Pressureless Sintering of SiC - Oxide Multiphase Ceramics for Protective Coating Applications

For hydrogen-fueled combustion, there exists a demand to improve coating materials that are capable of protecting SiCf/SiC CMC turbine material. Promising coating materials must be able to shield from harsh oxidation while working at extremely high temperatures. The work presented in this thesis aims to expand the understanding of two promising material systems for integrated environmental barrier coating (EBC) – thermal barrier coatings (TBC) by fabricating bulk composite ceramic samples and performing characterization to further understand their sintering behaviors. In this study, a processing procedure to consistently produce dense composite ceramics of PDC SiC – Y2Si2O7 and PDC SiC – Gd2Zr2O7 at varying ratios was established. Polymer-derived SiC (PDC SiC) has shown to be a suitable material for bonding to SiC/SiC CMCs. Y2Si2O7 and Gd2Zr2O7 were selected due to their low thermal conductivity and high stability at high temperatures and steam environment. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the microstructure and elemental distribution of both compositions. X-ray diffraction (XRD) was used to analyze the crystalline phase present in the two systems. It was demonstrated that both PDC SiC – oxide systems that vary SiC to oxide ratios can be sintered to high relative density (>90%), and the microstructure of the sintered composite ceramics showed uniform distribution of SiC and oxide phases.