Oxidation Behavior of HVAF-Sprayed NiCoCrAlY Coating in H2–H2O Environment

Sadeghimeresht, Esmaeil; Hooshyar, Hamed Hoseini; Markocsan, Nicolaie; Joshi, Shrikant V.; Nylén, Per

doi:10.1007/s11085-016-9637-9

Cited by 17 publications

(14 citation statements)

References 60 publications

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“…In comparison, coatings produced by the high velocity air-fuel (HVAF) method can be characterized by a relatively denser microstructure with less amount of oxides than the above thermal spray methods [18]. Although even the HVAF coatings are not entirely free from pores either [19], [20], among the above-mentioned processes, HVAF has the lowest flame temperature and highest flame velocity (T<1800 °C, V= 700-1500 m/s) [21]. These significantly affect the microstructural features, in particular in situ oxide formation, splat morphology, and porosity that can potentially enhance the level of protection imparted by these coatings and their corrosion behaviour [22].…”

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confidence: 99%

Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings

et al. 2018

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Chlorine-induced corrosion of HVAF-sprayed Ni21Cr and Ni5Al coatings was investigated in 5 vol.% O2 + 500vppm HCl + N2 with and without KCl at 600°C up to 168 h. Both coatings were protective in the absence of KCl. With KCl, Ni21Cr degraded through a two-stage mechanism: 1) formation of K2CrO4 followed by diffusion of Clthrough the oxide grain boundaries to yield chlorine and a nonprotective oxide, and 2) inward diffusion of chlorine though defects in the non-protective oxide, leading to breakaway oxidation. Cl-/Cl2 could not diffuse through the protective alumina scale formed on Ni5Al, hence the corrosion resistance increased.

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confidence: 99%

Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings

et al. 2018

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“…The morphology of the coatings shows some degree of lamellar microstructures, with the elongated axis of the impacted splats aligned with the substrate surface. The pore content is an important factor that can affect the corrosion behavior of the thermal-spray coatings [32][33][34][35][36][37]. The porosity level was around 2.6 ± 0.2, 3.3 ± 0.5 and 3.0 ± 0.3 vol % for Fe-based 1, Fe-based 2 and Fe-based 3, respectively, confirming that the coatings were slightly porous for a typical HVAF coating.…”

Section: As-sprayed and Corroded Cr3c2-nicrmentioning

confidence: 99%

“…The porosity level in coatings was measured as 0.3 ± 0.05, 0.5 ± 0.07, 0.7 ± 0.10 and 1.2 ± 0.15 vol % for the Ni, NiCr, NiAl and NiCoCrAlY coatings, respectively, verifying a less-porous microstructure of the Ni-based coatings than Fe-based coatings. Despite the use of the coarser Ni-based powders, the higher density of the Ni-based coatings obtained could be attributed to the low temperature and high velocity of inflight particles impacting the substrate [33]. However, some coatings still presented a degree of different microstructural features, such as pores, splat boundaries and so on, which could adversely affect the corrosion behavior.…”

Section: Single-layer and Bilayer Coatingsmentioning

confidence: 99%

“…Consistent with the OCP results, the simultaneous addition of Cr and Al to Ni-based coatings provided a more cathodic intermediate layer (higher OCP), which was highly beneficial for the bilayer coating with the Cr 3 C 2 -NiCr top layer. The composition of the NiCoCrAlY coating encouraged the formation of the γ-NiCoCr and β-NiAl phases and also defects within the coating (which develop the pitting) [33]. However, full support of the passive layer by Cr and Al together compromised the effect of the coatings' defects and undesired galvanic couples.…”

Section: Single-layer and Bilayer Coatingsmentioning

confidence: 99%

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Electrochemical Behavior of Bilayer Thermal-Spray Coatings in Low-Temperature Corrosion Protection

Sadeghimeresht

Markocsan

2017

Coatings

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Cr 3 C 2 -NiCr coatings are greatly used to protect critical components in corrosive environments and to extend their lifetime and/or improve functional performance. However, the pores formed during spraying restrict the coating's applicability area for many corrosion protection applications. To overcome this technical challenge, bilayer coatings have been developed, in which an additional layer (the so-called "intermediate layer") is deposited on the substrate before spraying the Cr 3 C 2 -NiCr coating (the so-called "top layer"). The corrosion behavior of the bilayer coating depends on the composition and microstructure of each layer. In the present work, different single-layer coatings (i.e., Cr 3 C 2 -NiCr, Fe-and Ni-based coatings) were initially sprayed by a high-velocity air fuel (HVAF) process. Microstructure analysis, as well as electrochemical tests, for example, open-circuit potential (OCP) and polarization tests, were performed. The potential difference (∆E) had a great influence on galvanic corrosion between the top and intermediate layers, and thus, the coatings were ranked based on the OCP values (from high to low) as follows: NiCoCrAlY > NiCr > Cr 3 C 2 -NiCr > NiAl > Fe-based coatings (alloyed with Cr) > pure Ni. The Ni-based coatings were chosen to be further used as intermediate layers with the Cr 3 C 2 -NiCr top layer due to their capabilities to show high OCP. The corrosion resistance (R p ) of the bilayer coatings was ranked (from high to low) as follows: NiCoCrAlY/Cr 3 C 2 -NiCr > NiCr/Cr 3 C 2 -NiCr > NiAl/Cr 3 C 2 -NiCr > Ni/Cr 3 C 2 -NiCr. It was shown that splat boundaries and interconnected pores are detrimental for corrosion resistance, however, a sufficient reservoir of protective scale-forming elements (such as Cr or/and Al) in the intermediate layer can significantly improve the corrosion resistance.

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“…By virtue of these, dense and adherent coatings with least in-situ phase decomposition/oxidation can be produced which are greatly desired in corrosion protection applications [26].…”

Section: Introductionmentioning

confidence: 99%

Effect of SiO2 Dispersion on Chlorine-Induced High-Temperature Corrosion of High-Velocity Air-Fuel Sprayed NiCrMo Coating

et al. 2018

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NiCrMo coatings with and without dispersed SiO2 were deposited using high velocity air-fuel (HVAF) technique. Thermogravimetric experiments were conducted in 5% O2+500 vppm HCl+N2 with and without a KCl deposit at 600 °C for up to 168 h. The SiO2-containing coating showed lower weight change due to formation of a protective and adherent Cr-rich oxide scale. SiO2 decelerated short-circuit diffusion of Cr 3+ through scale's defects, e.g., vacancies, and promoted the selective oxidation of Cr to form the protective Cr-rich oxide scale. Furthermore, the presence of SiO2 led to less subsurface depletion of Cr in the coating, and accordingly less corrosion of the substrate. The formed corrosion product on the SiO2-free coating was highly porous, non-adherent, and thick.

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Oxidation Behavior of HVAF-Sprayed NiCoCrAlY Coating in H2–H2O Environment

Cited by 17 publications

References 60 publications

Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings

Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings

Electrochemical Behavior of Bilayer Thermal-Spray Coatings in Low-Temperature Corrosion Protection

Effect of SiO2 Dispersion on Chlorine-Induced High-Temperature Corrosion of High-Velocity Air-Fuel Sprayed NiCrMo Coating

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