Characterization of the Degraded Microstructures of a Platinum Aluminide Coating

2001 ◽  
Vol 697 ◽  
Author(s):  
Hyungjun Kim ◽  
Mark E. Walter
Keyword(s):  
Bond Coat ◽  
Aluminide Coating ◽  
Thermal Exposure ◽  
Phase Evolution ◽  
Thermally Grown Oxide ◽  
Isothermal Heating ◽  
Platinum Aluminide ◽  
Barrier Coating ◽  
Micro Indentation

AbstractTo investigate phase evolution of β-(Ni,Pt)Al/γ-(Ni3Al) in thermal barrier coating bond coat systems, specimens were subjected to 1200°C cyclic and isothermal heating. By removing the thermally grown oxide (TGO) after every 10 hours of heating, aluminum (Al) depletion from the bond coat was accelerated. Non-accelerated and accelerated Al-depletion samples were examined with scanning electron microscopy after every 10 hours of cyclic and isothermal heating. Observations from after the first 10 hours of thermal exposure show distinct microstructural differences. After 50 hours of heating, cyclic accelerated Al-depletion samples show more distinct grain boundaries and a higher proportion of-(Ni3Al) phase than isothermalaccelerated Al-depletion samples. Through instrumented micro-indentation, trends in elastic modulus were determined for isothermal and cyclic accelerated Al-depletion specimens.

Failure of a Thermal Barrier System Due to a Cyclic Displacement Instability in the Thermally grown Oxide

2000 ◽  
Vol 645 ◽  
Author(s):  
Daniel R. Mumm ◽  
Anthony G. Evans
Keyword(s):  
Bond Coat ◽  
Large Scale ◽  
Thermal Exposure ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Oxide Interface ◽  
Barrier Coating ◽  
Out Of Plane ◽  
Plane Displacement ◽  
Thermally Grown

ABSTRACTThe mechanism controlling the cyclic failure of a commercial thermal barrier system has been investigated. The system comprises an electron-beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia thermal barrier coating (TBC), deposited on a (Ni Pt) Al bond coating. The thermally grown oxide (TGO) layer that forms between the TBC and bond coat at high temperature is unstable with respect to out of plane displacement, provided initial perturbations are present. With cyclic thermal exposure, the TGO displaces into the bond coat at periodic interfacial sites. The out-of-plane displacements induce strains above the TGO, normal to the interface, that cause cracking. The cracks nucleate either within the TBC layer or at the TBC/TGO interface, and extend laterally until they coalesce with cracks from other sites and coating failure occurs by large scale buckling. The TGO displacements are accommodated by visco-plastic deformation of the underlying bond coat, and are driven by a lateral component of the growth strain in the TGO. The susceptibility of the TGO to out-of-plane displacement depends critically upon the initial morphology of the metal/oxide interface. The observed material responses are compared with predictions of a ‘ratcheting’ model.

Fracture Behavior of Plasma-Sprayed Thermal Barrier Coatings with Different Bond Coats upon Cyclic Thermal Exposure

2009 ◽  
Vol 620-622 ◽  
pp. 343-346
Author(s):  
Young Seok Sim ◽  
Sung Il Jung ◽  
Jae Young Kwon ◽  
Je Hyun Lee ◽  
Yeon Gil Jung ◽  
...  
Keyword(s):  
Bond Coat ◽  
Fracture Behavior ◽  
Thermal Exposure ◽  
Thermally Grown Oxide ◽  
Fatigue Tests ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Bond Coats ◽  
Barrier Coating ◽  
Tbc Systems

The effects of bond coat nature in thermal barrier coating (TBC) systems on the delamination or fracture behavior of the TBCs with different bond coats prepared using two different processes—air plasma spray (APS) and high velocity oxyfuel (HVOF)—were investigated by cyclic thermal fatigue tests. The TBCs with the HVOF bond coat were delaminated or fractured after 3–6 cycles, whereas those with the APS bond coat were delaminated after 10 cycles or show a sound condition. These results indicate that the TBC system with the APS bond coat has better thermal durability than the system with the HVOF bond coat under long-term cyclic thermal exposure. The hardness values of the TBCs (top coats) in both systems are dependent on applied loads, irrespective of the hardness of the bond coats and the substrate. The values are not responded to the bond coat nature or the exposure time. Thermally grown oxide (TGO) layers in both cases consist of two regions with the inner TGO layer containing only Al2O3 and the outer TGO layer of mixed-oxide zone containing Ni, Co, Cr, Al in Al2O3 matrix. The outer TGO layer has a more irregular shape than the inner TGO layer, and there are many pores within the outer layer. At failure, the TGO thickness of the TBC system with the HVOF bond coat is 9–13 m, depending on the total exposed time, and that of the TBC system with the APS bond coat is about 20 m. The both TBC systems show the diffusion layer on the side of substrate in the interface between the bond coat and the substrate. The relationship between the delamination or fracture behavior and the bond coat nature has been discussed, based on the elemental analysis and microstructural evaluation.

