scholarly journals The Effects of High Temperature Exposure on the Durability of Thermal Barrier Coatings

2000 ◽  
Author(s):  
N. M. Yanar ◽  
M. J. Stiger ◽  
F. S. Pettit ◽  
G. H. Meier
Keyword(s):  
Electron Microscopy ◽  
Bond Coat ◽  
Physical Vapor Deposition ◽  
Thermally Grown Oxide ◽  
Phase Changes ◽  
Cross Sectional ◽  
Outward Diffusion ◽  
Bond Coats ◽  
Platinum Aluminide ◽  
Temperature Exposure

Abstract Yttria-stabilized Zirconia (YSZ) coatings deposited by electron beam physical vapor deposition on platinum aluminide and NiCoCrAlY bond coats on single crystal superalloy substrates have been oxidized at temperatures between 1000 and 1200°C in air. The cyclic oxidation lives of the systems with platinum aluminide bond coats were substantially longer than those with NiCoCrAlY bond coats. The thermally grown oxide (TGO) that develops between the bond coat and the TBC during oxidation, as well as the bond coat and the TBC adjacent to the TGO, have been examined in detail using optical metallography, scanning electron microscopy (SEM), and cross-sectional transmission electron microscopy (XTEM). The YSZ is observed to undergo significant amounts of sintering. The TGO grows by the inward diffusion of oxygen and the outward diffusion of aluminum. In some cases, the outward growth component incorporates some of the TBC into the TGO. The depletion of aluminum results in phase changes in the bond coats. Failure of the TBCs occurs after fixed amounts of oxidation which result in increasing amounts of elastic energy being stored in the TGO and YSZ as well as degradation of the TGO-bond coat interface. The fracture path changed as a function of exposure time and temperature with larger amounts of separation occurring at the TGO/BC interface for higher temperatures and longer exposures in dry air. Failure can be accelerated in the presence of water vapor, particularly if spinel formation is induced. Fracture occurs primarily in the oxides, in this case. The fracture surface for systems with platinum aluminide bond coats often contains precipitates, which are rich in refractory metals. These features do not appear to be prevalent with NiCoCrAlY bond coats.

Failure of the EB-PVD TBCs of Rare Earth Zirconates

2011 ◽  
Vol 686 ◽  
pp. 561-568
Author(s):  
Zhen Hua Xu ◽  
Li Min He ◽  
Feng Lu ◽  
Ren De Mu
Keyword(s):  
Thermal Expansion ◽  
Rare Earth ◽  
Bond Coat ◽  
Gas Turbines ◽  
Physical Vapor Deposition ◽  
Ceramic Coatings ◽  
Thermally Grown Oxide ◽  
Deposition Condition ◽  
Cross Sectional ◽  
Expansion Behavior

Thermal barrier coatings (TBCs) have very important applications in gas turbines for higher thermal efficiency and protection of components at high temperature. TBCs of rare earth materials such as lanthanum zirconate (La2Zr2O7, LZ), lanthanum yttrium zirconate (3wt% Y2O3- La2Zr2O7, 3YLZ), lanthanum cerium zirconate (La2(Zr0.7Ce0.3)2O7, LZ7C3) were prepared by electron beam-physical vapor deposition (EB-PVD). The compositions, crystal structures, thermal expansion behaviors, cross-sectional morphologies and cyclic oxidation behaviors of these coatings were studied. These coatings have partially deviated from their original compositions due to the different evaporation rates of oxides, and the deviation could be reduced by properly controlling the deposition condition. The thermal expansion behavior of LZ coating can be largely improved after doping with 3wt% Y2O3 and CeO2. The excess La2O3, chemical incompatibilities of the ceramic coatings with thermally grown oxide (TGO) layers, the visible cracks initiation, propagation and extension, the abnormal oxidation of bond coat, and the thermal expansion mismatch between ceramic coatings and bond coat are the primary factors for the spallation of LZ, 3YLZ and LZ7C3 coatings.

Transmission Electron Microscopy Investigations of an As-Processed Yttria-Stablilized zirconia on Platinum Aluminide Bond Coat

2000 ◽  
Vol 645 ◽  
Author(s):  
Judith C. Yang ◽  
Noel T. Nuhfer
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Bond Coat ◽  
Physical Vapor Deposition ◽  
Yttria Stabilized Zirconia ◽  
Stabilized Zirconia ◽  
Hollow Cone ◽  
X Ray ◽  
Platinum Aluminide ◽  
Transmission Electron

ABSTRACTWe examined an as-processed yttria-stabilized zirconia (YSZ) on platinum aluminide bond coat (BC), produced by electron beam physical vapor deposition, with transmission electron microscopy, including energy dispersive X-ray spectroscopy and hollow-cone diffraction. Columnar α-Al2O3 grains (∼100nm) formed at the interface between the BC and YSZ. A thin intermix (∼50nm) region was observed between the α-Al2O3 and YSZ. Hollow cone diffraction showed that the α-Al2O3 grains and the small-grained (∼10nm) YSZ near the α-Al2O3 are randomly oriented, without preferential texturing. No evidence of spinel formation was noted.

scholarly journals Evaluation of Commercial Coatings on MarM-002, IN-939 and CM-247 Substrates

