Effect of Thermal Cycling on Lifetime and Failure Mechanism of EB-PVD TBC with NiCoCrAlYZr Bondcoats

EB-PVD TBC with conventional MCrAlY bondcoats was widely used within the high temperature environments. The effect of oxidation frequency on the lifetime of TBC with NiCoCrAlYZr and the failure mechanism was investigated in this paper. The TBC systems with Zr-doped MCrAlY bondocats presented a longer lifetime after discontinuous oxidation than cyclic oxidation. Formation of thick TGO in the TBC-system with Zr-containing bondcoat did not result in an immediate failure. The crack propagation in the case of the Zr-doped NiCoCrAlY bondcoat at the TGO/bondcoat interface was hindered due to the inhomogeneous TGO morphology. The inner oxidation and pores hindered the above small cracks propagation and then result a longer lifetime. However, the lifetime of TBC-system with NiCoCrAlY+Zr bondcoat is significantly shorter in the cyclic than in the discontinuous test due to the rapid propagation of cracks under high frequency thermal cycling conditions.

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LC/8YSZ TBCs Thermal Cycling Life and Failure Mechanism under Extreme Temperature Gradients

Coatings ◽

10.3390/coatings11091051 ◽

2021 ◽

Vol 11 (9) ◽

pp. 1051

Author(s):

Kun Liu ◽

Xi Chen ◽

Kangping Du ◽

Yu Wang ◽

Jinguang Du ◽

...

Keyword(s):

High Temperature ◽

Surface Temperature ◽

Thermal Cycling ◽

Thermal Shock ◽

Failure Mechanism ◽

Extreme Temperature ◽

Temperature Gradients ◽

Accelerated Life Test ◽

Ceramic Layer ◽

Cycling Life

The purpose of this paper is to study the thermal shock resistance and failure mechanism of La2Ce2O7/8YSZ double-ceramic-layer thermal barrier coatings (LC/8YSZ DCL TBCs) under extreme temperature gradients. At high surface temperatures, thermal shock and infrared temperature measuring modules were used to determine the thermal cycling life and insulation temperature of LC/8YSZ DCL TBCs under extreme temperature gradients by an oxygen–acetylene gas flame testing machine. A viscoelastic model was used to obtain the stress and strain law of solid phase sintering of a coating system using the finite element method. Results and Conclusion: (1) Thermal cycling life was affected by the surface temperature of LC/8YSZ DCL TBCs and decreased sharply with the increase of surface temperature. (2) The LC ceramic surface of the failure coating was sintered, and the higher the temperature, the faster the sintering process. (3) Accelerated life test results showed that high temperature thermal cycling life is not only related to thermal fatigue of ceramic layer, but is also related to the sintering degree of the coating. (4) Although the high temperature thermal stress had great influence on the coating, great sintering stress was produced with sintering of the LC ceramic layer, which is the main cause of LC/8YSZ DCL TBC failure. The above results indicate that for new TBC ceramic materials, especially those for engines above class F, their sinterability should be fully considered. Sintering affects the thermal shock properties at high temperature. Our research results can provide reference for material selection and high temperature performance research.

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Influence of Martensitic Transformation on the Durability of TBC Systems (Invited)

Aerospace ◽

10.1115/imece2003-43203 ◽

2003 ◽

Cited By ~ 1

Author(s):

M. W. Chen ◽

M. L. Glynn ◽

D. Pan ◽

K. T. Ramesh ◽

K. J. Hemker ◽

...

Keyword(s):

High Temperature ◽

Thermal Cycling ◽

Bond Coat ◽

Transformation Strain ◽

Xrd Analysis ◽

Heating And Cooling ◽

Β Phase ◽

Transmission Electron ◽

High Temperature Xrd ◽

Tbc Systems

Microstructural evolution of bond coat with thermal cycling was characterized with transmission electron microscopy (TEM) and high temperature X-ray diffraction (HT-XRD) analysis. Before thermal cycling, the structure of asfabricated bond coat was confirmed to be a long-range ordered B2 β-phase. After thermal cycling to ∼28% of the cyclic life, the bond coat was found to transform into a Nirich L10 martensite (M) from its original B2 structure. The transformations, M ↔ B2, were demonstrated to be reversible and to occur on heating and cooling in each cycle. Quantitative high temperature XRD measurements verified the phase transformations produce about 0.7 % transformation strain. Finite element calculations incorporating the transformation strain indicate that the mertensitic transformation significantly influences the development of stresses and strains in TBC systems.

