Characterization of the interfaces formed at the silicon nitride superalloy joints

Abstract

In this study, silicon nitride ceramics (Si3N4) were joined by using a capacitor discharge technique with an Inconel 718 superalloy interlayer and heat-treated in order to determine possible reactions between these two materials. After capacitor discharge joining, some of the samples were heat-treated at 1100 degrees C under air and the resulting interfacial microstructure was characterized by using a scanning electron microscope (SEM) attached with an energy-dispersive x-ray spectrometer (EDS) and wavelength dispersive x-ray spectrometer (WDS). According to back-scattered electron images (BSE), all the joining samples were well bonded through the interlayer and cracks were not observed along the interlayer, interface and the ceramics. According to point SEM EDS and SEM WDS analysis, the reaction layer and nitrogen (N) were not detected but a small amount of silicon (Si) and aluminium (Al) was detected at the interlayer of as joined samples. For the heat-treated samples at 1100 degrees C, the symmetrical reaction layer was observed at both sides of the interlayer which is expanding towards the ceramic side and approximately 25-nm-thick another continuous reaction layer next to this was also determined. According to SEM EDS and SEM WDS point-line scan analysis along the metallic interface and ceramic side, nickel (Ni), iron (Fe) and chromium (Cr) were detected at the reaction layer next to the ceramic side, whereas mainly Cr, niobium (Nb), molybdenum (Mo), titanium (Ti) and Al were concentrated at the 25-nm-thick reaction layer.