Processing and properties of ZrB₂-ZrSi₂ matrix composites reinforced with continuous SiC fiber

The research presented in this thesis focuses on the processing, microstructure, and mechanical properties of ZrB₂-based composites. The main goal was to develop a process that incorporates high strength continuous SiC fiber in a ZrB₂-based matrix. In order to achieve this, the densification, microstructure, and mechanical properties of ZrB₂-ZrSi₂ monolithic ceramics were characterized along with various SiC fiber reinforced ceramic matrix composites (CMCs) utilizing the same matrix. There were two main areas of study in this thesis. The initial study demonstrated that additions of ZrSi₂ into a ZrB₂ ceramic increases densification at significantly reduced processing temperatures ≤1600ºC). This study revealed that low concentrations of ZrSi₂ (7.5 vol%) yield near fully dense (\u3e96% relative density) ZrB₂-based ceramics with strengths\u3e700 MPa. The microstructures exhibited well-dispersed second phases, with the exception of ZrB₂ containing 20 vol% ZrSi₂ that contained larger second phase regions (~40 µm). The second study demonstrated the ability to incorporate various grades of commercially available SiC fibers into a matrix based on the ZrB₂-ZrSi₂ ceramics developed in the initial study. Composites consisted of dense ZrB₂-ZrSi₂ matrices with SiC fiber loading ranging from 15 to 20 vol%. Apparent peak flexure strengths were reduced for ZrB₂-based CMCs incorporating continuous SiC fiber ( \u3c500 \u3eMPa), but strain to failure was increased up to 3%. Together these studies demonstrate the viability of using a ZrB₂-based matrix in a continuous SiC fiber reinforced CMC. Several key challenges were investigated to enable compatibility. The impact of SiC fiber reinforcement in ZrB₂-based CMC mechanical behavior was determined --Abstract, page iv