Ceramic-metal interface: Effect of titanium activity on interfacial microstructure formation in vacuum-brazed Al2O3/Al alloy joints

Plasma-assisted physical vapour deposition of titanium over an alumina surface, brazed with an aluminium alloy substrate using Al4047 filler, was conducted in a vacuum ranging from 1 × 10−3 to 10−5 mbar. Microstructure characterization, specifically focusing on the Al2O3-Ti coating interface, aims to explain what mechanism underlies the secure bonding of ceramics to metal and how vapour deposition and vacuum atmosphere play a crucial role in achieving this feasibility. Titanium enhanced the wetting characteristics of the alumina surface through chemical reactions. The TiO2 and Ti3Al reaction compounds were identified at the interface. The Ti-rich phase adjacent to the Al2O3 substrate becomes increasingly discontinuous with brazing time. At the Al2O3-Ti interface, a reaction layer of 0.5-1 μm thickness was observed at a brazing temperature of 582 °C held for 40min. In demonstrating defect-free, solidly packed joints, the proposed additive manufacturing approach affirms its suitability for fabricating Al2O3-Al composites at lower joining temperatures, based on the effect of titanium on interfacial bonding characteristics.