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Ping Xiao - One of the best experts on this subject based on the ideXlab platform.
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superior oxidation and spallation resistant nicocraly Bond Coat via homogenizing the yttrium distribution
Corrosion Science, 2019Co-Authors: Jie Lu, Chunshan Zhao, Xiaofeng Zhao, Ying Chen, Han Zhang, Ping XiaoAbstract:Abstract We present a novel approach to significantly improve the oxidation and spallation resistance of a NiCoCrAlY Bond Coat by homogenizing the yttrium distribution via powder milling and subsequent spark plasma sintering. The NiCoCrAlY Bond Coat fabricated by this method exhibits a much lower oxidation rate and a significantly better spallation resistance after isothermal oxidation at 1150 °C, compared with the counterpart fabricated from the un-milled powder. To understand the improvement in oxidation resistance, the microstructure of the Bond Coats, the chemistry and microstructure of the thermally grown oxides (TGOs), the TGO stresses and the interfacial chemistry are systemically investigated.
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The oxidation performance of plasma-sprayed NiAl Bond Coat: Effect of Hf addition in Bond Coat and substrate
Surface & Coatings Technology, 2018Co-Authors: Chunshan Zhao, Chengbo Xiao, Xiaofeng Zhao, Xin Wang, Ping XiaoAbstract:Abstract NiAl Bond Coats with and without Hf addition (0.1 at.%) were deposited on two types of superalloy substrates (i.e., DZ125L, no Hf, and DZ125, 0.51 at.% Hf) using plasma spraying technique, and isothermally oxidized at 1150 °C. It demonstrates that Hf addition in the Bond Coat is more effective than in the superalloy substrate for improving the Bond Coat oxidation resistance. In addition, though the substrate chemistry could affect the Bond Coat oxidation performance, this effect was very sensitive to the chemistry of the Bond Coat - obvious for the RE (reactive element)-free NiAl Bond Coat, but less obvious for the RE-containing Bond Coats (NiAlHf and NiCoCrAlY). Moreover, compared with the NiCoCrAlY Bond Coat, the NiAlHf Bond Coat showed significantly improved oxidation resistance, regardless of the substrate chemistry, suggesting that NiAlHf Bond Coat prepared by plasma spraying is a promising candidate for the thermal barrier Coating application.
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high temperature stress and its influence on surface rumpling in nicocraly Bond Coat
Acta Materialia, 2017Co-Authors: Lixia Yang, Xiaofeng Zhao, Ying Chen, Guangming Zhao, Ping XiaoAbstract:Abstract The objective of this work is to develop a methodology to measure the high temperature stress in the Bond Coat, and investigate its role on the surface rumpling. We first presented an analytical model to evaluate the high temperature stress using X-ray sin 2 Ψ technique coupling with the curvature measurement at room temperature. A typical NiCoCrAlY Bond Coat with a Hastelloy-X substrate was employed as a model sample. During exposure at 1150 °C, the Bond Coat was under tension at high temperature, increasing parabolically from 1.05 MPa after 12 h to 3.81 MPa after 120 h. To understand its effect on the surface rumpling, the Bond Coat surface roughness was recorded as a function of time, and compared with a bulk NiCoCrAlY alloy. A strong correlation between the Bond Coat stress and the surface roughness was identified. In addition, the origination of the Bond Coat stress and the rumpling mechanism were discussed. It was revealed that the high temperature stress in the Bond Coat was caused by the volume shrinkage from β-γ transformation, mainly due to the inter-diffusion. The grain sliding accompanied with diffusional creep in response to the Bond Coat stress controls the roughening.
