Observation of Heat Cycle Delamination Process with Surface Strain Measurement in Thermal Barrier Coating

2004 ◽  
Vol 261-263 ◽  
pp. 453-458
Author(s):  
Hiroyuki Waki ◽  
Izuru Nishikawa ◽  
K. Ogura
Keyword(s):  
Thermal Expansion ◽  
Strain Measurement ◽  
Laser Speckle ◽  
Surface Strain ◽  
Thermal Barrier ◽  
Heat Cycle ◽  
Bond Coating ◽  
Strain Behavior ◽  
Delamination Life ◽  
Plasma Sprayed

A surface strain measurement approach to understanding of delamination processes of thermal barrier coatings (TBCs) under heat cycle conditions was described in this paper. Heat cycle tests between the high temperature ranged from 1473K to 1073K and the relatively low temperature (573K) was carried out on thermal barrier coated type 304 stainless steel specimens. 8mass%Y2O3- ZrO2 and Al2O3 coatings were used for the TBCs. The surface strain behavior during the heat cycle test was measured using a laser speckle strain/displacement gauge (SSDG). It was found that the thermal expansion of a substrate was almost reflected on a surface strain if a delamination wasn't initiated, while the value of a surface strain decreased to the value of the thermal expansion of a ceramics-coating if the delamination of the ceramics-coating was initiated. The state of a subsurface delamination was able to be nondestructively inferred by the surface strain behavior. The delamination life of a ceramics-coating in the specimen with a low-pressure-plasma-sprayed (LPPS) bond-coating was found to be longer than that with an atmospheric-plasma-sprayed (APS) bond-coating. The large roughness of a bond-coating was also found to be effective in improving the delamination life of a ceramics-coating owing to the restriction of a crack propagation parallel to the interface between the ceramics-coating and the bond-coating.

scholarly journals Effect of APS Flash Bond Coatings on Furnace Cycle Lifetime of Disks and Rods

2019 ◽  
Author(s):  
Bruce A. Pint ◽  
Michael J. Lance ◽  
J. Allen Haynes ◽  
Edward J. Gildersleeve ◽  
Sanjay Sampath
Keyword(s):  
Crack Formation ◽  
Thermal Barrier ◽  
High Velocity Oxygen Fuel ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Bond Coatings ◽  
Bond Coating ◽  
Coating Roughness ◽  
Plasma Sprayed ◽  
Oxygen Fuel

Abstract Air plasma sprayed (APS) flash coatings on high velocity oxygen fuel (HVOF) bond coatings are well known to extend the lifetime of thermal barrier coatings. Recent work compared flash coatings of NiCoCrAlY and NiCoCrAlYHfSi applied to both rods and disk substrates of alloy 247. For rod specimens, 100-h cycles were used at 1100°C in wet air. Both flash coatings significantly improved the lifetime compared to HVOF-only and VPS-only MCrAlY bond coatings with no statistical difference between the two flash coatings. For disk specimens tested in 1-h cycles at 1100°C in wet air, the NiCoCrAlY flash coating significantly outperformed an HVOF-only NiCoCrAlYHfSi bond coating and a NiCoCrAlYHfSi flash coating. The flash coatings formed a mixed oxide-metal zone that appeared to inhibit crack formation and extend lifetime. In addition to the flash coating increasing the bond coating roughness, the underlying HVOF layer acted as a source of Al for this intermixed zone and prevented the oxide from penetrating deeper into the bond coating. The lower Y+Hf level in the Y-only flash coating appeared to minimize oxidation in the flash layer, thereby increasing the benefit compared to a NiCoCrAlYHfSi flash coating.

