Effect of the SiC content in the Ag-Cu+SiC composite brazing filler on the microstructure and mechanical properties of the Al₂O₃/TC4 brazing joint

The joining between Al₂O₃ and TC4 titanium alloy was realised using Ag-Cu+SiC composite filler metal. The effects of the mass fraction of SiC and the brazing temperature on microstructure and mechanical properties of the joint were investigated. It was found that the typical microstructure of the joint is Al₂O₃/Ti₃Cu₃O/Ag solid solution + Cu solid solution +TiC+Ti₅Si₃/TiCu₂/TiCu/TC4. The thickness of the reaction layer adjacent to the ceramic is increasing with the rising of the temperature and is decreasing with the growing mass fraction of the SiC. For the joint with a small amount of SiC, the reaction products distribute uniformly, while for the joint with a large amount of SiC, the reaction products tends to agglomerate. Reaction products of brazing change from agglomerated distribution to uniform distribution with the increase of brazing temperature. The shear strength of the joint first increases and then decreases with the increase of the brazing temperature and the SiC mass fraction. The highest shear strength of the joint reaches 98 MPa when the mass fraction of the strengthening phase is 3% and the brazing temperature is 870℃.