scholarly journals Challenges and Opportunities for Prime Reliant Thermal Barrier Coating Systems

2000 ◽  
Author(s):  
Anthony G. Evans
Keyword(s):  
Thermal Barrier Coatings ◽  
Large Scale ◽  
Thermal Protection ◽  
Crack Nucleation ◽  
Thermal Exposure ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Factors Affecting ◽  
Coating Durability ◽  
High Level

Abstract Thermal protection systems based on thermal barrier coatings are widely used in turbine engines for propulsion and power generation. They commonly comprise oxide thermal barriers coatings (TBCs) deposited on an intermetallic bond coat (BC), and provide simultaneous thermal and oxidation protection. The benefit of these coatings resides in their ability to inhibit degradation of the underlying structural superalloy component by thermo-mechanical fatigue and oxidation. Existing commercial coatings are well-engineered with established durability and cost benefits. However, they lose adhesion and spall from the underlying metal with cyclic thermal exposure. Because coating failure occurs in a stochastic manner, with no assured cyclic life, the coatings cannot be used in a prime-reliant manner. Prime reliability is only achievable if a high level of basic understanding is gained about failure mechanisms, and material responses, that arise upon thermal cycling. Because of differing manufacturing approaches and operating scenarios, several specific mechanisms are involved. Present understanding of these phenomena has highlighted several nuances and challenges in developing thermal barrier coatings for use as prime-reliant components. This talk will review the current understanding of factors affecting coating durability and presents relationships between the durability, the governing material properties and the salient morphological features. The durability of thermal barrier coatings is governed by a sequence of crack nucleation, propagation and coalescence events that accumulate prior to final failure by large scale buckling and spalling.

scholarly journals Mechanisms Controlling the Performance and Durability of Thermal Barrier Coatings

2000 ◽  
Author(s):  
Daniel R. Mumm ◽  
Anthony G. Evans
Keyword(s):  
Thermal Cycling ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Large Scale ◽  
Mechanical Performance ◽  
Thermal Protection ◽  
Crack Nucleation ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Barrier Coatings

Abstract Thermal protection systems based on ceramic thermal barrier coatings (TBCs) are used extensively to protect hot-section components in gas turbine engines. They comprise thermally insulating ceramic coatings, deposited on an aluminum-containing intermetallic bond coat (BC) that provides oxidation protection. A thin thermally-grown oxide (TGO layer forms between the TBC and BC during cyclic thermal exposure. Each of the system constituents evolves in service and all interact during thermal cycling to control the thermo-mechanical performance of the system. Exposed to thermal cycling conditions, TBC systems are susceptible to loss of adhesion and spalling failures. Multiple failure mechanisms exist, dependent upon differing thermal histoiy and processing approach for various coating systems. Coating failure is ultimately controlled by the large residual compression in the TGO and its role in amplifying the effects of imperfections in the vicinity of the TGO. The failure occurs through a process involving crack nucleation, propagation and coalescence events. For a particular commercial system, it is found that the TGO ‘ratchets’ into the bond coat with each thermal cycle, at an array of interfacial sites. The displacements induce strains in the superposed TBC that cause it to crack. The cracks extend laterally as the TGO ratcheting process proceeds, until the cracks from neighboring sites coalesce. Once this happens, the system fails by large scale buckling. It is shown that the displacements are ‘vectored’ by a lateral component of the growth strain in the TGO. The relative roles of bond coat visco-plasticity, initial interface morphology, and phase evolution are discuss. The behavior observed for this system is compared with predictions of a ratcheting model, as well as with the behavior observed for other commercial coating systems.

