Effects of glass composition and joining parameters on microstructural evolution and mechanical properties of Al2O3/Cu joints brazed with Bi2O3-B2O3-ZnO glass

Abstract Using nickel foil as an intermediate layer and Bi2O3-B2O3-ZnO (BBZ) glass as brazing fillers, metallurgical bonding between alumina ceramics (Al2O3) and coppers (Cu) was achieved by vacuum brazing. A series of brazing experiments were performed systematically to explore the optimal brazing process for bonding coppers and alumina ceramics with BBZ glass. Brazing occurred at different temperatures (T = 660, 680, 700, 720 °C) and dwelling times (t = 0, 20, 40, 60 min) with three kinds of BBZ glass braze. The microstructures of the joints were studied by scanning electron microscopy and the relationship between microstructures and shear strength was established. The interfacial microstructure of brazing joints varied with the shift of glass composition, while the reaction products were unaltered. Shear strength of the brazing joints depended on the distribution of ZnAl2O4 particles in the brazed seam and peaked on the BBZ10 joints obtained at 680 °C for 20 min. It were the higher ZnO content and longer brazing temperature dwelling time that made it easier for ZnAl2O4 particles to aggregate on the Al2O3 ceramics side to form a band-like distribution, which significantly reduced mechanical properties of Al2O3/Cu joints.