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.

Effect of Vanadium Contaminated Fuel on Bond Coat and Bond Coat/Top Coat Interface of Thermal Barrier Coatings

2011 ◽  
Vol 110-116 ◽  
pp. 886-891 ◽  
Author(s):  
Adeel Khalid ◽  
Zuhair M. Gasem
Keyword(s):  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Degradation Mechanism ◽  
Tetragonal Zirconia ◽  
Thermally Grown Oxide ◽  
Sem Analysis ◽  
Thermal Barrier ◽  
Low Grade ◽  
Isothermal Exposure ◽  
Barrier Coating

In the present paper, an attempt has been made to discuss the degradation mechanism of bond coat and bond coat/top coat interface in thermal barrier coating system in the presence of corrosive salts such Na2SO4 and V2O5.These salts come from impurities in low grade fuel used in gas turbine industry. Salt mixture of Na2SO4 + V2O5 was prepared and applied on surface of thermal barrier coating (TBC) specimens. The specimens were exposed isothermally to 900oC for 200, 400 and 700 hours. SEM analysis revealed the formation of thermally grown oxide (TGO) in specimens sprayed with corrosive salts. Results revealed that there was no degradation of either bond coat or bond coat/top coat interface up to 200 hours of isothermal exposure .Interface cracking and spallation was observed after 400 hours of isothermal exposure owing to depletion of zirconia stabilizer i.e yttria and phase transformation of tetragonal zirconia to monoclinic zirconia.

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.

Influence of Titanium in Nickel-Base Superalloys on the Performance of Thermal Barrier Coatings Utilizing γ−γ′ Platinum Bond Coats

2010 ◽  
Vol 133 (4) ◽  
Author(s):  
H. M. Tawancy ◽  
Luai M. Al-Hadhrami
Keyword(s):  
Thermal Barrier Coating ◽  
Bond Coat ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Ti Alloy ◽  
Coating System ◽  
Barrier Coating ◽  
Nickel Base Superalloys ◽  
Nickel Base ◽  
Thermally Grown

Titanium is a key element in nickel-base superalloys needed with aluminum to achieve the desired volume fraction of the strengthening γ′-phase. However, depending upon its concentration, titanium can degrade the adherence of aluminum oxide by forming TiO2 particles near the oxide-metal interface. This effect is extended to thermal barrier coating systems where in this case, the bond coat replaces the superalloy as the underlying substrate. Noting that the onset of failure of thermal barrier coating systems coincides with the first spall of the thermally grown oxide, titanium level in the superalloy can have an important effect on the useful life of the coating. Therefore, this study was undertaken to examine the effect of titanium on the performance of a thermal barrier coating system. Included in the study were two Ni-base superalloys with similar chemical composition except for the Ti content and a Pt-containing bond coat consisting of γ′+γ-phases all top coated with zirconia stabilized by 7 wt % yttria. Coating performance was evaluated from thermal exposure tests at 1150°C with a 24 h cycling period to room temperature. Various electron-optical techniques were used to characterize the microstructure. The coating system on the low-Ti alloy was found to outperform that on the high-Ti alloy. However, for both alloys, failure was observed to occur by loss of adhesion between the thermally grown oxide and underlying bond coat.

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