Brazing of Ceramics with Aluminum Based Fillers in Air

Direct brazing of ceramics in air offers technological and economical advantages compared to other brazing technologies as active brazing in vacuum processes, brazing of metallized ceramics or using glass solders. Commonly silver based fillers were used for this process. In this work new fillers based on aluminum are developed to decrease both the material costs and the needed brazing temperatures. Starting at pure aluminum the addition of different oxide forming elements like bismuth and vanadium was investigated as well as the influence of brazing temperature and time. The oxidation of the filler, the porosity and the infiltration of the ceramic were analyzed metallographically. Differential scanning calorimetry tests were used to determine the influence of the filler composition on the melting temperature and the reaction temperatures. The added elements oxidize and infiltrate the ceramic, what can allow a better connection between the filler and the ceramic. The aluminum fillers afford good ductility, as they are used as foils and oxidize only superficially, whereas the inner material of the brazed seam remains as metal. Having regard to the thermally induced stresses, the ductility and the lower brazing temperatures of typically 800 °C offer also advantages for the brazing of ceramic-to-metal-joints.