scholarly journals Numerical Study on Effect of Non-uniform CMAS Penetration on TGO Growth and Interface Stress Behavior of APS TBCs

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Zhenwei Cai ◽  
Zifan Zhang ◽  
Yingzheng Liu ◽  
Xiaofeng Zhao ◽  
Weizhe Wang
Keyword(s):  
Penetration Depth ◽  
Numerical Study ◽  
Thermally Grown Oxide ◽  
Global Model ◽  
Interface Stress ◽  
Interface Roughness ◽  
Air Plasma ◽  
Stress Behavior ◽  
Plasma Sprayed ◽  
Tgo Growth

AbstractThe penetration of CaO–MgO–Al2O3–SiO2 (CMAS) is one of the most significant factors that induce the failure of air-plasma-sprayed thermal barrier coatings (APS TBCs). The direct penetration of CMAS changes the thermal/mechanical properties of the top coat (TC) layer, which affects the thermal mismatch stress behavior and the growth of thermally grown oxide (TGO) at the TC/bond coat (BC) interface, thereby resulting in a more complicated interface stress state. In the present study, a two-dimensional global model of APS TBCs with half of the TC layer penetrated by CMAS is established to investigate the effect of non-uniform CMAS penetration on the interface stress behavior. Subsequently, a local model extracted from the global model is established to investigate the effects of interface morphologies and CMAS penetration depth. The results show that non-uniform CMAS penetration causes non-uniform TGO growth in APS TBCs, which consequently causes the stress behavior to vary along the interface. Furthermore, the CMAS penetration depth imposes a significant effect on the TC/TGO interface stress behavior, whereas the interface roughness exerts a prominent effect on the stress level at the BC/TGO interface under CMAS penetration. This study reveals the mechanism associated with the effect of non-uniform CMAS penetration on the interface stress behavior in APS TBCSs.

scholarly journals A Numerical Study about the Effect of Non-uniform CMAS Penetration on the TGO Growth and Interface Stress Behavior of APS TBCs

2021 ◽  
Author(s):  
Zhenwei CAI ◽  
Zifan ZHANG ◽  
Yingzheng Liu ◽  
Xiaofeng Zhao ◽  
Weizhe Wang
Keyword(s):  
Penetration Depth ◽  
Numerical Study ◽  
Thermally Grown Oxide ◽  
Interface Stress ◽  
Interface Roughness ◽  
Air Plasma ◽  
Stress Behavior ◽  
Alumino Silicate ◽  
Porous Microstructures ◽  
Tgo Growth

Abstract The penetration of calcium-magnesium-alumino-silicate (CMAS) is one of the most vital factors inducing the failure of air plasma sprayed thermal barrier coatings (APS TBCs). The CMAS penetration into the porous microstructures of TBCs changes the thermal/mechanical properties of top coat (TC) material, this brings about considerable thermal mismatch stress at the TC/bond coat (BC) interface, and accelerates the growth of the thermally grown oxide (TGO), finally leading to more complicated stress state at the interface. In present study, a two-dimensional global model of APS TBCs with half of the TC penetrated by CMAS is built to study effect of non-uniform CMAS penetration. Then, a local model extracted from the global are built to investigate the effect of interface morphologies and CMAS penetration depth. The results showed that non-uniform CMAS penetration in APS TBCs causes non-uniform TGO growth, which further leads to more complicated interface stress distribution. The CMAS penetration depth had a greater effect on the TC/TGO interface stress behavior, while the interface roughness had an more obvious influence on the stress level at BC/TGO interface under CMAS penetration.

NONDESTRUCTIVE IMPEDANCE SPECTROSCOPY EVALUATION OF THE BOND COAT OXIDATION IN THERMAL BARRIER COATINGS

2007 ◽  
Vol 14 (05) ◽  
pp. 935-943 ◽  
Author(s):  
L. YANG ◽  
Y. C. ZHOU ◽  
W. G. MAO ◽  
Q. X. LIU
Keyword(s):  
Impedance Spectroscopy ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Equivalent Circuit Model ◽  
Isothermal Oxidation ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Plasma Sprayed

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.

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

2010 ◽  
Vol 17 (03) ◽  
pp. 337-343 ◽  
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.

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

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.

Modelling of Crack Growth Near the Metallic-Ceramic Interface during Thermal Cycling of Air Plasma Sprayed Thermal Barrier Coatings

2007 ◽  
Vol 333 ◽  
pp. 263-268 ◽  
Author(s):  
A. Casu ◽  
J.L. Marqués ◽  
Robert Vaßen ◽  
Detlev Stöver
Keyword(s):  
Thermal Cycling ◽  
Crack Growth ◽  
Growth Direction ◽  
Maximum Energy ◽  
Interface Roughness ◽  
Cycle Phase ◽  
Temperature Cycle ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Plasma Sprayed

The lifetime under thermal cycling of a system consisting of an air plasma sprayed thermal barrier coating (TBC) deposited on a metallic bondcoat (BC) is determined by the subcritical growth of micro-cracks near the interface between both coatings. This growth mainly occurs during the cooling down phase, as shown by the acoustic emission monitoring during the thermal cycling. The factors controlling the stress level leading to the crack growth are the local curvature of the metallic-ceramic interface, the growth of an oxide scale (TGO) at such interface and the sintering of the TBC, the two last processes occurring during the high temperature cycle phase. Implementing all these factors, a model based on Finite Element Method (FEM) calculations is presented where growing cracks are incorporated by assigning soft properties to the FEM cells occupied by the cracks. Determining the growth direction for the maximum energy release rate at every cooling down step, the current crack extension during the cycling is tracked until it reaches a characteristic length corresponding to the TBC failure. The influence by the metallic-ceramic interface roughness and by the temperature gradient across the TBC is discussed.

scholarly journals Evaluation of Commercial Coatings on MarM-002, IN-939 and CM-247 Substrates

1996 ◽  
Author(s):  
J. G. Goedjen ◽  
G. P. Wagner
Keyword(s):  
Electron Beam ◽  
Vapor Deposition ◽  
Bond Coat ◽  
Physical Vapor Deposition ◽  
Thermally Grown Oxide ◽  
Department Of Energy ◽  
Superior Performance ◽  
Air Plasma ◽  
Bond Coats ◽  
Plasma Sprayed

As part of the U.S. Department of Energy Advanced Turbine Systems Program, the performance of Chromalloy RT122, RT122 over RT69 and the Howmet 150L bond coats were evaluated for use in the next generation of Westinghouse combustion turbines. Air plasma sprayed and electron beam physical vapor deposition 8% yttria stabilized zirconia thermal barrier coatings were applied to the bond coats. The coating systems were evaluated in air at 2102°F (1150°C), cooling to room temperature once per day. The life-limiting failure mode in both air plasma sprayed (APS) and electron beam - physical vapor deposition (EB-PVD) coating systems is the oxidation of the bond coat. The coating life is related to the growth rate and morphology of the thermally grown oxide. The superior performance of RT122 on MarM-002, the duplex bond coat system of RT122 over RT69 on MarM-002 and Howmet 150L on MarM-002 can be related to the development of a uniform, slow growing oxide scale. The development of a non-uniform oxidation front contributes to the reduced life of RT122 on IN-939 and CM-247.

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