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a prominent driving force for the spallation of thermal barrier Coatings chemistry dependent phase transformation of the Bond Coat
Acta Materialia, 2017Co-Authors: L T Wu, Ping Xiao, R T Wu, Toshio OsadaAbstract:Abstract The influence of substrate and Bond Coat chemistry on the degradation mechanism leading to the early spallation of thermal barrier Coatings (TBCs) has not been well understood despite years of research effort. This is largely due to the sheer number of factors (i.e. interfacial rumpling and oxide growth kinetics) that all seem to contribute to the degradation of TBCs. To clarify the chemical effect, extensive characterizations and in-depth analysis near the oxide-Bond Coat interface, were carried out on the isothermally exposed TBC specimens. It is evident that the formation of γ′ along the grain boundaries can significantly enhance rumpling, while martensitic transformation during cooling creates out-of-plane stresses and causes crack nucleation at the oxide-Bond Coat interface. These partial phase transformations in the β Bond Coat system were determined to be a prominent driving force for the TBC spallation. To prevent the early spallation of TBCs, it is necessary to minimize the formation rate of γ′ and martensitic phases, which can be achieved by tailoring the inherent substrate/Bond Coat composition as elucidated in this paper.
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a high performance nicocraly Bond Coat manufactured using laser powder deposition
Corrosion Science, 2017Co-Authors: Xiao Shan, Chunshan Zhao, Xiaofeng Zhao, Xin Wang, Ping Xiao, Aiping ZhangAbstract:Abstract A high performance NiCoCrAlY Bond Coat with dense dendritic microstructure was fabricated using laser powder deposition (LPD) technique. The thermally grown oxides (TGO) formed on the Coating deposited by laser powder deposition is predominantly alumina instead of the mix oxides usually formed on the Coatings prepared by air plasma spray and high velocity air fuel. Isothermal oxidation tests performed at 1150 °C reveal that the LPD Bond Coat shows significantly better spallation resistance and lower TGO growth rate. The superior spallation resistance of the TGO is further discussed in relation to the unique microstructure of the LPD Bond Coat.
Ung Yu Paik - One of the best experts on this subject based on the ideXlab platform.
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Thermal durability of thermal barrier Coatings with Bond Coat composition in cyclic thermal exposure
Surface & Coatings Technology, 2015Co-Authors: Zhe Lu, Sang Won Myoung, Yeon-gil Jung, Ung Yu PaikAbstract:Abstract The effects of Bond Coat composition on the microstructure evolution and thermal durability of thermal barrier Coating (TBC) were investigated through cyclic thermal exposure. The microstructure of the Bond Coat was controlled using various feedstock powders, such as NiCrAlY, NiCoCrAlY, and CoNiCrAlY, which were Coated on the Ni-based substrate using a high-velocity oxy-fuel process. The top Coat was prepared with high purity feedstock powder (METCO 204 C-XCL) using an air plasma spray (APS) process. The thermal durability of the TBCs was evaluated through the cyclic thermal fatigue (CTF) and thermal shock (TS) tests, including the microstructure evolution, the thermally grown oxide (TGO) growth behavior, and thermomechanical properties. After the CTF and TS tests, the TBC with the Ni-based Bond Coat showed a longer lifetime performance and less degradation in hardness value than those with the Ni–Co- and Co–Ni-based Bond Coats. The results indicate that the Bond Coat composition produce an obvious effect on the thermomechanical properties of the TBC system. The relationship between Bond Coat composition and thermal durability is extensively discussed, based on the microstructure evolution and element diffusion behavior.
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Control of Bond Coat microstructure in HVOF process for thermal barrier Coatings
Surface & Coatings Technology, 2014Co-Authors: Sang Won Myoung, Yeon-gil Jung, Zhe Lu, Byung-koog Jang, Ung Yu PaikAbstract:Abstract The microstructure of Bond Coat was optimized by controlling Coating parameters, such as spray distances, the gas flow ratio of air/oxygen/hydrogen, gun speed, and step distance, in high-velocity oxy-fuel process, and the effects of Coating parameters on the microstructure and thermomechanical properties were investigated. When the spray distance to the substrate shortened, the microstructure became dense and the hardness values were increased. As the amount of hydrogen increased in the fixed gas flow ratio, defects such as global pores and oxides were increased and the hardness values were decreased, showing a similar trend in oxygen. The Bond Coat with the step distance of 8 mm showed a slightly higher hardness value than that with the step distance of 5 mm, indicating that the gun speed did not have much effect on the hardness value. However, in thermal diffusivity, the Bond Coat with the step distance of 5 mm showed lower values than that with the step distance of 8 mm. The optimum Coating parameters could be proposed in HVOF process.
