Modeling of Thermal and Mechanical Behavior of ZrB₂-SiC Ceramics after High Temperature Oxidation

The effects of oxidation on heat transfer and mechanical behavior of ZrB 2 -SiC ceramics at high temperature are modeled using a micromechanics based finite element model. The model recognizes that when exposed to high temperature in air ZrB 2 -SiC oxidizes into ZrO 2 , SiO 2 , and SiC-depleted ZrB 2 layer. A steady-state heat transfer analysis was conducted at first and that is followed by a thermal stress analysis. A “global-local modeling” technique is used combining finite element with infinite element for thermal stress analysis. A theoretical formulation is developed for calculating the thermal conductivity of liquid phase SiO 2 . All other temperature dependent thermal and mechanical properties were obtained from published literature. Thermal stress concentrations occur near the pore due to the geometric discontinuity and material properties mismatch between the ceramic matrix and the new products. The predicted results indicate the development of thermal stresses in the SiO 2 and ZrO 2 layers and high residual stresses in the SiC-depleted ZrB 2 layer.