| Al2O3is one of the common ceramic materials with high hardness, corrosionresistance, heat resistance and many other excellent properties. The compositecomponents of ceramics/metal generated by diffusion bonding has stable quality andgood corrosion resistance, however, the joint has a larger residual stress and the ligationefficiency is a little low. The diffusion bonding processes and mechanism needs to befurther explored. In this paper, an auxiliary alternating electric field is applied on thebasis of conventional diffusion bonding of Al2O3/Ti, looking forward to making theconnection process better and improving the quality of the connection. SEM, EDS,XRD, XPS, TEM and so on are used to observe the microstructure, using shear test toanalysis its mechanical properties, summarize the influence law of various factors onthe quality of diffusion bonding joint.There are interactions among the various factors, such as bonding temperature,alternating electric field, holding time, pressure, etc., and they all make a certaininfluence on the microstructure and mechanical properties of Al2O3/Ti diffusionbonding joint. After the alternating electric field is applied, weak currents appear at theinterface and there is a exponential relation between time and the current; when thetemperature is constant, the interfacial current value increases with the alternatingvoltage improved; the thickness of reaction layer at connection interface and atomicdiffusion increase with the connection temperature rising and the holding timelengthening; pressure has effect on the plastic deformation of metal, an appropriatepressure helps improve the diffusion, but if the pressure is too large, the ceramicsubstrate is prone to emerge micro-cracking, so the strength of the joint reduces; aninterlayer applied can improve the interface connection conditions effectively increasethe degree of interfacial bonding, slowdown the residual stress, and improve theconnection strength. The shear strength of the joint varies with the influence factorschanging and there is an optimal value.An orthogonal design of three-factor and three-level about temperature, electricfield and time was used. The results show that the influence order of various factors onthe mechanical properties of joints is: temperature> alternating electric field> holdingtime; obtain the optimum process parameters:900℃/200V/3h/5MPa; the shear strengthof joint made by the best process is138.1MPa, and its high-temperature shear strength is higher than room temperature shear strength, the maximum strength reaches to176.8MPa when the temperature is200℃, and145.9MPa when the temperature is400℃. The fracture form of Al2O3/Ti diffusion bonding joint during shear is brittlefracture, which occurs mainly in the Ti3Al reaction layer. When the reaction layer is thin,the interfacial bonding strength is low, so cracks extending along the connectioninterface occur, when the adhesion strength of reaction layer is higher, the crack pathdeflects constantly and extends into the ceramics, so the reaction layer on fracture lookslike tearing lamellar, and the surface topography is undulating steps; the fractures arecleavage fracture.The microstructure analysis of Al2O3/Ti diffusion bonding joint shows that: phasesgenerated during the interface reaction are mainly Ti3Al and TiAl, reaction zone isdivided into Ti3Al zone and Ti3Al, TiAl mixed fine-grain zone, O atoms solid-solutionin the generation phases. The kinetics analysis of Al2O3/Ti interfacial reactions showthat the reaction rate constant rises with twmperature increasing and the reaction rateconstant with200V electric field applied is bigger than no electric field; the apparentactivation energy at200V is79.82KJ, which decreases22.69KJ compared with noelectric field, so applying an alternating electric field can promote the diffusion bonding.Make analysis and calculation of Al2O3/Ti diffusion bonding reactions from thethermodynamic view, there is ΔG <0, so the reaction can occur. The interfacial phasestructure of Al2O3/Ti diffusion bonding is Al2O3/TiAl[O]/Ti3Al[O]/α-Ti[Al]/β-Ti. |
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