Improving atmospheric plasma spraying of zirconate thermal barrier coatings based on particle diagnostics

Abstract

Lanthanum zirconate (La 2Zr 2O7) has been proposed as a promising material for thermal barrier coatings. During atmospheric plasma spraying (APS) of La 2Zr 2O7 a considerable amount of a2O3 can evaporate in the plasma flame, resulting in a non-stoichiometric coating. As indicated in the phase diagram of the La 2O 3-ZrO 2 system, in the composition range of pyrochlore structure, the stoichiometric La 2Zr 2O 7 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 (Gd 2Zr 2O 7) 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. © ASM International.