloy brazing with AgCuTi solder is 860oC and the shear strength of the joint is 86 MPa.Using AgCuTi solder brazing directly Si₃N₄ and nickel-based alloy in the article,brazing on both sides of the parent metal wetting is well,however,the residual stress is too large due to the difference in coefficient of thermal expansion on both sides of the base metal,resulting in the strength of the brazed joint is not high,the fracture occurred in the ceramic near the seam.The distribution of residual stress in the welded specimen is obtained by ANSYS finite element software.It is a weak area in the brazed joint at a narrow area of 0.2mm from the interface between the ceramic and the brazing interface.The crack will be in this position appearIn view of the problem that the residual stress of the welded joint is too large,the indirect brazing method is used to improve the wettability of the brazing filler metal and the base metal to relieve the residual stress of the joint.By magnetron sputtering of the Ti/Cu metal film was deposited on the Si₃N₄ ceramic surface,and then brazed with the same solder and the brazing temperature is 860oC.The effect of Cu metal film under different power on the microstructure and properties of brazed joint was studied.And it was found that with the increase of Cu target power,the shear strength of the joint increased first and then decreased.When the Cu target power at 220 W,the?111?plane orientation of the film and the substrate is the most stable,and the shear strength of up to 79 MPa,fracture occurred in the ceramic near the seam,the residual stress of the joint is still relatively large.Surface magnetron sputtering coating metallization can not achieve the purpose of alleviating residual stress.According to the dissolution mechanism of the brazing filler metal to the nickel-based alloy,design of Si₃N₄/AgCuTi/Cu/AgCu/nickel-based alloy and the middle layer of brazing filler metal multilayer composite brazing Si₃N₄ ceramic and nickel-based alloy.Successfully inhibited the formation of Fe2 Ti and Al Ni2 Ti intermetallic compounds in the weld and effectively relieved the residual stress in the joint.The typical structure of the resulting joint is:Si₃N₄ ceramics/Ti N+Ti5Si3 reaction layer/Ag?s,s?+Cu?s,s?/ Cu?s,s?/Ag?s,s?+Cu?s,s?/nickel based alloys.The effects of different Cu interlayer thickness on the microstructure and properties of Si₃N₄ ceramic/nickel-based alloy joints were,investigated the three-point bending strength of Si₃N₄ /AgCuTi/Cu/?AgCu?/nickel-based alloy is higher than that of the joint obtained by direct brazing with AgCuTi.It was found that when the thickness of Cu interlayer was 0.1mm,the three-point bending strength of the joint was 238 MPa,which was about 27% higher than that of AgCuTi solder.