Microstructure evolution of vacuum plasma sprayed CoNiCrAlY coatings after heat treatment and isothermal oxidation

Poza, P.; Grant, Patrick S.

doi:10.1016/j.surfcoat.2006.06.001

Cited by 65 publications

(21 citation statements)

References 26 publications

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“…High surface roughness increases the specific surface area for oxidation and also reduces the adhesion of the oxide scale during long-term service, as previously investigated [23]. The formation of mixed oxides has been also found in MCrAlY coatings deposited under vacuum atmosphere or by HVOF spraying and aged at 1000-1100 °C [24][25][26] and cannot be totally prevented, so that it is an important key issue to reduce their growth and to have a well adherent and dense oxide scale mostly composed of Al2O3 with low oxygen diffusivity, and able to reduce permeation of Ni and Cr as well as further oxygen infiltration. For this purpose the NiCoCrAlYRe particles have been herein processed to fabricate coatings with the above mentioned two phase structure, by reducing in-flight oxidation at their external surface and thus preventing Al depletion.…”

Section: Resultssupporting

confidence: 60%

Morphology and Microstructure of NiCoCrAlYRe Coatings after Thermal Aging and Growth of an Al2O3-Rich Oxide Scale

Girolamo

Brentari²,

Serra

2014

Coatings

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Abstract:The surface of metal parts operating at high temperature in energy production and aerospace industry is typically exposed to thermal stresses and oxidation phenomena. To this aim, plasma spraying was employed to deposit NiCoCrAlYRe coatings on metal substrates. The effects of early-stage oxidation, at ~1100 °C, on their microstructure were investigated. The partial infiltration of oxygen through some open pores and microcracks embedded in coating microstructure locally assisted the formation of a stable Al2O3 scale at the splat boundary, while the diffusion of Cr and Ni and the following growth of Cr2O3, Ni(Cr,Al)2O4 and NiO were restricted to Al depleted isolated areas. At the same time, a continuous, dense and well adherent Al2O3 layer grew on the top-surface, and was somewhere supported by a thin mixed oxide scale mainly composed of Cr2O3 and spinels. Based on these results, the addition of Re to the NiCoCrAlY alloy is able to enhance the oxidation resistance.

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Section: Resultssupporting

confidence: 60%

Morphology and Microstructure of NiCoCrAlYRe Coatings after Thermal Aging and Growth of an Al2O3-Rich Oxide Scale

Girolamo

Brentari²,

Serra

2014

Coatings

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“…It is widely recognised that the growth of the TGO during service causes progressive build-up of stress in the system, leading to the spallation of the ceramic top coat and eventually causing detrimental effects to the turbine engine components [20][21][22]. The continuous growth of the TGO due to aluminium diffusion from the MCrAlY bond coat results in subsequent  phase depletion at the oxide/bond coat interface [23][24][25][26][27][28], causing mechanical and chemical degradation of the coating. Degradation of the bond coat also occurs due to interdiffusion of element between the MCrAlY and the superalloy substrate.…”

Section: Introductionmentioning

confidence: 99%

Modelling and experimental study on β-phase depletion behaviour of HVOF sprayed free-standing CoNiCrAlY coatings during oxidation

Chen

Jackson

Voisey

et al. 2016

Surface and Coatings Technology

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This paper investigates the β-phase depletion behaviour during oxidation of free-standing CoNiCrAlY (Co-31.7%Ni-20.8%Cr-8.1%Al-0.5%Y, all in wt%) bond coats prepared by high velocity oxy-fuel (HVOF) thermal spraying. The microstructure of the coatings was characterised using scanning electron microscopy with energy dispersive X-ray (EDX) analysis and electron backscatter diffraction (EBSD). It comprises a two phase structure of fcc-Ni and bcc -NiAl, with grain sizes varying largely from 0.5 to 2 µm for both phases.Isothermal oxidation tests of the free-standing coatings were carried out at 1100 C for times up to 250 h. The phase depletion behaviour at the surface was measured and was also simulated using Thermo-Calc and DICTRA software. An Al flux function derived from an oxide growth model was employed as the boundary condition in the diffusion model. The diffusion calculations were performed using the TTNi7 thermodynamic database together with the MOB2 mobility database. Reasonable agreement was achieved between the measured and the predicted element concentration and phase fraction profiles after various 2 time periods. Grain boundary diffusion is likely to be important to element diffusion in this HVOF sprayed CoNiCrAlY coating due to the sub-micron grains. Keywords IntroductionThermal barrier coatings (TBCs) are widely used to protect high temperature components in turbine engines from harsh operating environments [1,2]. TBC systems consist of a ceramic top coat, a metallic bond coat and a superalloy substrate [3][4][5]. Additionally, a thermally grown oxide (TGO) forms at the interface between the top coat and the bond coat during service at elevated temperature due to the fact that oxygen permeates through the ceramic top coat and oxidises the bond coat. The durability of the overall TBC system is largely determined by the microstructural, chemical and mechanical characteristics of the bond coat due to interdiffusion of element between the MCrAlY and the superalloy substrate. This is not considered in the present paper but has been studied by others, e.g. [29][30][31][32][33][34][35][36][37][38][39][40][41]. In these research works, the emphasis has been on substrate/bond coat interdiffusion and specific comparisons between measured and predicted β-phase depletion at the oxide/bond coat interface have not been considered. On the other hand, several analytical models concerned with the oxidation of 4 two phase systems in which the secondary phase dissolves during oxidation have been reported, e.g. [42][43][44][45][46][47][48]. In these models, the secondary phase depletion behaviour during oxidation can generally be represented by the parabolic diffusion law, Eq. (1), ~√( 1) where is the width of the second phase depletion zone and is the oxidation time.Considering the significance of β depletion on the degradation of TBCs, therefore, the aims of the work reported in this paper were to investigate specifically the kinetics of β depletion at the oxide surface in free-standing MCrAlY coatings ...

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“…The accumulation of these low melting-point salts from flue-gas containing sulfates of sodium and potassium on the fire side surface of boiler tubes induces hot corrosion and is considered a root cause for the severe wastage of tube materials used for superheaters and reheaters in ''advanced'' steam-generating systems [4]. The continuing development of modern energy generation systems requires materials capable of withstanding increasing operating temperatures, mechanical loads and chemical degradation [5]. It is not possible for a single material to have different properties to meet the demand of today's industry.…”

Section: Introductionmentioning

confidence: 99%

Characterisation and Corrosion-Erosion Behaviour of Carbide based Thermal Spray Coatings

Chatha¹,

Sidhu²,

Sidhu³

2012

JMMCE

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Microstructure evolution of vacuum plasma sprayed CoNiCrAlY coatings after heat treatment and isothermal oxidation

Cited by 65 publications

References 26 publications

Morphology and Microstructure of NiCoCrAlYRe Coatings after Thermal Aging and Growth of an Al2O3-Rich Oxide Scale

Morphology and Microstructure of NiCoCrAlYRe Coatings after Thermal Aging and Growth of an Al2O3-Rich Oxide Scale

Modelling and experimental study on β-phase depletion behaviour of HVOF sprayed free-standing CoNiCrAlY coatings during oxidation

Characterisation and Corrosion-Erosion Behaviour of Carbide based Thermal Spray Coatings

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