Surface morphology of diffusion aluminide coatings

Streiff, R.; Muamba, J.M. N'Gandu; Boone, D.H.

doi:10.1016/0040-6090(84)90013-0

Cited by 24 publications

(12 citation statements)

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“…pct in the aluminum source, the corresponding pack is usually called a highactivity pack. [1,2,3] Otherwise, the pack is referred to as a low-activity one. [1,2,3] Although high-activity coatings are normally developed in a two-step process, as mentioned earlier, there are also numerous reports of these coatings having been developed in a single step by carrying out aluminizing directly above 1000 ЊC.…”

Section: Introductionmentioning

confidence: 99%

“…[1,2,3] Otherwise, the pack is referred to as a low-activity one. [1,2,3] Although high-activity coatings are normally developed in a two-step process, as mentioned earlier, there are also numerous reports of these coatings having been developed in a single step by carrying out aluminizing directly above 1000 ЊC. [3][4][5][6][7][8][9][10] Such a method of forming the high-activity coatings appears attractive, because it eliminates one processing step and leads to the formation of the final NiAl coating structure in a single treatment, as in the case of a low-activity coating.…”

Section: Introductionmentioning

confidence: 99%

“…In the aluminizing step of a two-step process, which is usually carried out at a temperature in the range 700 ЊC to 850 ЊC, [1,[12][13][14][15][16][17] a layer of an aluminum-rich phase, which is usually Ni 2 Al 3 or a mixture of Ni 2 Al 3 and hyperstoichiometric NiAl, forms on the substrate. This is a result of predominant inward diffusion of aluminum from the pack, which causes the coating layer to grow into the substrate starting from its surface.…”

Section: Introductionmentioning

confidence: 99%

“…During the subsequent diffusion treatment, which is usually carried out above 1000 ЊC and that forms a part of the conventional LTHA process, [1,[12][13][14][15][16][17] the outward diffusion of nickel from the unaffected substrate takes place. This Ni reacts with the aluminum available from the top Al-rich layer (formed during the aluminizing step) to form an outwardly grown NiAl layer in a similar fashion as the development of the outer layer in an HTLA coating (ONL in Figure 1(b)).…”

Section: Introductionmentioning

confidence: 99%

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Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process

Das

Joshi

Singh

1998

Metall Mater Trans A

132

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This study deals with the aluminizing of a directionally cast Ni-base superalloy, namely CM-247, by a single-step process using a high-activity pack. It is observed that significant incorporation of Al into the substrate surface during aluminizing continues over a period of about 1 hour and is not restricted merely to the first few minutes, as reported in the literature. Based on the microstructural details of the coatings formed at various stages of aluminizing, it is concluded that the coating growth in the above process takes place primarily by inward Al diffusion initially, followed by an intermediate stage when the growth involves both inward Al and outward Ni diffusion. In the final stages, the outward diffusion of Ni dominates the coating formation process. The above mechanism of coating formation is different from the one that prevails in the conventional two-step high-activity coating process in that the reaction front for the formation of NiAl remains spatially stationary despite the outward diffusion of nickel during the intermediate stage. It is also shown in the present study that the content of the Al source in the pack affects the coating structure significantly. It is further demonstrated that the microstructure of the aluminide coatings depends not only on the amount of Al incorporated in the sample during aluminizing but also on the time over which the uptake of this Al takes place.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process

Das

Joshi

Singh

1998

Metall Mater Trans A

132

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“…Los aluminuros anteriormente descritos pueden ser modificados agregando otros elementos para aumentar su resistencia a la oxidación y/o a la corrosión por sales fundidas y, actualmente, en la industria, se emplean aluminuros modificados con silicio, cromo y platino, principalmente. Los aluminuros de platino se producen mediante electrodeposición de unos 7-8 mm de platino antes del proceso de aluminizado que, a su vez, se lleva a cabo por cementación o por CVD [18] . El recubrimiento resultante puede ser de dos tipos: con dos fases, de PtAl 2 y NiAl, cuando el aluminizado se lleva a cabo a 700 °C (Fig.…”

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High temperature corrosion resistant coatings for gas turbine components

Agüero

2007

Rev. metal.

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P Pa al la ab br ra as s c cl la av ve eOxidación. Corrosión. Recubrimientos. Generación eléctrica. Aeronáutica. Turbina.High temperature corrosion resistant coatings for gas turbine components A Ab bs st tr ra ac ct t Hot section gas turbine components are made of superalloys, developed to withstand high temperatures in conditions in which mechanical stresses are high and that require high surface stability. However, during the 50s it became evident that compositions resulting in high mechanical strength for these materials were not compatible with those offering optimal protection from the working environments. The idea of employing protective coatings over materials with high mechanical strength resulted therefore from this situation. Presently, both aeronautic and power generation turbines operate at temperatures within the 900-1400 °C, thanks to these coatings, indispensable for their correct operation. In this work, the principal degradation mechanisms in these operating conditions and the different type of coatings presently employed by the industrial sector are described, beginning by the oldest Ni or Co aluminides, following with the addition of other metals such as Pt, Cr, etc. to the former coatings in order to increase their useful life, continuing with the overlay MCrAlY coatings and finishing with the thermal barrier coating systems. Moreover, the corresponding deposition techniques industrially employed to deposit these coatings are described, and finally, an insight of the latest research lines currently being developed is also included.

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Effect of prealuminizing diffusion treatment on microstructural evolution of high-activity pt-aluminide coatings

Das

Singh

Joshi

2000

Metall Mater Trans A

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The effect of prealuminizing (or prior) diffusion treatment on the evolution of Pt-aluminide coatings on the Ni-based superalloy CM-247 has been studied by using a single-step, high-activity aluminizing process. Coatings generated without any prior diffusion treatment, as well as those formed by adopting two extreme prior-diffusion schedules (at 850 ЊC for 0.5 hours and at 1034 ЊC for 5 hours), were investigated by analyzing the coating structures at various stages of aluminizing. When the dilution of the Pt layer, caused by its interdiffusion with the substrate during the prior diffusion treatment, is only marginal (as in the case of no prior diffusion and diffusion at 850 ЊC for 0.5 hours), the equilibrium Pt-aluminide coating structure evolves through the formation of two transient layers during the initial stages of aluminizing. In contrast, for diffusion at 1034 ЊC for 5 hours, which results in extensive dilution of the Pt layer, the two-phase equilibrium structure (PtAl 2 in a matrix of NiAl) in the outer layer of the coating is found to develop during very early stages of aluminizing and remains unchanged, even over extended periods of aluminizing. Further, in the case of prior diffusion at 1034 ЊC for 5 hours, Pt is found to remain distributed to a greater extent over the entire thickness of the coating than in the cases of limited prior diffusion treatment. The present findings underline the significance of the nature of the prior-diffusion schedule on the microstructural evolution of Pt-aluminide coatings. It has also been found that a prealuminizing diffusion treatment is particularly important for Ptaluminide coatings from the point of view of coating adhesion to the substrate.

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Surface morphology of diffusion aluminide coatings

Cited by 24 publications

References 1 publication

Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process

Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process

High temperature corrosion resistant coatings for gas turbine components

Effect of prealuminizing diffusion treatment on microstructural evolution of high-activity pt-aluminide coatings

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