2019 Volume 127 Issue 12 Pages 878-886
ZrB2/ZrAlC composite ceramics were successfully synthesized from Zr, Al, graphite and ZrB2 powders by using a spark plasma sintering method. The volume content of ZrAlC has a major impact on the fracture toughness. ZrAlC-rich (≥70 vol.%) composite ceramics exhibit much higher fracture toughness than do ZrB2-rich (≥60 vol.%) composite ceramics. The evidently larger ZrAlC grains in the ZrAlC-rich composite ceramics lead to a longer crack propagation path for toughening. Both the Vickers hardness and Young’s modulus of composite ceramics increase slightly with an increase in the ZrB2 volume content. The evident oxidation of composite ceramics at 1000°C results in the formation of Al18B4O33 and Al4B2O9. At 1200°C, the composite ceramics exhibit a fluffy and porous top oxidized layer composed of whiskers of Al18B4O33 and Al4B2O9 grains, and the thickness of the oxidized layer and oxidation mass gain increase with an increase in the ZrAlC volume content. The ZrB2-rich composite ceramics with less than 40 vol.% ZrAlC content do not exhibit apparently larger oxidation mass gain than does the pure ZrB2 ceramic after oxidation at 1200°C and higher temperatures. The composition-dependent microstructure and properties provide a comprehensive insight for the development of high-temperature composite ceramics based on ZrAlC and ZrB2.