Study Of Microstructure And Mechanical Properties Of Nickel-base Superalloy/Si3N4 Ceramic Brazed Joint

Si₃N₄ceramics because of its excellent high wear resistance,high hardness,high corrosion resistance,high temperature stability and low thermal expansion coefficient and other advantages,has been widely used in various fields,such as high-precision bearings,automotive engine parts,high temperature electronic equipment,high frequency communication equipment,artificial joints and solar cells,to provide a more reliable material for industrial production.However,Si₃N₄ceramic material is inherently brittle and difficult to machine,presenting significant challenges in manufacturing complex parts.But connecting Si₃N₄ceramics with metals to form composite components can largely overcome these drawbacks.GH4169 superalloy is a type of nickel-based alloy with excellent performance,which can operate stably in extreme environments and has good corrosion resistance,creep resistance,weldability,and machinability.It has been widely used in fields such as aerospace,petrochemical,power generation.Therefore,achieving a connection between Si₃N₄ceramics and GH4169 high-temperature alloy has significant scientific significance in promoting the application of Si₃N₄ceramics in extreme environments such as high temperature,high pressure,and high speed.In this paper,AgCuTi composite filler was used to braze GH4169 superalloy and Si₃N₄ceramics at different brazing temperatures,and AgCuTi+W foil or foam Cu composite filler metal was used to braze GH4169 superalloy and Si₃N₄ceramics at different brazing temperatures and different holding times.The formation mechanism of interfacial reaction products and its effect on mechanical properties were studied.By brazing GH4169/Si₃N₄with AgCuTi,it is found that the typical structure of the joint is GH4169/Ti₂Ni/Ti Cu₂/Ag（s,s）/Ti Cu/Cu（s,s）/Ti N+Ti₅Si₃/Si₃N₄.During brazing,the active elements in the composite filler metal will diffuse towards the side of the two base materials,forming Ti-Cu and Ti-Ni intermetallic compounds on the alloy side and Ti₅Si₃+Ti N mixture on the ceramic side.The uniform structure of Ag（s,s）,Cu（s,s）and Ti-Cu compounds formed in the brazing area.The shear strength of GH4169/AgCuTi/Si₃N₄brazed joint increased first and then decreased,and reached 179.4 MPa when the brazed joint was kept at880℃for 15 min.When brazing GH4169 superalloy and Si₃N₄ceramics withAgCuTi composite filler/W foil/AgCuTi composite filler,it is found that the typical microstructure of the joint is GH4169 superalloy/Ti Ni₃/Ti Cu/Ag（s,s）/Ti Cu₂/Cu（s,s）/Ti₅Si₃+Ti N/Si₃N₄.With the increase of brazing temperature and holding time,the thickness of Ti-Cu reaction layer on GH4169 superalloy side and the thickness of mixture reaction layer on Si₃N₄ceramic side increased.When the brazing temperature is too low or the holding time is too short,the interface reaction layer of GH4169/AgCuTi+W/Si₃N₄brazing joint is too thin,which makes the joint fail to form a stable connection.When the brazing temperature is too high or the holding time is too long,the brittle phase in the interface of GH4169/AgCuTi+W/Si₃N₄brazing joint overgrows.The shear strength of the joint is reduced.Finally,the shear performance is the best when the temperature is kept at 880℃for 10 min,and the shear performance can reach 212.5 MPa.When using AgCuTi composite filler metal/foam Cu/AgCuTi composite filler metal to braze GH4169 superalloy and Si₃N₄ceramics,It is found that the typical structure of the joint is GH4169/Ti₂Ni/Ti Cu/Cu（s,s）/Ti Cu₂/Ag（s,s）/Ti Cu/Ti₅Si₃+Ti N/Si₃N₄.The shear strength of GH4169/AgCuTi+Cu foam/Si₃N₄brazing joint firstly increased and then decreased with the increase of brazing temperature,and then increased and then decreased with the extension of holding time.Finally,the shear strength of the brazing joint at 850℃for 10 min is the best,which can reach 210.1MPa.At a low holding time,the wetting time of the molten filler on the base metal surface is shorter,and the diffusion time of Ti elements in the filler to the ceramic side is shorter,resulting in a thin reaction layer on the ceramic side,which is easy to crack.With the further increase of holding time,the fluidity of the liquid filler increases and the thickness of the reaction layer on the ceramic side increases.However,the reaction layer mixed with Ti₅Si₃and Ti N belongs to the hard compound layer,and the thermal expansion coefficient of the compound layer is not matched with the Si₃N₄ceramic and AgCuTi composite filler metal,which leads to the residual stress in the joint and causes the fracture in the ceramic.