Study On Active Brazing Of Alumina Ceramic To Metal

A12O3 ceramics is the most widely used in vacuum electric device for the connection between A12O3 ceramics and Kovar alloy or other metal. It is therefore important to develop brazing filler metals to effectively bond A12O3 ceramics and metal.In this research, we used Cu63Sn10Ti23Ni4 powder and thin strip active filler to replace Ag-based filler metal and successfully bonded A12O3 ceramics with a variety of metal like Cr12 steel, Kovar alloy and nickel plating SPCE steel. The interfacial micro structure and composition distribution of A12O3/filler and A12O3/metal reaction layer with different active brazing fillers was observed by SEM、EDS and XRD. The interface reaction mechanism of Ceramics with filler was discussed. The effect of brazing process on the wetTab.ility and A12O3/Cr12 steel joint was investigated, The brazing of A12O3/Kovar alloy, A12O3/nickel plated SPCE steel under the best brazing process were investigated. The shear strength of joints was tested and the A12O3/ Kovar alloy joint fracture mode are discussed in this paper. The weld residual stress of A12O3 / nickel plating SPCE steel was simulated by the numerical simulation method, and the method to relieve residual stress was discussed. The conclusions are as follows:(1)Study of wettability of Cu67Sn10Ti23Ni4 active filler on A12O3 ceramics, the precursor film phenomenon occurring on the A12O3 ceramics surface, which shows its excellent wettability. Using Cu-Sn-Ti-N active filler brazing A12O3 ceramics, the spreadability is increase as increasing the holding time and brazing temperature. In the brazing temperature 920℃, holding time 10 min, the spreading area was 1.62cm2. Filler/ceramic has about 20 μm thick reaction interface layer, which enrichment of a large number of Ti elements for Cu2Ti4O by EDS and XRD analysis.(2) A12O3 ceramic/Cu-Sn-Ti-Ni/Cr12 steel has a good bonding. In brazing process, The Fe element of the base of steel diffuse into filler layer. Ti elements of filler diffuse into the both side of the base metal and forming TiFe2 and TiC compounds in filler layer on the side of steel base metal. The maximum shear strength of the joints was 118 MPa, which was achieved when the brazing temperature was 920 ℃ and holding time was 10 min.(3) A12O3 ceramic was bonded to Kovar alloy successfully by using the Cu-Sn-Ti-Ni active brazing filler metal at the 920 ℃ for 10 min. It has a good wetting and metallurgical bond between filler and the both side of the base metal. A1aO3/brazing interface generated a reaction layer about 1μm thick. The reaction layer was mainly composed of CU3TiO4 and A1Ti. Brazing layer was mainly composed of Cu(s,s)、NiTi and TiFe2. The fracture was occurred on the interface of A12O3 and brazing by Shear energy spectrum analysis.(4) A12O3 ceramic was not successful to bond with SPCE alloy by using the Cu-Sn-Ti-Ni active brazing filler metal. But by adding Cu stress buffer layer, it is successfully. Numerical simulation indicates that there are tensile stress and compressive stress in ceramic and metal respectively. The maximum of axial stress in the ceramic side is 108 MPa in the joint of A12O3/Steel. When adding 0.3 mm copper stress buffer layer, the middle joint stress of the ceramic side decreased significantly.