Microstructure And Properties Of Partial Transient Liquid Phase Bonding Joint Of Si₃N₄ With Nickel-Based Superalloy

Silicon nitride(Si₃N₄)ceramics is an advanced high-temperature structural ceramic.However,due to the inherent brittleness of Si₃N₄ ceramic materials and the limitation of preparation technology,it is difficult to obtain large-sized and complex-shaped ceramic components.Nickel-based superalloys also have good high-temperature strength,stiffness and good fracture toughness.Combining high-temperature-resistant ceramic materials with a metal matrix to make high-temperature-resistant parts can meet the requirements for use in the aviation field and has a good application prospect.Taking advantage of the characteristics of solid solution between Au-Ni,this article used partial transient liquid phase(PTLP)connection method to connect Si₃N₄ and nickel-based alloy GH4169 to explore the effect of different connection temperature,holding time,connection pressure and other process parameters on the microstructure and mechanical properties of the joint Characterize and simulated the change of residual stress in the joint,and conducted a preliminary study on the diffusion dynamics during the PTLP connection process,and expounded the joint organization change rule and connection mechanism in the PTLP connection.Through the exploration of the joining process,it was found that increasing the joining temperature and prolonging the holding time within a certain range can increase the bonding strength of the interface,and the sufficient inter-diffusion between Au-Ni formed a uniformly distributed Ni[Au]solid solution,which improved the strength of the joint favorable.However,when the connection temperature exceeds 1150°C and holding time more than 120 min,the brittle phase Ni₃Ti precipitated in the Ni[Au]solid solution,which reduced the ability to relieve residual stress and leaded to a decrease in the mechanical properties of the joint.When the connection temperature was 1100°C,the holding time 90 min,and the connection pressure 0.8 MPa,the maximum shear strength of the joint at room temperature was130 MPa.The joint had good high temperature resistance.The strength at 800°C was similar to that at room temperature,and the shear strength was still close to 60 MPa at 1000°C.Exploring the influence of the change of the intermediate layer on the joint,it was found that although increasing the Ti content could increase the interface bonding strength,excessive Ti destroyed the Au-Ni solid solution system,resulting in the formation of a large number of brittle intermetallic phases and the joint shear strength is reduced.The lower Ti content in the intermediate layer could prevent the formation of brittle phases in large quantities,but the interface bonding strength was reduced due to the reduction of interface reactants,and the mechanical properties of the joint still declined.The thinning of the Ni layer leaded to the appearance of massive Ni₃Ti between the solid solutions of the joint.The growth of Ni₃Ti took away the Ni that was originally dissolved in Ni[Au],hindered the formation of solid solutions,and reduced the strength of the joint.In order to further alleviate the residual stress of the joint,Ni foam was introduced in the middle layer.In order to prevent the liquid phase from directly contacting and dissolving all the foam skeletons,Ni foil was added as a barrier layer.Studies had found that when the Ni foil was too thick,the bonding between the Ni foil and the Ni foam depended only on the diffusion bonding of the foam skeleton and Ni.Fewer bonding sites resulted in low bonding strength and decreased mechanical properties of the joint.The thinner Ni foil was melted through by the liquid phase,causing the Ni foam to basically collapse,losing the ability to relieve residual stress through deformation,and reducing the mechanical properties of the joint.The use of100?m thick Ni foil could effectively block most of the Au elements from contacting the Ni foam,while avoiding excessive collapse of the foam skeleton.The maximum joint strength was 60 MPa.This article described the interface connection mechanism of PTLP connecting Si₃N₄/GH4169:during the connection process,Au-Ni diffusion would generate a liquid phase,and Ti in the molten liquid phase would react with Si₃N₄ to form Ti N.Free Si could continue to combine with Ti or Ni.With the increase of the joining temperature and the extension of the holding time,the Ni element in the Ni foil continued to diffuse into the liquid phase.The Ni content in the liquid phase exceeded the maximum load of the liquid phase,and part of the liquid phase begon to transform into a solid phase until the isothermal solidification process When completed,the liquid phase is completely transformed into a solid phase.At the connection interface on the nickel-based alloy side,the degree of element interdiffusion between Ni foil and GH4169 increased with the increase of heating time and connection temperature.Combined with the calculation of diffusion kinetics,the PTLP connection was analyzed.The growth rate of the interface reaction layer at the connection temperature of 1100°C was 6.102×10^-8m/s^1/2,and the apparent activation energy of the growth of the reaction layer was determined to be 563k J/mol.The theoretical calculation of the isothermal solidification time between Au-Ni used in the experiment requires at least30 min.Raman spectroscopy was used to characterize the distribution of residual stress on the ceramic side of the joint.The maximum value of residual stress near the joint was nearly 500 MPa.When the distance is far enough from the weld,the ceramic stress was approximately zero.Image J-OOF2-ABAQUS jointly simulated the refined finite element model,and the stress distribution of the simulation resulted corresponds to the phase distribution of the microstructure.