Abstract
To reveal the structure-property relationships of the microstructure and the thermal conductivities of the coatings, Er2O3 coatings were directly deposited on an aluminum alloy substrate without bond coating by chelate flame spraying (CFS). The thermal insulation capability, thermal conductivity, microstructure, porosity, and splats of each coating were studied as a function of thickness. The coating with a thickness of 300 μm exhibited a high ΔT value that was 43.1% higher than that of the 100 μm-thick coating deposited with the same spray conditions. The 100 μm-thick coating exhibited low thermal conductivity, which decreased from 4.56 Wm−1K−1 to 2.57 Wm −1K−1 in the semistable phase (500 °C and 600 °C); this was mainly due to its special microstructure, which contained more mesh splats and higher porosity (28.3%) than the 300 μm-thick coating. Moreover, the effects of the microstructure on the thermal insulation capacities of the CFS coatings were determined. The results showed that as-deposited thick coatings offered higher heat conduction in the studied temperature range (from room temperature to 600 °C) than thin coatings. To conclude, this study also provides a new test method to determine thermal conductivity and thermal insulation capacity.
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