Study On Technology And Mechanism Of Electric-assisted Diffusion Bonding Of Alumina Ceramic To Ti

Al₂O₃ceramic is applied extensively for its excellent strength, hardness, dielectricproperty, thermal shock resistance and thermal expansion coefficient. However, the costis very high for the long joinning time and high joining temperature, which will lead tolower efficiency the same time. A new joining process was introduced based on theproblems above in this research. The microstructure and mechanical properties werestudied based on theorical analysis and experiment research. The mechanism ofinterfacial reaction was analysed based on thermodynamics and kinetics.The optimum processing parameters （heating to900℃, holding for2h, pressure for5MPa） was acquired through the study on microstructure and mechanical properties. Theshear strength was73.3MPa and the interfacial structure was Al₂O₃/TiO2+TiAl/TiAl3+Ti/Ti with the thickness of the reaction layers being3.5μm. The fracturemorphology of the joint was brittle cleavage fracture.The electric field assisted joining was implemented in order to promote interfacialreaction and improve the load-transfer ability of the joint. The result that the reactionlayer thickened and shear strength increased with the rise of the voltage with the samestructure of Al₂O₃/TiO2+TiAl/Ti3Al+Ti/Ti with the condition without field. The diffusionof the reaction layer went up to5.5μm and the shear strength increased to110MPa whenthe voltage was1100V, which had a43%rise in the thickness of reaction layer and50%rise in the shear strength.The electronic field-assisted diffusion bonding could increase the shear strength ofthe joint with the same processing parameter. Meanwhile, the joining time andtemperature could decrease when the strength of the joint remain the same, which couldweaken the bad effect of the high temperature and long joining time. The producingefficiency would be improved, which could keep the stability of the size of the structure.The mechanism of electronic-field-assisted diffusion bonding of alumina toTitanium included interfacial polarization，the bonding of the interface at outer electronicfield and the electro-migration of the atoms. The movement of elements at the interfacewas driven by outer electronic field and chemical potential gradient at a settingtemperature. Comparing with the bonding of non-outer electronic field, the speed ofelement movement was greatly improved. The whole process of the interface formingcan be divided into three stages: physical contact, the activation and polarization ofcontact surface and the forming of interfacial reaction layer.The calculation of interface thermodynamics showed that the free energy of thesystem was all minus values, which indicated that the reaction could performspontaneously. The study on the interface kinetics indicated that the electric field couldraise the diffusion coefficient of the atoms and reduce the fiffusion activation energy. The diffusion coefficient of O, Al and Ti had a rise of267.8%,51.6%,45.8%respectively.The fiffusion activation energy of those atoms had a reduction of61.0%,51.6%,45.8%respectively.