Hot corrosion studies of HVOF NiCrBSi and Stellite-6 coatings on a Ni-based superalloy in an actual industrial environment of a coal fired boiler

Sidhu, T. S.; Prakash, S.; Agrawal, R. D.

doi:10.1016/j.surfcoat.2006.02.047

Cited by 66 publications

(40 citation statements)

References 14 publications

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“…Nevertheless, these mechanisms cannot solely interpret the sudden increase of thickness reduction that occurs during laser glazing at 300 W. As illustrated in Fig. 6(c), a deep notch can be noticed at the intermediate region of the melting pool of ST-Glazing (13). This verifies that laser treatment at 300 W causes a significant outward flow of the liquid from the center to the edges of the melting pool.…”

Section: Single-pass Lasermentioning

confidence: 90%

“…Figure 5(b) shows the maximum reduction in thickness of ST-HVOF coating after laser treatment versus beam power for different scan rates. With increasing the laser power up to 250 W, the coating thickness reduction gradually increases reaching 37 lm for ST-Glazing (10); however, further rising the power to 300 W results in a sudden increase in the coating thickness reduction to 135 lm for ST-Glazing (13). The gradual increase of thickness reduction during laser glazing can be explained, first, by elimination of voids, pores, and nonuniformities of ST-HVOF coating structure leading to the formation of highly dense glazing layers (see Fig.…”

Section: Single-pass Lasermentioning

confidence: 99%

“…For instance, APS technique has led to the deposition of Stellite 6 coating with non-uniform chemical composition and high level of porosity in the range of $2-3.5% ( Ref 11,12). In case of HVOF-sprayed Stellite 6 coating, although a lower porosity of $2% is obtained, the formation of undesirable oxide phases during deposition process has been frequently reported ( Ref 10,13,14). The residual porosity increases the abrasive wear rate and facilitates the diffusion of corrosive species through the surface pores into the underlying coating layers; eventually, debonding and spallation of Stellite 6 coatings take place due to accumulation of corrosion products at the coating/substrate interface ( Ref 15,16).…”

Section: Introductionmentioning

confidence: 99%

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Laser Surface Treatment of Stellite 6 Coating Deposited by HVOF on 316L Alloy

Razavi

2016

J. of Materi Eng and Perform

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This research aimed to study the effects of laser glazing treatment on microstructure, hardness, and oxidation behavior of Stellite 6 coating deposited by high velocity oxygen fuel (HVOF) spraying. The assprayed Stellite 6 coating (ST-HVOF) was subjected to single-pass and multiple-pass laser treatments to achieve the optimum glazing parameters. Microstructural characterizations were performed by x-ray diffractometry and field emission scanning electron microscopy equipped with energy-dispersive spectroscopy. Two-step optimization showed that laser treatment at the power of 200 W with a scan rate of 4 mm/s causes a surface layer with a thickness of 208 ± 32 lm to be remelted, while the underlying layers retain the original ST-HVOF coating structure. The obtained sample (ST-Glazing) exhibited a highly dense and uniform structure with an extremely low porosity of $0.3%, much lower than that of ST-HVOF coating (2.3%). The average microhardness of ST-Glazing was measured to be 519 Hv 0.3 indicating a 17% decrease compared to ST-HVOF (625 Hv 0.3 ) due to the residual stress relief and dendrite coarsening from submicron size to $3.4 lm after laser treatment. The lowest oxidation mass gain was obtained for STGlazing by 2 mg/cm 2 after 8 cycles at 900°C indicating 52 and 84% improvement in oxidation resistance in comparison to ST-HVOF and bare 316L steel substrates, respectively.

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Section: Single-pass Lasermentioning

confidence: 90%

Section: Single-pass Lasermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Laser Surface Treatment of Stellite 6 Coating Deposited by HVOF on 316L Alloy

Razavi

2016

J. of Materi Eng and Perform

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“…At the same time, high velocity oxyfuel (HVOF) sprayed stellite 6 coating (300 lm thick) was reported [11] as having better hot corrosion resistance in coal-burning environment which was attributed to the formation of thick and continuous protective scales composed of spinel CoCr 2 O 4 on top of CoO and Cr 2 O 3 . In another study [12], HVOF-sprayed stellite 6 coating in molten salts exhibited beneficial effects of inter-splat oxides on corrosion propagation into the coating at 525°C.…”

