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.

Mechanical Properties of Thermal Barrier Coatings at Room Temperature

2005 ◽  
Vol 290 ◽  
pp. 336-339 ◽  
Author(s):  
G. Guidoni ◽  
Y. Torres Hernández ◽  
Marc Anglada
Keyword(s):  
Mechanical Properties ◽  
Thermal Barrier Coatings ◽  
Room Temperature ◽  
Inconel 625 ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Bending Tests ◽  
Four Point Bending ◽  
Barrier Coating ◽  
Plasma Sprayed

Four point bending tests have been carried out on a thermal barrier coating (TBC) system, at room temperature. The TBC system consisted of a plasma sprayed Y-TZP top coat with 8 % in weight of Yttria, a bond coat of NiCrAlY and a Ni-based superalloy Inconel 625 as substrate. The TBC coating was deposited on both sides of the prismatic specimens. Efforts have been done in detecting the damage of the coating by means of Maltzbender et al [1] model.

Near-Interface Crack Initiation in Thermal Barrier Coatings

1999 ◽  
Vol 586 ◽  
Author(s):  
Z. Zhang ◽  
T. E. Bloomer ◽  
J. Kameda ◽  
S. Sakurai
Keyword(s):  
Tensile Stress ◽  
Thermal Barrier Coatings ◽  
Volume Effect ◽  
Thermal Barrier ◽  
Cracking Behavior ◽  
Barrier Coatings ◽  
Stressed Volume ◽  
Four Point Bending ◽  
Principal Tensile Stress ◽  
Similar Mode

ABSTRACTThe delamination behavior of thermal barrier coatings (TBC) in transition ducts of inservice used combusters has been characterized using a protruded four-point bending testing technique recently developed by the authors. A reinforced protruded TBC specimen allowed the formation of TBC cracks adjacent to the TBC/alumina interface in a similar mode to inservice TBC failure. Finite element stress analysis showed that a peak transverse stress appeared in a protruded TBC part away from the interface and a large principal tensile stress operated on planes inclined to the interface. It was found that the onset of near-interface TBC cracks in the protruded TBC specimen did not occur under the high transverse and principal tensile stresses. The critical local tensile stress for the onset of TBC cracks near the interface, estimated to be 127 MPa, was lower than that of the near-center TBC. The near-interface TBC cracking behavior in the protruded TBC tests is discussed in light of the residual stress distribution and stressed volume effect.

In-Plane Cracking Behavior Near and Away from Interface of Thermal Barrier Coatings and Thermally Grown Oxides

2000 ◽  
Vol 645 ◽  
Author(s):  
Z. Zhang ◽  
J. Kameda ◽  
A. H. Swanson ◽  
S. Sakurai
Keyword(s):  
Tensile Stress ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Element Analysis ◽  
Cracking Behavior ◽  
Barrier Coatings ◽  
Thermally Grown Oxides ◽  
Out Of Plane ◽  
Point Bend ◽  
Thermally Grown

ABSTRACTThe initiation characteristics of in-plane cracks near and away from the interface of thermal barrier coatings (TBC) and thermally grown oxides (TGO) have been studied using a protruded four-point bend testing technique together with a finite element analysis. In-plane TBC cracks were initiated near and away from the TBC/TGO interface, respectively, in protruded specimens without and with grooved substrates. It was shown that the onset of in-plane TBC cracks near or away from the interface in the protruded TBC tests was controlled by the out-of-plane tensile stress but not by the principal tensile stress acting upon an inclined plane to the interface. The critical local tensile stress for the initiation of TBC cracks near the interface was found to be 20% lower than that away from the interface. The TBC cracking near and away from the TBC/TGO interface is discussed in light of the residual stress distribution through the TBC thickness.

Nonlinear Thermo-Mechanical Coupled Modeling for the Analysis of Stress Distribution in Air-Plasma-Sprayed Thermal Barrier Coatings

2013 ◽  
Vol 577-578 ◽  
pp. 41-44
Author(s):  
Yu Hui Chen ◽  
Shun Cong Zhong ◽  
Xiao Xiang Yang
Keyword(s):  
Stress Distribution ◽  
Thermal Barrier Coatings ◽  
Computational Models ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Coupled Modeling ◽  
Barrier Coatings ◽  
Thermal Transfer ◽  
Depth Direction ◽  
Plasma Sprayed

Thermo-mechanical coupled modeling of air-plasma-sprayed (APS) thermal barrier coatings (TBCs) on Ni-based alloy was investigated. In the computational models, the stress distribution in the depth direction of the TBCs and also the influence of mechanical properties in heating, dwelling and cooling thermal cycles, were investigated. Nonlinear relationship (e.g., convective heat transfer between surrounding environment and coatings, and thermal transfer between the different layers etc.) was considered in the modeling. The results showed that the stress significantly reduced in the dwelling stage because of stress relaxation. The maximum stress occurred in the peak at the BC/TGO interface and it was amplified at the cooling stage. Moreover, the internal stress in the BC and TGO layer had a slight increase when TGOs thickness increased whilst the stress in the TBC and Sub were essentially unchanged. In the present work, the cracks in BC coating and the BC/TGO interface cracks were simulated as well. The failure mechanism I/II of TBCs had been investigated and the results showed that there was no stress concentration in the vicinity of cracks near the peak at the top coating layer, however, due to crack propagation, factures happened near the peak at the BC/TGO interface.

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