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Microstructural Evolution of GdZ and DySZ Based EB-PVD TBC Systems After Thermal Cycling at High Temperature

Volume 4: Ceramics; Concentrating Solar Power Plants; Controls, Diagnostics and Instrumentation; Education; Electric Power; Fans and Blowers ◽

10.1115/gt2013-94061 ◽

2013 ◽

Author(s):

Ahmed Umar Munawar ◽

Uwe Schulz

Keyword(s):

High Temperature ◽

Thermal Cycling ◽

Physical Vapor Deposition ◽

Temperature Stability ◽

Life Time ◽

Double Layers ◽

Inlet Temperature ◽

High Temperature Stability ◽

Turbine Inlet Temperature ◽

Tbc Systems

Lower thermal conductivity and high temperature stability are the two properties which are highly desired from ceramic top coat materials in TBC systems. Gadolinium Zirconate, Gd2Zr2O7, (GdZ) and Dyprosia Stabilized Zirconia (DySZ) are two of the candidate materials with such properties and consequently the TBC system would be able to work at higher turbine inlet temperature (TIT) or the lifetime can be increased. In the present study, life time measurements are done for single and double layered Electron Beam Physical Vapor Deposition (EB-PVD) GdZ and DySZ samples by thermal-cycling tests. The double layered TBCs consisted of a thin 7YSZ layer and, on top, the new candidate material. Both single and double layered samples of GdZ and DySZ have shown similar or better lifetimes than the standard 7YSZ samples. However, single layered TBCs showed better lifetime results than the respective double layers. In this study, changes in the microstructure, diffusion of elements and sintering of the TBC materials with aging are observed.

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Effects of Bond-Coat Preoxidation and Surface Finish on Isothermal and Cyclic Oxidation, High Temperature Corrosion and Thermal Shock Resistance of TBC Systems

Materials Science Forum ◽

10.4028/www.scientific.net/msf.369-372.607 ◽

2001 ◽

Vol 369-372 ◽

pp. 607-614 ◽

Cited By ~ 24

Author(s):

Daniel Monceau ◽

Fabrice Crabos ◽

André Malié ◽

Bernard Pieraggi

Keyword(s):

High Temperature ◽

Thermal Shock ◽

Surface Finish ◽

Bond Coat ◽

Thermal Shock Resistance ◽

Cyclic Oxidation ◽

High Temperature Corrosion ◽

Shock Resistance ◽

Tbc Systems

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Characterization of TBC Systems with NiPtAl or NiCoCrAlYTa Bond Coatings after Thermal Cycling at 1100°C: A Comparative Study of Failure Mechanisms

Materials Science Forum ◽

10.4028/www.scientific.net/msf.595-598.213 ◽

2008 ◽

Vol 595-598 ◽

pp. 213-221 ◽

Cited By ~ 6

Author(s):

Aurélie Vande Put ◽

Djar Oquab ◽

Daniel Monceau

Keyword(s):

High Temperature ◽

Comparative Study ◽

Thermal Cycling ◽

Nickel Aluminide ◽

Morphological Changes ◽

Failure Mechanisms ◽

Bond Coatings ◽

Failure Path ◽

Tbc Systems

During service, TBC can suffer degradation by CMAS, FOD, erosion or spallation. Whereas the first three are due to foreign particles, the last one is related to thermal cycling. When subjected to high temperature exposures followed by rapid coolings under oxidizing conditions, a TBC system undergoes morphological changes and stress development. This will initiate cracks which propagate and finally lead to failure by spallation. Consequently, the aim of the present study is to understand better the mechanisms responsible for such spallation events. Two kinds of TBC systems with different bond coatings (NiCoCrAlYTa or Pt-modified nickel aluminide bond coatings) are thermally cycled. Subsequently, SEM investigations on TBC systems after spallation concentrate on failure path, defect, morphological and microstructural changes to propose way for improving TBC system lifetime.

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Influence of Interfacial Characteristics on the Mechanical Properties of Continuous Fiber Reinforced Nial Composites

MRS Proceedings ◽

10.1557/proc-273-145 ◽

1992 ◽

Vol 273 ◽

Cited By ~ 10

Author(s):

Randy R. Bowman

Keyword(s):

