Influence of High-Temperature Oxidation on the Strength of Ceramics Based on ZrB2

The residual strength of composite ceramic materials based on zirconium boride constitutes more than 50% of their initial strength after oxidation at a temperature of 1500 degrees C with holding for 50 h or at a temperature of 1600 degrees C with holding for 2 h. It is shown that the process of softening of the ceramics is caused by heterogeneities formed in the scale in the form of delaminations of individual zirconium-dioxide grains or groups of these grains from the base, especially in the ZrB2-15% SiC system. As a result of the addition of Mo2C, WC, and W2B5, the residual strength increases due to the formation of denser and thinner oxidized layers. However, due to the presence of pores and cracks, this level of strength cannot be preserved. At the same time, the initial level of strength can be preserved in the ZrB2-15% MoSi2 system characterized by the formation of a dense scale and fine zirconium-oxide grains in the process of oxidation. The residual strength is affected by the structure of the scale, the thickness and size of inclusions inside it, and internal stresses.