Microstructure and Thermal Shock Resistance of ZrB_2 and ZrB_2-20vol% SiC Composites from Aqueous Tape Casting

The microstructure and thermal shock resistance of ZrB2 and ZrB2-20vol% SiC(ZS20) composites prepared by aqueous tape casting and hot-pressing were investigated.Zr-B-C and Zr-B-W solid solution phases were formed in ZS20 composites,but not formed in ZrB2 samples.The diffraction peaks for ZrB2 of ZS20 composites shifted to higher 2θ values possibly due to the formation of solid solution phases which resulted in a decrease in lattice parameters.The critical thermal shock values for ZrB2 and ZS20 were measured to be 298℃ and 306℃ respectively using water quench tests.The thermal shock resistance of ZrB2 and ZS20 were also calculated and compared with the experimental data.The results revealed that the measured thermal shock resistance of ZS20 composites was lower than the calculated ones,which might be due to the thermal residual stress in the samples resulted from the difference in thermal expansion coefficient of ZrB2 matrix and SiC second phase as well as the solid solutions phases.