Delamination toughness of electron beam physical vapor deposition (EB-PVD) Y2O3–ZrO2 thermal barrier coatings by the pushout method: Effect of thermal cycling temperature

2008 ◽  
Vol 23 (9) ◽  
pp. 2382-2392 ◽  
Author(s):  
M. Tanaka ◽  
Y.F. Liu ◽  
S.S. Kim ◽  
Y. Kagawa
Keyword(s):  
Electron Beam ◽  
Thermal Cycling ◽  
Bond Coat ◽  
Physical Vapor Deposition ◽  
Thermally Grown Oxide ◽  
Test Method ◽  
Thermal Barrier ◽  
Barrier Coating ◽  
Delamination Toughness ◽  
Cycling Temperature

A pushout test method was used to quantify effect of thermal cycling temperatures on the delamination toughness of an electron beam physical vapor deposited thermal barrier coating (EB-PVD TBC). The delamination toughness, Γi, was related to the maximum thermal cycling temperature, Th, equal to 1000, 1025, 1050, and 1100 °C. The measured delamination toughness varied from 9 to 95 J/m2. At Th = 1000 °C, Γi attained a maximum value, larger than that of the as-deposited sample and decreasing with increased Th. During the thermal cycling tests, the thermally grown oxide (TGO) was formed between the TBC and the bond coat deposited onto the superalloy substrate. Inside the TGO layer, mixture of Al2O3 and ZrO2 oxides was observed close to the TBC side with nearly pure Al2O3 phases close to the bond-coat side. During the pushout test, delamination occurred at the interface of the mixture and pure Al2O3 layer with an exception for Th = 1100 °C specimens where delamination also occurred at the interface between the TGO and bond-coat layers. The effect of thermal cycling temperatures on the delamination toughness is discussed in terms of the microstructural change and delamination behavior.

TGO Formation with NiCoCrAlYTa Bond Coat Deposition Using APS and HVOF Method

2015 ◽  
Vol 1125 ◽  
pp. 18-22 ◽  
Author(s):  
S. Mohd Zulkifli ◽  
Muhammad Azizi Mat Yajid ◽  
Mohd Hasbullah Idris ◽  
M. Daroonparvar ◽  
Halimaton Hamdan
Keyword(s):  
Bond Coat ◽  
Oxidation Process ◽  
Thermally Grown Oxide ◽  
Inconel 625 ◽  
Thermal Barrier ◽  
Air Plasma Spray ◽  
Air Plasma ◽  
Continuous Layer ◽  
Barrier Coating ◽  
Coating Failure

Formation of thin and continuous layer of thermally grown oxide (TGO) in thermal barrier coating (TBC) are essential in order to avoid coating failure for high temperature applications. As-sprayed high velocity oxy-fuel (HVOF) bond coat can provide more uniform TGO layer in TBC system and much less oxide compare to air plasma spray (APS). In this paper, both APS and HVOF method are used to deposit NiCoCrAlYTa bond coat on Inconel 625 substrate followed by topcoat, YSZ deposition. Pre-oxidation process was done in normal oxygen furnace at 1000°C for 12 to 24 hours to study the characteristic of TGO formation via these two different methods. From the result obtained, it shows that HVOF method provide better TGO formation as compared to APS.

R&D Status and Needs for Improved EB-PVD Thermal Barrier Coating Performance

2000 ◽  
Vol 645 ◽  
Author(s):  
C. Leyens ◽  
U. Schulz ◽  
M. Bartsch ◽  
M. Peters
Keyword(s):  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Gas Turbines ◽  
Systems Approach ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Factors Affecting ◽  
Performance Improvements ◽  
Barrier Coating ◽  
Temperature Capability

ABSTRACTThe key issues for thermal barrier coating development are high temperature capability and durability under thermal cyclic conditions as experienced in the hot section of gas turbines. Due to the complexity of the system and the interaction of the constituents, performance improvements require a systems approach. However, there are issues closely related to the ceramic top coating and the bond coat, respectively. Reduced thermal conductivity, sintering, and stresses within the ceramic coating are addressed in the paper as well as factors affecting failure of the TBC by spallation. The latter is primarily governed by the formation and growth of the thermally grown oxide scale and therefore related to the bond coat. A strategy for lifetime assessment of TBCs is discussed.