Mechanical Properties ◽

High Temperature ◽

Thermal Cycling ◽

Oxidation Resistance ◽

Cyclic Oxidation ◽

Room Temperature ◽

Matrix Cracking ◽

High Temperature Strength ◽

Interfacial Bond ◽

The Matrix

ABSTRACTAs part of a study to assess NiAl-based composites as potential high-temperature structural materials, the mechanical properties of polycrystalline NiAl reinforced with 30 vol.% continuous single crystal Al2O3 fibers were investigated. Composites were fabricated with either a strong or weak bond between the NiAl matrix and Al2O3 fibers. The effect of interfacial bond strength on bending and tensile properties, thermal cycling response, and cyclic oxidation resistance was examined. Weakly-bonded fibers increased room-temperature toughness of the composite over that of the matrix material but provided no strengthening at high temperatures. With effective load transfer, either by the presence of a strong interfacial bond or by remotely applied clamping loads, Al2O3 fibers increased the high-temperature strength of NiAl but reduced the strain to failure of the composite compared to the monolithic material. Thermal cycling of the weakly-bonded material had no adverse effect on the mechanical properties of the composite. Conversely, because of the thermal expansion mismatch between the matrix and fibers, the presence of a strong interfacial bond generated residual stresses in the composite that lead to matrix cracking. Although undesirable under thermal cycling conditions, a strong interfacial bond was a requirement for achieving good cyclic oxidation resistance in the composite. In addition to the interfacial characterization, compression creep and room temperature fatigue tests were conducted on weakly-bonded NiAl/Al2O3 composites to further evaluate the potential of this system. These results demonstrated that the use of A12O3 fibers was successful in improving both creep and fatigue resistance.

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Microstructural Evolution of GdZ and DySZ Based EB-PVD TBC Systems After Thermal Cycling at High Temperature

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4025006 ◽

2013 ◽

Vol 135 (10) ◽

Cited By ~ 3

Author(s):

Ahmed Umar Munawar ◽

Uwe Schulz ◽

Giovanni Cerri

Keyword(s):

High Temperature ◽

Thermal Cycling ◽

Physical Vapor Deposition ◽

Temperature Stability ◽

Double Layers ◽

Inlet Temperature ◽

High Temperature Stability ◽

Turbine Inlet Temperature ◽

Barrier Coating ◽

Tbc Systems

Lower thermal conductivity and high temperature stability are the two properties which are highly desired from ceramic top coat materials in thermal barrier coating (TBC) systems. Gadolinium zirconate, Gd2Zr2O7 (GdZ) and dyprosia stabilized zirconia (DySZ) are two of the candidate materials with such properties and consequently the TBC system would be able to work at higher turbine inlet temperature (TIT) or the lifetime can be increased. In the present study, lifetime measurements are done for single and double layered electron beam physical vapor deposition (EB-PVD) GdZ and DySZ samples by thermal-cycling tests. The double layered TBCs consisted of a thin 7YSZ layer and, on top, the new candidate material. Both single and double layered samples of GdZ and DySZ have shown similar or better lifetimes than the standard 7YSZ samples. However, single layered TBCs showed better lifetime results than the respective double layers. In this study, changes in the microstructure, diffusion of elements and sintering of the TBC materials with aging are observed.

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Compositional Factors Affecting the Oxidation Behavior of Pt-Modified γ-Ni+γ’-Ni3Al-Based Alloys and Coatings

Materials Science Forum ◽

10.4028/www.scientific.net/msf.595-598.239 ◽

2008 ◽

Vol 595-598 ◽

pp. 239-247 ◽

Cited By ~ 13

Author(s):

N. Mu ◽

Takeshi Izumi ◽

L. Zhang ◽

Brian Gleeson

Keyword(s):

High Temperature ◽

Gas Turbines ◽

Cyclic Oxidation ◽

Oxidation Behavior ◽

Thermally Grown Oxide ◽

Factors Affecting ◽

Barrier Coating ◽

Α Al2o3 ◽

Slow Growing ◽

Tbc Systems

Many high-temperature coatings rely on the formation of a continuous and adherent thermally grown oxide (TGO) scale of α-Al2O3 for extended resistance to degradation. For instance, the durability and reliability of thermal barrier coating (TBC) systems in gas turbines are critically linked to the oxidation behavior and stability of an alumina-forming β-NiAl-based bond coat. This study focuses primarily on the development of unique Pt+Hf-modified γ′-Ni3Al+γ-Ni coating compositions that form highly adherent, slow-growing TGO scales during both isothermal and cyclic oxidation at high temperature. Recent findings on the isothermal and cyclic oxidation behavior of γ′+γ alloys and coatings will be discussed, with particular emphasis on the effects of Pt, Al and Hf contents and distributions. Inferred reasons for the observed “Pt effect” will also be presented.

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KUBOTA ALLOY KHR12C

Alloy Digest ◽

10.31399/asm.ad.ss0738 ◽

1999 ◽

Vol 48 (3) ◽

Keyword(s):

High Temperature ◽

Physical Properties ◽

Thermal Cycling ◽

Tensile Properties ◽

Casting Alloy ◽

Type Ii ◽

Temperature Performance

Abstract Kubota alloy KHR12C is an austenitic Fe-Cr-Ni-Nb casting alloy developed from the well known HH type II grade. This alloy is superior to other grades in components that are subjected to frequent thermal cycling and shock. The alloy is available in both centrifugal and static castings. This datasheet provides information on composition, physical properties, and tensile properties as well as creep. It also includes information on high temperature performance as well as casting and joining. Filing Code: SS-738. Producer or source: Kubota Metal Corporation.

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