Improvement of microstructure and mechanical properties of Sapphire/Kovar alloy joints brazed with Ag-Cu-Ti composite filler by adding B powders

Abstract

The brazed joint of sapphire transparent ceramic and Kovar alloy was prepared using AgCuTi and AgCuTiB composite filler, and the main focus was the effect of B element on the wetting behavior, interface composition and joint mechanical performance. The reliable joint of sapphire transparent ceramic and Kovar alloy was obtained by vacuum brazing with AgCu28-6Ti-0.45B (wt%) composite filler. The typical interfacial structure of the joint brazed at 825 °C for 10 min was determined as sapphire/Ti3Cu3O/Ag(s,s) + Cu(s,s) + disperse TiB/TiFe2 + TiNi3/Kovar. The results showed that the addition of B could contributed to an optimized interfacial structure via (i) in-situ forming fine TiB whisker reinforcement phase and refining the interface structure and (ii) reducing the diffusion degree of alloy side elements to inhibit the generation of brittle phase, and the maximum shear strength of the joint with AgCu28-6Ti-0.45B (wt%) reached 125 MPa more than twice the joint without B additive. On the other hand, the wetting experiment showed that the addition of B as a solid particle decreased the fluidity of the composite filler, and when the addition of B was excessive, no dense TiB whiskers were produced in the interface. This study provides ideas for the optimization and improvement of sapphire composite connection, and points out that the generation of reinforcing phase is accompanied by the reduction of fluidity, so it is necessary to reasonably control the proportion of reinforcing phase.