Investigation of the morphologies of chelate flame-sprayed metal oxide splats

This paper reports an investigation of Er2O3 splats formed by metal-ethylenediaminetetraacetic acid (EDTA) complex particles that were applied onto aluminum alloy substrates by flame spraying. The splat morphologies and coating microstructures were analyzed under different conditions. The effects of the in-flight particle temperature of the carrier gases and the impact particle deposition temperature on solidification of the molten droplets were evaluated with a rotating dodecahedron stage operated at velocities of 30, 75, and 90 rpm and with different temperatures and angles of incidence. Various techniques were used to analyze the surfaces and cross sections of the splats and coatings formed under the different conditions. Most of the splats underwent transitions from disk shapes (ratio > 85 %) to irregular shapes (circularity of 0.61-0.80) with increasing rotational velocity. The spray process provided a coating with a porosity of 23.3 % at a powder flow rate of 20 g/min. The temperature reached during the chelate flame spraying (CFS) process and the condensing velocity of the deposited splat, rather than the in-flight particle temperature, were found to control the splat morphology. This synergistic condensation effect paves the way to successful deposition of high-temperature structural ceramic coatings such as Er2O3 with the CFS method.