Quantitative Analysis Of The Relationship Between Microstructures And Thermal Conductivity Of Atmospheric Plasma Sprayed Thermal Barrier Coatings

Nowadays, Yttria-stabilized zirconia (YSZ) coatings have found widespread application as thermal barrier coatings (TBCs) due to its performance advantage, such as low thermal conductivity and coefficient of thermal expansion, good toughness, high strength, good corrosion resistance and thermal shock resistance, and less cost. However, TBCs in the future need to face lower thermal conductivity; thus, the current research on TBCs face many challenges. It is necessary to analyze the factors that affect the thermal conductivity of the coatings. The microstructural of the thermal barrier coating is comprised by the phases, the pores,the cracks, the splat interfaces, and the grain boundary and so on. The thermal conductivity of the coating is related with them. Due to the splat interfaces, it is difficult to analyze the information about the effects of them. To avoid this problem, the bulk YSZ ceramics were prepared via a hot-pressing sintering method. Based on electron backscatter diffraction images (EBSD) of yttria-stabilized zirconia (YSZ) ceramics, the thermal conductivities of grain boundaries and the tetragonal phase are determined by finite element models. This is part of the study of this article. The quantitative relationship between the microstructure and thermal conductivity of YSZ coatings is developed. By comparing the microstructural characteristics of YSZ coatings with simulated models of splat interfaces, a calculation model of the thermal conductivity is established having an error less than 10%. Based on finite element models, the effect coefficients of pores, cracks, splat interfaces, the monoclinic phase, and grain boundaries are calculated. This is another part of the article.We achieved some good results as follows:(1) The bulk YSZ ceramics were prepared via a hot-pressing sintering method. Ceramics with different grain sizes were achieved by using different annealing methods. To retain the same phase composition, the dwell time was changed. Based on the EBSD images of bulk yttria-stabilized zirconia (YSZ) ceramics, the thermal conductivity of the tetragonal phase and grain boundaries were calculated using finite element models.(2) Finite element models based on the EBSD images of the coatings and the idealized models of splat interfaces were generated to analyze the thermal conductivities of the coatings. The percentage errors between the calculated results and experimental findings was less than 10%.(3) The effect coefficients of splat interfaces by comparing the presence or absence of splat interfaces about the coatings and interactive effect of pores, cracks and splat interfaces by comparing the presence or absence of pores and cracks in the matrix were calculated using a finite element model based on the EBSD images and idealized models of splat interfaces.(4) The effect coefficients of pores, cracks by comparing the presence or absence of pores and cracks about the coatings, the monoclinic phase by comparing the presence or absence of monoclinic phase about the coatings, and grain boundaries by comparing the presence or absence of grain boundaries about the coatings were calculated using a finite element model based on the EBSD images.