Aluminide coating of iron

Heckel, R. W.; Yamada, Michio; Ouchi, Chiaki; Hickl, Anthony J.

doi:10.1016/0040-6090(77)90270-x

Cited by 15 publications

(23 citation statements)

References 7 publications

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“…The results of Heckel et al (8) have shown that phase is present on the surface between 1053 and 1273 K after the aluminizing of Fe in a pure A1 pack [NH4C1-activated + 35 weight percent (w/o)A1]. The ~ phase has a narrow composition range [70-72 atom percent (a/o)A1] and this value is consistent with present theoretical predictions.…”

Section: Discussionsupporting

confidence: 94%

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Surface Al Composition as a Result of the Pack Aluminizing of Iron

Akuezue

Stringer

1988

J. Electrochem. Soc.

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A method of estimating the surface concentration of A1 during aluminizing of pure Fe in NH4Cl-activated pure A1 pack at 1000-1400 K is presented. This model notes that a liquid phase is present on the surface of aluminizing iron specimens in a pack containing a pure aluminum source, and modifies earlier models to take account of the diffusion through this liquid layer. The new model results in predictions of surface composition in good agreement with experiment, and further shows that such a pack may behave as a "high activity" pack at low temperatures, and as a "low activity" pack at high temperatures.Pack aluminizing is a process in which A1 is diffusionally introduced into the surface of a metallic component using a halide species to transport the aluminum to the component surface. The aluminum-rich surface layer provides oxidation and corrosion resistance in severe high temperature environments. Initially, a powder mixture involving a source of aluminum, which may be a pure A1 or an appropriate aluminum-containing alloy; an activator, which is a halide salt, often NH4C1; and A1203, which acts as an inert diluent, are tumbled together S ~ as to obtain a thorough mixture. This pack mixture together with the components to be aluminized are placed in an iron retort or an A1203 crucible which must have either a gas-tight seal or a semiopen cover. This assembly is then placed in a furnace, in the ease of the semiopen coZcered vessel under an inert atmosphere. Pack aluminizing is usually carried out at temperatures in the range of 1023-1473 K.The first systematic attempt to relate the effect of pack variables to coating structure was that of Goward and Boone (1). The surface concentration of A1 after aluminizing is not identical with the pack A1 concentration, or that predicted by the corresponding phase equilibrium diagram, but falls below the pack concentration by various amounts depending primarily upon the pack AI activity and type of activator used (2, 3). The structure of packs using a pure aluminum source after coating reveals the presence of an Al-depleted zone in the pack next to the coated specimen (1-7). A semi-quantitative model of a saltactivated pack aluminizing process by Levine and Caves (2) proposes that gaseous A1 halides generated in the pack diffuse through the Al-depleted zone in the PaCk adjacent to the specimen surface and that the A1 activity at the coating surface is constant. Siegle et al.(3) predicted the surface A1 composition as a function of temperature in aluminized pure Ni by balancing the rate constants for diffusion in the solid phase, Ks, with that for the A1 deposition at the surface, Kg. A later model (4) considered activator depletion within the A1 depletion zone in the ease of condensable halides.In the analysis of the solid-state diffusional process during aluminizing, the pack is regarded as an infinite source of A1 which is transported to the surface of the sample through the porous medium represented by the diluent powder. It is important to be able to predict the surface c...

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Section: Discussionsupporting

confidence: 94%

“…These results, together with those of previous studies (1,8) have been used to develop and validate a simple model for the aluminizing process. ~Present address: Electric Power Research Institute, Pal0 Alto, California 94303.…”

Section: Aluminizing Modelmentioning

confidence: 58%

Surface Al Composition as a Result of the Pack Aluminizing of Iron

Akuezue

Stringer

1988

J. Electrochem. Soc.

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“…As an initial assessment of the diffusion behavior, modeling was attempted by applying an existing software program COSIM (coating oxidation and substrate interdiffusion model) developed by Nesbitt 9 and a simple mathematic model proposed by Heckel et al 10. COSIM implements a finite‐difference model and aims to model one‐dimensional, diffusional transport associated with high‐temperature oxidation and interdiffusion of overlay‐coated substrates.…”

Section: Introductionmentioning

confidence: 99%

Interdiffusional degradation of oxidation‐resistant aluminide coatings on Fe‐base alloys

Zhang

Liu

Pint

2007

Materials & Corrosion

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One of the potential degradation modes of oxidation-resistant iron aluminide coatings is the loss of Al from the coatings into Fe-base substrate alloys that typically contain no Al. To address this issue, interdiffusion between aluminide coatings and steel substrates was studied for times up to 10,000 h in the temperature range of 500-800 8C. Coatings were synthesized in a laboratory chemical vapor deposition (CVD) reactor on representative commercial ferritic alloy Fe-9Cr-1Mo and type 304L austenitic stainless steel. The microstructural and compositional changes after diffusion anneals were examined in detail. An initial attempt to model the interdiffusion behavior was carried out by applying an existing software program COSIM (coating oxidation and substrate interdiffusion model). Complementary work was conducted using a simple mathematic model developed by Heckel et al. Reasonable agreement was observed between the simulated and experimental composition profiles for the aluminide coatings on ferritic alloys. Model results were then applied to predict coating lifetime.

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“…Hickl and Heckel [2] reported a mathematical treatment of the diffusion process for the nickel aluminide coatings produced by pack cementation, which could predict the coating thickness and the surface composition. Later this was extended to iron aluminide coatings [3]. They assumed a two-step pack aluminizing process involving initial influx of aluminum in a high activity pack where a Ni 2 Al 3 (y) phase was formed and a subsequent partial homogenization under zero influx of aluminum, where, the required phase, NiAl (h) was produced at the surface.…”

Section: Introductionmentioning

confidence: 99%