TITLE:
Crystallographic Polymorphs Changes of the Yttria Stabilized Zirconia under Humidity
AUTHORS:
Daniel Moreno, Giora Kimmel, Doron Lord, Yohanan Nahmana, Ariel Yehuda Cohen, Moshe Shapira, Rony Shnek
KEYWORDS:
Yttria-Stabilized Zirconia, Abradable Coating, Hydrothermal Aging, Phase Transformation, Rietveld Refinement
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.14 No.6,
November
10,
2026
ABSTRACT: One of the major sources of efficiency loss in gas turbine engines is the leakage of high-pressure gases through the clearance between rotating blade tips and the stationary shroud. To minimize this leakage in the high-temperature turbine section, yttria-stabilized zirconia (YSZ)-based abradable coatings are commonly applied by plasma spraying. These coatings provide a self-adjusting sealing system that enables minimal tip clearance during engine operation. In this study, a commercial YSZ-based abradable coating (Metco 2460NS) was exposed to a humid environment at 60˚C for 85 weeks, after which a decrease in hardness was observed. The phase composition before and after exposure was characterized by X-ray diffraction (XRD) coupled with Rietveld refinement. The results revealed significant phase evolution during aging, accompanied by a progressive reduction in mechanical bond strength. The observed mechanical performance degradation was associated with phase transformations within the YSZ coating. The stabilization of zirconia by yttrium is primarily attributed to the formation of oxygen vacancies in the crystal lattice. Prolonged exposure to moisture may alter the defect chemistry and promote local yttrium redistribution or depletion, thereby destabilizing the cubic and tetragonal phases and mainly, increasing the fraction of the monoclinic phase. The associated volume expansion of the monoclinic phase can generate localized stresses and microcracking, ultimately compromising coating integrity. These findings suggest that prolonged hydrothermal exposure promotes phase destabilization and contributes to the deterioration of the mechanical performance of YSZ-based abradable coatings.