Loss of Y from NiCrAlY powder during air plasma spraying

This study involves changes in microstructures and chemical compositions of NiCrAlY particles that occurred during an air plasma spraying of the powder. In this work the spraying particles were rapidly cooled and collected at a spraying distance just before the coating deposition in order to study the mid-flight transformation. Microscopy analysis of the particle cross-sections reveals that different structural and chemical transformations took place presumably depending on the flight path in relation to the plasma plume. Particle A group has a tendency to show some increase in Al and Y contents, possibly due to an evaporation of γ-(Ni solid solution) and β-(NiAl). Accompanying β grain growth can sometimes be observed. Particle B group often forms a large amount of Al-Y rich oxide due to an increase in oxygen activity during flight. This results in a significant reduction of Y in the particle. The coating produced using the same set of spraying parameter shows a heterogeneous structure with respect to the distribution of Y.