The effect of YB4 addition in ZrB2-SiC composites on the mechanical properties and oxidation performance tested up to 2000 °C (original) (raw)

The influence of YB 4 and Y 2 O 3 on densification, mechanical properties and oxidation performance of ZrB 2-SiC (ZS) composite was studied. The oxidation tests were performed in static air up to temperature of 1650°C for 1 h as well as under dynamic conditions of oxyacetylene torch at 2000°C. Static oxidation of ZS led to the formation of protective silica-based glass on the surface. However, ablation tests showed absence of silica in ablation centre. Only dense zirconia layer was left on the top of ZS. Composites with Y-containing additives exhibited significantly inferior oxidation performance in static conditions, since severe spallation and deeper degradation of the material were observed. On the contrary, the depth of material degradation after ablation was comparable with ZS. Samples were covered by solid solution of zirconia and yttria. Due to very low vapor pressure, yttriabased oxidation products are of interest considering even higher application temperatures exceeding 2000°C. 2 2 (3) The monolithic ZrB 2 possesses a poor oxidation resistance. This is due to the emerging B 2 O 3 formation which is liquid above 450°C and wets the ZrO 2 grains until it volatilizes above temperatures of 1100°C due to the high vapor pressure. Above this temperature, the oxidation protection is provided by SiO 2 (reaction (3)) which is significantly less volatile and more viscous compared to the boron oxide. This glassy layer reduces the diffusion into the bulk material and prevents the