Strong ZrC ceramics at high temperatures with the addition of W

The effect of W addition on densification, microstructure, and mechanical properties of ZrC ceramics was investigated. W reacted with carbon in ZrC to form WC, which resulted in the formation of ZrC _1-x at 1300-1700°C, while WC was further dissolved in ZrC to form a (Zr _1-y W _y )C _1-x solid solution at 1800-2000°C. The relative density of ZrC with 5 mol% W (ZW5, 96.8%) was markedly higher than that of pure ZrC (Z0, 94.8%). ZW5 exhibited a fine homogeneous microstructure with a grain size (2.6 ± 0.5 μm) much smaller than that of Z0 (10.9 ± 3.0 μm), while excess W addition (10 mol%) in ZrC adversely affected the densification and the microstructure. The flexure strength of Z0 was 446 ± 46 MPa at room temperature, which almost linearly decreased to 281 ± 10 MPa at 1800°C in a high-purity flowing argon atmosphere. The flexure strength of ZW5 was 512 ± 40 MPa at room temperature, and had no degradation even up to 1800°C. The fine and homogeneous microstructure of ZW5 and the removal of oxygen impurity from the grain boundaries promoted the enhancement of high-temperature mechanical properties.