Mechanical properties and grain orientation evolution of zirconium diboride-zirconium carbide ceramics

摘要

The effect of ZrC on the mechanical response of ZrB2 ceramics has been evaluated from room temperature to 2000 degrees C. Zirconium diboride ceramics containing 10 vol% ZrC had higher strengths at all temperatures compared to previous reports for nominally pure ZrB2. The addition of ZrC also increased fracture toughness from similar to 3.5 MPa root m for nominally pure ZrB2 to 4.3 MPa root m due to residual thermal stresses. The toughness was comparable with ZrB2 up to 1600 degrees C, but increased to 4.6 MPa root m at 1800 degrees C and 2000 degrees C. The increased toughness above 1600 degrees C was attributed to plasticity in the ZrC at elevated temperatures. Electron back-scattered diffraction analysis showed strong orientation of the ZrC grains along the [001] direction in the tensile region of specimens tested at 2000 degrees C, a phenomenon that has not been observed previously for fast fracture (crosshead displacement rate = 4.0 mm min(-1)) in four point bending. It is believed that microstructural changes and plasticity at elevated temperature were the mechanisms behind the ultrafast reorientation of ZrC.