Processing and characterization of ZrB2-based ultra-high temperature 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 550 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 m in diameter surrounded by porous ZrB₂ cell boundaries approximately 20 m thick. ZrB₂-based fibrous monoliths had four point bend strength of 450 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.