A. Kobayashi, J. Zhang, Osaka University, Joining and Welding Research Institute (JWRI), Osaka, Japan
ZrO2 based thermal barrier coatings prepared using plasma spraying are frequently modified by mixing some kinds of additives such Al2O3, in order to improve their oxygen ion resistance. Using gas tunnel type plasma spraying characterized by higher plasma temperature and better plasma stability, zirconia coatings with various mixing ratio of alumina were achieved to generate graded functional microstructure. Because of the plasma stability, the coating micro-structural parameters such as the thickness, mixing ratio of alumina and porosity were well reproduced by keeping the spraying parameter to be constant. The surface and cross-sectional morphologies of the coatings were imaged by SEM (Scanning Electron Microscope) and OM (Optical Microscopy). Based on the SEM photos, the coating thickness was measured and the alumina content ratio was evaluated, while the coating porosity (the porosity profile over the cross-section and the average porosity) was obtained from the image analysis of the optical photos. The coating hardness was measured with a micro Vicker hardness tester and the thermal conductivity was measured based on the principle of steady heat flux between two parallel hot plates. The results showed that the mixing of alumina increased the coating hardness and lowered the coating porosity, while did not deteriorate the thermal resistance.
Summary: ZrO2 based thermal barrier coatings prepared using plasma spraying are frequently modified by mixing some kinds of additives such Al2O3, in order to improve their oxygen ion resistance. Using gas tunnel type plasma spraying characterized by higher plasma temperature and better plasma stability, zirconia coatings with various mixing ratio of alumina were achieved to generate graded functional microstructure. Because of the plasma stability, the coating micro-structural parameters such as the thickness, mixing ratio of alumina and porosity were well reproduced by keeping the spraying parameter to be constant. The surface and cross-sectional morphologies of the coatings were imaged by SEM (Scanning Electron Microscope) and OM (Optical Microscopy). Based on the SEM photos, the coating thickness was measured and the alumina content ratio was evaluated, while the coating porosity (the porosity profile over the cross-section and the average porosity) was obtained from the image analysis of the optical photos. The coating hardness was measured with a micro Vicker hardness tester and the thermal conductivity was measured based on the principle of steady heat flux between two parallel hot plates. The results showed that the mixing of alumina increased the coating hardness and lowered the coating porosity, while did not deteriorate the thermal resistance.
