Unveiling the reaction products in heat treated Si3N4-Ti joined ceramics by transmission electron microscopy

Joining is a crucial process for the production of complex-shaped advanced engineering materials. Deep understanding of ceramic-metal interfaces during joining or following heat-treatment steps is therefore of important concern in designing the new systems. Capacitor discharge joining (CDJ) method was firstly carried out to compose the ceramic-metal joint material by silicon nitride (Si3N4)-titanium (Ti) constituents. Afterwards, heat treatment was performed on the Si3N4-Ti joints in air atmosphere at 1000 degrees C temperature to reveal the interface reactions and phases. Reaction layer that occurred between the Si3N4 and Ti interfaces and new phase formations were examined by transmission electron microscopy (TEM)-based various imaging and chemical analysis techniques. Electron transparent samples for TEM characterization were prepared by focused ion beam (FIB) milling and lifting method. Based on the detailed TEM results, Si and N diffusion arising from the Si3N4 ceramic was observed towards Ti metal foil side and further interacted with Ti atoms. The upshot of current diffusion was that Ti3N2 reaction layer with 50 nm thickness was formed at the interface while titanium silicon nitride (Ti6Si3N) matrix phase including dendritic-shaped Ti2N grains occurred in the Ti interlayer. It is believed that our TEM-based microscopy results not only provide the knowledge on ceramic-metal joint materials by CDJ method, but also contribute new insights on the development of various new joint systems.