Superlattice of the β phase in aluminized coatings on IN-713LC and MAR-M 247

Shen, Pouyan; Chou, Cheng‐Chun; Tsai, M.J.; Lin, Chun-Chu

doi:10.1016/0025-5416(87)90257-6

Cited by 4 publications

(4 citation statements)

References 4 publications

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“…As mentioned earlier, it is known that the high-activity aluminizing processes are usually carried out in two steps. [1,[12][13][14][15][16][17] The aluminizing in the present study, however, was carried out in a single step at 1034 ЊC. The microstructural evolution of the coatings formed by such a single-step process, as tracked by characterizing specimens aluminized for varying lengths of time, is discussed in this section.…”

Section: B Mechanism Of Coating Formation In a Single-step High-actimentioning

confidence: 99%

“…[12,13,[16][17][18] The type and exact chemistry of precipitates that form are, however, greatly dependent on the composition of the substrate superalloy. [2,16,18] From SEPMA analysis, the precipitates in the present case were found to contain W apart from Ni, Cr, and Al as the major elements. Figure 6 shows a few of these precipitates along with the corresponding X-ray dot maps of W, Cr, Ni, and Al.…”

Section: Phase Constitution Of the Coatingsmentioning

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

133

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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: B Mechanism Of Coating Formation In a Single-step High-actimentioning

confidence: 99%

Section: Phase Constitution Of the Coatingsmentioning

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

133

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High temperature oxidation of Ni2AlTi

Lee

Shen

1989

J Mater Sci

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The isothermal oxidation process in bulk and powdered Ni2AITi (L21 structure) has been studied in the temperature range of 600 to 1200°C in air by means of X-ray diffraction and scanning electron microscopy. At 900 and 1200 ° C, the transient oxides, NiO and TiO2 were formed in the initial stage on the outer surface. Subsequent oxidation was dominated by outward diffusion of aluminium, resulting in the formation of a Ni3Ti layer beneath an internal precipitation layer containing AI203-NiAI204 aggregates, NiTiO 3 and Ni3Ti. Formation of NiTiO3 and NiAI204 at the expense of NiO, Ti02 and AI203 indicated the reaction among constituent oxides also occurred in the late stage of oxidation at 900 and 1200 °c. Only NiO and TiOz were identified in specimens oxidized at 600°C up to 24h. The oxidation rate of NizAITi is of the same order of magnitude as the dilute y-NiAI alloy at 1200 °C. IntroductionAluminized coatings prepared on nickel-based superalloys by the pack cementation method provide better protection against high temperature oxidation and hot corrosion than do the uncoated substrates [1][2][3][4]. It was generally accepted that the interdiffusion between aluminium and nickel resulted in a/?-NiAI phase on the alloy surface which improved both the hot corrosion and the oxidation resistance [1, 2, 5]. According to metallographic, compositional and X-ray diffraction studies [1][2][3][4][5], high temperature oxidation resulted in the formation of the sesquioxide layer which resisted further oxidation of the aluminized coatings on superalloys. A recent transmission electron microscopy (TEM) study of the oxidation products of the aluminized coatings on Rene 80 indicated that the cubic oxides (RO and R304) and the sesquioxide (R203) , where R represents cations, have preferred orientation relationships to the gamma phase initially. However, such crystallographic relationships disappeared when the oxide particles were greater than a certain critical size [6]. Gamma phase, gamma prime phase and Ni2A1 phase were formed by the degradation of the beta phase in the coating and had preferred orientation relationships to the beta phase [6].Recent scanning transmission electron microscopy (STEM) studies of the aluminized coatings on the nickel-based superalloys of Ren6 80, INTI3LC and MAR-M247 showed that the beta matrix in diffusion zone may not necessarily be of B2 (NiAI) structure but can also be of L2~ (Ni2A1Ti) structure depending on the titanium content of the alloy [7,8]. The high temperature creep study of polycrystalline NizA1Ti [9] found that the creep strength of Ni2 A1Ti is about three times that of NiA1. The deformation behaviour of single-and polycrystaltine specimens of Ni2A1Ti were tested in compression in the temperature range 923 to 1283°K and the operative slip systems characterized

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Microstructures and crystallographic relationships in aluminized coatings on IN713LC and MAR-M247

Hwang

Shen

1987

Materials Science and Engineering

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Superlattice of the β phase in aluminized coatings on IN-713LC and MAR-M 247

Cited by 4 publications

References 4 publications

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 oxidation of Ni2AlTi

Microstructures and crystallographic relationships in aluminized coatings on IN713LC and MAR-M247

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