Sintering Behavior of Plasma-Sprayed Sm2Zr2O7 Coating

2010 ◽  
Author(s):  
Jianhua Yu ◽  
Huayu Zhao ◽  
Shunyan Tao ◽  
Xiaming Zhou ◽  
Chuanxian Ding
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
High Temperature ◽  
Thermal Expansion Coefficient ◽  
Thermal Barrier Coating ◽  
Expansion Coefficient ◽  
Sintering Behavior ◽  
Thermal Barrier ◽  
Barrier Coating ◽  
Plasma Sprayed

Plasma-sprayed thermal barrier coating (TBC) systems are widely used in gas turbine blades to increase turbine entry temperature (TET) and better efficiency. Yttria stabilized zirconia (YSZ) has been the conventional thermal barrier coating material because of its low thermal conductivity, relative high thermal expansion coefficient and good corrosion resistance. However the YSZ coatings can hardly fulfill the harsh requirements in future for higher reliability and the lower thermal conductivity at higher temperatures. Among the interesting TBC candidates, materials with pyrochlore structure show promising thermo-physical properties for use at temperatures exceeding 1200 °C. Sm2Zr2O7 bulk material does not only have high temperature stability, sintering resistance but also lower thermal conductivity and higher thermal expansion coefficient. The sintering characteristics of ceramic thermal barrier coatings under high temperature conditions are complex phenomena. In this paper, samarium zirconate (Sm2Zr2O7, SZ) powder and coatings were prepared by solid state reaction and atmosphere plasma spraying process, respectively. The microstructure development of coatings derived from sintering after heat-treated at 1200–1500 °C for 50 h have been investigated. The microstructure was examined by scanning electron microscopy (SEM) and the grain growth was analyzed in this paper as well.

Thermomechanical Evaluation and Thermal Expansion Behavior of Plasma-Sprayed Thermal Barrier Coatings

2009 ◽  
Vol 631-632 ◽  
pp. 85-90 ◽  
Author(s):  
Kenta Takagi ◽  
Akira Kawasaki ◽  
Yoshio Harada ◽  
Masakazu Okazaki
Keyword(s):  
Thermal Expansion ◽  
Thermal Barrier Coatings ◽  
Preliminary Investigation ◽  
Thermomechanical Analysis ◽  
Thermal Barrier ◽  
Continuous Change ◽  
Free Standing ◽  
Barrier Coatings ◽  
Plasma Sprayed ◽  
Thin Samples

We are investigating the feasibility of measuring thermal expansion coefficient (CTE) of free-standing thermal barrier coatings with a practical thickness of several hundred micrometers by mean of a widespread thermomechanical analysis toward its industrial standardization. First of all, this study conducted the preliminary investigation for the accurate measurement of thin samples with dense yettria-stabilized zirconia (YSZ) ceramics. With a sample supporting jig and proper conditions, even the usual thermomechanical analysis could give the accurate CTE values of thin samples down to 0.3mm thick. Also it showed good reproducibility with small measurement error less than 5%. In actual, this modified method could provide the reasonable CTE values of plasma-sprayed YSZ samples with thickness of >0.3mm. Further investigation with this method found a slight monotonic decrease in the CTE with annealing. This decrease was estimated to arise from the continuous change of microstructure which still went on even after saturation of sintering shrinkage. All the results demonstrated the present method to be available for the industrial standard.

scholarly journals The Effect of Coating Composition and Geometry on Thermal Barrier Coatings Lifetime

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Bruce A. Pint ◽  
Michael J. Lance ◽  
J. Allen Haynes
Keyword(s):  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Average Lifetime ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Barrier Coatings ◽  
Bond Coatings ◽  
Bond Coating ◽  
Negative Effect ◽  
Plasma Sprayed

Several factors are being investigated that affect the performance of thermal barrier coatings (TBC) for use in land-based gas turbines where coatings are mainly thermally sprayed. This study examined high velocity oxygen fuel (HVOF), air plasma-sprayed (APS), and vacuum plasma-sprayed (VPS) MCrAlYHfSi bond coatings with APS YSZ top coatings at 900–1100 °C. For superalloy 247 substrates and VPS coatings tested in 1 h cycles at 1100 °C, removing 0.6 wt %Si had no effect on average lifetime in 1 h cycles at 1100 °C, but adding 0.3%Ti had a negative effect. Rod specimens were coated with APS, HVOF, and HVOF with an outer APS layer bond coating and tested in 100 h cycles in air + 10%H2O at 1100 °C. With an HVOF bond coating, initial results indicate that 12.5 mm diameter rod specimens have much shorter 100 h cycle lifetimes than disk specimens. Much longer lifetimes were obtained when the bond coating had an inner HVOF layer and outer APS layer.

