Influence of ceramic top coat and thermally grown oxide microstructures of air plasma sprayed Sm2SrAl2O7 thermal barrier coatings on the electrochemical impedance behavior

In this paper, the impedance spectroscopy technique was employed to examine nondestructively the isothermal oxidation of air plasma sprayed (APS) thermal barrier coatings (TBCs) in air at 800°C. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also used to characterize the microstructure evolution of TBCs. After oxidation, the thermally grown oxide (TGO), which was mainly composed of alumina as confirmed by EDX, formed at the upper ceramic coat/bond coat interface, the lower bond coat/substrate interface, and the bond coat. Impedance diagrams obtained from impedance measurements at room temperature were analyzed according to the equivalent circuit model proposed for the TBCs. Various observed electrical responses relating to the growth of oxides and the sintering of YSZ were explained by simulating the impedance spectra of the TBCs.

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Failure mechanisms associated with the thermally grown oxide in plasma-sprayed thermal barrier coatings

Acta Materialia ◽

10.1016/s1359-6454(00)00171-3 ◽

2000 ◽

Vol 48 (15) ◽

pp. 3963-3976 ◽

Cited By ~ 454

Author(s):

A Rabiei

Keyword(s):

Thermal Barrier Coatings ◽

Failure Mechanisms ◽

Thermally Grown Oxide ◽

Thermal Barrier ◽

Barrier Coatings ◽

Plasma Sprayed ◽

Thermally Grown

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MICROSTRUCTURAL EVOLUTION AND RESIDUAL STRESSES OF AIR-PLASMA SPRAYED THERMAL BARRIER COATINGS UNDER THERMAL EXPOSURE

Surface Review and Letters ◽

10.1142/s0218625x10013965 ◽

2010 ◽

Vol 17 (03) ◽

pp. 337-343 ◽

Cited By ~ 3

Author(s):

JAE-YOUNG KWON ◽

JAE-HYOUN KIM ◽

SANG-YEOP LEE ◽

YEON-GIL JUNG ◽

HYUN CHO ◽

...

Keyword(s):

Thermal Barrier Coatings ◽

Microstructural Evolution ◽

Thermal Exposure ◽

Thermally Grown Oxide ◽

Thermal Barrier ◽

Air Plasma ◽

Barrier Coatings ◽

Before And After ◽

Peak Areas ◽

Plasma Sprayed

Microstructural evolution and fracture behavior of zirconia ( ZrO2 )-based thermal barrier coatings (TBCs) were investigated under thermal exposure. New ZrO 2 granule with 8 wt.% yttria ( Y2O3 ) with a deformed hollow morphology was developed through a spray drying process and employed to prepare TBCs. The thermal exposure tests were conducted at 1210°C with a dwell time of 100 h till 800 h. The residual stress at the interface between top coat and thermally grown oxide (TGO) layer was measured using a nanoindentation technique before and after thermal exposure. Vertical cracks on the top coat were newly formed and interlamellar cracks at the interface were enhanced after the thermal exposure of 800 h. Especially, partial delamination was observed at the interface after the thermal exposure of 800 h in TBC samples tested. The microstructural evolution in the top coat could be defined through load–displacement curves, showing a higher load or a less displacement after the thermal exposure of 800 h. The stress state was strongly dependent on the TGO geometry, resulting in the compressive stresses at the "valleys" or the "troughs," and the tensile stresses at the "crests" or peak areas, in the ranges of -500 to -75 MPa and of +168 to + 24 MPa, respectively. These stress terms incorporated with resintering during thermal exposure affected the mechanical properties such as hardness and elastic modulus of the top coat.

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The Impedance Spectroscopy Study of the Oxides Layer in Thermal Barrier Coatings

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.281.510 ◽

2018 ◽

Vol 281 ◽

pp. 510-515

Author(s):

Zi Yuan Wang ◽

Min Wang ◽

Ya Jie Yuan ◽

Wei Pan

Keyword(s):

Impedance Spectroscopy ◽

Thermal Barrier Coatings ◽

Thermally Grown Oxide ◽

Thermal Barrier ◽

Relaxation Processes ◽

Impedance Spectra ◽

Air Plasma ◽

Barrier Coatings ◽

Different Temperatures ◽

Plasma Sprayed

Air-plasma-sprayed (APS) thermal barrier coatings (TBCs) were oxidized in air at different temperatures for 1000h and sequentially investigated by impedance spectroscopy (IS) and scanning electron microscopy (SEM). After oxidation at temperatures higher than 900°C, a thermally grown oxide (TGO) layer was formed at the bond coat/topcoat interface in TBCs. The impedance spectra of oxidized TBCs typically contains two relaxation processes that stem from the yttria-stabilized zirconia (YSZ) topcoat of TBCs and the TGO layer. The TGO resistivity that obtained by simulating the impedance spectra increased with the increasing of annealing temperature, demonstrating the growth and the densification of TGO layer.

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