Improving Atmospheric Plasma Spraying of Zirconate Thermal Barrier Coatings Based on Particle Diagnostics

Lanthanum zirconate (La₂Zr₂O₇) has been proposed as a promising material for thermal barrier coatings. During atmospheric plasma spraying (APS) of La₂Zr₂O₇ a considerable amount of La₂O₃ can evaporate in the plasma flame, resulting in a non-stoichiometric coating. As indicated in the phase diagram of the La₂O₃-ZrO₂ system, in the composition range of pyrochlore structure, the stoichiometric La₂Zr₂O₇ has the highest melting point and other compositions are eutectic. APS experiments were performed with a TriplexPro?-200 plasma torch at different power levels to achieve different degrees of evaporation and thus stoichiometry. For comparison, some investigations on gadolinium zirconate (Gd₂Zr₂O₇) were included, which is less prone to evaporation and formation of non-stoichiometry. Particle temperature distributions were measured by the DPV-2000 diagnostic system. In these distributions, characteristic peaks were detected at specific torch input powers indicating evaporation and solidification processes. Based on this, process parameters can be defined to provide stoichiometric coatings that show good thermal cycling performance.