Study Of Ag-CuO Based Filler Metals And Technology For Oxide Ceramics Brazing

Ceramic materials exhibit many desirable high temperature performances and also provide environmental stability in harsh conditions. However, the applications of large or complex components is limited by the processing cost, and manufacturing smaller components and joining them together is a desire. The properties of joints will be greatly affected by high temperature and oxidation environment. A recently- developed technique for joining these components, referred to as reactive air brazing (RAB), has shown vast potential for these applications. Different from the traditional active metal brazing, RAB uses a liquid-phase oxide-metal melt at high temperature and the process does not require a vacuum or inert atmosphere.In this paper, the Ag-CuO system and the Ag-CuO-Ti system filler metals are prepared by Ag, CuO, Ti powder, and these filler metals are carried out with RAB on alumina and zirconia substrate respectively. The melting characteristics and spread abilities of the filler metals, microhardness, microstructure, interface phases composition and strength of the joints were measured or analyzed through different scanning calorimetry, spreading tests, optical microscopic structure inspection, SEM and energy spectrum analysis, X-ray diffraction analysis and four-point bending tests.The research results are as follows:1) Small amount of Ti adding to the Ag-CuO system filler metals improved the spreading properties of the filler metals, and the effect of adding 0.5mol%Ti is best. The comprehensive performance of spreading properties, interface microhardness transition and joint strength of Ag-8CuO-0.5Ti filler metal are best at 1100℃and holding 10min.2) In the process of brazing, the filler metal elments diffuses to the ceramic substrates. The Al element in alumina ceramic substrates and the Zr element in zirconia ceramic substrates also diffuse to the filler metals. Adding a small amount of Ti to Ag-CuO system filler metals, the black transition layer accumulation reduced in the interface of alumina ceramic, and a large number of brazes infiltrated alumina ceramic materials.3) The interfaces of Ag-CuO/Al2O3 occured interfacial reactions, the reaction products were CuAlO2 and CuAl2O4, but no interfacial reactions at the interface of the Ag-CuO/ZrO2. Both the interfaces of Ag-CuO-Ti/Al2O3 and Ag-CuO-Ti/ZrO2 occured interfacial reactions, reaction products were CuAl2O4, TiO2 and ZrTiO4, TiO2 respectively.4) In the test range, the four-point bending strength of alumina and zirconia were best at the Ag-8CuO of the Ag-CuO system filler metals, respectively reached 206.11MPa, 454.58MPa. Adding 0.5mol%Ti to Ag-8CuO increased the joint strength. The four-point bending strength of alu mina ceramic joints and zirconia ceramic joints brazed by Ag-8CuO-0.5Ti filler metal were the highest at 1100℃and holding for 10min, respectively reached 212.36MPa, 503.44MPa, about 66%, 84% of the ceramic materials strength, and the fracture mode of ceramic joints were brittle fracture.