Effects of an Electroplated Platinum Interlayer on the Morphology and Phases of Chemically‐Vapor‐Deposited Alumina on Single‐Crystal, Nickel‐Based Superalloy

Su, Yi‐Feng; Torzilli, Michele A.; Meyer, J. D.; Rawn, Claudia J.; Lance, Michael J.; Ruppi, S.; Lee, Woo Y.

doi:10.1111/j.1151-2916.2002.tb00409.x

“…Also, the microcracks appearing on the TGO surface ( Figure 6(b)) could be attributed to the phase transformation of metastable Al 2 O 3 phases to the thermodynamically stable phase, ␣-Al 2 O 3 , as we have previously reported. [18,20] After 50 hours of oxidation, the classic duplex TGO microstructure was observed for this sample. It is known that there are three stages involved in an oxidation process: transient, steady, and breakaway stages.…”

Section: A Tgo Morphology Formed On Uncoated René N5mentioning

confidence: 99%

Effects of an α-Al2O3 thin film on the oxidation behavior of a single-crystal Ni-based superalloy

Su

¹

,

Lee

²

,

Allard

³

et al. 2004

Metall Mater Trans A

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A ϳ150-nm-thick coating layer consisting of ␣-Al 2 O 3 as the major phase with a minute amount of -Al 2 O 3 was deposited on the surface of a single-crystal Ni-based superalloy by chemical vapor deposition (CVD). Within 0.5 hours of oxidation at 1150°C, the resulting thermally grown oxide (TGO) formed on the coated alloy surface underwent significant lateral grain growth. Consequently, within this time scale, the columnar nature of the TGO became established. After 50 hours, a network of ridges was clearly observed on the TGO surface instead of equiaxed grains typically observed on the uncoated alloy surface. Comparison of the TGO morphologies observed with and without the CVD-Al 2 O 3 layer suggested that the transient oxidation of the alloy surface was considerably reduced. Also, the CVD-Al 2 O 3 layer significantly reduced the growth rate of the TGO and improved its spallation resistance, while slowing the internal oxidation of Ta-rich areas that were present in the superalloy as-casting defects. These results demonstrated that this thin ␣-Al 2 O 3 coating could be used as a means of favorably altering the TGO morphology and growth kinetics for no bond coat thermal barrier coating (TBC) applications.

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“…We have also previously observed whisker growth on a similar single-crystal Ni-based superalloy surface, unless the substrate was coated with a Pt interlayer. [11] Furthermore, we have recently observed that a very short preoxidation (ϳ1 minute) at 1050°C with a CO 2 ϩ H 2 gas mixture, prior to the CVD-Al 2 O 3 step, could be a practical way of significantly reducing the degree of whisker formation on the Ni-based superalloy surface. As we will report in this article, this observation motivated us to study (1) the effect of the CO 2 ϩ H 2 preoxidation on the surface nature of the single-crystal Nibased superalloy, and (2) the effect of this preoxidized layer on the nucleation and growth behavior of CVD ␣-Al 2 O 3 .…”

Section: Introductionmentioning

confidence: 99%

Effects of preoxidation on the nucleation and growth behavior of chemically vapor-deposited α-Al2O3 on a single-crystal Ni-based superalloy

He

¹

,

Su

²

,

Allard

³

et al. 2004

Metall Mater Trans A

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A chemical vapor deposition (CVD) procedure was developed for preparing a high-quality ␣-Al 2 O 3 coating layer on the surface of a single-crystal Ni-based superalloy using AlCl 3 , CO 2 and H 2 as precursors. A critical part of this procedure was a short-time preoxidation step (1 min) with CO 2 and H 2 in the CVD chamber, prior to introducing the AlCl 3 precursor. Without this preoxidation step, extensive whisker formation was observed on the alloy surface. Characterization results showed that the preoxidation step resulted in the formation of a continuous oxide layer (ϳ50 nm) on the alloy surface. The outer part of this layer (ϳ20 nm) appeared to contain mixed oxides, whereas the inner part (ϳ30 nm) mainly consisted of ␣-Al 2 O 3 grains with -Al 2 O 3 as a minor phase. We observed that the nucleation of ␣-Al 2 O 3 in the preoxidized layer was promoted by (1) rapid heating (10 seconds) of the alloy surface to the temperature region where ␣-Al 2 O 3 was expected to nucleate; (2) the low oxygen pressure environment of the preoxidation step, which kept the rate of oxidation low; and (3) contamination of the reactor chamber with HfCl 4 . The preoxidized layer served as an effective diffusion barrier for mitigating the interaction with some of the alloying elements such as Co and Cr with the CVD precursors and eliminating whisker formation on the alloy surface.

show abstract

Effects of preoxidation on the nucleation and growth behavior of chemically vapor-deposited α-Al2O3 on a single-crystal Ni-based superalloy

He

¹

,

Su

²

,

Lee

³

et al. 2004

Metall Mater Trans A

View full text Add to dashboard Cite

A chemical vapor deposition (CVD) procedure was developed for preparing a high-quality ␣-Al 2 O 3 coating layer on the surface of a single-crystal Ni-based superalloy using AlCl 3 , CO 2 and H 2 as precursors. A critical part of this procedure was a short-time preoxidation step (1 min) with CO 2 and H 2 in the CVD chamber, prior to introducing the AlCl 3 precursor. Without this preoxidation step, extensive whisker formation was observed on the alloy surface. Characterization results showed that the preoxidation step resulted in the formation of a continuous oxide layer (ϳ50 nm) on the alloy surface. The outer part of this layer (ϳ20 nm) appeared to contain mixed oxides, whereas the inner part (ϳ30 nm) mainly consisted of ␣-Al 2 O 3 grains with -Al 2 O 3 as a minor phase. We observed that the nucleation of ␣-Al 2 O 3 in the preoxidized layer was promoted by (1) rapid heating (10 seconds) of the alloy surface to the temperature region where ␣-Al 2 O 3 was expected to nucleate; (2) the low oxygen pressure environment of the preoxidation step, which kept the rate of oxidation low; and (3) contamination of the reactor chamber with HfCl 4 . The preoxidized layer served as an effective diffusion barrier for mitigating the interaction with some of the alloying elements such as Co and Cr with the CVD precursors and eliminating whisker formation on the alloy surface.Al 2 O 3 (s) ϩ 6HCl (g) ϩ 3CO (g) 2AlCl 3 (g) ϩ 3H 2 (g) ϩ 3CO 2 (g) →

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Effects of an Electroplated Platinum Interlayer on the Morphology and Phases of Chemically‐Vapor‐Deposited Alumina on Single‐Crystal, Nickel‐Based Superalloy

Cited by 4 publications

References 31 publications

Effects of an α-Al2O3 thin film on the oxidation behavior of a single-crystal Ni-based superalloy

Effects of an α-Al2O3 thin film on the oxidation behavior of a single-crystal Ni-based superalloy

Effects of preoxidation on the nucleation and growth behavior of chemically vapor-deposited α-Al2O3 on a single-crystal Ni-based superalloy

Effects of preoxidation on the nucleation and growth behavior of chemically vapor-deposited α-Al2O3 on a single-crystal Ni-based superalloy

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