Enhanced Thermal Shock Resistance and Mechanical Characteristics of Microwave Sintered ZrB₂-SiC-MgO Composites

The potential to utilize ZrB₂ based ceramics for high-temperature space applications requires excellent thermal shock resistance. Therefore, the present study describes the use of water quenching method to determine the thermal shock resistance of microwave sintered ZrB₂-25 SiC (vol. %) and ZrB₂-25 SiC-2 MgO (vol. %) composites at 400 °C, 800 °C and 1200 °C. The MgO incorporation enhanced the ability of ZrB₂-25 SiC (vol. %) composite to withstand thermal shock due to the higher fracture toughness and flexural strength. The crack deflection was observed as the primary toughening mechanism after thermal shock. The ZrB₂-SiC-MgO composite demonstrated outstanding thermal shock resistance with a critical thermal shock temperature difference of 974.41 °C, surpassing that of ZrB₂-SiC composite by 1.6 times. Post thermal shock test at 1200 °C, the maximum microhardness of 14.99 ± 1.29 GPa, maximum compression strength of 769.01 ± 36.66 MPa, maximum fracture toughness of 5.98 ± 0.39 MPa.m^0.5 and maximum critical energy release rate of 76.05 ± 9.89 J/m² were observed for ZrB₂-25 SiC-2 MgO (vol. %) composition. The addition of MgO to ZrB₂-SiC resulted in exceptional performance in microhardness, compression strength, and fracture toughness following thermal shock testing at 1200 °C. Specifically, the ZrB₂-SiC-MgO composite retained 94.16%, 91.28%, and 95.52% of its pre thermal shock values for these mechanical properties, emphasizing its thermal stability and resistance to degradation under high-temperature conditions.