Solidification mechanism and quantitative characterization of Fe-based amorphous splat formed by plasma sprayed droplets with different in-flight status

The paper aims at the quantitative characterization of solidification morphologies of plasma sprayed Fe-based amorphous splats. The spraying power was adjusted to provide the particles with different in-flight status. The SprayWatch-2i diagnostics system was employed to measure the real-time velocity and surface temperature of droplets for the estimation of the melting index (M.I.). The mirror polished stainless steel with 250 °C preheating temperature was utilized to collect individual splat. The solidity, flattening degree, as well as other basic geometric parameters of splat were calculated based on the 3D morphology. The spreading mechanism of droplet was discussed at length and the solidification type of splat was classified by the combination of solidity and flattening degree. The results indicate that with the increment of spraying power, the average surface temperature increases remarkably, while the changes in velocity are not so obvious. The molten droplet can spread into three types of splat, namely, disk-like type, flower-like type and fragmented type. The combination of solidity and flattening degree is effective in the characterization of the solidification type of the droplet. Generally, the splats tend to be more irregular and the flattening degree is inclined to be larger under higher spraying power.