The Middle Tier Of The Amorphous Composite Brazing, Diffusion Bonding Of Si3n4 Ceramics Numerical Simulation And Process Optimization

This paper adopting amorphous composite layer to connect Si₃N₄ceramic by usingbrazing-diffusion bonding, establishes the brazing-diffusion bonding process model whichis based on the research of dynamics during connection process. Based on ANSYS virtualexperimental platform and using nonlinear finite element analysis, the finite elementnumerical computation model of brazing-diffusion bonding temperature field is established.The finite element numerical calculation model of the stress field is established which isbased on the elastic-plastic finite element theory, and the process parameters’ effect on theresidual stress of Si₃N₄ceramic is discussed.Adopting Ti-Zr-Cu-B amorphous/Cu/Ti-Zr-Cu-B amorphous to connect Si₃N₄ceramic by using brazing-diffusion bonding, the interface reaction layer’s growth accordswith parabolic equation controlled by diffusion. In1323K, reaction layer growth factor （J1）is1.007×10^-7m/s1/2. In the1283¹343K temperature range, reaction layer growthactivation energy is253.6kJ/mol. Isothermal solidification layer （X） and isothermalsolidification time （t） meet parabola relationship. In1323K, isothermal solidification ratefactor （J2） is3.7×10^-7m/s1/2. Reaction layer’s growth and isothermal solidification arecarried out at the same time, and the two dynamic process are changed by the timecoordination at a certain temperature to obtain higher bonding strength of room temperatureand high temperature. By changing the thickness of brazing metal’s foil layer and copperlayer, it is confirmed that the metal layer’s thickness near ceramic has a significant influenceon the interface reaction layer’s thickness during connecting Si₃N₄ceramics and metal bybrazing-diffusion bonding. When the connection temperature and time are given, theconnection strength directly depends on the thickness of copper layer. Obviously thethickness of the brazing has the best value which is about70μm in the test conditions ofthis paper.Based on the Si₃N₄ceramic’s brazing and diffusion bonding process model, it isdescribed that the method of choosing connection parameters. For specific ceramics’connection, firstly the optimal reaction layer’s thickness （Z C） should be determinedaccording to the test’s results and the literature data to obtain higher connection strength inthe selected connection temperature. Secondly, the best thickness of both brazing metal’sfoil layer （Wmax） and copper layer （WCu） is selected according to theZ Cto obtain the best isothermal solidification layer’s thickness （XCu+XC） ensuring the joint’s heat resistance.Finally, the connection time （t） is decided according to the selected Wmaxand WCu.According to the proposed model and choosing parameters as above order, the connectionstrength and joint’s heat resistance are ensured.On the establishment of calculating respectively the three-dimensional finite elementnumerical model of temperature field and stress field of Si₃N₄ceramic by brazing-diffusionbonding, the temperature field nephogram and the equivalent stress nephogram are obtainedwhen the joint is cooled to room temperature. The uniform temperature model is verified.Based on the calculation of temperature field, the distribution of residual stress duringwelding is studied qualitatively. From analysising numerical simulation, it can be seen thatthe ceramic surface near the connection interface is the joint’s weak zone of Si₃N₄ceramicby brazing-diffusion bonding. Appropriate test temperature and thickness of transition layercan reduce the joint’s residual stress and improve the joint’s heat resistance. The diffusionmodels of Si, Ti, Cu, Zr and other elements in the interface are established, and thenumerical simulation is conducted. Compared to the measured results, the model in acertain extent reflects the elements’ diffusion behavior in the interface well, so it isreasonable.