Microstructural and Performance Analyses of Thermally Sprayed Electric Resistance Heating Systems as De-Icing Elements

This study investigates the microstructure and efficiency of coating-based heating elements produced by deposition of various powders, including aluminum oxide (Al₂O₃), alumina-titania (Al₂O₃-TiO₂), nickel-chromium (NiCr), and copper, using flame spraying, suspension plasma spraying, high-velocity oxyfuel (HVOF) spraying, and cold spraying techniques. The main goals are to assess the dielectric strength of flame and plasma sprayed alumina, compare the electrical resistivity of HVOF and flame sprayed NiCr, and obtain coating cross-sectional images to shed light on the challenges and potential of different heating element designs. The Al₂O₃ layer produced by suspension plasma spraying appeared to be more reliable due to its cauliflower-like structure, corundum content, and hygroscopic properties. Resistivity was found to be higher in the flame sprayed NiCr than in the HVOF deposit mainly due to discontinuities and imperfections such as cracks, pores, and oxygen content. The micrographs taken from sample cross-sections show penetration of flame-sprayed NiCr into the flame-sprayed Al₂O₃ and Al₂O₃-TiO₂ layers, which decreases the effective thickness of the dielectric. However, interlocking between NiCr and Al₂O₃-TiO₂ coatings can be beneficial when cohesion is a concern.