The Experts below are selected from a list of 26691 Experts worldwide ranked by ideXlab platform
P. C. Patnaik - One of the best experts on this subject based on the ideXlab platform.
-
Pre-oxidation and TGO growth behaviour of an air-plasma-sprayed thermal Barrier Coating
Surface and Coatings Technology, 2008Co-Authors: Weijie R. Chen, Basil R. Marple, R S Lima, X Wu, P. C. PatnaikAbstract:In thermal Barrier Coating (TBC) systems, spinel and nickel oxide formed in an oxidizing environment are believed to be detrimental to TBC durability during service at high temperatures. The present study shows that in an air-plasma-sprayed (APS) TBC with Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat, pre-oxidation treatments in low-pressure oxygen environments can suppress the formation of the detrimental oxides by promoting the formation of an Al2O3layer at the ceramic topcoat/bond coat interface. The development of the thermally grown oxide (TGO) layer generally exhibits a three-stage growth phenomenon that resembles high temperature creep. The pre-oxidation treatments reduce the growth rate and extend the steady-state growth stage, leading to an improved durability. Crack propagation in the TBC proceeds via opening and growth of pre-existing discontinuities in the ceramic topcoat, assisted by crack nucleation and growth associated with the TGO. Crack propagation during thermal cycling appeared to be controlled by TGO growth, and the maximum crack length and TGO thickness generally have a power law relationship. Crown Copyright © 2008.
-
The growth and influence of thermally grown oxide in a thermal Barrier Coating
Surface and Coatings Technology, 2006Co-Authors: Weijie R. Chen, Basil R. Marple, X Wu, P. C. PatnaikAbstract:The growth of a thermally grown oxide (TGO) layer and its influence on cracking was studied in an air-plasma sprayed (APS) thermal Barrier Coating (TBC) following thermal cycling. The TGO that formed upon thermal exposure in air was comprised predominantly of layered chromia and spinels, as well as some oxide clusters of chromia, spinel and nickel oxide. The increase in thickness of the TGO exhibited a three-stage growth phenomenon. Cracks formed mostly at oxide clusters as well as at the opening of discontinuities. Crack propagation during cyclic oxidation appeared to be related to TGO growth, with a nearly linear relationship between crack length and TGO thickness. Crown Copyright © 2006.
-
oxidation and crack nucleation growth in an air plasma sprayed thermal Barrier Coating with nicraly bond coat
Surface & Coatings Technology, 2005Co-Authors: W R Chen, X Wu, Basil R. Marple, P. C. PatnaikAbstract:Abstract The oxidation behavior of an air-plasma-sprayed thermal Barrier Coating (APS-TBC) system was investigated in both air and low-pressure oxygen environments. It was found that mixed oxides, in the form of (Cr,Al)2O3·Ni(Cr,Al)2O4·NiO, formed heterogeneously at a very early stage during oxidation in air, and in the meantime, a layer of predominantly Al2O3 grew rather uniformly along the rest of the ceramic/bond coat interface. The mixed oxides were practically absent in the TBC system when exposed in the low-pressure oxygen environment, where the TBC had a longer life. Through comparison of the microstructures of the APS-TBC exposed in air and low-pressure oxygen environment, it was concluded that the mixed oxides played a detrimental role in causing crack nucleation and growth, reducing the life of the TBC in air. The crack nucleation and growth mechanism in the air-plasma-sprayed TBC is further elucidated with emphasis on the Ni(Cr,Al)2O4 and NiO particles embedded in the chromia.
X Wu - One of the best experts on this subject based on the ideXlab platform.
-
the crack number density theory on air plasma sprayed thermal Barrier Coating
Surface & Coatings Technology, 2019Co-Authors: X WuAbstract:Abstract A crack number density (CND) theory model is developed for air-plasma-sprayed thermal Barrier Coating (TBC), which describes the evolution of crack number and size distribution as function of exposure time. The model is compared in good agreement with experimental measurements from quasi-isothermal-cyclic oxidation tests. Both the CND model and experimental observations indicate that thermally-grown oxides (TGO) are responsible for crack nucleation and growth. The model can be used to define TBC failure (spallation) by coalescence of microcracks into a maximum allowable crack size with a given probability.
-
Pre-oxidation and TGO growth behaviour of an air-plasma-sprayed thermal Barrier Coating
Surface and Coatings Technology, 2008Co-Authors: Weijie R. Chen, Basil R. Marple, R S Lima, X Wu, P. C. PatnaikAbstract:In thermal Barrier Coating (TBC) systems, spinel and nickel oxide formed in an oxidizing environment are believed to be detrimental to TBC durability during service at high temperatures. The present study shows that in an air-plasma-sprayed (APS) TBC with Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat, pre-oxidation treatments in low-pressure oxygen environments can suppress the formation of the detrimental oxides by promoting the formation of an Al2O3layer at the ceramic topcoat/bond coat interface. The development of the thermally grown oxide (TGO) layer generally exhibits a three-stage growth phenomenon that resembles high temperature creep. The pre-oxidation treatments reduce the growth rate and extend the steady-state growth stage, leading to an improved durability. Crack propagation in the TBC proceeds via opening and growth of pre-existing discontinuities in the ceramic topcoat, assisted by crack nucleation and growth associated with the TGO. Crack propagation during thermal cycling appeared to be controlled by TGO growth, and the maximum crack length and TGO thickness generally have a power law relationship. Crown Copyright © 2008.
