Abstract
A wide range of manufacturing processes are used to supply yttria stabilized zirconia powders for plasma sprayed TBC applications. From previous studies it is known that the difference in coating properties can potentially result from variations in powder feedstock as a consequence of particle inflight behavior and particle impact. An additional strong contribution to splat variation results from changes in the particle in flight behavior. In order to understand the variation in particle condition as a consequence of different powder morphologies, a detailed diagnostic analysis was carried out for plasma densified (PD), fused and crushed (FC) and agglomerated & sintered (A&S) powders. In this study a “3D multiple sensors” based integrated approach was used to evaluate these differences. Direct feed back sensors were used for optimization and combined with sophisticated diagnostics for in-depth studies. To obtain comparable results, three batches of commercial powders were sized to the same specification. For a given set of spraying parameters the recorded spray stream characteristics such as plume position, particle temperature, size and velocity deviated strongly for the given morphologies. By optimizing injection, the different powders can be made to follow nominally similar trajectories. This study reveals the sensitivity of each powder to process parameters and the variability in particle state that can result from it. Some techniques are suggested to optimally inject the different powders and to achieve similar particle states for these morphologies
