Bonding Mechanisms in Silicon Nitride Brazing

We investigated the wetting behavior and reactions of different metals on Si3N4 using sessile drop measurements, analysis of reaction layers, and measurements of strengths of joined bars. Active metals, such as Al and Ti, and alloys that contain them react with Si3N4 and cause wetting and spreading at the interface. Al‐Si3N4 reaction at 900°C produced a thin layer of Al2O3 at the interface. Reaction between Si3N4 and Ag‐Cu‐To braze alloys at 900°C resulted in a complex microstructure in the reaction zone that contained TiN and titanium silicides. Breaking strengths of Si3N4 bars joined with the Ag‐Cu‐Ti braze alloys were higher than those for Si3N4 joined with Al, primarily because of the better wetting by the Ag‐Cu‐Ti alloys. Nonreactive metals and alloys such as Sn, In, Ag‐Cu, and Ag‐Cu‐Sn neither wet, spread, nor adhere to Si3N4 substrates.