Controlling the spray stream is important to not only achieve the required structure & properties in coatings but also to clearly isolate and understand the role of other clusters of variables such as the various substrate and deposition conditions on the microstructure and properties of coatings. This is vital to design coatings for high performance applications and in the ongoing efforts towards achieving prime-reliance. Hence this study explores a few strategies to control the spray stream for better reproducibility with the aid of in-flight particle and plume sensors.

At the very basic, the spray stream can be controlled by either controlling the torch parameters (passive sensor method) or by directly controlling the spray stream itself using particle & plume sensors such as DPV 2000, TDS (active sensor method). It has been identified that the particle T & V can be controlled actively in two ways. One is by altering the torch parameters in a narrow range and the other is by varying the torch parameters in a wide range (latter not dealt here). 8%YSZ of two different morphologies (angular and hollow spherical) with similar size distributions (10-75m) were used for the study employing a N₂-H₂ plasma. It has been found that controlling the particle T & V by altering the torch parameters in a narrow range (active sensor method in narrow range) reduces the variability in the coating thickness & weight by a third in comparison to the passive method. Variation in other coating properties made by both methods is compared and presented in detail.