Diffusion bonding of SiC ceramics with interlayers of metallic titanium foils and PVD titanium coatings

Abstract

Silicon carbide (SiC) is a candidate material for high‐temperature structural aerospace applications due to its thermal and mechanical properties. Joining technologies enable the fabrication of complex shaped components needed for such applications. Various interlayers and processing conditions were used to form diffusion bonds between SiC substrates. Interlayers of titanium (Ti) foils and physically vapor deposited Ti coatings were used in the thicknesses of 10 and 20 μm with processing hold times of 1, 2, and 4 h. Polished cross sections of resulting diffusion bonds were analyzed using scanning electron microscopy (SEM) coupled with energy‐dispersive spectroscopy (EDS) and using transmission electron microscopy (TEM). From the TEM analysis, selected‐area diffraction patterns for Ti3SiC2, Ti5Si3Cx, and TiSi2 were observed. Moreover, TiC and an unknown phase were present in diffusion bonds formed with metallic titanium foil. From the SEM/EDS analyses, intermediate phases of Ti5Si3Cx and TiC were found to be present in microcracked diffusion bonds. With the thinner Ti interlayers and/or longer processing time, microcracking was alleviated or eliminated due to the presence of the more stable and lower thermal expansive phases of Ti3SiC2 and TiSi2. Detailed analysis of microstructures and the probable phases that formed in the bonded regions is presented.