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Thermal fatigue behavior of air-plasma sprayed thermal barrier Coating with Bond Coat species in cyclic thermal exposure
Materials, 2013Co-Authors: Zhe Lu, Govindasamy Balakrishnan, Jeongseung Lee, Sang Won Myoung, Yeon-gil Jung, Ung Yu PaikAbstract:The effects of the Bond Coat species on the delamination or fracture behavior in thermal barrier Coatings (TBCs) was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF) for 1429 cycles. The TBC with the Bond Coat prepared by the air-plasma spray (APS) method showed a good condition at the interface between the top and Bond Coats after cyclic furnace thermal fatigue (CFTF) for 1429 cycles, whereas the TBCs with the Bond Coats prepared by the high-velocity oxygen fuel (HVOF) and low-pressure plasma spray (LPPS) methods showed a partial cracking (and/or delamination) and a delamination after 780 cycles, respectively. The TBCs with the Bond Coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50%) after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the Bond Coat prepared by the APS showed the highest adhesive strength before and after the FTF.
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effect of Bond Coat nature and thickness on mechanical characteristic and contact damage of zirconia based thermal barrier Coatings
Surface & Coatings Technology, 2006Co-Authors: Jaeyoung Kwon, Yeon-gil Jung, Ung Yu PaikAbstract:Abstract Mechanical characterization and contact damage of zirconia-based thermal barrier Coatings (TBCs) have been investigated using nanoindentation and Hertzian indentation tests. Two types of TBC systems with different Bond Coat thicknesses of 60 ± 20 and 280 ± 20 μm were prepared using two different processes: air plasma spraying (APS) and high-velocity oxygen fuel (HVOF). Top Coats were Coated onto each Bond Coat using the APS process. The TBC system with the Bond Coat formed using the HVOF process shows a step-like decrease in mechanical properties on passing from the substrate to the top Coat, and the Bond Coat formed using the HVOF process indicates higher values of E and H than that prepared using the APS process. The mechanical properties directly affect indentation stress–strain curves of the TBC systems, and the stress–strain curves of the TBC system with the APS Bond Coat are significantly lower than those with the HVOF process. The Bond Coat thickness plays an important role in limiting the effect of damage, indicating that the thin Bond Coat enhances contact damage and transmits the damage to the substrate, whereas the thick Bond Coat limits the damage to within the Bond Coat at a relatively low load of P = 500 N. As the indentation load and the number of cycles increase, the contact damage is enhanced and becomes more severe in the TBC system with the APS Bond Coat. The fracture modes in the top Coat and between the top Coat and the Bond Coat of the TBC system are dependent on the Bond Coat nature, including the accumulation of damage and its development at high loads of 1000 and 1500 N. The TBC system with the APS Bond Coat shows a bigger and more intensive damage region.
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mechanical characterization and thermal behavior of hvof sprayed Bond Coat in thermal barrier Coatings tbcs
Surface & Coatings Technology, 2006Co-Authors: Hyung Jun Jang, Yeon-gil Jung, Dong Ho Park, Jung Chel Jang, Sung Churl Choi, Ung Yu PaikAbstract:Abstract The mechanical properties, hardness H and modulus E, of thermal barrier Coatings (TBCs) have been determined as a function of the thickness of Bond Coats (0.08, 0.14, and 0.28 mm) prepared using a high-velocity oxygen fuel (HVOF) thermal spray process. The top Coatings were fabricated by an air plasma spray (APS) process. Behavior in a given thermal environment was assessed from the H and E values, and from estimates of the contact damage. Thermal fatigue tests were conducted at T = 950 and 1100 °C using dwell times of 10 and 100 h at T = 950 °C, and 10 hr for T = 1100 °C. The formation of the thermally grown oxide (TGO) layer is influenced by both the temperature and the dwell time, but is independent of the thickness of the Bond Coat. The H and E values of the top Coatings and the Bond Coats, respectively, show an abrupt increase after thermal fatigue, with a discontinuity occurring at the interface between the Bond Coat and the top Coating, while the thickness of the Bond Coat plays a lesser role in influencing the mechanical properties. The evolution of contact damage at the subsurface and cyclic fatigue of the top Coating has been investigated using Hertzian indentation. After the thermal fatigue tests, the contact damage is enhanced, while radial cracking on the top surface is suppressed. The contact damage is mainly affected by the temperature, showing severe damage in the substrate with decreasing thickness of the Bond Coat. The effects of the thermal fatigue condition on mechanical properties, contact damage, and cyclic fatigue are discussed and related to the resintering of the top Coating and the formation of the TGO layer.
