Processing and Characterization of ZrB₂-based Monolithic and Fibrous Monolithic Ceramics

Zirconium diboride (ZrB2) based ultra-high temperature ceramics either unmodified or with SiC particulate additions of 10, 20, or 30 volume percent were prepared by conventional hot pressing. The ZrB2-SiC compositions had improved four-point bend strength compared to the ZrB2 prepared in our laboratory as well as other reported ZrB2 or ZrB2-SiC materials. Strength and toughness increased as the amount of SiC increased. Measured strengths ranged from sim550 MPa for ZrB2 to over 1000 MPa for ZrB2-30% SiC. Likewise, toughness increased from 3.5 MPa to more than 5 MPa over the same composition range. The addition of SiC also improved oxidation resistance compared to pure ZrB2. Co-extrusion processing was used to produce ZrB2-based ultra-high temperature ceramics with a fibrous monolithic structure. Samples had dense ZrB2-30 vol% SiC cells approximately 100 mgrm in diameter surrounded by porous ZrB2 cell boundaries approximately 20 mgrm thick. ZrB2-based fibrous monoliths had four point bend strength of sim450 MPa, about half of a conventional ZrB2-SiC ceramic with the cell composition. Preliminary analysis of fracture behavior found that ZrB2-based fibrous monoliths did not exhibit graceful failure because the difference in strength between the cell and cell boundary of the current materials was not sufficient.