A Study of An Yttria-Doped Zirconia Coating With Electron Microprobe Wavelength Dispersive Compositional Mapping

1997 ◽  
Vol 3 (S2) ◽  
pp. 897-898
Author(s):  
Ryna B. Marinenko ◽  
David S. Bright ◽  
Eric B. Steel
Keyword(s):  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Thermal Barrier ◽  
Jet Engines ◽  
Zirconia Coating ◽  
Crystal Forms ◽  
Spray Process ◽  
Plasma Sprayed ◽  
Micrometer Scale

Yttria-doped zirconia plasma-sprayed thermal barrier coatings (TBC’s) have been used successfully to improve the performance and extend the life of industrial equipment such as jet engines. For this reason, there is considerable interest in understanding and improving the plasma spray process and resulting TBC’s. A collaborative research program exists between Sandia National Laboratories and the National Institute of Science and Technology (NIST) to study the materials and processes used in preparing the coatings as well as the relationship between the physical properties of the coating and its microstructure.The purpose of this work was to determine the elemental compositions on a micrometer scale of an yttria-doped zirconia coating. The cubic and tetragonal crystal forms of the yttria-doped zirconia have the most favorable thermal expansion coefficient, therefore providing the most effective thermal barrier. The Y concentration in these crystal phases is known to be 6-7 wt%, while the less desirable monoclinic phase, having a less favorable thermal expansion coefficient, contains less that 3 wt% Y.

scholarly journals Effect of Air Plasma Sprayed Flash Bond Coatings on Furnace Cycle Lifetime of Disks and Rods

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Bruce A. Pint ◽  
Michael J. Lance ◽  
J. Allen Haynes ◽  
Edward J. Gildersleeve ◽  
Sanjay Sampath
Keyword(s):  
Crack Formation ◽  
Thermal Barrier ◽  
Vacuum Plasma Spray ◽  
Air Plasma ◽  
Bond Coatings ◽  
Bond Coating ◽  
Vacuum Plasma ◽  
Coating Roughness ◽  
Plasma Sprayed ◽  
Oxygen Fuel

Abstract Air plasma sprayed (APS) flash coatings on high velocity oxygen fuel (HVOF) bond coatings are well known to extend the lifetime of thermal barrier coatings (TBCs). Recent work compared flash coatings of NiCoCrAlY and NiCoCrAlYHfSi applied to both rods and disk substrates of alloy 247. For rod specimens, 100 h cycles were used at 1100 °C in wet air. Both flash coatings significantly improved the lifetime compared to HVOF-only and vacuum plasma spray (VPS)-only MCrAlY bond coatings with no statistical difference between the two flash coatings. For disk specimens tested in 1 h cycles at 1100 °C in wet air, the NiCoCrAlY flash coating significantly outperformed an HVOF-only NiCoCrAlYHfSi bond coating and a NiCoCrAlYHfSi flash coating. The flash coatings formed a mixed oxide-metal zone that appeared to inhibit crack formation and therefore extend lifetime. In addition to the flash coating increasing the bond coating roughness, the underlying HVOF layer acted as a source of Al for this intermixed zone and prevented the oxide from penetrating deeper into the bond coating. The lower Y+Hf content in the Y-only flash coating appeared to minimize oxidation in the flash layer, thereby increasing the benefit compared to a NiCoCrAlYHfSi flash coating.

Evaluation on the Delamination Life of Isothermally Aged Plasma Sprayed Thermal Barrier Coating

2009 ◽  
Vol 33 (2) ◽  
pp. 162-168 ◽  
Author(s):  
Dae-Jin Kim ◽  
In-Hwan Shin ◽  
Jae-Mean Koo ◽  
Chang-Sung Seok ◽  
Moon-Young Kim
Keyword(s):  
Thermal Barrier Coating ◽  
Thermal Barrier ◽  
Barrier Coating ◽  
Delamination Life ◽  
Plasma Sprayed
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