Oxide scale growth on MCrAlY bond coatings after pulsed electron beam treatment and deposition of EBPVD-TBC

The oxygen permeability of an undoped polycrystalline -Al 2 O 3 wafer that was exposed to oxygen potential gradients was evaluated at temperatures up to 1973 K. Oxygen preferentially permeated through the grain boundaries of -Al 2 O 3 . The main diffusion species, which were attributed to oxygen permeation, depended on oxygen partial pressures (P O2 ), forming oxygen potential gradients. Under oxygen potential gradients generated by P O2 below about 1 Pa, oxygen permeation occurred by oxygen diffusing from regions of higher P O2 to regions of lower P O2 . By contrast, under oxygen potential gradients generated by P O2 above about 1 Pa, oxygen permeation proceeded by aluminum diffusing from regions of lower P O2 to regions of higher P O2 . In other words, O 2 molecules were adsorbed onto a surface at higher P O2 and subsequently dissociated into oxygen ions (forming Al 2 O 3 ), while oxygen ions on the opposite surface at lower P O2 were desorbed by association into O 2 molecules (decomposition of Al 2 O 3 ). The grain-boundary diffusion coefficients of oxygen and aluminum as a function of P O2 were determined from the oxygen permeation constants.

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“…[3][4][5][6][7] Thus, suppressing masstransfer through the -Al 2 O 3 scale is anticipated to further improve the durability of TBCs.…”

Section: Introductionmentioning

confidence: 99%

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

2009

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“…Localized Y concentration enrichment in the TGO or the pegs has been observed by several authors [17,[22][23][24]40]. EDS analysis in the TEM by Mercer and co-workers [40] revealed nano-scale oxides based on Y 2 O 3 and HfO 2 inside the pegs.…”

Section: Discussionmentioning

confidence: 71%

Program Evaluation for U.S. Army Lifelong Learning Centers (LLCs): Extension to Military Operational Speciality (MOS)-Based LLCs

Clanciola¹

2008

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Standard Form 298 (Rev. 8/98) REPORT DOCUMENTATION PAGEPrescribed by ANSI Std. Z39.18 Form Approved OMB No. 0704-0188The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, A team from academia, Air Force laboratories and industry has been assembled to develop a design code for one of the prevailing failure m in thermal barrier systems used for aero-turbines. The failure mechanism to be addressed occurs in systems with twophase bond coats an manifest as abrupt delamination along the interface between the thermally grown oxide (TGO) and the intermetallic bond coat. The code integrate several important time/cycle dependent phenomena, each with associated constituent models for: interface adhesion, bond deformation, sintering in the thermal barrier layer, etc. In this the second year of the project, efforts have focused on experim characterization of the various layers and the development of hierarchical models, both of which are needed to characterize and define salient governing phenomena. A previously developed interfacial delamination model is being adapted for this problem, and integration of t efforts will provide the pathway to the TBC design code. FA9550-05-1-0173, FA9550-05-1-0203, FA9550-05-1-0229, FA9550-05-1-0039, FA9550-05-1 Reset MEANS II: KNOWLEDGE ORIENTED MATERIALS ENGINEERING OF LAYERED THERMAL BARRIER SYSTEMS (NOMELT) AFOSR Grant Nos: AbstractA team from academia, Air Force laboratories and industry has been assembled to develop a design code for one of the prevailing failure modes in thermal barrier systems used for aero-turbines. The failure mechanism to be addressed occurs in systems with two-phase bond coats and is manifest as abrupt delamination along the interface between the thermally grown oxide (TGO) and the intermetallic bond coat. The code will integrate several important time/cycle dependent phenomena, each with associated constituent models for: interface adhesion, bond coat deformation, sintering in the thermal barrier layer, etc. In this the second year of the project, efforts have focused on experimental characterization of the various layers and the development of hierarchical models, both of which are needed to characterize and define the salient governing phenomena. A previously developed interfacial delamination model is being adapted for this problem, and integration of these efforts will provide the pathway to the TBC design code. Research ObjectivesThe main objective of NOMELT is to develop a code that facilitates the more aggressive design of multilayered thermal barrier systems. This code will incorporate the most important underlying micro-mechanical processes and permit industrial engineers to...

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“…MCrAlY coatings have been deposited using a number of techniques, such as 1) plasma deposition: atmospheric plasma spraying (APS), low-pressure plasma spraying (LPPS), vacuum plasma spraying (VPS); 2) sputtering: chemical vapor deposition (CVD), electron-beam physical vapor deposition (EB-PVD); 3) flame spraying: high velocity oxy-fuel spraying (HVOF), high velocity air-fuel spraying (HVAF), 4) cold spraying and so on [27][28][29][30][31]. Flame spraying techniques can produce coatings comparable to other deposition techniques with a proper selection of the process parameter.…”

Section: Deposition Techniquesmentioning

confidence: 99%

Asset Liability Management for Tanzania Pension Funds

Zhang

2018

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Linköping 2018Front page images: (1) low magnification of snowflake like α-Al 2 O 3 formed on polished coating surface after 10 h oxidation; (2) blade-like transient Al 2 O 3 formed on shot-peened coating surface after 100 min oxidation; (3) spinel island formed on polished coating surface after 10 min oxidation. AbstractMCrAlY coatings (M=Ni and/or Co) have been widely used for the protection of superalloy components against oxidation and hot corrosion in the hot sections of gas turbines. The drive to improve engine combustion efficiency while reducing emissions by increasing the operation temperature brings a big challenge for coating design. As a result, the need for improvement of MCrAlY coatings for better oxidation resistance is essential.Formation of a stable, dense, continuous, and slow-growing α-Al 2 O 3 layer, on the MCrAlY coating surface, is the key to oxidation protection, since the protective α-Al 2 O 3 scale offers superior oxidation resistance due to its lower oxygen-diffusion rate as compared with other oxides. The ability of a MCrAlY coating to form and maintain such a protective scale depends on the coating composition and microstructure, and can be improved through optimization of deposition parameters, modification of coating surface conditions, and so on. Part of this thesis work focuses on studying the effect of post-deposition surface treatments on the oxidation behavior of MCrAlX coatings (X can be yttrium and/or other minor alloying elements). The aim is to gain fundamental understanding of alumina scale evolution during oxidation which is important for achieving improved oxidation resistance of MCrAlX coatings. Oxide scale formed on coatings at initial oxidation stage and the effect of surface treatment were investigated by a multi-approach study combining photo-stimulated luminescence, microstructural observation and weight gain. AcknowledgementsThe present project is financed by Siemens Industrial Turbomachinery AB, Swedish Energy Agency through KME consortium -ELFORSK, and are therefore grateful

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Oxide scale growth on MCrAlY bond coatings after pulsed electron beam treatment and deposition of EBPVD-TBC

Cited by 94 publications

References 6 publications

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

Mass-Transfer Mechanism of Alumina Ceramics under Oxygen Potential Gradients at High Temperatures

Program Evaluation for U.S. Army Lifelong Learning Centers (LLCs): Extension to Military Operational Speciality (MOS)-Based LLCs

Asset Liability Management for Tanzania Pension Funds

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