-
The growth and influence of thermally grown oxide in a thermal Barrier Coating
Surface and Coatings Technology, 2006Co-Authors: Weijie R. Chen, Basil R. Marple, X Wu, P. C. PatnaikAbstract:The growth of a thermally grown oxide (TGO) layer and its influence on cracking was studied in an air-plasma sprayed (APS) thermal Barrier Coating (TBC) following thermal cycling. The TGO that formed upon thermal exposure in air was comprised predominantly of layered chromia and spinels, as well as some oxide clusters of chromia, spinel and nickel oxide. The increase in thickness of the TGO exhibited a three-stage growth phenomenon. Cracks formed mostly at oxide clusters as well as at the opening of discontinuities. Crack propagation during cyclic oxidation appeared to be related to TGO growth, with a nearly linear relationship between crack length and TGO thickness. Crown Copyright © 2006.
-
oxidation and crack nucleation growth in an air plasma sprayed thermal Barrier Coating with nicraly bond coat
Surface & Coatings Technology, 2005Co-Authors: W R Chen, X Wu, Basil R. Marple, P. C. PatnaikAbstract:Abstract The oxidation behavior of an air-plasma-sprayed thermal Barrier Coating (APS-TBC) system was investigated in both air and low-pressure oxygen environments. It was found that mixed oxides, in the form of (Cr,Al)2O3·Ni(Cr,Al)2O4·NiO, formed heterogeneously at a very early stage during oxidation in air, and in the meantime, a layer of predominantly Al2O3 grew rather uniformly along the rest of the ceramic/bond coat interface. The mixed oxides were practically absent in the TBC system when exposed in the low-pressure oxygen environment, where the TBC had a longer life. Through comparison of the microstructures of the APS-TBC exposed in air and low-pressure oxygen environment, it was concluded that the mixed oxides played a detrimental role in causing crack nucleation and growth, reducing the life of the TBC in air. The crack nucleation and growth mechanism in the air-plasma-sprayed TBC is further elucidated with emphasis on the Ni(Cr,Al)2O4 and NiO particles embedded in the chromia.
Shengkai Gong - One of the best experts on this subject based on the ideXlab platform.
-
thermal Barrier Coating bonded by al2o3 y2o3 y2o3 stabilized zro2 laminated composite Coating prepared by two step cyclic spray pyrolysis
Corrosion Science, 2014Co-Authors: Ye Dong He, Deren Wang, Hui Peng, Shengkai GongAbstract:Abstract Thermal Barrier Coating bonded by (Al 2 O 3 –Y 2 O 3 )/(Y 2 O 3 -stabilized ZrO 2 ) (YSZ) laminated Coating has been developed on Ni-based superalloy by two-step cyclic pyrolysis. It is demonstrated, from cyclic oxidation tests at 1100 °C, that YSZ top coat and alloy substrate can be bonded together effectively by the (Al 2 O 3 –Y 2 O 3 )/YSZ laminated Coating, showing good resistance to oxidation, cracking, spallation and buckling. These beneficial effects can be attributed to the sealing effect of the designed multi-sealed compact bond coat with α-Al 2 O 3 layers, the decrease of thermal stresses, the increase of fracture toughness in such bond coat and no interdiffusion between the substrate and bond coat.
-
lanthanum titanium aluminum oxide a novel thermal Barrier Coating material for applications at 1300 c
Journal of The European Ceramic Society, 2011Co-Authors: Shengkai Gong, Huibin XuAbstract:Abstract Considerable efforts are being invested to explore new thermal Barrier Coating (TBC) materials with higher temperature capability to meet the demand of advanced turbine engines. In this work, LaTi2Al9O19 (LTA) is proposed and investigated as a novel TBC material for application at 1300 °C. LTA showed excellent phase stability up to 1600 °C. The thermal conductivities for LTA Coating are in a range of 1.0–1.3 W m−1 K−1 (300–1500 °C) and the values of thermal expansion coefficients increase from 8.0 to 11.2 × 10−6 K−1 (200–1400 °C), which are comparable to those of yttria stabilized zirconia (YSZ). The microhardness of LTA and YSZ Coatings were in the similar level of ∼7 GPa, however, the fracture toughness value was relatively lower than that of YSZ. The lower fracture toughness was compensated by the double-ceramic LTA/YSZ layer design, and the LTA/YSZ TBC exhibited desirable thermal cycling life of nearly 700 h at 1300 °C.
