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Monday, May 15, 2006 - 9:00 AM
EAP10.1

On The Reproducibility of Air Plasma Spray Process and Control of Particle State

V. Srinivasan, A. Vaidya, T. Streibl, M. Friis, Center for Thermal Spray Research, Stony Brook, NY; S. Sampath, S.U.N.Y at Stony Brook, Stony Brook, NY

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.


Summary: Controlling particle state is important to not only achieve the required microstructure and 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 aforementioned attributes. This is important to design coatings for high performance applications and in the ongoing efforts towards achieving prime reliance. This study examines the variabilities in particle state and explores a few strategies to control them for improved reproducibility with the aid of in-flight particle and plume sensors.// The particle state can be controlled by controlling the torch parameters or by directly controlling the particle state itself via feedback from particle and plume sensors such as DPV2000 & TDS. There exist at least a few control protocols to control the particle state (predominantly temperature and velocity) with judicious choice of critical parameters. In the present case the particle state has been controlled by varying the critical torch parameters in a narrow range using 8% YSZ of angular morphology (fused and crushed) with 10-75 microns size distrubutions in conjunction with a N2-H2 laminar (non-swirl) plasma.// Two important results emerge. (1) The particle state resulting from averaged individual particle measurements (DPV 2000) is surprisingly stable with variabilities in T < 1% and variability in V of < 4%. Ensemable approaches yield a somewhat higher variability (5%). In spite of this the variability in basic coating attributes such as a thickness and weight is surprisingly large. (2) Applying a much simpler control strategy to only control the particle injection and hence the particle trajectory results in reduced variabilities in coating attributes.