Doris Sebold - One of the best experts on this subject based on the ideXlab platform.
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improvement of eb pvd thermal barrier Coatings by treatments of a vacuum plasma sprayed Bond Coat
Surface & Coatings Technology, 2008Co-Authors: Uwe Schulz, O. Bernardi, Robert Vaßen, Andrea Ebachstahl, Doris SeboldAbstract:Abstract The lifetime of electron beam physical vapor deposited (EB-PVD) thermal barrier Coating (TBC) systems with conventional 7 YSZ ceramic top layers was investigated in 1 h thermal-cyclic testing at 1100 °C. The single crystal alloy CMSX-4 and the polycrystalline IN 100 alloy that had been Coated with a vacuum plasma-sprayed MCrAlY Bond Coat were chosen as substrate materials. A fully plasma-sprayed TBC system was studied as well. Several Bond Coat treatments such as smoothing, annealing in vacuum or air, and grit blasting were employed in order to study their effects on TBC life, and particularly the underlying mechanisms of thermally grown oxide (TGO) formation. Variations in TGO microstructure and especially occurrence or absence of the mixed zone have been correlated to the Bond Coat treatments. Spallation of the TBCs is mainly related to TGO formation that is influenced by the Bond Coat pre-treatment. The longest lifetime has been achieved by smoothing the Bond Coat prior to any heat treatment, followed by vacuum annealing prior to EB-PVD top Coat deposition. TBC lifetimes were longer on CMSX-4 than on IN100 substrates. The surface roughness of the Bond Coat did not influence TBC life much.
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Improvement of EB-PVD thermal barrier Coatings by treatments of a vacuum plasma-sprayed Bond Coat
Surface and Coatings Technology, 2008Co-Authors: Uwe Schulz, O. Bernardi, A. Ebach-Stahl, Robert Vaßen, Doris SeboldAbstract:The lifetime of electron beam physical vapor deposited (EB-PVD) thermal barrier Coating (TBC) systems with conventional 7 YSZ ceramic top layers was investigated in 1 h thermal-cyclic testing at 1100 ??C. The single crystal alloy CMSX-4 and the polycrystalline IN 100 alloy that had been Coated with a vacuum plasma-sprayed MCrAlY Bond Coat were chosen as substrate materials. A fully plasma-sprayed TBC system was studied as well. Several Bond Coat treatments such as smoothing, annealing in vacuum or air, and grit blasting were employed in order to study their effects on TBC life, and particularly the underlying mechanisms of thermally grown oxide (TGO) formation. Variations in TGO microstructure and especially occurrence or absence of the mixed zone have been correlated to the Bond Coat treatments. Spallation of the TBCs is mainly related to TGO formation that is influenced by the Bond Coat pre-treatment. The longest lifetime has been achieved by smoothing the Bond Coat prior to any heat treatment, followed by vacuum annealing prior to EB-PVD top Coat deposition. TBC lifetimes were longer on CMSX-4 than on IN100 substrates. The surface roughness of the Bond Coat did not influence TBC life much. ?? 2008 Elsevier B.V. All rights reserved.
Xiaofeng Zhao - One of the best experts on this subject based on the ideXlab platform.
