Microstructure Effect of Intermediate Coat Layer on Corrosion Behavior of HVAF-Sprayed Bi-Layer Coatings

Sadeghimeresht, Esmaeil; Markocsan, Nicolaie; Nylén, Per

doi:10.1007/s11666-016-0484-7

Cited by 19 publications

(12 citation statements)

References 37 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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Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings

et al. 2018

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“…The protective scale forming elements such as Cr or/and Al are not depleted during the HVAF spraying process and preserved for oxidation protection (see EDS point analysis in Figure a,b). This is a consequence of the negligible in situ oxide pick up or phase transformation during HVAF spraying …”

Section: Resultsmentioning

confidence: 99%

Effect of water vapor on the oxidation behavior of HVAF‐sprayed NiCr and NiCrAlY coatings

Sadeghimeresht

Eklund

Simon

et al. 2018

Materials & Corrosion

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Isothermal oxidation behavior of NiCr and NiCrAlY coatings deposited onto low alloy 16Mo3 steel by high‐velocity air fuel (HVAF) process was investigated in 5% O2 + 20% H2O + N2 at 600 °C for 168 h. Whereas NiCrAlY showed lower mass gain compared to NiCr, both coatings succeeded in maintaining the integrity with the substrate during the exposure without any breakaway oxidation. A thin Cr‐rich oxide scale (Cr2O3) formed on NiCr, and a thin mixed oxide scale (Al2O3 with NiCr2O4) formed on NiCrAlY significantly increasing the oxidation protection in the presence of water vapor.

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“…The as-sprayed Cr3C2-NiCr coating (Figure 3a) revealed a uniform distribution of Cr3C2 particles (dark gray) in the NiCr binder (light gray). The microstructure images and the corresponding EDS point analysis showed coatings with relatively few defects, including pores, and a negligible oxygen pick-up owing to the high velocity (700-1200 m/s) [30] and low temperature (<1800 °C) [31] of the in-flight particles in the HVAF process . No sign of splats could be seen in Figure 3a, confirming that the particles were well-splashed and plastically deformed during the HVAF process, which provided a good cohesion (particle/particle bonding).…”

Section: As-sprayed and Corroded Cr3c2-nicrmentioning

confidence: 97%

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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Microstructure Effect of Intermediate Coat Layer on Corrosion Behavior of HVAF-Sprayed Bi-Layer Coatings

Cited by 19 publications

References 37 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

Effect of water vapor on the oxidation behavior of HVAF‐sprayed NiCr and NiCrAlY coatings

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

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