Thermal barrier coatings formed by flame-spray with metal–EDTA

Nowadays, the selection of a suitable spray method to design the coating microstructure such as its porosity, is key to effectively improving the properties of the base materials. In this study, the microstructures and thermal insulation capability of chelate flame-sprayed erbium oxide (Er2O3) and yttrium oxide (Y2O3) coatings directly deposited on aluminum alloy (A5052) substrates were investigated. A rotation apparatus and cooling agent (liquid nitrogen) were used during the synthesis to cool the substrate and control the deposited particles' shape or form during film deposition. The results show that the Y2O3 coatings had higher thermal insulation capability than the Er2O3 coatings. It is worth noting that the thermal insulation capacity of the Y2O3 and Er2O3 coatings synthesized by cooling the substrate with liquid nitrogen was improved. For thicknesses of 90–128 μm and cross-sectional porosities of 12%–33% of the Y2O3 coatings, a temperature drop (ΔTf = 37 °C) of the porous structure Y2O3 coating at 440 °C and an increase from 0.10 to 0.32 of ΔTf per unit micron (°C μm–1) were observed. This was due to the coating having a more undulated layer surface and more complicated microstructures. Therefore, it is a new idea with the chelate flame-spray method to synthesize thermal barrier coatings on low-melting-point-metal materials.