The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Xiaofeng Zhao - One of the best experts on this subject based on the ideXlab platform.
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effect of Internal Oxidation on the interfacial morphology and residual stress in air plasma sprayed thermal barrier coatings
Surface & Coatings Technology, 2018Co-Authors: Jishen Jiang, Weizhe Wang, Xiaofeng ZhaoAbstract:Abstract Significant Internal Oxidation was found in air plasma sprayed (APS) thermal barrier coating (TBC) samples with double-layered high velocity oxy-fuel (HVOF) NiCoCrAlY bond coats. The volumetric fraction of Internal oxides within the bond coat increased from 5% to 38% during 799 h isothermal exposure at 1150 °C, indicating significant swelling of the Internal oxides. This swelling behavior not only significantly increases the thickness of the bond coat layer from 175 μm to 260 μm, but also probably elevates the risk of interfacial failure in the TBCs, due to the roughness change at the interface and the huge residual stress generated. Thus, different finite element (FE) models were established to understand the role of the Internal oxides in interfacial morphology and residual stress. The Internal Oxidation behavior was modeled on experimental results. The FE results showed that although the Internal Oxidation only slightly increased the interfacial roughness, significant changes were found in the patterns of the stress component S22 and the interfacial normal stress along the interface, increasing the risk of micro-cracks and changing the crack locations.
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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, Xiao Shan, Xiaofeng Zhao, 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.
R C Newman - One of the best experts on this subject based on the ideXlab platform.
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Internal Oxidation of ag xin alloys at low homologous temperature
Corrosion Science, 2020Co-Authors: Y Ghaffari, R C Newman, K Daub, S Y PersaudAbstract:Abstract Internal Oxidation of Ag-xIn alloys (x = 10, 13, 16 at%) was studied in an air atmosphere at a relatively low homologous temperature (240 °C), where lattice diffusion is negligible. After exposure, metallic Ag nodules were present on the surfaces of all alloys, expelled to relieve stress due to Internal Oxidation, confirming that such coarse morphologies can be produced by short-circuit transport. Crystallographic orientation and grain boundary misorientation were found to influence nodule expulsion tendency, and the propensity for Internal or external Oxidation. Further analytical TEM characterization was used to study the nanoscale morphology and chemistry of nodules and Internal oxide(s).
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an atom probe tomography study of Internal Oxidation processes in alloy 600
Acta Materialia, 2016Co-Authors: Brian Langelier, S Y Persaud, R C Newman, Gianluigi A BottonAbstract:Abstract Internal Oxidation in Alloy 600 (Ni–16Cr–9Fe) involves the inward diffusion of O, which preferentially reacts with solute elements (e.g. Cr, Fe) forming Internal oxide precipitates. In this work, the Internal Oxidation process and its resultant metal-oxide heterostructures are systematically analyzed in 3D at the finest length scales, using atom probe tomography (APT). Internal Oxidation is induced by exposure of Alloy 600 to 480 °C hydrogenated steam, with an oxygen partial pressure below the dissociation pressure of the solvent metal oxide, NiO. Following exposure, nodules of metallic Ni are observed on the sample surface, originating from material that is expelled to relieve compressive stresses generated by Internal Oxidation. Probing the material immediately below the surface reveals these nodules to be directly connected to their parent grains via Ni-rich metal channels. The matrix metal is intertwined with a continuous network of oxides, which are primarily FeCr 2 O 4 . The continuous interface between oxides and matrix provides the short-circuit diffusion pathways necessary for Ni expulsion. Deeper below the surface, oxides are observed as particles, rather than a continuous network, and are often aligned on matrix planes. The small oxide particles are Cr 2 O 3 , which is also found to be the composition at the centres of many larger FeCr 2 O 4 oxides. This indicates that oxides first precipitate as Cr 2 O 3 , then later grow as FeCr 2 O 4 when local depletion of Cr changes which phase is most energetically-favourable. Initial comparisons indicate that some fundamental findings in this work are applicable to known Internal Oxidation systems at lower and higher temperatures.
