Interfacial microstructure of partial transient liquid phase bonded Si3N4-to-Inconel 718 joints

This work presents transmission electron microscopy (TEM) analysis of the interfacial microstructure in Si3N4-to-Inconel 718 joints with Ni interlayers produced by partial transient liquid phase bonding (PTLPB). Ti and Cu microfoils have been inserted between Si3N4 and the Ni interlayer and joining has been performed at lower temperatures than previous PTLPBs of Si3N4 with the same insert metals. The TEM work is focused on phase identification of the reaction layers between the Si3N4 and the Ni interlayer. According to the TEM analysis, most of the Cu precipitates without reacting with Ti and Ni. Si diffused in the filler metal and thin reaction layer formed at the interface between Si3N4 and the filler metal producing good bond-formation and hence, high interfacial strength. No interfacial fractures occurred after cooling from the bonding temperature of 900 °C, which supports the results observed in the TEM analysis. This work confirms that this joining process can produce a more heat resistant Si3N4-to-Inconel 718 joint than active brazing using Ag–Cu–Ti alloys.