Abstract
Plasma spraying of large-scale components (such as paper mill rolls, rocket exit nozzles, parts of the land-based turbines for power generation, thermally sprayed free-standing tubes, etc.) and also powder spheroidization) are just several examples of industrial applications where the processing time and costs are critical. To ensure productivity and cost-effectivity of the process, it is beneficial to use plasma torches which can process high powder throughputs, i.e. with feed rates in tens of kilograms per hour. Such torches must have sufficiently high enthalpy and plasma temperature, to ensure homogeneous particle treatment and high deposition efficiency. Hybrid water-stabilized plasma (WSP-H) system with its enthalpy of more than 140 MJ/kg and plasma temperature of 25 000 K is able to process up to 40 kg of powders per hour. Since the WSP-H torch consumes typically only 15 slm of Ar at full power of 180 kW, it is a very powerful and also economical tool that meets all the prerequisites for large-scale plasma spraying applications. Spraying of three representative ceramics: alumina, zircon, and yttria-stabilized-zirconia is presented in this study. It reveals only limited influence of increasing powder throughput on particle velocity, temperature and coating microstructure. Deposition efficiency of the processes is discussed and the deposited coatings are analyzed by SEM and XRD.