Section: Introductionmentioning

confidence: 99%

Laser Clad and HVOF-Sprayed Stellite 6 Coating in Chlorine-Rich Environment with KCl at 700 °C

et al. 2017

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Laser clads and HVOF coatings from a stellite 6 alloy (Co-Cr-W-C alloy) on 304 stainless steel substrates were exposed both bare and with KCl deposits in 500 ppm HCl with 5% O 2 for 250 h at 700°C. SEM/EDX and PXRD analyses with Rietveld refinement were used for assessment of the attack and for analysis of the scales. The bare samples suffered from scale spallation and the scale was mostly composed of Cr 2 O 3 , CoCr 2 O 4 and CoO, although due to dilution haematite (Fe 2 O 3 ) was detected in the scale formed on the laser clad sample. A small amount of hydrated HCl was detected in bare samples. While the corrosion of the bare surfaces was limited to comparatively shallow depths and manifested by g and M 7 C 3 carbide formation, the presence of KCl on the surface led to severe Cr depletion from the HVOF coating (to 1 wt%). Both inward and outward diffusion of elements occurred in the HVOF coating resulting in Kirdendall voids at the coatingsteel interface. The laser clad sample performed significantly better in conditions of the KCl-deposit-induced corrosion. In addition to the oxides, CoCl 2 was detected in the HVOF sample and K 3 CrO 4 was detected in the laser clad sample. Thermodynamic calculations and kinetic simulations were carried out to interpret the oxidation and diffusion behaviours of coatings.

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“…La utilización de combustibles de baja calidad, frecuente en turbinas de gases industriales y motores diesel, que pueden contener como impurezas vanadio y azufre, puede dar lugar a reacciones con los estabilizantes de la circona, sobre todo cuando las barreras están fabricadas por la técnica de plasma debido a su porosidad, dando lugar a la corrosión por sales fundidas de carácter electroquímico (9)(10)(11)(12)(13). La disminución del contenido en itria desestabiliza la circona, favoreciendo el proceso de transformación a circona monoclínica.…”

Section: Introductionunclassified

Degradación de barreras térmicas por sales fundidas

Utrilla¹,

Poza²,

Gómez-García³

et al. 2008

Bol. Soc. Esp. Ceram. Vidr.

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Las barreras térmicas son sistemas multicapa que se aplican a sustratos metálicos para mejorar su resistencia a la temperatura. El material utilizado en el trabajo es un sustrato base níquel (Inconel 600) con recubrimiento multicapa de NiCrAlY y ZrO 2 parcialmente estabilizada con Y 2 O 3 (Y-PSZ) depositado por plasma atmosférico. La presencia de contaminantes, como S, V o Na presentes en combustibles de baja calidad, puede dar lugar a reacciones con este óxido estabilizador de la circona (Y 2 O 3 ), originando una desestabilización estructural de la circona por disminución del contenido en itria. En esta comunicación se ha realizado un estudio sistemático de la degradación del material frente a determinados agentes corrosivos a elevada temperatura. Sobre la superficie de las muestras se añadieron mezclas de 40% Na 2 SO 4 -60% V 2 O 5 y se trataron isotérmicamente a 800 ºC durante 48 y 144 horas. Finalmente, se evaluó la modificación de las propiedades por efecto de los agentes agresivos. Mediante la técnica de espectroscopía de impedancia electroquímica (EIS) se estimó la degradación de la barrera térmica. El estudio de la evolución microestructural se realizó mediante técnicas de microscopía óptica (MO), electrónica de barrido ambiental (ESEM) y difracción de rayos X (DRX). Palabras clave: Barreras térmicas, sales fundidas, proyección por plasma atmosférico, microscopía electrónica de barrido, espectroscopia de impedancia electroquímica. Corrosion of thermal barrier coating by molten salts.Thermal barrier coatings (TBC) are frequently used to provide thermal insulation to metallic components. The material used in this investigation comprises a ceramic top layer, ZrO 2 8Y 2 O 3 (Y-PSZ), and an overlay coating, Ni22Cr10Al1Y, air plasma sprayed on to a nickel base alloy Inconel 600 substrate. Yttria stabilizes the cubic phase zirconia, but it can react with S, V and Na contaminants contained in many low-quality industrial fuels. A decrease in the yttria content promotes the transformation to monoclinic ZrO 2 . The materials were subjected to an isothermal air furnace test under 40% Na 2 SO 4 -60% V 2 O 5 mixtures at 800 ºC for 48 and 144h. The degradation of the coating was analyzed by electrochemical impedance spectroscopy (EIS). The microstructure was characterized by enviromental scanning electron microscopy (ESEM), X-ray microanalysis (EDX) and x ray diffracction (XRD).

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Hot corrosion studies of HVOF NiCrBSi and Stellite-6 coatings on a Ni-based superalloy in an actual industrial environment of a coal fired boiler

Cited by 66 publications

References 14 publications

Laser Surface Treatment of Stellite 6 Coating Deposited by HVOF on 316L Alloy

Laser Surface Treatment of Stellite 6 Coating Deposited by HVOF on 316L Alloy

Laser Clad and HVOF-Sprayed Stellite 6 Coating in Chlorine-Rich Environment with KCl at 700 °C

Degradación de barreras térmicas por sales fundidas

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