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superior oxidation and spallation resistant nicocraly Bond Coat via homogenizing the yttrium distribution
Corrosion Science, 2019Co-Authors: Jie Lu, Chunshan Zhao, Xiaofeng Zhao, Ying Chen, Han Zhang, Ping XiaoAbstract:Abstract We present a novel approach to significantly improve the oxidation and spallation resistance of a NiCoCrAlY Bond Coat by homogenizing the yttrium distribution via powder milling and subsequent spark plasma sintering. The NiCoCrAlY Bond Coat fabricated by this method exhibits a much lower oxidation rate and a significantly better spallation resistance after isothermal oxidation at 1150 °C, compared with the counterpart fabricated from the un-milled powder. To understand the improvement in oxidation resistance, the microstructure of the Bond Coats, the chemistry and microstructure of the thermally grown oxides (TGOs), the TGO stresses and the interfacial chemistry are systemically investigated.
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The oxidation performance of plasma-sprayed NiAl Bond Coat: Effect of Hf addition in Bond Coat and substrate
Surface & Coatings Technology, 2018Co-Authors: Chunshan Zhao, Chengbo Xiao, Xiaofeng Zhao, Xin Wang, Ping XiaoAbstract:Abstract NiAl Bond Coats with and without Hf addition (0.1 at.%) were deposited on two types of superalloy substrates (i.e., DZ125L, no Hf, and DZ125, 0.51 at.% Hf) using plasma spraying technique, and isothermally oxidized at 1150 °C. It demonstrates that Hf addition in the Bond Coat is more effective than in the superalloy substrate for improving the Bond Coat oxidation resistance. In addition, though the substrate chemistry could affect the Bond Coat oxidation performance, this effect was very sensitive to the chemistry of the Bond Coat - obvious for the RE (reactive element)-free NiAl Bond Coat, but less obvious for the RE-containing Bond Coats (NiAlHf and NiCoCrAlY). Moreover, compared with the NiCoCrAlY Bond Coat, the NiAlHf Bond Coat showed significantly improved oxidation resistance, regardless of the substrate chemistry, suggesting that NiAlHf Bond Coat prepared by plasma spraying is a promising candidate for the thermal barrier Coating application.
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high temperature stress and its influence on surface rumpling in nicocraly Bond Coat
Acta Materialia, 2017Co-Authors: Lixia Yang, Xiaofeng Zhao, Ying Chen, Guangming Zhao, Ping XiaoAbstract:Abstract The objective of this work is to develop a methodology to measure the high temperature stress in the Bond Coat, and investigate its role on the surface rumpling. We first presented an analytical model to evaluate the high temperature stress using X-ray sin 2 Ψ technique coupling with the curvature measurement at room temperature. A typical NiCoCrAlY Bond Coat with a Hastelloy-X substrate was employed as a model sample. During exposure at 1150 °C, the Bond Coat was under tension at high temperature, increasing parabolically from 1.05 MPa after 12 h to 3.81 MPa after 120 h. To understand its effect on the surface rumpling, the Bond Coat surface roughness was recorded as a function of time, and compared with a bulk NiCoCrAlY alloy. A strong correlation between the Bond Coat stress and the surface roughness was identified. In addition, the origination of the Bond Coat stress and the rumpling mechanism were discussed. It was revealed that the high temperature stress in the Bond Coat was caused by the volume shrinkage from β-γ transformation, mainly due to the inter-diffusion. The grain sliding accompanied with diffusional creep in response to the Bond Coat stress controls the roughening.
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a high performance nicocraly Bond Coat manufactured using laser powder deposition
Corrosion Science, 2017Co-Authors: Xiao Shan, Chunshan Zhao, Xiaofeng Zhao, Xin Wang, Ping Xiao, Aiping ZhangAbstract:Abstract A high performance NiCoCrAlY Bond Coat with dense dendritic microstructure was fabricated using laser powder deposition (LPD) technique. The thermally grown oxides (TGO) formed on the Coating deposited by laser powder deposition is predominantly alumina instead of the mix oxides usually formed on the Coatings prepared by air plasma spray and high velocity air fuel. Isothermal oxidation tests performed at 1150 °C reveal that the LPD Bond Coat shows significantly better spallation resistance and lower TGO growth rate. The superior spallation resistance of the TGO is further discussed in relation to the unique microstructure of the LPD Bond Coat.
