A Processing–Microstructure Correlation in ZrB 2 –SiC Composites Hot-pressed under a Load of 10 MPa

Abstract

Monolithic ZrB 2 ceramic and its composites, with 5 to 30 vol. % SiC, has been prepared by hot pressing at temperatures of 1700, 1850 and 2000 °C, for 30 minutes under relatively low pressure of 10 MPa. Densification behavior of ZrB 2 -based composites is improved by the addition of SiC particulates. The fracture surface of monolithic ZrB 2 ceramics shows a grained structure, with faceted ZrB 2 grains, as the fracture appears to spread prevalently along an intergranular path. The ZrB 2 /ZrB 2 boundary interface is seemingly free of any secondary phases. The microstructure of ZrB 2 –30 vol. % SiC composite, hot-pressed at 1700 °C, is consistent with measured porosity for the sample that has ~8% open pores, nearly without closed pores. It seems that mechanical interlocking between ZrB 2 and SiC is an important mechanism for densification. In the microstructure of specimens consolidated at 1850 °C, neck formation between ZrB 2 particles is visible. In contrast, relatively fully dense samples are obtained by hot-pressing at 2000 °C. Intergranular SiC particles inside ZrB 2 grains show the occurrence of mass transfer among ZrB 2 particles, which in effect brings the elimination of pores to a fortunate ending. Efficient mixing of starting powders is very critical in order to achieve a fine-grained homogenous microstructure.