A study of yttrium‐modified aluminide coatings on IN 738 alloy

Tu, D.; Lin, Chun Chieh; Liao, S. J.; Chou, Jonq-Yeu

doi:10.1116/1.573734

Cited by 19 publications

(2 citation statements)

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“…[6,[10][11][12][13] Some coating work has been conducted to incorporate Y, Zr, and/or Hf during aluminizing by pack cementation or gas-phase pack. [11,14] Also, other hybrid methods have been pursued. [15,16] However, in actual manufacturing practice, these coating approaches are found to be unsuitable [17] because of inherent processing irreproducibility in terms of precisely controlling the dopant concentration and distribution in the coating matrix.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of Hf dopant incorporation during the early stage of chemical vapor deposition aluminide coating growth under continuous doping conditions

Kim

Meyer

et al. 2004

Metall Mater Trans A

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A laboratory-scale chemical vapor deposition (CVD) reactor was used to perform "continuous" Hf doping experiments while the surface of a single-crystal Ni alloy was being aluminized to form an aluminide (␤-NiAl) coating matrix for 45 minutes at 1150°C. The continuous doping procedure, in which HfCl 4 and AlCl 3 were simultaneously introduced with H 2 , required a high HfCl 4 /AlCl 3 ratio (Ͼϳ0.6) to cause the precipitation of Hf-rich particles (ϳ0.1 m) at grain boundaries of the coating layer, with the overall Hf concentration of ϳ0.05 to 0.25 wt pct measured in the coating layer by glow-discharge mass spectroscopy (GDMS). Below this ratio, Hf did not incorporate as a dopant into the growing coating layer from the gas phase, as the coating matrix appeared to be "saturated" with other refractory elements partitioned from the alloy substrate. In comparison, the Hf concentration in the aluminide coating layer formed on pure Ni was in the range of ϳ0.1 wt pct, which was close to the solubility of Hf estimated for bulk NiAl. Interestingly, the segregation of Hf and the formation of a thin ␥Ј-Ni 3 Al layer (ϳ0.5 m) at the coating surface were consistently observed for both the alloy and pure-Ni substrates. The formation of the thin ␥Ј-Ni 3 Al layer was attributed to an increase in the elastic strain of the ␤-NiAl phase, associated with the segregation of Hf as well as other refractory alloying elements at the coating surface. This phenomenon also implied that the coating layer was actually growing at the interface between the ␥Ј-Ni 3 Al layer and the ␤-NiAl coating matrix, not at the gas/coating interface, during the early stage of the coating growth.

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Section: Introductionmentioning

confidence: 99%

Mechanisms of Hf dopant incorporation during the early stage of chemical vapor deposition aluminide coating growth under continuous doping conditions

Kim

Meyer

et al. 2004

Metall Mater Trans A

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“…The beneficial effects of reactive elements such as Hf, Y, and Zr on the oxidation performance of Ni-based superalloys and coating materials have been well documented. [7][8][9][10][11][12][13] In this study, we examined a sequential Hf doping procedure, which consisted of (1) "prehafnizing" the alloy surface with HfCl 4 and H 2 , and (2) sequentially aluminizing with AlCl 3 and H 2 . Our major objectives were to (1) determine the effects of the prehafnizing procedure on the morphological development of the subsequent aluminide coating matrix and the distribution of Hf in the coating matrix and (2) compare the effectiveness of the sequential procedure to that of the continuous procedure that was previously studied.…”

Section: Introductionmentioning

confidence: 99%

Effects of prehafnizing on morphological development of a chemical vapor deposition aluminide coating formed on single-crystal Ni-based superalloy

Meyer

Lee

2004

Metall Mater Trans A

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We examined a sequential Hf doping procedure, which consisted of (1) "prehafnizing" the surface of a single-crystal Ni-based superalloy (RENÉ N5) with HfCl 4 and H 2 , and (2) aluminizing with AlCl 3 and H 2 , as a means of incorporating Hf as a dopant in the aluminide coating matrix. The prehafnized layer on RENÉ N5 substrate significantly altered the growth behavior and therefore the morphology of the resulting aluminide coating. With the prehafnizing step, the coating layer became much thinner with a significant amount of Hf incorporated as Hf-rich phases (Hf 2 Ni 7 , Hf 3 Ni 7 , and/or Hf 8 Ni 21 ). However, the Hf-rich phases segregated to the coating surface and retarded the inward Al diffusion required to form the ␤-NiAl coating matrix. The sequential Hf doping procedure provided a mechanism to incorporate a significant amount of Hf in the coating, but did not produce a uniform distribution of Hf as a dopant. The results were compared to those observed for a continuous doping procedure that was previously studied, and were discussed in the context of understanding the limitations of these procedures.

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Synthesis of Hf‐Doped CVD β‐NiAl Coating by Continuous Doping Procedure

Kim

Meyer

et al. 2001

Elevated Temperature Coatings

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A study of yttrium‐modified aluminide coatings on IN 738 alloy

Cited by 19 publications

References 0 publications

Mechanisms of Hf dopant incorporation during the early stage of chemical vapor deposition aluminide coating growth under continuous doping conditions

Mechanisms of Hf dopant incorporation during the early stage of chemical vapor deposition aluminide coating growth under continuous doping conditions

Effects of prehafnizing on morphological development of a chemical vapor deposition aluminide coating formed on single-crystal Ni-based superalloy

Synthesis of Hf‐Doped CVD β‐NiAl Coating by Continuous Doping Procedure

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