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Internal Oxidation of alloy 690 in hydrogenated steam
Corrosion Science, 2015Co-Authors: S Y Persaud, S Ramamurthy, R C NewmanAbstract:Abstract Alloy 690 was exposed to a hydrogenated steam environment at 480 °C and 1 bar, considered to simulate primary water in a pressurized water reactor. The possibility of Internal Oxidation in Alloy 690 was evaluated and the likely relevance to SCC in primary water is discussed. Initial surface imaging revealed intragranular metallic Ni nodules, indicating that Internal Oxidation had occurred. Grain boundaries provided a short circuit for outward Cr diffusion and an external surface oxide was observed at grain boundaries. FIB trenching was used to study Oxidation phenomena occurring beneath the surface and EDX elemental maps were generated.
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Internal Oxidation of alloy 600 exposed to hydrogenated steam and the beneficial effects of thermal treatment
Corrosion Science, 2014Co-Authors: S Y Persaud, Gianluigi A Botton, Andreas Korinek, J Huang, R C NewmanAbstract:Abstract Alloy 600 in the solution annealed (SA) and thermally treated (TT) conditions was exposed to a hydrogenated steam environment considered to simulate primary water in pressurized water reactors. The likely susceptibility to primary water stress corrosion cracking (PWSCC) was evaluated using the Internal Oxidation model. A FIB was used to extract cross-sections from Alloy 600 samples and elemental maps were generated; Internal Oxidation was observed intragranularly in all cases, resulting in expulsion of metallic nickel to the surface. Intergranular Oxidation and embrittlement was observed in SA samples, while a thick and dense Cr-rich oxide was formed intergranularly on TT samples.
S Y Persaud - One of the best experts on this subject based on the ideXlab platform.
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Internal Oxidation of ag xin alloys at low homologous temperature
Corrosion Science, 2020Co-Authors: Y Ghaffari, R C Newman, K Daub, S Y PersaudAbstract:Abstract Internal Oxidation of Ag-xIn alloys (x = 10, 13, 16 at%) was studied in an air atmosphere at a relatively low homologous temperature (240 °C), where lattice diffusion is negligible. After exposure, metallic Ag nodules were present on the surfaces of all alloys, expelled to relieve stress due to Internal Oxidation, confirming that such coarse morphologies can be produced by short-circuit transport. Crystallographic orientation and grain boundary misorientation were found to influence nodule expulsion tendency, and the propensity for Internal or external Oxidation. Further analytical TEM characterization was used to study the nanoscale morphology and chemistry of nodules and Internal oxide(s).
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an atom probe tomography study of Internal Oxidation processes in alloy 600
Acta Materialia, 2016Co-Authors: Brian Langelier, S Y Persaud, R C Newman, Gianluigi A BottonAbstract:Abstract Internal Oxidation in Alloy 600 (Ni–16Cr–9Fe) involves the inward diffusion of O, which preferentially reacts with solute elements (e.g. Cr, Fe) forming Internal oxide precipitates. In this work, the Internal Oxidation process and its resultant metal-oxide heterostructures are systematically analyzed in 3D at the finest length scales, using atom probe tomography (APT). Internal Oxidation is induced by exposure of Alloy 600 to 480 °C hydrogenated steam, with an oxygen partial pressure below the dissociation pressure of the solvent metal oxide, NiO. Following exposure, nodules of metallic Ni are observed on the sample surface, originating from material that is expelled to relieve compressive stresses generated by Internal Oxidation. Probing the material immediately below the surface reveals these nodules to be directly connected to their parent grains via Ni-rich metal channels. The matrix metal is intertwined with a continuous network of oxides, which are primarily FeCr 2 O 4 . The continuous interface between oxides and matrix provides the short-circuit diffusion pathways necessary for Ni expulsion. Deeper below the surface, oxides are observed as particles, rather than a continuous network, and are often aligned on matrix planes. The small oxide particles are Cr 2 O 3 , which is also found to be the composition at the centres of many larger FeCr 2 O 4 oxides. This indicates that oxides first precipitate as Cr 2 O 3 , then later grow as FeCr 2 O 4 when local depletion of Cr changes which phase is most energetically-favourable. Initial comparisons indicate that some fundamental findings in this work are applicable to known Internal Oxidation systems at lower and higher temperatures.