-
the thermal cycling behavior of lanthanum cerium oxide thermal Barrier Coating prepared by eb pvd
Surface & Coatings Technology, 2006Co-Authors: Shengkai Gong, Huibin XuAbstract:Abstract Bulk material and Coatings of Lanthanum–Cerium Oxide (La2Ce2O7) with a fluorite structure were studied as a candidate material for thermal Barrier Coating (TBC). It has been showed that such material has the properties of low thermal conductivity about four times lower than YSZ, the difference in the thermal expansion coefficient between La2Ce2O7 and bond coat is smaller than that of YSZ in TBC systems, high phase stability between room temperature and 1673 K, about 300 K higher than that of the YSZ. The Coating prepared by electron beam physical vapor deposition (EB–PVD) showed that it has good thermal cycling behavior, implying that such material can be a promising thermal Barrier Coating material. The deviation of Coating composition from ingot can be overcome by the addition of excess La2O3 during ingot preparation and/or by adjusting the process parameters.
David R Clarke - One of the best experts on this subject based on the ideXlab platform.
-
Spalling failure of a thermal Barrier Coating associated with aluminum depletion in the bond-coat
Acta Materialia, 1999Co-Authors: E. A.g. Shillington, David R ClarkeAbstract:A plasma-sprayed thermal Barrier Coating is observed to spall after oxidation at 1121 °C from a CoNiCrAlY bond-coated superalloy at the interface between the thermally grown oxide (TGO) and the zirconia thermal Barrier Coating (TBC). Phase characterization by photostimulated luminescence and X-ray diffraction, as well as microstructural characterization by scanning electron microscopy, indicates that the spalling is associated with the conversion of the initially formed α-alumina thermally grown oxide to α-chromia and a (CoNi)(CrAl) spinel. It is proposed that the phase conversion occurs after the alumina TGO has cracked on thermal cycling and the underlying bond-coat alloy is depleted of aluminum with concurrent enrichment of the oxide by Cr, Co and Ni. The observations suggest that monitoring the luminescence intensity as a function of oxidation time might form the basis of a nondestructive tool for detecting the onset of failure based on the disappearance of α-alumina.
-
observation of subcritical spall propagation of a thermal Barrier Coating
Journal of the American Ceramic Society, 1998Co-Authors: Valter Sergo, David R ClarkeAbstract:Observations are reported of the room-temperature propagation of a spalling failure mode of a thermal Barrier Coating (TBC) from its bond coat after oxidation. The Coating is a Y2O3-stabilized ZrO2 Coating formed by electron-beam deposition on a Ni-Co-Cr-Al-Y bond coat. The spall shape evolution and stress redistribution as the spall propagates are reported. The failure propagates primarily as an interface crack between the bond coat and the thermally grown aluminum oxide (TGO) formed on the underside of the TBC during oxidation. The observations are consistent with subcritical propagation of an interface crack between the TGO and bond coat assisted by the presence of moisture. An estimate of 9 J/m2 is made of the fracture resistance in air of the interface.
Sahn Nahm - One of the best experts on this subject based on the ideXlab platform.
-
Thermal durability of ytterbium silicate environmental Barrier Coating prepared by suspension plasma spray
Journal of the Korean Ceramic Society, 2020Co-Authors: Soo Min Park, Sahn NahmAbstract:Owing to their superior high-temperature stability, SiC-based ceramic matrix composites are widely used in turbine engine components for launch vehicles and other applications in the aerospace industry. However, because of the deterioration that occurs in these materials in high-temperature wet operating environments, researchers have developed environmental Barrier Coating technologies to protect the substrate. In this study, a top coat was prepared using Yb_2SiO_5 and Yb_2Si_2O_7 as the third-generation Coating of a rare-earth silicate with high thermal, chemical, and mechanical stability in high-temperature environments above 1400 °C. A new bond coat was prepared, incorporating Si, whose thermal expansion coefficient is similar to that of the SiC substrate, and Hf, which is expected to significantly contribute to high-temperature stability. The Coating was prepared by suspension plasma spraying rather than atmospheric plasma spraying to realize a fine Coating particle structure; to densify the Coating layers, secondary densification Coatings were created using ytterbium (III) nitrate pentahydrate (Yb(NO_3)_3∙5H_2O) and tetraethyl orthosilicate (C_8H_20O_4Si). The prepared specimens were measured in terms of weight change and weight change ratio with respect to temperature under high-temperature flames (1400 ℃ and 1700 ℃). After the secondary densification Coating, the microstructure of the specimen was observed to be denser and the surface layer of the Coating exhibited crystallinity. For the tested samples, a decrease in weight was observed. The largest weight loss was observed under the 1700 ℃ flame.