1996 ◽  
Author(s):  
J. G. Goedjen ◽  
G. P. Wagner
Keyword(s):  
Electron Beam ◽  
Vapor Deposition ◽  
Bond Coat ◽  
Physical Vapor Deposition ◽  
Thermally Grown Oxide ◽  
Department Of Energy ◽  
Superior Performance ◽  
Air Plasma ◽  
Bond Coats ◽  
Plasma Sprayed

As part of the U.S. Department of Energy Advanced Turbine Systems Program, the performance of Chromalloy RT122, RT122 over RT69 and the Howmet 150L bond coats were evaluated for use in the next generation of Westinghouse combustion turbines. Air plasma sprayed and electron beam physical vapor deposition 8% yttria stabilized zirconia thermal barrier coatings were applied to the bond coats. The coating systems were evaluated in air at 2102°F (1150°C), cooling to room temperature once per day. The life-limiting failure mode in both air plasma sprayed (APS) and electron beam - physical vapor deposition (EB-PVD) coating systems is the oxidation of the bond coat. The coating life is related to the growth rate and morphology of the thermally grown oxide. The superior performance of RT122 on MarM-002, the duplex bond coat system of RT122 over RT69 on MarM-002 and Howmet 150L on MarM-002 can be related to the development of a uniform, slow growing oxide scale. The development of a non-uniform oxidation front contributes to the reduced life of RT122 on IN-939 and CM-247.

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 Degradation of the Mechanical Properties of Aluminide Coatings as a Result of Thermal Cycling

2000 ◽  
Author(s):  
Mark Walter ◽  
Hyungjun Kim
Keyword(s):  
Bond Coat ◽  
State Of The Art ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Bond Coats ◽  
Aluminide Coatings ◽  
Platinum Aluminide ◽  
Pack Cementation Process ◽  
Super Alloy ◽  
Thermally Grown

Abstract Thermal barrier coatings (TBCs) are typically composed of a ceramic top coat, a thermally grown oxide, and an aluminide bond coat. These three layers each have specific roles in protecting super alloy substrates. State-of-the-art TBCs use Zirconia for the ceramic top coat and develop Alumina thermally grown oxide. Although the bond coats almost universally contain aluminides, their composition and processing vary greatly. In this work, a platinum aluminide bond coat system which was processed using an unactivated pack cementation process is studied. This bond coat system was formed on 1 inch diameter CMSX-4 super alloy disks.

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.

Nano Indentations Studies of WC/C and TiN/(Ti,Al)N Multilayer PVD Coatings Combined with Cross-sectional Electron Microscopy Observations

2001 ◽  
Vol 697 ◽  
Author(s):  
N.J.M. Carvalho ◽  
J.Th.M. De Hosson
Keyword(s):  
Electron Microscopy ◽  
Physical Vapor Deposition ◽  
Amorphous Structure ◽  
Fracture Mechanisms ◽  
Accurate Information ◽  
Cross Sectional ◽  
Cracking Mechanisms ◽  
Load Displacement ◽  
A New Technique ◽  
Titanium Aluminum Nitride

AbstractMultilayers of tungsten carbide/carbon (WC/C) with an amorphous structure and multilayers of titanium nitride/titanium-aluminum nitride (TiN/(Ti,Al)N) with a polycrystalline structure, prepared by physical vapor deposition, have been subjected to nanoindentation testing. The investigation has been aimed at establishing whether the load-displacement responses provides accurate information on the fracture mechanisms and whether such mechanisms can be characterized using a new technique for cross-sectional electron microscopy of the nanoindentations. Analysis of the load-displacement curves showed that they can be used to identify the cracking mechanisms occurring in the multilayers and that cross-sectioning of the nanoindentations is necessary if a more complete understanding of the multilayer coatings behavior is required.

Examples of the Use of Optical Spectroscopy to Detect Damage of Thermal Barrier Coatings During Cyclic Oxidation

2012 ◽  
Author(s):  
Claudia Rinaldi ◽  
Ada del Corno ◽  
Francesco Enrichi
Keyword(s):  
Thermal Cycling ◽  
Compressive Stress ◽  
Optical Spectroscopy ◽  
Residual Life ◽  
Phase Changes ◽  
Thermal Barrier ◽  
Bond Coats ◽  
Barrier Coating ◽  
Automatic Mapping ◽  
Temperature Exposure

This paper describes some examples of the use of two optical spectroscopy techniques to study thermal barrier coating (TBC) degradation preceeding failure. The first part describes photoluminescence piezospectroscopy (PLPS) results obtained on a series of specimens with EB-PVD TBC and Pt -aluminised bond coats. The monotonic decrease of the alumina compressive stress level with ageing and thermal cycling confirms that TGO compressive stress levels can be used as residual life indicators in this type of coating. The automatic mapping system implemented by RSE (Ricerca sul Sistema Energetico) provides precise and reliable results about the level of damage at the BC/TBC interface, well before failure; mapping provides data regarding the precise positions where the first macroscopic detachment (a few millimeters wide) occurs. As PLPS is not applicable to thermal-sprayed APS TBCs, the second part of the paper describes some examples of the contribution that Raman spectroscopy can provide to detect phase changes due to degradation preceeding failure of the TBCs. Possible problems relating to the presence of undesired RE elements in the ceramic layer due to strong fluorescence are also described; solutions are proposed. Finally, examples of how innovative confocal microRaman produces maps evidencing areas where high temperature exposure and thermal cycling-produced phase transformation of the Yttria partially stabilised Zirconia from tetragonal to monoclinic (which typically occurs during cracking processes preceeding final TBC failure) are provided.

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.

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.

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