Enhanced Characteristics of HVOF-sprayed MCrAlY Bond Coats for TBC Applications

Rajasekaran, B.; Mauer, Georg; Vaßen, Robert

doi:10.1007/s11666-011-9668-3

Cited by 75 publications

(33 citation statements)

References 15 publications

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“…For instance, spraying distance, powder flow, gas flow, and powder size of HVOF process have a significant influence on microstructure of coating, giving different coating oxidation performance [103]. Moreover, the impact of surface treatment on coatings oxidation resistance differs in coatings produced by different deposition techniques.…”

Section: Role Of 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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Section: Role Of Deposition Techniquesmentioning

confidence: 99%

Asset Liability Management for Tanzania Pension Funds

Zhang

2018

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“…The TBC systems did not show any delamination or cracking at the interface between the top and bond coats or between the buffer layer and the top coat. The samples with the buffer layer showed a relatively irregular interface between the buffer layer and the top coat, while all of the samples showed a relatively smooth interface between the bond and top coats in the SLC TBCs or between the bond coat and the buffer layer in the DLC TBCs, compared with the interface between the buffer layer and the top coat, owing to the coating method [39,40]. The particle velocity in the HVOF system for the bond coat can be produced up to 700 m/sec, and that in the APS system for the buffer layer is 350 m/sec.…”

Section: Microstructure Of As-prepared Tbcsmentioning

confidence: 99%

Thermal durability and fracture behavior of layered Yb-Gd-Y-based thermal barrier coatings in thermal cyclic exposure

Jung

et al. 2017

Surface and Coatings Technology

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The effects of structural design on the thermal durability of Yb-Gd-Y-based thermal barrier coatings (TBCs) were investigated through thermal cyclic exposure tests, such as furnace cyclic thermal fatigue (FCTF) and jet engine thermal shock (JETS) tests. The effects of composition in the bond coat and feedstock purity for the buffer layer on its lifetime performance were also examined. To overcome the drawbacks of Yb-Gd-Y material with poor thermal durability due to poor mechanical properties and low coefficient of thermal expansion, a buffer layer was introduced in the Yb-Gd-Y-based TBC systems. In the FCTF tests, the TBC with the CoNi-based bond coat and the buffer layer of regular purity showed a longer lifetime performance than other TBCs, especially the TBCs without the buffer layer.In the JETS tests, the TBC with the Ni-based bond coat and the buffer layer of high purity showed a sound condition after 2000 cycles, showing better interfacial stability for TBC with the Ni-based bond coat rather than that with the CoNi-based bond coat in the single layer coatings without the buffer layer. The buffer layer effectively enhanced the thermal durability in slow temperature change, while the bond-coat composition and the feedstock purity for the buffer layer were found to be important factor to improve the thermal durability of the TBC in fast temperature change. Finally, these research findings allow us to control the structure, composition, and feedstock purity in TBC system for improving the thermal durability in cyclic thermal environments.

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“…To maintain a sufficient aluminum supply for the formation of protective alumina (also termed as thermally grown oxide, TGO), a fully dense MCrAlY bond coat was usually deposited using high velocity oxy-fuel (HVOF) technique. However, the surface of a dense bond coat prepared by HVOF is relatively smooth (e.g., varying from 2 to 8 μm [6]), which could not ensure a good interlocking with the yttria stabilized zirconia (YSZ) top coat. Although the rough surface of the bond coat can be achieved by HVOF, the porosity of the coating will increase [6].…”

Section: Introductionmentioning

confidence: 99%

“…However, the surface of a dense bond coat prepared by HVOF is relatively smooth (e.g., varying from 2 to 8 μm [6]), which could not ensure a good interlocking with the yttria stabilized zirconia (YSZ) top coat. Although the rough surface of the bond coat can be achieved by HVOF, the porosity of the coating will increase [6]. To improve the surface roughness of the bond coat, a second rough MCrAlY layer, deposited using either APS or HVOF, was applied on the dense MCrAlY bond coat.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, the in-flight oxidation of MCrAlY particles during APS process could decrease the aluminum content as well as inhibit the Al outward diffusion, which may shorten the lifetime of the TBC system [8][9][10]. To avoid this detrimental effect, the HVOF technique is employed to fabricate the rough outer layer through manipulating the powder size and spaying parameters [6], which is relatively dense and free of in-flight oxidation compared with the APS technique. In addition, there is no need to change the spraying gun during bond coat deposition.…”

Section: Introductionmentioning

confidence: 99%

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Role of internal oxidation on the failure of air plasma sprayed thermal barrier coatings with a double-layered bond coat

Zou

Jia

Yang

et al. 2017

Surface and Coatings Technology

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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

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Enhanced Characteristics of HVOF-sprayed MCrAlY Bond Coats for TBC Applications

Cited by 75 publications

References 15 publications

Asset Liability Management for Tanzania Pension Funds

Asset Liability Management for Tanzania Pension Funds

Thermal durability and fracture behavior of layered Yb-Gd-Y-based thermal barrier coatings in thermal cyclic exposure

Role of internal oxidation on the failure of air plasma sprayed thermal barrier coatings with a double-layered bond coat

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