“…The phase content of each sample is shown in Table 2. The thermal conductivity of the monoclinic phase is higher than those of the cubic phase and tetragonal phase, so the monoclinic phase content plays an important role in increasing the thermal conductivity of TBCs [8]. In this study, the monoclinic phase contents of samples are very similar: all about 5%.…”
Section: Phase Contentmentioning
confidence: 61%
“…Hence, the thermal conductivity is often affected by multiple factors. Chen et al [8] analyzed the relationship between the microstructure and thermal conductivity quantitatively using multiple linear regression, and they found that the porosity significantly affects the thermal conductivity at a fixed temperature, while the monoclinic phase content has a great influence on the thermal conductivity at higher temperatures.…”
Atmospheric plasma spray (APS) yttria-stabilized zirconia coatings have a complex microstructure with a variety of pores that significantly reduce the thermal conductivity. APS thermal barrier coatings (TBCs) with a similar monoclinic phase were prepared. The pore sizes and distributions of the coatings were obtained by scanning their cross-section via SEM; the scanned areas were over 1 mm × 2 mm and more than 23,000 pores for each coating were analyzed. Multiple linear regression was used to analyze the porosity data and then to determine the quantitative relationship between different types of pores and thermal conductivity. Results revealed that the different pores have different effects on decreasing the thermal conductivity. The small, vertical pores have the biggest effect, while the horizontal pores also play a significant role in decreasing the thermal conductivity.
“…The phase content of each sample is shown in Table 2. The thermal conductivity of the monoclinic phase is higher than those of the cubic phase and tetragonal phase, so the monoclinic phase content plays an important role in increasing the thermal conductivity of TBCs [8]. In this study, the monoclinic phase contents of samples are very similar: all about 5%.…”
Section: Phase Contentmentioning
confidence: 61%
“…Hence, the thermal conductivity is often affected by multiple factors. Chen et al [8] analyzed the relationship between the microstructure and thermal conductivity quantitatively using multiple linear regression, and they found that the porosity significantly affects the thermal conductivity at a fixed temperature, while the monoclinic phase content has a great influence on the thermal conductivity at higher temperatures.…”
Atmospheric plasma spray (APS) yttria-stabilized zirconia coatings have a complex microstructure with a variety of pores that significantly reduce the thermal conductivity. APS thermal barrier coatings (TBCs) with a similar monoclinic phase were prepared. The pore sizes and distributions of the coatings were obtained by scanning their cross-section via SEM; the scanned areas were over 1 mm × 2 mm and more than 23,000 pores for each coating were analyzed. Multiple linear regression was used to analyze the porosity data and then to determine the quantitative relationship between different types of pores and thermal conductivity. Results revealed that the different pores have different effects on decreasing the thermal conductivity. The small, vertical pores have the biggest effect, while the horizontal pores also play a significant role in decreasing the thermal conductivity.
“…Since the m-ZrO 2 contains a small amount of Y 2 O 3 , it has the lowest point defect concentration; therefore, a coating with higher m-ZrO 2 content would have higher thermal conductivity at elevated temperature. Consequently, the effect of m-ZrO 2 content on thermal conductivity becomes vital at high temperature [27]. With the increase in m-phase content, the thermal conductivity of the coatings increases.…”
Section: Relationship Between Microstructure and Thermal Conductivitymentioning
Abstract:In this paper, the effect of microstructure on the thermal conductivity of plasma-sprayed Y 2 O 3 stabilized ZrO 2 (YSZ) thermal barrier coatings (TBCs) is investigated. Nine freestanding samples deposited on aluminum alloys are studied. Cross-section morphology such as pores, cracks, m-phase content, grain boundary density of the coated samples are examined by scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). Multiple linear regressions are used to develop quantitative models that describe the relationship between the particle parameters, m-phase content and features of the microstructure such as porosity, crack-porosity, and the length density of small and big angle-cracks. Moreover, the relationship between the microstructure and thermal conductivity is investigated. Results reveal that the thermal conductivity of the coating is mainly determined by the microstructure and grain boundary density at room temperature (25 • C), and by the length density of big-angle-crack, monoclinic phase content and grain boundary density at high temperature (1200 • C).
“…As the porosity of fine-powder coatings consists mainly from pores and cracks of fine-and medium-range (96.7%), and it can be concluded that these ranges of pore sizes and shapes contribute largely to the thermal insulation property and play the primary role in determining thermal insulation value of coatings. The high thermal insulation exhibited by fine-powder coatings can be related to the greater number of interfaces between the pores and the matrix of the coating [16]. In addition, the relative high thermal insulation of fine-powder coatings can be related to the higher fine pore density (number of fine pores per unit area), as can be noticed in SEM images in Figure 4.…”
In the thermal spraying process, the porosity of ceramic coatings contributes directly to the efficiency of the thermal insulation. The size, shape, and distribution of the pores determine the level of both thermal and sintering resistance. In this work, three different atmospheric plasma sprayed (APS) alumina coatings were fabricated with the same spraying parameters using alumina powders with fine, medium, and coarse particle size. The microstructure of the obtained coatings was analyzed regarding the obtained total porosity, pore size, and pore shape. It was found that it is expedient to divide the pore size range into fine, medium, and large sizes. The shape was characterized with regard to the circularity aspect. In this way, all types of cracks can be considered as oblate pores and were included in the calculation of the total porosity. In the case of using fine feedstock powder, the densest coatings were produced among all coatings, and the fraction of fine pores and cracks are thereby substantially higher. However, the total porosity increases with increasing feedstock powder size. A connection was also made between thermal insulation and porosity fraction which includes fine pores and cracks.
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