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.

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.

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.

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.

Finite Element Modelling of TBC Failure Mechanisms by Using XFEM

2018 ◽  
Author(s):  
Safa Mesut Bostancı ◽  
Ercan Gürses ◽  
Demirkan Çöker
Keyword(s):  
Finite Element ◽  
Thermal Barrier Coatings ◽  
Failure Mechanisms ◽  
Crack Spacing ◽  
Experimental Results ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Finite Element Software ◽  
Four Point Bending ◽  
Average Crack

Thermal Barrier Coatings have been widely used in modern turbine engines to protect the nickel based metal substrate from the high temperature service conditions, 1600–1800 K. In this study, some of the failure mechanisms of typical Air Plasma Sprayed Thermal Barrier Coatings (TBC) used in after-burner structures composed of three major layers: Inconel 718 substrate, NiCrAlY based metallic bond coat (BC) and Yttria Stabilized Zirconia (YSZ) based ceramic top coat (TC) are investigated. Investigation of the cracking mechanism of TBC in terms of design and performance is very important because the behavior of TBCs on ductile metallic substrates is brittle. To this end, four-point bending experiments conducted in Kütükoğlu (2015) is analyzed by using the Extended Finite Element Method (XFEM). All the analyses are conducted with the commercial finite element software ABAQUS. Three different models with varying TC and BC thicknesses are studied under four-point bending. It is observed that multiple vertical cracks are initiated in the TC. Cracks initiate at the top of YSZ and propagate through the whole TC. It is observed that the average crack spacing increases with the increasing thickness of the TC. Numerical results are found to be consistent with the experimental results. In other words, the average crack spacing for three different models are similar with the experimental results.

scholarly journals A Simulation Study on the Crack Propagation Behavior of Nanostructured Thermal Barrier Coatings with Tailored Microstructure

Coatings ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 722
Author(s):  
Lei Zhang ◽  
Yu Wang ◽  
Wei Fan ◽  
Yuan Gao ◽  
Yiwen Sun ◽  
...  
Keyword(s):  
Tensile Stress ◽  
Crack Propagation ◽  
Thermal Barrier Coatings ◽  
Element Model ◽  
Nano Particles ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Propagation Behavior ◽  
Stress Zone ◽  
Crack Propagation Behavior

The initiation and propagation of cracks are crucial to the reliability and stability of thermal barrier coatings (TBCs). It is important and necessary to develop an effective method for the prediction of the crack propagation behavior of TBCs. In this study, an extended finite element model (XFEM) based on the real microstructure of nanostructured TBCs was built and employed to elucidate the correlation between the microstructure and crack propagation behavior. Results showed that the unmelted nano-particles (UNPs) that were distributed in the nanostructured coating had an obvious “capture effect” on the cracks, which means that many cracks easily accumulated in the tensile stress zone of the adjacent UNPs and a complex microcrack network formed at their periphery. Arbitrarily oriented cracks mainly propagated parallel to the x-axis at the final stage of thermal cycles and the tensile stress was the main driving force for the spallation failure of TBCs. Correspondingly, I and I–II mixed types of cracks are the major cracking patterns.

scholarly journals Influence of substrate twisting on Young's modulus measured by four-point bending test for thermal barrier coatings

2017 ◽  
Vol 4 (5) ◽  
pp. 16-00714-16-00714
Author(s):  
Masahiko KATO ◽  
Yuuki MATSUO ◽  
Hiroyuki WAKI ◽  
Satoru TAKAHASHI ◽  
Hiroyuki AKEBONO ◽  
...  
Keyword(s):  
Young’S Modulus ◽  
Thermal Barrier Coatings ◽  
Young's Modulus ◽  
Bending Test ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Four Point Bending ◽  
Four Point Bending Test ◽  
Influence Of Substrate

scholarly journals Tailoring Periodic Vertical Cracks in Thermal Barrier Coatings Enabling High Strain Tolerance

Coatings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 720
Author(s):  
Ghazanfar Mehboob ◽  
Tong Xu ◽  
Guang-Rong Li ◽  
Guan-Jun Yang ◽  
Adnan Tahir ◽  
...  
Keyword(s):  
Thermal Barrier Coatings ◽  
High Strain ◽  
Strain Energy Release ◽  
Element Model ◽  
Underlying Mechanism ◽  
Critical Value ◽  
Thermal Barrier ◽  
Cracking Behavior ◽  
Barrier Coatings ◽  
Strain Tolerance

Lifetime is a basic support for the thermal insulation function of thermal barrier coatings (TBCs). Therefore, extending the life span is essential to develop next-generation TBCs. For this objective, the columnar structure formed by vertical cracks appears to make sense. However, the underlying mechanism is still unclear. This work scrutinizes the influence of periodic vertical cracks on cracking behavior in order to tailor high strain tolerant TBCs. A finite element model was evolved to explore the crack behavior influenced by thermal mismatch strain between substrate and coating. The virtual crack closure technique (VCCT) was used to describe the propagation of crack under load. It is found clearly that the space between two vertical cracks (short for SVC) along the in-plane direction has a noteworthy influence on the strain tolerance of TBCs. Results indicate that the strain energy release rate (SERR) and stresses at the pre-crack tip increase continuously with the increase of the SVC, suggesting that the driving force for cracks is increasing. The crack is not propagated when the SVC is very small, whereas the crack grows continuously with the increase of the SVC. The growth of a crack can be prevented by reducing the SVC. A critical value for the SVC was found. When the SVC is less than the critical value, the SERR can be dramatically reduced. Thus, the SVC of periodic cracks can be tailored to obtain TBCs with high strain tolerance.

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