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.

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.

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.

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.

Depletion Model of Aluminum in Bond Coat for Plasma-Sprayed Thermal Barrier Coatings

2009 ◽  
Vol 75 ◽  
pp. 31-35 ◽  
Author(s):  
Chang Che ◽  
G.Q. Wu ◽  
Hong Yu Qi ◽  
Z. Huang ◽  
Xiao Guang Yang
Keyword(s):  
Mathematical Model ◽  
Thermal Barrier Coating ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Thermal Exposure ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Barrier Coating ◽  
Plasma Sprayed

The aluminum depletion of NiCrAlY bond coat in an air-plasma-sprayed thermal barrier coating (TBC) has been studied by experimental and simulative approaches. Upon thermal exposure, Al depletion regions were observed. The depletion of aluminum is resulting from Al diffusion towards the surface of bond coat and into substrate. A mathematical model of Al depletion was presented. The model is able to explain the observed results in a qualitative way and has been shown that Al depletes within the bond coat by diffusion.

Thermal and Mechanical Characteristics of Thermal Barrier Coatings in Cyclic Thermal Fatigue Systems

2012 ◽  
Vol 260-261 ◽  
pp. 438-442
Author(s):  
Kang Hyeon Lee ◽  
Sang Won Myoung ◽  
Min Sik Kim ◽  
Seoung Soo Lee ◽  
Eun Hee Kim ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Thermal Barrier Coatings ◽  
Microstructural Evolution ◽  
Thermal Fatigue ◽  
Thermal Exposure ◽  
Fatigue Tests ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Bond Coats

In this study, the relationship between microstructural evolution and mechanical properties of thermal barrier coatings (TBCs) has been investigated through different thermal fatigue systems, electric thermal fatigue (ETF) and flame thermal fatigue (FTF), including the thermal stability through the interface between the bond and top coats. The TBC system with the thicknesses of 300 µm in both the top and bond coats was prepared with METCO 204 NS and AMDRY 962, respectively, with the air plasma spray (APS) system using 9MB gun. To observe the oxidation resistance and thermal stability of TBC, the thermal exposure tests were performed with both thermal fatigue tests at a surface temperature of 850 °C with a temperature difference of 200 °C between the surface and bottom of sample, for 12,000 EOH in designed apparatuses. The hardness values are slightly increased due to the densification of top coat with increasing the thermal exposure time in both thermal fatigue tests. The influence of thermal fatigue condition on the microstructural evolution and interfacial stability of TBC is discussed.

Effect of Top Coat Thickness on Thermal Stability in Thermal Barrier Coatings

2012 ◽  
Vol 260-261 ◽  
pp. 460-465
Author(s):  
Tae Sik Jang ◽  
Sang Won Myoung ◽  
Hyun Sung Kim ◽  
Zhe Lu ◽  
Geun Ho Cho ◽  
...  
Keyword(s):  
Crack Formation ◽  
Thermal Exposure ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Thermal Stabilities ◽  
Barrier Coating ◽  
Indentation Methods ◽  
Indentation Impression ◽  
Defect Species

The microstructural evolution related to the thickness of thermal barrier coating (TBC) and their thermal stabilities have been investigated with a specific attention to defect species as well as to its morphology with the thermal exposure time. The TBCs with different thicknesses of 600 and 2,000 µm were prepared by air plasma spray (APS) process and the thermal exposure tests were performed at 950C in a furnace with a dwell time of 100 hrs till 500 hrs. The thickness of thermally grown oxide (TGO) layer in the TBC with 2,000 µm is thinner than that with 600 µm. Also, the TBC with 2,000 µm is more efficient in improving the oxidation resistance of bond coat than that with 600 µm. Vickers indentation methods are used to evaluate the interfacial stabilities. Indentation impression and crack formation of the TBC of 600 µm is easily occurred in comparison with that of 2,000 µm, showing relatively longer cracks, independent of thermal exposure. However, the crack formation and propagation through the interface does not observed in the TBC with 2,000 µm, showing crack propagation through the top coat near the interface. These results imply that the interfacial stability of TBC can be also improved with increasing the coating thickness.

scholarly journals Thermal Fatigue Behavior of Air-Plasma Sprayed Thermal Barrier Coating with Bond Coat Species in Cyclic Thermal Exposure

