Potential thermal barrier coating systems from Al microparticles. Mechanisms of coating formation on pure nickel

Pedraza, F.; Mollard, M.; Rannou, B.; Balmain, J.; Bouchaud, B.; Bonnet, Gilles

doi:10.1016/j.matchemphys.2012.03.053

Cited by 40 publications

(42 citation statements)

References 29 publications

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“…This research was focused on the changes taking place in aluminium particles to be used in slurries to aluminize stainless steels and Ni-base superalloys [9][10][11]. A more environmentally-friendly approach for slurries is investigated within the European project ''Particoat' ' [12], in which Al microparticles (1-20 lm) are added to simple mixtures of water (solvent) and organic binders [13] with no additional chemical compounds.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of Micro-Sized Aluminium Particles: Hollow Alumina Spheres

et al. 2013

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Oxidized aluminium microparticles have recently been proposed for manufacturing new, environmentally-friendly, protective coatings on stainlesssteels and Ni-base alloys. The oxidation mechanisms of spherical aluminium microparticles of an average particle size of 3.5 lm were studied. Accordingly, simultaneous differential thermal analysis-thermogravimetry tests were carried out in air at different temperatures, always above aluminium melting temperature. Scanning electron microscopy and XRD were also used for the interpretation of results. Weight gain and energy results were explained in terms of the different structural changes taking place in aluminium particles. Dehydroxylation process was identified. The transformation of amorphous alumina to c-Al 2 O 3 was numerically evaluated and the alumina phase transformation (c-Al 2 O 3 ?a-Al 2 O 3 ) was also studied. The temperature ranges revealed the appearance of metastable phases (h-Al 2 O 3 ). Complete oxidation of particles can be obtained at 1,300°C in \1 h, although this also takes place at lower temperatures if enough oxidation time is used. Activation energy of oxidation process at high temperature was also estimated, taking a value of 334 kJ/mol. High temperature oxidation causes the formation of hollow alumina spheres, without any aluminium left inside them.

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Section: Introductionmentioning

confidence: 99%

Oxidation of Micro-Sized Aluminium Particles: Hollow Alumina Spheres

et al. 2013

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“…2. Such mechanisms were thoroughly described in previous works [4,12,13]. Once the slurry containing the passivated Al microparticles is dried and annealing at sufficiently high temperatures starts, the phase transformation of the alumina shell surrounding the Al particles results in cracks through which Al diffuses out and wets the Ni-based substrate [4].…”

Section: Resultsmentioning

confidence: 95%

“…Such mechanisms were thoroughly described in previous works [4,12,13]. Once the slurry containing the passivated Al microparticles is dried and annealing at sufficiently high temperatures starts, the phase transformation of the alumina shell surrounding the Al particles results in cracks through which Al diffuses out and wets the Ni-based substrate [4]. Then, Ni dissolves in molten Al [12] and the subsequent greatly exothermic reactions between Al and Ni bring about the synthesis of the Alrich nickel aluminides by a self-propagating combustion mechanism [13].…”

Section: Resultsmentioning

confidence: 99%

“…After spray onto four nickel-based superalloys with different composition and crystal structure (Table 1) and dry in air, the slurries were annealed at 700°C/2 h and additional 1100°C/2 h in Ar(g). The traces of O 2 (2 vpm) and H 2 O (5 vpm) in Ar were shown to be sufficient to grow the [4]. The slurry TBCs were compared with industrially manufactured low activity out-of-pack (70Cr-30Al donor, NH 4 F activator, treated at 1080°C for 6 h in vacuum) and high activity pack cemented (60Cr-40Al donor, NaCl activator, Al 2 O 3 filler treated at 860°C for 6 h in argon and subsequently annealed at 1120°C for 2 h in vacuum).…”

Section: Methodsmentioning

confidence: 99%

“…This system is often based on a top ceramic coat of yttria stabilized zirconia (YSZ) made by electron beam physical vapour deposition (EB-PVD) with columnar structure to comply with thermal cycling, an intermediate aAl 2 O 3 thermally grown oxide (TGO) to attach the YSZ and to provide oxidation protection and an underlying b-NiPtAl diffusion coating that acts as an aluminium reservoir [1]. New low-cost and environmentally friendly coatings were recently proposed in the European project ''Particoat'' [2] in which a water-based slurry containing Al microparticles was sprayed and annealed [3] onto pure nickel [4] and different nickel-based superalloys [5] or steels [6]. The isothermal oxidation behaviour of these coatings onto a pure Ni [7] and a René N5 superalloy [8] indicated faster oxidation kinetics and faster b-NiAl ?…”

Section: Introductionmentioning

confidence: 99%

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Oxidation Resistance of Thermal Barrier Coatings Based on Hollow Alumina Particles

et al. 2015

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Thermal barrier coatings were synthesized in a single step process from a slurry containing Al microspheres onto different Ni-based superalloys. Upon growth of the coating a top coat of hollow alumina spheres linked to an aluminium diffused coating through an alumina TGO formed. The isothermal and cyclic oxidation tests at different temperatures (900 till 1100°C) up to 1000 h or 1500 cycles revealed progressive growth of different thermal oxides depending on the substrate composition. Faster degradation of the coatings occurred in the titanium-rich substrates (e.g. IN-738LC and PWA1483) compared to the titanium-poor ones (CM-247LC and René N5). By comparing with conventional low activity aluminide coatings, it appeared that the incorporation of alloying elements (notably Ti and Ta) to the diffused layers upon the high activity slurry coating process is responsible for such fastest degradation.

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Influence of water vapour on the oxidation behaviour of a conventional aluminide and a new thermal barrier coating system sintered from a slurry

Brossard

Bouchaud

Pedraza

2013

Materials & Corrosion

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In this work, the effect of water vapour on a new thermal barrier coating system synthesised from a slurry containing Al microparticles was studied under isothermal regime at 1100 °C for short oxidation times (50 h). Both dry air and argon gas atmospheres were investigated with increasing water vapour contents (0, 5, 10% RH, relative humidity) and the oxidation mechanisms and growth kinetics of the oxide scales were compared to conventional aluminide coatings up to 50% RH. The phase transformations occurring in the coating were characterised by local Raman micro‐spectrometry with complementary analytical techniques (X‐ray diffraction and FEG‐ESEM/EDS). The results demonstrated that water vapour does not exert a great influence on the oxidation of this type of coatings once an α‐Al2O3 scale is stabilised after an appropriate sintering of the coating. In contrast the combined effect of water vapour and oxidation onto oxide scales grown from raw aluminide coatings was shown to trigger delayed transformation of θ into α‐Al2O3, the appearance of pores and spallation, in particular in air + x %RH.

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Potential thermal barrier coating systems from Al microparticles. Mechanisms of coating formation on pure nickel

Cited by 40 publications

References 29 publications

Oxidation of Micro-Sized Aluminium Particles: Hollow Alumina Spheres

Oxidation of Micro-Sized Aluminium Particles: Hollow Alumina Spheres

Oxidation Resistance of Thermal Barrier Coatings Based on Hollow Alumina Particles

Influence of water vapour on the oxidation behaviour of a conventional aluminide and a new thermal barrier coating system sintered from a slurry

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