The influence of spray distance on the assessment of porosity in YSZ thermal barrier coating

Three types of plasma-sprayed ZrO2 stabilized by 8 wt. % Y2O3 (YSZ) thermal barrier coatings (TBCs) were prepared by changing spray distance (70,100,130) mm. Porosity measurement is a key factor to identify the performance of thermal barrier coatings (TBCs). Combination of image analysis (IA) and Mercury intrusion porosimetry (MIP) techniques were used to analyze the porosity and pore size distribution. The porosity was categorized based on pore size (diameter). To optimize the thermal properties and maintained them during service, it will be important to design TBCs with optimal porosity. Hence, the characterization of the microstructure and the determination of porosity consider as important part in the assessment of YSZ coatings. Microstructure evaluation Post processing images of FESEM was performed using Image J software. XRD inspection used to characterize phases which present in plasma spray coating. In general, the porosity is inhomogeneously distributed and the coatings showed a large difference of pore sizes. Both IA and MIP showed that the porosity changed as a result of the spray distance changing for all investigated coatings. XRD results showed that all three types of coatings were mainly composed of t'–ZrO2 phase and a small amount of m-ZrO2 phase.