Abstract
The triplex-torch design providing three stable arcs in power and geometry promises a stable, quasi-laminar plasma jet leading to an uniform plasma and thus an uniform particle distribution. Additionally, the three powder injectors lead to an extended powder feed rate, resulting in a lower spraying time. This paper deals with particle properties of YSZ (SM 204NS) with respect to their injection location and powder feed rate and the resulting coating microstructure and porosity levels. Concerning the injection conditions, the three powder jets can be clearly identified. Their location depends on the spraying distance and less pronounced on the injection velocity. Interestingly, if the different powder-sizes are grouped and the jet cross-section is plotted for the different size cuts, the position of each size cut varies. Thus, a local separation of the powder takes place in the jet. The powder feed rate was varied from 30 to 320 g/min. Accordingly to this variation, the particles mean temperature was lowered from 3050°C down to 2650°C, and the velocity values dropped from 230 m/s to 155 m/s. Regarding the achieved coating thickness, up to a powder feed rate of approximately 210 g/min the thickness is increasing with no dramatic change in the porosity values. More powder does not lead to a thicker coating but results in a significantly higher porosity. Moreover, the microstructure of the coatings obtained by using a higher feed rate exhibits more segmentation cracks.
