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2242 |
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Wednesday, May 05, 2010, Sophia Room 9:00 AM Process Diagnostics 2 |
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Loading effect in plasma spraying: from in-flight particle state distributions to diagnostic reliability |
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Kentaro Shinoda / Center for Thermal Spray Research
Stony Brook University, USA Yang Tan / Center for Thermal Spray Research, Stony Brook University, USA Sanjay Sampath/ Center for Thermal Spray Research, Stony Brook University, USA Gopal Dwivedi*/ Stony Brook University, USA |
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The effect of powder loading rate on in-flight particle state parameters such as particle temperature and velocity cannot be negligible in plasma spraying of yttria-stabilized zirconia for thermal barrier coating applications. Increasing powder feed rate generally decreases the plasma plume enthalpy, resulting in the decrease in the particle temperature and velocity. Thus, the loading rate will affect the molten degree of particles and may also affect the diagnostic result when a powder feed rate different from that of spray conditions is used in diagnostics. However, since the loading effect is determined by a balance between the plasma and particle plume enthalpies, it was difficult to evaluate this effect quantitatively. In this study, we investigate the effect of loading rate on in-flight particle state distributions in plasma spraying of yttria-stabilized zirconia. Commercially available diagnostic systems were utilized to measure particle temperature and velocity distributions as well as their average. Particle distribution changes were examined when spray parameters were varied such as powder feed rate, stand-off distance, and gas composition. Particle temperature distribution could be fitted with multiple peaks. As increasing the powder feed rate, a peak locating at a lower particle temperature increased. The same peak also increased with increasing the stand-off distance or under-injecting powder to the plasma plume. These suggests that the increase of semi-molten particles with increasing the loading rate. This effect was more significant in lower plasma enthalpy conditions. Some implications on diagnostic reliability will also be presented. |