scholarly journals Effect of Plasma Pretreatment on Thermal Durability of Thermal Barrier Coatings in Cyclic Thermal Exposure

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Sang-Won Myoung ◽  
Zhe Lu ◽  
Yeon-Gil Jung ◽  
Byung-Koog Jang ◽  
Young-Soo Yoo ◽  
...  
Keyword(s):  
Bond Coat ◽  
Thermal Exposure ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Bond Coats ◽  
Thermal Durability ◽  
Thermomechanical Characteristics ◽  
Barrier Coating ◽  
Plasma Pretreatment ◽  
Surface Modified

Plasma pretreatment on the top and bond coats was performed and its influence on the thermal durability of thermal barrier coating (TBC) system was investigated through cyclic thermal exposure. Two types of bond coat were prepared by different methods, namely, air plasma spray (APS) and high-velocity oxy-fuel (HVOF), and two kinds of feedstock powder were employed for preparing the top coat in APS process. The better thermal durability was achieved in the vertically cracked TBC with the surface modified bond coat or with the bond coat prepared by APS process. The hardness and fracture toughness values of TBCs increased because of densification of the top coat during cyclic thermal exposure, and the bond coat prepared by HVOF process showed higher values than that by APS process. The TBCs with the surface modified bond coat were more efficient in improving adhesive strength than those without plasma pretreatment on the bond coat. The relationship between microstructure evolution and thermomechanical characteristics of TBCs with plasma pretreatment was discussed in cyclic thermal exposure.

Development of a Thermal Barrier Coating Life Model

2003 ◽  
Author(s):  
K. Chan ◽  
S. Cheruvu ◽  
R. Viswanathan
Keyword(s):  
Gas Turbine ◽  
Bond Coat ◽  
Thermally Grown Oxide ◽  
Experimental Program ◽  
Thermal Barrier ◽  
Barrier Coating ◽  
Life Model ◽  
Useful Life ◽  
Plasma Sprayed ◽  
Kinetics Of

Thermal barrier coatings (TBCs) are widely used on the first stage turbine buckets and vanes of land-based (F and G class) gas turbine machines. These coatings normally fail by spallation due to delamination of the ceramic layer along the vicinity of the thermally grown oxide (TGO)/TBC interface. The failure processes involve several mechanisms including oxidation of the bond coat, thermomechanical fatigue, sintering, and spallation of the TBC. This paper describes the development of an analytical tool for predicting the useful life of TBCs for land-based gas turbine applications. The analytical model, called TBCLIFE, has been developed to treat bond coat oxidation, sintering and spallation of the TBC, as well as effects of coating thickness and substrate curvature on TBC spallation. In addition, a parallel experimental program has also been initiated to evaluate the durability of a plasma-sprayed TBC under isothermal and thermal cycling exposures. These results will be used to determine the kinetics of TGO scale growth and the material constants for the TBC life model. The TBC life model will be applied to predicting TBC life as a function of cycle time and the results will be presented as coating life diagrams. The utility of a coating life diagram for estimating the remaining life of TBC will be illustrated and discussed.

Effect of Temperature-Dependent Properties on Cyclic Plasticity of Bond Coat in Thermal Barrier Systems

2013 ◽  
Vol 535-536 ◽  
pp. 193-196
Author(s):  
Luo Chuan Su ◽  
Jian Guo Li ◽  
Wei Xu Zhang ◽  
Tie Jun Wang
Keyword(s):  
Bond Coat ◽  
Thermally Grown Oxide ◽  
Cyclic Plasticity ◽  
Effect Of Temperature ◽  
Thermal Barrier ◽  
Temperature Dependent ◽  
Barrier Coating ◽  
Thermal Growth ◽  
Key Factor ◽  
Temperature Dependent Properties

The accumulation of cyclic plasticity in bond coat (BC) is a key factor controlling the displacement instability of the thermally grown oxide (TGO) in thermal barrier systems. The cyclic plasticity is affected by the component material properties, which vary observably with the service temperature. A numerical model with the behavior of creep and thermal growth in TGO under thermal cycling is used to explore the effect of temperature-dependent properties on cyclic plasticity in BC. The influence of temperature-dependent Young's modulus of thermal barrier coating (TBC), TGO, BC and substrate, thermal expansion coefficient of TBC, BC and substrate, and the yield strength of BC on cyclic plasticity in BC is discussed respectively.

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