Comparison and parametric analysis of SPS coatings fabricated via torch conventional and Cascaded

The selection of the spray torch is crucial for the fabrication of suspension plasma-sprayed coatings. Compared to plasma torch with a single cathode/anode, cascaded torch provides a more stable voltage, a lower arc current and less plasma gases. In this study, SPS coatings were successively fabricated using conventional and cascaded plasma torches, both equipped with a mechanical injector. A parametric study was conducted to evaluate the effects of five different process parameters: suspension mass load, spray distance, plasma power, spray step, and substrate roughness on the coating properties, especially the coating porosity. Afterward, the porosity of the coatings was investigated by imaging and a multivariate analysis on the collected experimental data was carried out. The results indicated that: (1) The porosity of SPS coatings manufactured by both torches followed a consistent trend relative to the process parameters. Specifically, the porosity of the SPS coatings decreases with increasing suspension mass loading and plasma power, while it shows an opposite trend by increasing spray distance, substrate roughness and spray step; (2) The coatings fabricated by cascaded torch exhibit lower porosity compared to those fabricated with the conventional torch. Additionally, the coating microstructure obtained with the cascaded torch has a distinctive plume-like morphology.