Microstructure and Sintering Mechanism of TiB<sub>2</sub>-ZrO<sub>2</sub>-SiC Composite

Abstract

A ceramic TiB2-20wt% (2mol% Y2O3-ZrO2) composite has a high three-point bending strength of 1200MPa. However, this composite lacks sinterability, so that glass encapsulation HIP'ing is required to obtain a full dense sintered compact. However, addition of 2.5-5.0wt% SiC improved the sinterability drastically. TiB2-19.5wt% (2mol% Y2O3-ZrO2)-2.5wt%SiC was densified to 96% of its theoretical density by vacuum sintering at 1700°C for 14.4ks, and this sintered compact was hot isostatically pressed (HIP'ed) without glass encapsulation. In this work, the microstructure and sintering mechanism of TiB2-19-19.5wt% (2mol% Y2O3-ZrO2)-2.5-5.0wt% SiC were investigated. TiB2-19-19.5wt% (2mol% Y2O3-ZrO2)-2.5-5.0wt% SiC was densified drastically above 1600°C. TiB2-1.0-10.0wt% SiC had the same sinterability as TiB2-19-19.5wt% (2mol%Y2O3-ZrO2)-2.5-5.0wt% SiC. Therefore, SiC improved the sinterability of TiB2, regardless of the presence of ZrO2. The microstructure of HIP'ed compacts was observed with a SEM and a TEM. Enriched areas of SiC were not observed with the SEM. However, TEM observation showed that thin strip-like grain boundary phases consisting of Ti, Si and Zr exist between grain boundaries of TiB2 and ZrO2, and that (Ti, Zr)5Si3 exists at the triple points of grain boundaries. These grain boundary phases were formed by the reaction among SiC, Ti, and Zr. These were entirely or partially liquid phase at the sintering temperature of 1700°C. As a result, TiB2-19-19.5wt% (2mol% Y2O3-ZrO2)-2.5-5.0wt% SiC was densified by liquid phases sintering, which was the main mechanism in which sinterability was improved by the addition of SiC.