Improved thermal shock and corrosion resistance of α-Al2O3/AlPO4 coating with PAA addition

Abstract

Abstract During thermal cycling, cracks are usually generated in ceramic coatings due to their differing thermal expansion coefficient with the substrate, and inevitably lead to the coating failing. Improving the thermal shock property of ceramic coatings is crucial but remains a big challenge for their usage. In this work, we fabricated a uniform and dense α-Al2O3/AlPO4 coating at 500 °C by thermo-chemical reaction method. With PAA addition, the α-Al2O3 nanoparticles were homogeneously embedded and fully wrapped by the AlPO4 matrix, which effectively suppressed the shrinkage of AlPO4 transformation and leaded to a coating without pores and cracks. With the coating deposited, the corrosion current Icorr of the substrate was sharply dropped from 1.98 μA·cm−2 to 0.00064 μA·cm−2 and the corrosion resistance was increased by a factor of 3094. More importantly, the bonding between α-Al2O3 and AlPO4 was strengthened by forming a co-lattice interface. Due to the excellent bonding formed inside the coating and at its interface with the substrate, the composite coating exhibited superior thermal shock resistance. No cracks appeared even after the coating suffering 300 thermal shock cycles at 600 °C-water cycling condition, which provides the possibility for the coating to keep well in a long run when in service. This new thermo-chemical reaction method not only sheds a light on low-temperature synthesis of α-Al2O3 coating with high bonding strength, but also provides a strategy for enhancing thermal shock property of other ceramic coatings.