High-temperature degradation of the in-situ laser-glazed plasma sprayed LaMgAl11O19 thermal barrier coating exposed to Ca-Mg-Al-silicate deposits

Abstract High-temperature degradation of the plasma sprayed LaMA coating before and after in-situ laser-glazing under CMAS attacks at 1350 °C for 1 h, 12 h and 48 h was comparatively investigated. Results indicate that a dense laser-glazed top layer was successfully created in-situ for a ～1 mm thick LaMA coating. It behaved as a sealing layer and reservoir of Al3+, Mg2+ and La3+. Melted CMAS penetration was accordingly effectively arrested accompanied by crystallizations of the CaAl2Si2O8 anorthite, MgAl2O4 spinel and Ca2La8(SiO4)6O2 apatite. CMAS-induced degradation mainly occurred near the surface of the laser-glazed dense LaMA top layer. While significant penetration of the melted CMAS along the entire thickness occurred to the as-sprayed LaMA coating without laser-glazing treatments after 48 h degradation. Ca2La8(SiO4)6O2 apatite phase did not crystallize for the as-sprayed LaMA due to the much reduced local La3+ concentration in melted CMAS resulted from its porous microstructure. Effects of laser-glazing on the CMAS-induced degradation of the plasma sprayed LaMA was carefully analyzed and discussed in terms of the coating’s chemical composition, microstructure and surface physical chemistry characteristics base on XRD, SEM/EDS and TEM results.