Comparison of in-Flight Particle Properties, Splat Formation, and Coating Microstructure for Regular and Nano-YSZ Powders

In this study the relationship between the parameters of the atmospheric plasma spraying process and the in-flight properties of the particles was determined experimentally by using the DPV2000 system. The coating microstructure was investigated using analysis of SEM images. The morphology of individual splats was studied to shed light on the relationship between the in-flight particle properties and the coating characteristics. The spatial particle velocity and temperature distributions were determined by moving the DPV2000 sensing head in two directions. Coating microstructure was studied for different spraying parameters, e.g. stand-off distance, arc current, powder feed rate and Ar/ He mixture in the plasma gas. A Mat lab code was constructed for porosity analysis of the SEM images of the coating. The coating cross-section analysis showed that the total porosity of the coating increased with decreasing arc current, increasing stand-off distance, decreasing powder feed rate, and increasing helium flow rate. Two different materials were used for the APS coating: the regular (r-YSZ) feed stock and the nano size (n-YSZ) agglomerated powder. The results illustrate that the r- YSZ coating has higher total porosity at higher arc currents than n-YSZ coating. The splat flattening behavior was examined at different substrate temperatures, and different surface roughness for both powders. The results indicate that the flattening degree increased for highly polished substrates at high temperatures for the two materials but the values for n-YSZ were higher than those for the r-YSZ. Circularity of the splats increased as the arc current increased and the stand-off distance decreased. The n-YSZ splats had higher circularity values. This study showed the operating regimes in which the use of n-YSZ yields improved coating properties.