Some aspects of elemental behaviour in HVOF MCrAlY coatings in high-temperature oxidation

Yuan, Kun; Peng, Ru Lin; Li, Xinhai; Johansson, Sten; Wang, Yandong

doi:10.1016/j.surfcoat.2014.11.053

Cited by 67 publications

(26 citation statements)

References 72 publications

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“…The progressive loss of Al causes the β phase to deplete at the coating surface, leading to the microstructural instability of the coating [13][14][15]. The loss of β phase also occurs at the coating/substrate interface due to the interdiffusion between the coating and substrate [16][17][18][19][20][21][22][23][24][25][26][27]. Eventually, the MCrAlY coating becomes non-protective when the complete loss of the β phase occurs.…”

Section: Introductionmentioning

confidence: 99%

Some aspects on modelling of the β-phase depletion behaviour under different oxide growth kinetics in HVOF CoNiCrAlY coatings

Chen

McCartney

2017

Surface and Coatings Technology

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In this paper, β-phase depletion behaviour of free-standing high velocity oxy-fuel (HVOF) thermally sprayed CoNiCrAlY coatings was studied. Microstructural analysis showed a twophase microstructure of γ-Ni matrix and β-NiAl secondary phase after heat treatment. Fine grains were found around the sprayed particle boundaries and coarse grains were retained as the original particle structure, with grain sizes varying from 2 to 0.5 µm or even less for both phases. The β-phase depletion behaviour was investigated during isothermal oxidation and was also modelled through diffusion calculations. A previously developed β-phase depletion model was utilised to study the evolution of β-phase depletion under different oxide growth kinetics. Three oxide growth models were tried: 1) Meier model, 2) thermogravimetric analysis (TGA) model, and 3) experimentally fitted oxide growth model. The oxide growth kinetics were converted to Al flux functions which were used as the boundary conditions in the DICTRA modelling. It is shown that the results obtained from the three models exhibit good agreements between the measured and predicted results for times up to 100 h at 1100 C, but discrepancies were noted at longer oxidation times. Further improvements on closely 2 modelling the oxidation kinetics and the effective diffusion behaviour are needed to minimise the discrepancies at longer oxidation times.

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Section: Introductionmentioning

confidence: 99%

Some aspects on modelling of the β-phase depletion behaviour under different oxide growth kinetics in HVOF CoNiCrAlY coatings

Chen

McCartney

2017

Surface and Coatings Technology

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“…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.…”

mentioning

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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“…With the effect of high temperature, the particles are still oxidized in flight and during the deposition on the substrate material. 10 Using the APS method, there are many internal oxide formations in the coating because of the excessively high temperatures due to plasma during the deposition of the coating. Since the concentration of the Y element is much lower than those of the other elements, Y can be entirely depleted.…”

Section: Thermal-cycling Test Of the Coated Specimensmentioning

confidence: 99%

Thermal-cycling behavior of CoNiCrAlY bonds coated with thermal barrier coatings (TBCs) produced with atmospheric plasma spraying (APS)

Kaplan¹,

Uyaner²,

Karaoğlanlı³

2017

Mater. Tehnol.

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Thermal barrier coatings (TBCs) are commonly applied as a thermal insulation in order to protect against environmental influences in the components of high-temperature gas turbines and jet engines. Gas-turbine components are affected by aggressive conditions of the environment during the service, being subjected to failures such as corrosion, thermal shock and oxidation. Plasma-spray technology is used to produce metallic bonds and ceramic top coats as a cost-effective method to prolong the lifetime of TBCs. In the present research, CoNiCrAlY bond-coat and YSZ top-coat powders included in the TBCs were deposited onto Inconel 718 superalloy substrates using atmospheric plasma spraying (APS). The TBCs were exposed to a furnace cycling test at 1150°C and one-hour cycles. The presence of porosity and cracks facilitating the diffusion of oxygen in the top-coating structure led to the formation of thermally grown oxides (TGOs) at the interface. In addition, the most effective factors of failures were the formation and growth of mixed oxides at the bond/top-coat interface and the presence of imperfections. According to the test results, an increasing number of thermal cycles resulted in a decrease in the lifetime of the TBCs related to the sintering of the top coating due to the effect of high temperature. Keywords: thermal barrier coatings (TBCs), thermal cycling, Inconel 718 superalloy, atmospheric plasma spraying (APS), CoNiCrAlY, ytrria-stabilized zirconia (YSZ) Prevleke s toplotno pregrado (angl. TBCs) se obi~ajno uporabljajo kot toplotna izolacija, ki {~iti komponente visoko temperaturnih plinskih turbin ali reaktivnih motorjev. Na komponente plinskih turbin vplivajo agresivni vplivi okolja, katerim so izpostavljene med obratovanjem, zato pride do okvar, kot so: korozija, termi~ni {ok in oksidacija. Tehnologija plazemskega napr{evanja je cenovno ugodna tehnologija za izdelavo kovinskih in kerami~nih prevlek. V~lanku avtorji predstavljajo raziskavo v kateri sta bila na podlago iz zlitine Inconel 718 s tehnologijo plazemskega napr{evanja v zra~ni atmosferi nane{ena vezivna prevleka CoNiCrAlY in prekrivni sloj iz YSZ prahu. Izdelani prevleki sta bili nato izpostavljeni termi~nem utrujanju v pe~i pri 1150°C z ve~imi enournimi cikli. Prisotnost poroznosti in razpok olaj{a difuzijo kisika v zgornjo plast prevleke kar vodi do nastanka termi~no induciranega oksida (TGO) na povr{ini prevleke. Poleg tega sta bila najpomembnej{a dejavnika za nastanek napak tvorba me{anih oksidov na meji med vezno in vrhno plastjo ter prisotnost drugih nepravilnosti. Rezultati preizkusov so pokazali, da pove~anje {tevila termi~nih ciklov zmanj{uje dobo trajanja TBC prevlek, zaradi sintranja zgornje plasti pri povi{anih temperaturah. Klju~ne besede: prevleke s toplotno pregrado, toplotni (termi~ni) cikel, superzlitina Inconel 718, plazemsko napr{evanje, CoNiCrAlY, cirkon stabiliziran z itrijem

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Some aspects of elemental behaviour in HVOF MCrAlY coatings in high-temperature oxidation

Cited by 67 publications

References 72 publications

Some aspects on modelling of the β-phase depletion behaviour under different oxide growth kinetics in HVOF CoNiCrAlY coatings

Some aspects on modelling of the β-phase depletion behaviour under different oxide growth kinetics in HVOF CoNiCrAlY coatings

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

Thermal-cycling behavior of CoNiCrAlY bonds coated with thermal barrier coatings (TBCs) produced with atmospheric plasma spraying (APS)

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