Enhanced properties in Si3N4/Cu joints via in-situ constructing a micro-network of Cu-Ti reinforcements induced by Ag-xTiH2 composite filler

Particle-reinforced composite fillers allow precise control of joint microstructure to enhance mechanical performance. However, traditional designs often reduce joint deformability and face issues like particle agglomeration and poor interfacial wettability. To overcome these limitations, a micro-network of Cu-Ti reinforcements within the brazing seam via Ag- x TiH 2 composite filler was developed in this work, which enabled the fabrication of high-strength Si 3 N 4 /Cu joints. Optimal results were achieved with the Ag-4TiH 2 filler, wherein a eutectic liquid formed at the Ag-4TiH 2 /Cu interface during the initial brazing stage. Simultaneously, undissolved Ti reacts with Cu to yield submicron Cu 4 Ti 3 -dominated reinforcements. On the Si 3 N 4 surface, hypostoichiometric TiN/TiN 0 . 61 /TiN 0 . 5 nanocrystals grow sequentially, which is beneficial for enhancing interfacial wettability and bonding reliability. A maximum average shear strength of 186.9 MPa was obtained, a 57.6 % improvement over the conventional AgCuTi filler. The fracture mechanism underwent a notable transformation: brittle failure at mixed regions of Si 3 N 4 and the reaction layer in AgCuTi joints was replaced by ductile failure at the interface between the Cu matrix and the brazing seam in Ag-4TiH 2 joints. The Cu 4 Ti 3 -dominated micro-network offers distinct advantages by enabling controllable in-situ growth that prevents agglomeration while maintaining joint deformability through the synergy effect of the abundant retention of ductile Ag(s, s) and decent elastic modulus and yield strength increment, and regulates the interface reaction to yield a thinner Ti-N layer instead of a TiN/Ti 5 Si 3 dual-layer. These features collectively contribute to the notable mitigation of residual stress within Si 3 N 4 /Cu joints.