Technical Study On Brazing Of Aluminia Ceramic To Kovar Alloy

In order to meet the requirement of joining alumina ceramic to Kovar alloy in ceramic electric appliance, active brazing of alumina ceramic to Kovar alloy was carried out using Ag-Cu-Ti commercial brazing alloy. The Ag-Cu eutectic+TiH2 active powder brazes were investigated to reduce cost and control the content of Ti. The microstructure and properties of the joints were discussed experimentally and theoretically.The microstructure of alumina ceramic/Ag-Cu-Ti/Kovar alloy brazed joint was analyzed. The results showed that the reaction between Ti and alumina was affected by the interaction of Ti-Ni, Ti-Fe and Ti-Co. The microstructure of the joint was TiO+TiFe+TiNi3/Ag-Cu eutectic/TiFe2+TiNi3/TiFe2+Cu(s, s)+Ag(s, s) when brazing temperature was 900℃and holding time was 5min. The reaction between Ti and O at the alumina ceramic/brazing alloy interface decreased and the TiFe2, TiNi3 intermetallic compounds increased as the brazing temperature and holding time increasing.The shear stress was tested to evaluate the mechanical property of the joint. The results showed the maximum shear stress was 144MPa, which was achieved when the brazing temperature was 900℃and holding time was 5min. The leak rate of the joint was less than 1.6×10-9Pa·m3/s. The both properties satisfied the application requirement.Using Kovar alloy as the intermediate layer, the joining of large size alumina ceramic and stainless steel was carried out. The residual stress distribution of joint was investigated by numerical simulation and the joint shape was designed upon the FEM results. The alumina ceramic/Kovar/stainless steel was joined successfully with the optimum joint shape.For the Ag-Cu eutectic+TiH2 active powder brazes, the dehydrogenation of TiH2 was the key factor of the joint quality. By means of DSC, the process of TiH2 dehydrogenation was studied, according to which the brazing schedule was made. When brazing temperature was 950℃and holding time was 5min, the maximum shear stress 163MPa was got and it was higher than that of alumina ceramic/Ag-Cu-Ti/Kovar alloy joint.