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In this study, (Gd0.9Yb0.1)2Zr2O7 (GYbZ)/yttria-stabilized zirconia (YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were prepared by plasma spray-physical vapor deposition (PS-PVD). The microstructure, mechanical performance, and thermal shock behavior of coatings prepared with spraying distances of 600, 800, and 1000 mm were investigated. The GYbZ coating prepared with a spraying distance of 600 mm showed a closely packed columnar structure. However, the GYbZ coatings prepared with spraying distances of 800 and 1000 mm showed a quasi-columnar structure. The GYbZ coating prepared with a spraying distance of 800 mm had the thickest columnar crystals with obvious inter-columnar gaps. In addition, this coating exhibited excellent mechanical performance and the best thermal shock resistance. The primary failure patterns appearing during thermal shocking on the surface of TBCs can be classified into the following five types: caves, exfoliation, delamination cracks, spalled areas, and radiate cracks. Furthermore, the failure behavior of these coatings in water-quenching tests is clarified. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) are suffering from severe degradations by the melted Ca-Mg-Al-silicates (CMAS) deposits during high-temperature operation. The present study evaluated the CAMS-induced degradation to the sintered gadolinium magnesium hexaaluminate (GdMgAl 11 O 19 , GdMA) ceramic bulk at 1260-1500 °C for 48 h to 100 h, and compared its CMAS resistance with the air plasma sprayed GdMA coating counterpart at 1350 °C. Results indicate that the well crystallized GdMA ceramic bulk suffered from more and more serious infiltration of the melted CMAS and microstructure destructions with extended exposure time and enhanced temperature. No barrier layer consisted of corrosion products formed to prevent the melted CMAS penetration during such a process. While, the APS GdMA coating with more amorphous phase as a chemical active component seemed much better to behave as a barrier layer to stop the melted CMAS penetration and corrosion degradation by sacrificing a thin surface layer of the GdMA coating. [Display omitted] • Spark plasma sintered Gd-Mg-Al oxide under CMAS attack is reported for the first time. • Gd-Mg-Al oxide ceramic bulk seriously destroyed by the CMAS attacks at 1260-1500 ºC. • Gd-Mg-Al oxide coating had better CMAS resistance than the sintered ceramic bulk. • Amorphous phase within APS Gd-Mg-Al oxide coating effectively stopped the CMAS penetration. [ABSTRACT FROM AUTHOR]

• Dense columnar LaMgAl 11 O 19 (LaMA) sealing layer is in-situ created by laser-glazing. • Dense columnar LaMA layer shows good interface compatibility and thermal stability. • In-situ generated dense LaMA layer exhibits much better CMAS resistance at 1350 °C. • La, Mg and Al from the dense LaMA layer arrest the melted CMAS very effectively. 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 CaAl 2 Si 2 O 8 anorthite, MgAl 2 O 4 spinel and Ca 2 La 8 (SiO 4) 6 O 2 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. Ca 2 La 8 (SiO 4) 6 O 2 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. [ABSTRACT FROM AUTHOR]