Volcanic Ash‐Induced Decomposition of EB‐PVD Gd₂Zr₂O₇ Thermal Barrier Coatings to Gd‐Oxyapatite, Zircon, and Gd,Fe‐Zirconolite

Abstract

The resistance of EB-PVD Gd 2 Zr 2 O 7 thermal barrier coatings against high-temperature infiltration and subsequent degradation by molten volcanic ash is investigated by microstructural analysis. At 1200°C, EB-PVD Gd 2 Zr 2 O 7 coatings with silicarich, artificial volcanic ash (AVA) overlay show a highly dynamic and complex recession scenario.

Effects of cation substitution and temperature on the interaction between thermal barrier oxides and molten CMAS

“…It has been reported that in related experiments using EB-PVD GdZO coatings and an artificial volcanic ash (AVA) with much less CaO than the CMAS used herein (Si:Ca ratio of ∼10.4 vs. ∼1.4), apatite is still the initial silicate crystallization product. 29 The same study showed that the Gd:Ca ratio in the apatite increased moderately at longer reaction times. These results suggest that Gd-apatite growth is still favored compared to other silicates even in cases where the reaction is limited by the CaO availability.…”

Thermal cycling performances of multilayered yttria‐stabilized zirconia/gadolinium zirconate thermal barrier coatings

“…Point 2 was made on a bright island‐shaped phase within the CMAS layer. The intensive Zr peaks and relatively weak Si, Gd, Ca peaks imply that this might be Gd/Ca/Si co‐stabilized ZrO 2 . Due to the dissolution of GZO, the original profile of GZO coating could not be determined.…”

“…Gd, Si and Ca had a relatively higher concentration on Point 3; while Zr had a relatively higher concentration on point 4. It can be deduced that the lighter phase was Gd/Ca/Si co‐stabilized ZrO 2 , while the darker phase was an apatite Ca 2 Gd 8 (SiO 4 ) 6 O 2 phase …”

“…The intensive Zr peaks and relatively weak Si, Gd, Ca peaks imply that this might be Gd/ Ca/Si co-stabilized ZrO 2 . 56 Due to the dissolution of GZO, the original profile of GZO coating could not be determined. Therefore, it is impossible to determine whether these ZrO 2 were formed by re-precipitation or they were residuals of dissolved GZO.…”

Lanthanum zirconate based thermal barrier coatings: A review

“…Drexler et al showed that TBCs with a good resistance against the CMAS must have a vigorously interaction with the molten CMAS, which result in rapid crystallization of the refractory oxide phase that form a sealing layer, stopping further penetration of the molten CMAS [79]. Rare earth pyrochlore materials, such as Ga2Zr2O7 and La2Zr2O7 were found to be highly effective in resisting high-temperature penetration of the molten CMAS debris and volcanic ash for prolonged durations [80][81][82][83]. This resistance is attributed to the formation of a sealing layer made of crystalline Ca-apatite phase (Ca2Gd8(SiO4)6O2 and Ca2La8(SiO4)6O2) which prevents further infiltration of the liquid CMAS into the TBC [80,83].…”