Active metal brazing of Si3N4/Cu joint via a Cu-Sn-Ti filler: oxygen participation tailored interfacial microstructure and mechanical properties

Active metal brazing of Si 3 N 4 /Cu joints typically forms a rigid TiN/Ti 5 Si 3 interface that suffers from significant thermal mismatch. This study demonstrates an alternative strategy for engineering the interfacial reaction pathway using a (Cu20Sn) 100-x Ti x filler. A distinct Cu 2 Ti 4 O interfacial layer formed through oxygen participation in the interfacial reaction during brazing. Thermodynamic analysis reveals that the Ti-O reactions possess a significantly greater driving force than conventional Ti-N and Ti-Si reactions. The resulting Cu 2 Ti 4 O phase establishes a beneficial coefficient of thermal expansion (CTE) gradient across the joint, thereby effectively mitigating interfacial thermal stress. Joint brazed with 5 wt% Ti achieved the highest shear strength of 137.3 MPa, which is attributed to the optimized morphology of a discontinuous Cu 2 Ti 4 O layer and the reduced brittle CuSn 3 Ti 5 precipitation. These results demonstrate a new approach for interfacial engineering of non-oxide ceramic joints, confirming that trace oxygen can act as an effective microstructural modifier.