Improving Contact Damage Resistance of Thermal Barrier Coatings by Incorporating Buffer Layer

2009 ◽  
Vol 620-622 ◽  
pp. 319-322
Author(s):  
Sung Il Jung ◽  
Young Seok Sim ◽  
Jae Hyun Kim ◽  
Je Hyun Lee ◽  
Yeon Gil Jung ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Thermal Barrier Coatings ◽  
Dwell Time ◽  
Thermal Exposure ◽  
Thermal Barrier ◽  
Lower Stress ◽  
Stress Strain ◽  
Barrier Coatings ◽  
Bond Coats ◽  
Tbc Systems

The effects of the introduction of a buffer layer between the bond and top coats on the indentation stress-strain behavior and the contact damage were investigated in air-plasma sprayed (APS) zirconia (ZrO2)–based thermal barrier coatings (TBCs). The microstructure is relatively continuous in the TBC system with the buffer layer, showing Zr, Ni, Cr, and Mg elements between the top and bond coats, whereas the Zr element suddenly disappears by passing the interface between the top and bond coats. The TBC system with the buffer layer shows less strain than that without the buffer layer in the higher stress regions above about 1.3 GPa, while both TBC systems become soft by forming the top coat in the lower stress regions compared with the substrate. The stress–strain curve in both TBC systems is dependent on the dwell time of thermal exposure condition. The TBC system with the buffer layer shows the lower stress-strain curves than that without the buffer layer in thermal cycles with the relatively short dwell time of 1 h, showing the reverse trend with the relatively long dwell time of 10 h. Subsurface damage in substrate is reduced at both indentation loads of P = 500 N and P = 2000 N by introducing the buffer layer, independent of thermal exposure. Therefore, the TBC system with the buffer layer is more efficient in protecting the substrate from contact environments than that without the buffer layer, showing cracking or delamination between the top coat and the buffer layer in the TBC system with the buffer layer.

Determination of the Structure and Chemistry of Thermally Grown Oxides in Thermal Barrier Coatings

1999 ◽  
Vol 5 (S2) ◽  
pp. 854-855
Author(s):  
M.R. Brickey ◽  
J.L. Lee
Keyword(s):  
Thermal Barrier Coatings ◽  
Nickel Aluminide ◽  
Physical Vapor Deposition ◽  
Thermal Exposure ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Engine Operation ◽  
Barrier Coatings ◽  
Combustion Gas ◽  
Thermally Grown

Thermal barrier coatings (TBCs) insulate gas turbine hot section components from the hot (∽1200 - 1450°C) combustion gas exhaust stream. An airline company can save millions of dollars per year by using TBCs to protect vital engine components and to improve fuel efficiency. TBCs typically consist of an 8 wt.% yttria-partially-stabilized zirconia (YPSZ) ceramic topcoat deposited on a platinum-nickel-aluminide (Pt-Ni-Al) bondcoat covering a nickel-based superalloy substrate. Thermal exposure during YPSZ electron beam-physical vapor deposition (EB-PVD) and engine operation promotes the formation of a thermally grown oxide (TGO) between the Pt-Ni-Al and the YPSZ layers. Stresses can develop at the Pt-Ni-Al/TGO and TGO/YPSZ interfaces due to TGO growth and thermal expansion coefficient mismatch. These stresses eventually cause spallation of the YPSZ, leaving the metallic substrate vulnerable to high temperature degradation since exhaust temperatures are often higher than the melting temperature of most nickel-based superalloys (∽1200 - 1450°C).

Oxidation Behavior of Thermal Barrier Coatings on Copper Substrates

2010 ◽  
Vol 66 ◽  
pp. 74-79
Author(s):  
Jana Schloesser ◽  
Martin Bäker ◽  
Joachim Rösler ◽  
Robert Pulz
Keyword(s):  
Thermal Cycling ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Thermal Protection ◽  
Rocket Engine ◽  
Copper Substrate ◽  
Thermally Grown Oxide ◽  
Substrate Material ◽  
Thermal Barrier ◽  
Barrier Coatings

In rocket engine combustion chambers, the cooling channels experience extremely high temperatures and environmental attack. Thermal protection can be provided by Thermal Barrier Coatings. Due to the need of good heat conduction, the inner combustion liner is made of copper. The performance of a standard coating system for nickel based substrates is investigated on copper substrates. Thermal cycling experiments are performed on the coated samples. Due to temperature limitations of the copper substrate material, no thermally grown oxide forms at the interface of the thermal barrier coating and the bond coat. Delamination of the coatings occurs at the interface between the substrate and the bond coat due to oxide formation of the copper at uncoated edges. In real service a totally dense coating can probably not be assured which is the reason why this failure mode is of importance. Different parameters are used for thermal cycling to understand the underlying mechanisms of delamination. Furthermore, laser heating experiments account for the high thermal gradient in real service. Pilot tests which led to a delamination of the coating at the substrate interface were performed successfully.