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Internal Oxidation of alloy 690 in hydrogenated steam
Corrosion Science, 2015Co-Authors: S Y Persaud, S Ramamurthy, R C NewmanAbstract:Abstract Alloy 690 was exposed to a hydrogenated steam environment at 480 °C and 1 bar, considered to simulate primary water in a pressurized water reactor. The possibility of Internal Oxidation in Alloy 690 was evaluated and the likely relevance to SCC in primary water is discussed. Initial surface imaging revealed intragranular metallic Ni nodules, indicating that Internal Oxidation had occurred. Grain boundaries provided a short circuit for outward Cr diffusion and an external surface oxide was observed at grain boundaries. FIB trenching was used to study Oxidation phenomena occurring beneath the surface and EDX elemental maps were generated.
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Internal Oxidation of alloy 600 exposed to hydrogenated steam and the beneficial effects of thermal treatment
Corrosion Science, 2014Co-Authors: S Y Persaud, Gianluigi A Botton, Andreas Korinek, J Huang, R C NewmanAbstract:Abstract Alloy 600 in the solution annealed (SA) and thermally treated (TT) conditions was exposed to a hydrogenated steam environment considered to simulate primary water in pressurized water reactors. The likely susceptibility to primary water stress corrosion cracking (PWSCC) was evaluated using the Internal Oxidation model. A FIB was used to extract cross-sections from Alloy 600 samples and elemental maps were generated; Internal Oxidation was observed intragranularly in all cases, resulting in expulsion of metallic nickel to the surface. Intergranular Oxidation and embrittlement was observed in SA samples, while a thick and dense Cr-rich oxide was formed intergranularly on TT samples.
Ping Xiao - One of the best experts on this subject based on the ideXlab platform.
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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, Xiao Shan, Xiaofeng Zhao, 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.
I Karaman - One of the best experts on this subject based on the ideXlab platform.
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effect of Internal Oxidation on wear behavior of ultrafine grained nb zr
Acta Materialia, 2011Co-Authors: G Purcek, O Saray, F Rubitschek, Thomas Niendorf, H J Maier, I KaramanAbstract:The influence of surface modification by Internal Oxidation on dry sliding wear behavior of ultrafine-grained (UFG) Nb–Zr was investigated using a pin-on-disc type tribometer. The results show that improvement in strength by grain refinement via equal-channel angular pressing/extrusion has no substantial effect on the wear resistance of the non-oxidized UFG samples as compared to the coarse-grained material. This was attributed to the complex wear mechanisms operating in this alloy, such as adhesion leading to smearing, tribo-chemical reactions resulting in strong oxidative wear and also abrasion bringing about scratches and deep grooves. However, Internal Oxidation by heat-treatment significantly improved the wear resistance of Nb–Zr, especially under low to medium applied pressures due to the hardened diffusion zone with ZrO2 nanoparticles formed in the subsurface layer. Moreover, the improvement was more pronounced in the UFG material, which is attributed to increased diffusion in the UFG microstructure. When the applied pressure was increased above 0.5 MPa, however, the wear rate increased considerably due to the elimination of the hardened subsurface layer. Still, even under high pressures, the oxidized samples demonstrated lower weight loss as compared to non-oxidized samples. Based on the investigations of the worn surfaces, it was determined that Internal Oxidation mostly eliminates the complex wear mechanisms operational in the non-oxidized samples, especially under low/medium loads. Improvement in wear properties by Internal Oxidation along with enhanced mechanical properties and previously demonstrated good biocompatibility and superior fatigue performance make Internally oxidized UFG NbZr a promising candidate for biomedical applications in the human body.
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improvement of the fatigue performance of an ultrafine grained nb zr alloy by nano sized precipitates formed by Internal Oxidation
Scripta Materialia, 2008Co-Authors: Thomas Niendorf, H J Maier, D Canadinc, Guney Guven Yapici, I KaramanAbstract:The formation of nano-sized precipitates in an ultrafine-grained Nb–Zr alloy was investigated. ZrO2 precipitates induced by Internal Oxidation during heat treatment at low homologous temperatures significantly intensify the hardness of the surface layer without deterioration of the surface quality, and thus significantly improve the fatigue performance.