Enhancement of amorphous phase formation in alumina–YSZ coatings deposited by suspension plasma spray process

In the present work on pseudo-eutectic alumina–yttria stabilized zirconia (YSZ) composite, the influence of spray parameters on amorphous phase formation during suspension plasma spray deposition is investigated. Several variables were evaluated as the most probable key factors influencing the amorphous phase formation. These variables include powder feed size, in-flight particle characteristics (temperature and velocity), spraying robot travel speed, preheating the substrate, number of deposition passes and the presence of bond coat. It was found that larger particle size, higher robot speed and substrate preheating lead to larger amounts of amorphous phase. Moreover, it is shown that particle velocity and temperature need to be reasonably low to get greater amorphous content while the presence of a bond coat has no significant influence on the amorphous phase formation. In contrast, increasing the number of deposition passes is detrimental to this phase. This work also discusses some correlations observed between the amorphous phase content and the in-flight particle characteristics and coating grain sizes.

► Parametric study of amorphous phase content in suspension plasma spray ► Larger feed (a few microns compared with nano) provides more amorphous content. ► Lower in-flight particle velocity results in more amorphous phase. ► Particle temperature influences not strongly amorphous phase formation. ► Mixing and melting are key factors in amorphous phase formation.