scholarly journals Thermal durability of thermal barrier coatings with layered bond coat in cyclic thermal exposure

2014 ◽  
Vol 122 (1432) ◽  
pp. 982-988 ◽  
Author(s):  
Min-Sik KIM ◽  
Sang-Won MYOUNG ◽  
Zhe LU ◽  
Je-Hyun LEE ◽  
Yeon-Gil JUNG ◽  
...  
Keyword(s):  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Thermal Exposure ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Thermal Durability

scholarly journals Thermal Stability of YSZ Thick Thermal Barrier Coatings Deposited by Suspension and Atmospheric Plasma Spraying

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 984
Author(s):  
Shiqian Tao ◽  
Jiasheng Yang ◽  
Minglong Zhai ◽  
Fang Shao ◽  
Xinghua Zhong ◽  
...  
Keyword(s):  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Thermal Aging ◽  
Thermal Exposure ◽  
Atmospheric Plasma Spraying ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Aps Coatings ◽  
Steel Substrates

Two types of segmentation-crack structured yttria-stabilized zirconia (YSZ) thick thermal barrier coatings (>500 μm, TTBCs) were deposited onto the stainless steel substrates using atmospheric plasma spraying (APS) and suspension plasma spraying (SPS) process, respectively. In this work, thermal aging behaviors, such as the microstructures, phase compositions, grain growth, and mechanical properties of APS TTBCs and SPS TTBCs, were systematically investigated. Results showed that both as-sprayed TTBCs exhibited a typical segmentation-crack structure in the through-thickness direction. APS coatings mainly comprised of larger columnar crystals, while a large number of smaller equiaxed grains existed in SPS coatings. Both of the coatings underwent tetragonal-monoclinic phase transformation after 155 °C/40 h heat treatment. The poorer phase stability of SPS TTBCs may have a connection with smaller grain size. Thermal-aged APS and SPS coatings exhibited a significant increase in H and E values with the rising of thermal aging temperature, and for the samples that thermal aged at 1550 °C, the H and E values increased sharply during initial stage then decreased after 80 h due to the phase decomposition. The segmented APS coatings had weak bonding between the lamellaes during thermal exposure, which caused the mean Vickers hardness value of APS TTBCs to be much lower than that of SPS TTBCs.

Conjugate heat transfer modeling of a turbine vane endwall with thermal barrier coatings

2019 ◽  
Vol 123 (1270) ◽  
pp. 1959-1981 ◽  
Author(s):  
Xing Yang ◽  
Zhenping Feng ◽  
Terrence W. Simon
Keyword(s):  
Heat Transfer ◽  
Thermal Barrier Coatings ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Thermal Protection ◽  
Design Stage ◽  
Thermal Barrier ◽  
Cooling Effectiveness ◽  
Barrier Coatings ◽  
Turbine Vane

ABSTRACTAdvanced cooling techniques involving internal enhanced heat transfer and external film cooling and thermal barrier coatings (TBCs) are employed for gas turbine hot components to reduce metal temperatures and to extend their lifetime. A deeper understanding of the interaction mechanism of these thermal protection methods and the conjugate thermal behaviours of the turbine parts provides valuable guideline for the design stage. In this study, a conjugate heat transfer model of a turbine vane endwall with internal impingement and external film cooling is constructed to document the effects of TBCs on the overall cooling effectiveness using numerical simulations. Experiments on the same model with no TBCs are performed to validate the computational methods. Round and crater holes due to the inclusion of TBCs are investigated as well to address how film-cooling configurations affect the aero-thermal performance of the endwall. Results show that the TBCs have a profound effect in reducing the endwall metal temperatures for both cases. The TBC thermal protection for the endwall is shown to be more significant than the effect of increasing coolant mass flow rate. Although the crater holes have better film cooling performance than the traditional round holes, a slight decrement of overall cooling effectiveness is found for the crater configuration due to more endwall metal surfaces directly exposed to external mainstream flows. Energy loss coefficients at the vane passage exit show a relevant negative impact of adding TBCs on the cascade aerodynamic performance, particularly for the round hole case.

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.

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