Materials ◽  
2013 ◽  
Vol 6 (8) ◽  
pp. 3387-3403 ◽  
Author(s):  
Zhe Lu ◽  
Sang-Won Myoung ◽  
Yeon-Gil Jung ◽  
Govindasamy Balakrishnan ◽  
Jeongseung Lee ◽  
...  
Keyword(s):  
Thermal Barrier Coating ◽  
Thermal Fatigue ◽  
Bond Coat ◽  
Fatigue Behavior ◽  
Thermal Exposure ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coating ◽  
Thermal Fatigue Behavior ◽  
Plasma Sprayed

scholarly journals Isothermal and Cyclic Oxidation of an Air Plasma-Sprayed Thermal Barrier Coating System

1996 ◽  
Author(s):  
J. Allen Haynes ◽  
Mattison K. Ferber ◽  
Wallace D. Porter ◽  
E. Douglas Rigney
Keyword(s):  
Thermal Barrier Coating ◽  
Oxidation Kinetics ◽  
Bond Coat ◽  
High Mass ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Reaction Products ◽  
Barrier Coating ◽  
Plasma Sprayed ◽  
Tbc Systems

Thermogravimetric methods for evaluating bond coat oxidation in plasma-sprayed thermal barrier coating (TBC) systems were assessed by high-temperature testing of TBC systems with air plasma-sprayed (APS) Ni-22Cr-10Al-1Y bond coatings and yttria-stabilized zirconia top coatings. High-mass thermogravimetric analysis (at 1150°C) was used to measure bond coat oxidation kinetics. Furnace cycling was used to evaluate APS TBC durability. This paper describes the experimental methods and relative oxidation kinetics of the various specimen types. Characterization of the APS TBCs and their reaction products are discussed.

Characterization of Thermally Grown Oxide on Cold Sprayed CoNiCrAlY Bond Coat in Thermal Barrier Coating

2011 ◽  
Vol 696 ◽  
pp. 324-329 ◽  
Author(s):  
Abreeza Manap ◽  
Dowon Seo ◽  
Kazuhiro Ogawa
Keyword(s):  
Electron Microscopy ◽  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Oxidation Behavior ◽  
Mixed Oxides ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Bond Coats ◽  
Barrier Coating ◽  
Thermally Grown

This paper presents the results of a study of the microstructure and oxidation behavior of thermal barrier coating (TBC) with air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) top coat and CoNiCrAlY bond coat deposited using two different spraying techniques, low pressure plasma spray (LPPS) and cold spray (CS). The objective is to investigate the thermally grown oxide (TGO) thickness and oxide scale composition of TBC subjected to isothermal oxidation and creep tests at 900 °C by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX) analyses in order to evaluate the reliability of the CS technique. It was found that the TGO thicknesses for TBC with CS bond coats were smaller and the TGO was composed of mainly alumina with little or no mixed oxides. TGO growth rate was also affected by the applied stress. Smaller TGO thicknesses were observed for the non-creep TBC for both CS and LPPS bond coats. Overall findings indicate that the oxidation behavior of the TBC with CS bond coat is superior compared to that of the TBC with LPPS bond coat.

scholarly journals Cracking Behaviour of an Air-Plasma-Sprayed Thermal Barrier Coating

2009 ◽  
Author(s):  
W. R. Chen ◽  
X. Wu ◽  
B. R. Marple ◽  
X. Huang ◽  
P. C. Patnaik
Keyword(s):  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coating ◽  
Ceramic Bond ◽  
Maximum Crack ◽  
Plasma Sprayed ◽  
Thermally Sprayed

The degradation of a thermal barrier coating (TBC) system is dominated by the formation and growth of a thermally grown oxide (TGO) layer between the ceramic topcoat and metallic bond coat, leading to a separation near the ceramic/bond coat interface during service. Crack propagation in a thermally sprayed TBC normally proceeds via the opening and growth of pre-existing discontinuities in the ceramic layer near the ceramic/bond coat interface region assisted by cracking associated with the evolution of the TGO. The combined effect of these degradation processes results in premature TBC failure. In the present study, TGO growth and cracking behaviours were investigated under cyclic oxidation conditions with different cycle frequencies. The results showed a likely relationship between the maximum crack length and TGO thickness, suggesting that the establishment of an empirical formula may be possible to serve as the basis for a TBC life prediction model.

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