Formation mechanism and high temperature mechanical property characterization of SiC depletion layer in ZrB₂/SiC ceramics

When ZrB₂/SiC ceramics are exposed to high temperatures, a SiC depletion layer will appear near the material surface. Due to the degradation of mechanical properties for the SiC depletion layer, the ZrB₂/SiC ceramics might fail initially at the SiC depletion layer. Based on chemical reaction analysis and microstructural observation, a pore evolution model is presented to characterize the formation mechanisms of the SiC depletion layer, which can calculate the variation in the volume fraction of each constituent during the oxidation process. The micromechanical models are developed to analyze the mechanical properties of the SiC depletion layer during high temperature oxidation. It is found that relative modulus and relative strength of the SiC depletion layer initially decrease and then gradually rise with the increase of oxidation time. As the SiC content of ZrB₂/SiC ceramics increases, the porosity of SiC depletion layer increases as well, whereas the mechanical properties significantly decrease.