Optimization of the active element and reinforcement proportion for improving joint strength of brazed Si₃N₄/42CrMo

Micron-TiN particles and Ti powder were introduced into the AgCu powder filler to design a particle-reinforced composite filler. This TiN particle (TiNp) modified brazing material was adopted to reliably braze Si3N4 ceramics onto 42CrMo steel, and the ratio of active element Ti to TiNp reinforcement was optimized for joint strength improvement. The reaction layer's thickness (TiN+Ti5Si3) adjacent to the ceramic decreased by introducing TiNp. Nevertheless, the reaction layer's thickness (TiC) at the 42CrMo side did not vary too much. TiNp showed excellent wettability with Ag-Cu-Ti braze, and there was no obvious reaction at the interface. Cu-Ti intermetallic compounds were formed and randomly distributed in the brazing seam. When the TiNp content did not exceed 8 vol.%, the joints' mechanical properties first sharply decreased and then remained basically unchanged when Ti increased. Raising the TiNp content to 10 vol.%, the joint strength showed the changing trends of first increasing and then dropping by increasing Ti content. The bending strength reached the maximum value of 396 MPa when 8 vol.% TiNp and 4 wt.% Ti were adopted.