A recent trend of development in thermally sprayed ceramic coatings is to decrease their most defining attribute, brittleness. One possible strategy to improve ductility is to alter the coating towards a finer microstructure: Due to the smaller size of the splats, the amount of crack-arresting interfaces increases. High-velocity suspension flame-spraying (HVSFS) is an emerging thermal spraying technique, which utilizes a liquid as the powder carrier instead of gas, as in the more traditional spraying techniques. This allows for nano- or submicrometer-sized granular structures to be achievable with HVSFS. The aim of this work is to evaluate the brittleness of suspension sprayed aluminum oxide (Al_2O_3) -coatings with various methods, including Vickers indentation fracture toughness, 4-point bending and High-Velocity Particle Impactor. Coatings were sprayed with HVSFS using suspensions of isopropanol and water solvents. Additionally, high-velocity oxy-fuel (HVOF) -sprayed commercially available Al_2O_3-powder feedstock was used as a reference. Differences in the melting degrees of the HVSFS-coatings were found, leading to different cracking behaviors in all tests. Both HVSFS-coatings showed improvements in strain-to-fracture, while one showed improvements in energy absorbance and fracture toughness compared to traditional HVOF-coating.
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