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role of internal oxidation on the failure of air plasma sprayed thermal barrier Coatings with a double layered Bond Coat
Surface & Coatings Technology, 2017Co-Authors: Lixia Yang, Xiaofeng Zhao, Xiao Shan, Ping XiaoAbstract:Abstract Failure of air plasma sprayed (APS) thermal barrier Coatings (TBCs) with a double-layered Bond Coat was investigated. The Bond Coat consists of a dense layer near the substrate side and a porous layer on the surface. Both were made of NiCoCrAlY alloy and deposited using high velocity oxygen-fuel technique. After thermal cycling, a large amount of internal oxides formed (up to 45% in volume fraction), introducing a significant volume expansion both in in-plane and perpendicular direction in the Bond Coat. However, the presence of the ceramic top Coat can suppress the Bond Coat in-plane swelling thus lowering the internal oxidation rate. Compared with the fully dense Bond Coat, the interface roughness of the porous Bond Coat increases significantly when internal oxidation occurs. There is a strong correlation between the internal oxidation and the interface roughness. In addition, both the beneficial and detrimental effects of internal oxidation on TBC failure were discussed. It is proposed that a fully dense Bond Coat with a proper surface roughness should have a longer thermal cycling lifetime.
Yeon-gil Jung - One of the best experts on this subject based on the ideXlab platform.
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Effects of microstructure design and feedstock species in the Bond Coat on thermal stability of thermal barrier Coatings
International Journal of Nanotechnology, 2018Co-Authors: Soo-hyeok Jeon, Sang Won Myoung, Yeon-gil Jung, Byung Il Yang, Zhe LuAbstract:The effects of the microstructure design and feedstock species in a Bond Coat on the thermal stability of thermal barrier Coatings (TBCs) were investigated through thermal shock (TS) tests. Three kinds of feedstock (AMDRY 9951 : cobalt (Co)-based feedstock, AMDRY 997 : nickel (Ni)-based feedstock, and AMDRY 9624 : Ni-based feedstock) were employed for the single layer Bond Coat and the first layer in the double layer Bond Coat, which were prepared by high velocity oxy-fuel process. The second layer in the Bond Coat and the top Coat was formed by air plasma spray process using Ni-based metallic powder (AMDRY 962) and 8YSZ (METCO 204 C-NS), respectively. The TS tests were performed till more than 50% of the region spalled in the TBC. The TBC system with the Co-based Bond Coat showed a better thermal durability than those with the Ni-based Bond Coats. The TBC systems with the double layer in the Bond Coat showed a better lifetime performance than those with the single layer, independent of the feedstock species.
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Thermal durability of thermal barrier Coatings with Bond Coat composition in cyclic thermal exposure
Surface & Coatings Technology, 2015Co-Authors: Zhe Lu, Sang Won Myoung, Yeon-gil Jung, Ung Yu PaikAbstract:Abstract The effects of Bond Coat composition on the microstructure evolution and thermal durability of thermal barrier Coating (TBC) were investigated through cyclic thermal exposure. The microstructure of the Bond Coat was controlled using various feedstock powders, such as NiCrAlY, NiCoCrAlY, and CoNiCrAlY, which were Coated on the Ni-based substrate using a high-velocity oxy-fuel process. The top Coat was prepared with high purity feedstock powder (METCO 204 C-XCL) using an air plasma spray (APS) process. The thermal durability of the TBCs was evaluated through the cyclic thermal fatigue (CTF) and thermal shock (TS) tests, including the microstructure evolution, the thermally grown oxide (TGO) growth behavior, and thermomechanical properties. After the CTF and TS tests, the TBC with the Ni-based Bond Coat showed a longer lifetime performance and less degradation in hardness value than those with the Ni–Co- and Co–Ni-based Bond Coats. The results indicate that the Bond Coat composition produce an obvious effect on the thermomechanical properties of the TBC system. The relationship between Bond Coat composition and thermal durability is extensively discussed, based on the microstructure evolution and element diffusion behavior.
