Processing and characterization of ZrB-based ultra-high temperature monolithic and fibrous monolithic ceramics

Zirconium diboride (ZrB) 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 ZrB-SiC compositions had improved four-point bend strength compared to the ZrB prepared in our laboratory as well as other reported ZrB or ZrB-SiC materials. Strength and toughness increased as the amount of SiC increased. Measured strengths ranged from ∼550 MPa for ZrB to over 1000 MPa for ZrB-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 ZrB. Co-extrusion processing was used to produce ZrB -based ultra-high temperature ceramics with a fibrous monolithic structure. Samples had dense ZrB-30 vol% SiC cells approximately 100 μm in diameter surrounded by porous ZrB cell boundaries approximately 20 μm thick. ZrB-based fibrous monoliths had four point bend strength of ∼450 MPa, about half of a conventional ZrB -SiC ceramic with the cell composition. Preliminary analysis of fracture behavior found that ZrB-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. © 2004 Kluwer Academic Publishers.