Publication Date:
2019
Description:
a) When mCMAS/mYSZ ≤0.2, the melt reacts with YSZ fellow a grain boundary attack mechanism and a c‐ZrO2 phase is generated by the diffusion of Ca into the YSZ grains; b) When CMAS increases to a certain concentration, a dissolution‐precipitation reaction occurs instead, in which the original YSZ grains can reprecipitate as Y‐lean m‐ZrO2 after being dissolved by the molten CMAS.
Abstract
Recently, nanostructured thermal barrier coatings have received considerable attention because of some superior properties in comparison with their conventional counterpart. In this study, nanostructured 8 wt% yttria‐stabilized zirconia (n‐YSZ) coatings were deposited by atmospheric plasma spraying, and the degradation behavior caused by molten calcium‐magnesium‐aluminon‐silicate (CMAS) attack was investigated. Results showed that the thermo‐chemical reaction product between CMAS and YSZ (both powders and coatings) is different with the change of CMAS content. At low CMAS concentration, a cubic phase is generated by the diffusion of Ca into YSZ grains. As compared to the conventional YSZ, less C‐ZrO2 is detected for n‐YSZ. When CMAS reaches a certain concentration (eg 15 mg/cm2), disruptive phase transformation from tetragonal to monoclinic will occur and the reaction is more readily for n‐YSZ. Two different chemical reaction mechanisms governing the CMAS content effect were proposed. It should be noted that the nanozone in the coatings plays an important role in the CMAS degradation process, which enhances CMAS infiltration rate and accelerates the chemical reaction, leading to a poor CMAS resistance of the nanostructured coating than that of the conventional counterpart.
Print ISSN:
0002-7820
Electronic ISSN:
1551-2916
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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