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Control of Bond Coat microstructure in HVOF process for thermal barrier Coatings
Surface & Coatings Technology, 2014Co-Authors: Sang Won Myoung, Yeon-gil Jung, Zhe Lu, Byung-koog Jang, Ung Yu PaikAbstract:Abstract The microstructure of Bond Coat was optimized by controlling Coating parameters, such as spray distances, the gas flow ratio of air/oxygen/hydrogen, gun speed, and step distance, in high-velocity oxy-fuel process, and the effects of Coating parameters on the microstructure and thermomechanical properties were investigated. When the spray distance to the substrate shortened, the microstructure became dense and the hardness values were increased. As the amount of hydrogen increased in the fixed gas flow ratio, defects such as global pores and oxides were increased and the hardness values were decreased, showing a similar trend in oxygen. The Bond Coat with the step distance of 8 mm showed a slightly higher hardness value than that with the step distance of 5 mm, indicating that the gun speed did not have much effect on the hardness value. However, in thermal diffusivity, the Bond Coat with the step distance of 5 mm showed lower values than that with the step distance of 8 mm. The optimum Coating parameters could be proposed in HVOF process.
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Thermal fatigue behavior of air-plasma sprayed thermal barrier Coating with Bond Coat species in cyclic thermal exposure
Materials, 2013Co-Authors: Zhe Lu, Govindasamy Balakrishnan, Jeongseung Lee, Sang Won Myoung, Yeon-gil Jung, Ung Yu PaikAbstract:The effects of the Bond Coat species on the delamination or fracture behavior in thermal barrier Coatings (TBCs) was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF) for 1429 cycles. The TBC with the Bond Coat prepared by the air-plasma spray (APS) method showed a good condition at the interface between the top and Bond Coats after cyclic furnace thermal fatigue (CFTF) for 1429 cycles, whereas the TBCs with the Bond Coats prepared by the high-velocity oxygen fuel (HVOF) and low-pressure plasma spray (LPPS) methods showed a partial cracking (and/or delamination) and a delamination after 780 cycles, respectively. The TBCs with the Bond Coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50%) after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the Bond Coat prepared by the APS showed the highest adhesive strength before and after the FTF.
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effect of Bond Coat nature and thickness on mechanical characteristic and contact damage of zirconia based thermal barrier Coatings
Surface & Coatings Technology, 2006Co-Authors: Jaeyoung Kwon, Yeon-gil Jung, Ung Yu PaikAbstract:Abstract Mechanical characterization and contact damage of zirconia-based thermal barrier Coatings (TBCs) have been investigated using nanoindentation and Hertzian indentation tests. Two types of TBC systems with different Bond Coat thicknesses of 60 ± 20 and 280 ± 20 μm were prepared using two different processes: air plasma spraying (APS) and high-velocity oxygen fuel (HVOF). Top Coats were Coated onto each Bond Coat using the APS process. The TBC system with the Bond Coat formed using the HVOF process shows a step-like decrease in mechanical properties on passing from the substrate to the top Coat, and the Bond Coat formed using the HVOF process indicates higher values of E and H than that prepared using the APS process. The mechanical properties directly affect indentation stress–strain curves of the TBC systems, and the stress–strain curves of the TBC system with the APS Bond Coat are significantly lower than those with the HVOF process. The Bond Coat thickness plays an important role in limiting the effect of damage, indicating that the thin Bond Coat enhances contact damage and transmits the damage to the substrate, whereas the thick Bond Coat limits the damage to within the Bond Coat at a relatively low load of P = 500 N. As the indentation load and the number of cycles increase, the contact damage is enhanced and becomes more severe in the TBC system with the APS Bond Coat. The fracture modes in the top Coat and between the top Coat and the Bond Coat of the TBC system are dependent on the Bond Coat nature, including the accumulation of damage and its development at high loads of 1000 and 1500 N. The TBC system with the APS Bond Coat shows a bigger and more intensive damage region.