Degradation of Suspensions for Plasma Spraying: A Technical Note

This study investigates how the degradation of yttria suspensions over time affects coating quality in suspension plasma spraying (SPS), comparing coatings produced from a fresh batch at six months post-delivery with those from a significantly aged batch at eighteen months. While particle velocity and temperature in the plasma plume remained largely unchanged between batches, the aged suspension produced distinct coating defects colloquially termed “speckles”—localized agglomeration artifacts seeded by incompletely melted particles that propagate and develop internal cracking with successive deposition passes. The findings underscore the importance of suspension shelf life as a process variable and highlight the risk of quality degradation when expired or improperly stored suspensions are used in SPS applications.