Thermal resistance determination of Sm₂Zr₂O₇ + 8YSZ composite type of TBC

The determination of thermal resistance related to splat boundaries in composite TBC (thermal barrier coating) systems and expressed as splat-to-splat heat transfer coefficient was analyzed. Sm₂Zr₂O₇ and conventional 8YSZ powders were used for coatings deposition by atmospheric plasma spraying. Two types of internal morphology were deposited: monolayered type (Sm₂Zr₂O₇, 8YSZ) and composite TBCs (Sm₂Zr₂O₇ + 8YSZ with weight ratios of 75/25, 50/50 and 25/75). The primary investigation was related to microstructural characterization of ceramic layers (pores and cracks architecture description), thermal diffusivity and conductivity characterization by laser flash analysis and theoretical models. The thermal conductivity was initially calculated on the basis of thermal diffusivity, heat capacity and density measurement as a function of temperature. Those values were corrected due to the presence of pores (microstructural analysis) and effective vales of thermal conductivity were calculated. These values were used as the basis for additional calculations based on the Hasselman-Johnson model of thermal conductivity for composite materials. Based on quantitative data from image analysis and porosity corrected thermal conductivity for monolayered and composite TBC systems, the thermal boundary conductivity (splat-to-splat heat transfer coefficient) was calculated as a function of temperature for Sm₂Zr₂O₇ + 8YSZ composite systems.