Solid-state diffusion bonding of silicon nitride using titanium foils

This article presents an effective way to control the interfacial reaction during solid-state diffusion bonding of silicon nitride (Si3N4) using titanium foils. The interfacial structure and its growth kinetics were analyzed in detail with scanning electron microscopy (SEM), electron-probe microanalysis (EPMA), and X-ray diffraction (XRD). The actual phase sequence of the joint interfaces bonded at temperatures between 1473 and 1673 K is concluded to be Si3N4/Ti5Si3(N)/α-Ti(N)+Ti5Si3(N), which is different from the phase sequence observed at room temperature after bonding. The joints are very weak due to the formation of a brittle Ti5Si3(N) layer at the interface. To suppress the growth of the Ti5Si3 layer, a nitrogen-solution treatment of titanium foils prior to each bonding experiment is implemented. Although a perfect prevention of the Ti5Si3(N) layer formation is not achieved with this treatment, it is shown that the growth of the layer is effectively suppressed enough to improve the joint strength to a level 3 times higher than the case in which pure titanium is employed.