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 ZrC1-x at 1300-1700 degrees C, while WC was further dissolved in ZrC to form a (Zr1-yWy)C1-x solid solution at 1800-2000 degrees C. The relative density of ZrC with 5mol% 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 +/- 0.5m) much smaller than that of Z0 (10.9 +/- 3.0m), while excess W addition (10mol%) in ZrC adversely affected the densification and the microstructure. The flexure strength of Z0 was 446 +/- 46MPa at room temperature, which almost linearly decreased to 281 +/- 10MPa at 1800 degrees C in a high-purity flowing argon atmosphere. The flexure strength of ZW5 was 512 +/- 40MPa at room temperature, and had no degradation even up to 1800 degrees 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.