Comprehensive Numerical Simulation of Stress and Damage Fields under Thermo-Mechanical Loading for TBC-Coated Ni-Based Superalloy

2018 ◽  
Vol 774 ◽  
pp. 137-142 ◽  
Author(s):  
Hiroaki Katori ◽  
Masayuki Arai ◽  
Kiyohiro Ito
Keyword(s):  
Numerical Simulation ◽  
Constitutive Equation ◽  
Thermal Barrier Coatings ◽  
Peak Stress ◽  
Thermal Barrier ◽  
High Temperature Creep ◽  
Wave Loading ◽  
Element Analysis ◽  
Barrier Coatings ◽  
Start Up

A finite element analysis code was developed to accurately predict stress and damage fields in thermal barrier coatings (TBCs) systems subjected to thermo-mechanical loadings. An inelastic constitutive equation for TBCs, and a Chaboche-type viscoplastic constitutive equation for Ni-based super alloys (IN738LC) were employed to simulate high temperature creep and cyclic deformation. Simulations of the TBC/IN738LC system subjected to two types of loading, namely, a triangle-wave loading and a GT-operation loading, were performed using the developed analysis code. The results confirmed that the stress and damage fields in the TBC/IN738LC system could be simulated accurately, and provided us with credible results regarding the crack occurrence. Additionally, the analysis under the GT-operation loading conditions revealed that a peak stress generated during the start-up operation would lead to delamination of the TBC, while a peak stress at the shut-down would lead to cracking in the substrate.

scholarly journals Protruded Four-Point Bending Testing Method and Characterization of Near Interface Cracking in Thermal Barrier Coatings

1999 ◽  
Author(s):  
Zhehua Zhang ◽  
T. E. Bloomer ◽  
J. Kameda ◽  
S. Sakurai
Keyword(s):  
Stress Distribution ◽  
Thermal Barrier Coatings ◽  
Local Stress ◽  
Thermal Barrier ◽  
Element Analysis ◽  
Cracking Behavior ◽  
Barrier Coatings ◽  
Testing Method ◽  
Four Point Bending ◽  
Plasma Sprayed

A protruded four-point bending testing method has been developed to characterize the crack initiation of thermal barrier coatings (TBC) near the interface. Two types of protruded TBC specimens, with and without a reinforcement attached on the top of the protruded TBC, were prepared from in-service used transition ducts made of TBC (6% Y2O3 stabilized ZrO2) and bond coatings (NiCoCrAlY) plasma-sprayed over a superalloy substrate. In the unreinforced protruded TBC specimen tests, pre-existing TBC cracks extended in the transverse direction while near interface TBC cracking did not occur. The reinforced protruded TBC specimen hindered the transverse TBC cracking and allowed the formation of TBC cracks adjacent to the oxidized TBC/bond coating interface in a similar mode to in-service TBC spalling. The onset of TBC cracks was identified by a change in the loading rate in the elastic deformation regime. The local stress distribution at the edges of the reinforced protruded TBC was analyzed using finite element analysis. The critical local tensile stress for the initiation of TBC cracks near the interface was estimated for the in-service used transition duct. The near interface TBC cracking behavior in the protruded TBC tests is discussed in light of the applied and residual stress distribution.

A Study on Crack Configurations in Thermal Barrier Coatings

2017 ◽  
Author(s):  
Robert Eriksson ◽  
Krishna Praveen Jonnalagadda
Keyword(s):  
Crack Growth ◽  
Thermal Barrier Coatings ◽  
Slow Crack Growth ◽  
Propagation Model ◽  
Thermal Barrier ◽  
Element Analysis ◽  
Barrier Coatings ◽  
Barrier Coating ◽  
Observed Damage ◽  
Crack Paths

Spallation of thermal barrier coatings subjected to thermal fatigue occurs through cracking in or close to the metal–ceramic interface. To better match an experimentally observed damage progression curve with initially slow crack growth followed by rapid crack growth, a multitude of crack paths were modeled in a finite element analysis. Comparisons with experimental data enabled the most likely crack path to be identified. It was shown that the most likely failure type for the studied TBC system was crack initiation from pre-existing defects in the thermal barrier coating which propagated into the interface, leading to spallation. The results were used to fit a crack propagation model.

Bending Fatigue of Thermal Barrier Coatings

2017 ◽  
Author(s):  
Robert Eriksson ◽  
Zhe Chen ◽  
Krishna Praveen Jonnalagadda
Keyword(s):  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Base Alloy ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Element Analysis ◽  
Barrier Coatings ◽  
Bending Fatigue ◽  
Lower Load ◽  
Delamination Damage

Thermal barrier coatings (TBCs) are ceramic coatings used in gas turbines to lower the base metal temperature. During operation, the TBC may fail through, for example, fatigue. In the present study, a TBC system deposited on a Ni-base alloy was tested in tensile bending fatigue. The TBC system was tested as-sprayed and oxidized and two load levels were used. After interrupting the tests, at 10000–50000 cycles, the TBC tested at the lower load had extensive delamination damage whereas the TBC tested at the higher load was relatively undamaged. At the higher load, the TBC formed vertical cracks which relieved the stresses in the TBC and retarded delamination damage. A finite element analysis was used to establish a likely vertical crack configuration (spacing and depth) and it could be confirmed that the corresponding stress drop in the TBC should prohibit delamination damage at the higher load.

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