Properties of ZrB₂―SiC―CrB₂ ceramics obtained by vacuum sintering

Abstract

Vacuum sintering of ceramics based on ZrB₂ has been carried out at the temperature range 1800―2100 °C with an exposure of one hour. Chromium diboride activate the sintering process of ceramics due to compression in the liquid phase of the sintering mode. As a result of sintering, an interaction occurs between the components and the formation of new high-temperature phases: CrB, ZrC and complex solid solutions based on them. Adding CrB₂ to the base composite ZrB₂―10% (wt.) SiC in an amount of 10% (wt.) allows to obtain a dense material already at a temperature of 1950 °C, with high mechanical strength which is approximately 500 MPa and oxidation resistance at a temperature of from 1200 to 1500 °C, where the oxidation rate does not more than 5 mg/cm² ·h. Subsequen addition of chromium boride reduces grain boundary strength, as evidenced by the values of K_1C and grain boundary strength, oxidation resistance also worsens due to the high evaporation of chromium at a test temperature of 1500 °C. Oxide scale of ceramics consists of three layers: the upper borosilicate glass, second layer of zirconium oxide, third silicon oxide and chromium borides and a layer with depleted elements of silicon and boron. Comparison of ceramics obtained by vacuum sintering with ceramics obtained by hot pressing shows that they almost do not differ in the level of physical mechanical properties at the same density level. Full text download