ZrB2 – SiC ceramics: Residual stresses and mechanical properties

The stress-strain state of ZrB₂-SiC ultra-high-temperature ceramics, produced using commercial powders with different impurity levels, was investigated by X-ray diffraction. Upon analysis of ZrB₂ and SiC diffraction lines shift, the level of thermal stresses (strains) of the different phases was determined. An increase of internal stresses in ceramics with rising viscous-brittle transition temperatures, T_ve, was attributed to increased grain boundary strength. Ceramics, for which high T_ve and high level of internal stresses were estimated, exhibited high strength, up to 700 MPa at 1400 °C. A field of compressive thermal stresses in the matrix phase resulted to be necessary for achieving high strength at low-temperatures. On the contrary, the presence of low-melting impurities at the grain boundaries negatively impacted on the stress level in ZrB₂ boundaries in the high temperature regime.