Characterization of the alumina scale formed on coated and uncoated doped superalloys

K. A. Unocic; C. M. Parish; B. A. Pint

doi:10.1016/j.surfcoat.2011.07.044

Characterization of the alumina scale formed on coated and uncoated doped superalloys

K. A. Unocic, C. M. Parish, B. A. Pint

Research output: Contribution to journal › Article › peer-review

30 Scopus citations

Abstract

To investigate the mechanisms by which Y and La dopants affect the oxidation behavior of Ni-base single-crystal superalloys, the oxide scales formed on two variants of a commercial X4 alloy, each with and without a MCrAlYHfSi coating were characterized. The alloy systems were oxidized for 100h at 1100°C and then examined using analytical transmission electron microscopy. Without a coating, a duplex scale was formed on the superalloy surface comprised of an outer Ni-rich spinel-type layer and an inner columnar α-Al₂O₃ layer. In this case, Hf and Ti were found segregated to the alumina grain boundaries in the outer part of the scale on both alloys but only Hf was detected near the metal-alumina interface. There was no evidence of Ta, Y or La segregation to the alumina scale grain boundaries after this exposure. The scale formed on the alloys with the thermally sprayed coating was primarily alumina, and Y and Hf segregated to the alumina grain boundaries for both alloys. There was evidence of Ti-rich oxides in the outer part of the scale indicating that Ti had diffused through the coating into the thermally grown oxide but La was not found.

Original language	English
Pages (from-to)	1522-1528
Number of pages	7
Journal	Surface and Coatings Technology
Volume	206
Issue number	7
DOIs	https://doi.org/10.1016/j.surfcoat.2011.07.044
State	Published - Dec 25 2011

Funding

The coatings were deposited at Stonybrook Univ. with assistance from Prof. C. Weyant. At ORNL, H. Longmire, M. Howell, T. Lowe, D. Coffey, R.A. Meisner and L. Walker assisted with the experimental work. Authors also thank L.F. Allard Jr. and S. Dryepondt for providing useful comments and discussions. The authors are grateful to J. Caola, C. Henry and L. Fu, of FEI, Hillsboro, OR for the use of the Tecnai Osiris TEM/STEM. This research was sponsored by the U.S. Department of Energy , Office of Coal and Power R&D , Office of Fossil Energy , (R. Dennis program manager), and the SHaRE User Facility, sponsored by the Scientific User Facilities Division , Office of Basic Energy Sciences , and the U.S. Department of Energy.

Funders	Funder number
Office of Coal and Power R&D
Scientific User Facilities Division
U.S. Department of Energy
Office of Fossil Energy
Basic Energy Sciences

Keywords

Alumina
Bond coat
HVOF
Segregation
Superalloy MCrAlY

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10.1016/j.surfcoat.2011.07.044

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title = "Characterization of the alumina scale formed on coated and uncoated doped superalloys",

abstract = "To investigate the mechanisms by which Y and La dopants affect the oxidation behavior of Ni-base single-crystal superalloys, the oxide scales formed on two variants of a commercial X4 alloy, each with and without a MCrAlYHfSi coating were characterized. The alloy systems were oxidized for 100h at 1100°C and then examined using analytical transmission electron microscopy. Without a coating, a duplex scale was formed on the superalloy surface comprised of an outer Ni-rich spinel-type layer and an inner columnar α-Al2O3 layer. In this case, Hf and Ti were found segregated to the alumina grain boundaries in the outer part of the scale on both alloys but only Hf was detected near the metal-alumina interface. There was no evidence of Ta, Y or La segregation to the alumina scale grain boundaries after this exposure. The scale formed on the alloys with the thermally sprayed coating was primarily alumina, and Y and Hf segregated to the alumina grain boundaries for both alloys. There was evidence of Ti-rich oxides in the outer part of the scale indicating that Ti had diffused through the coating into the thermally grown oxide but La was not found.",

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AU - Parish, C. M.

AU - Pint, B. A.

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N2 - To investigate the mechanisms by which Y and La dopants affect the oxidation behavior of Ni-base single-crystal superalloys, the oxide scales formed on two variants of a commercial X4 alloy, each with and without a MCrAlYHfSi coating were characterized. The alloy systems were oxidized for 100h at 1100°C and then examined using analytical transmission electron microscopy. Without a coating, a duplex scale was formed on the superalloy surface comprised of an outer Ni-rich spinel-type layer and an inner columnar α-Al2O3 layer. In this case, Hf and Ti were found segregated to the alumina grain boundaries in the outer part of the scale on both alloys but only Hf was detected near the metal-alumina interface. There was no evidence of Ta, Y or La segregation to the alumina scale grain boundaries after this exposure. The scale formed on the alloys with the thermally sprayed coating was primarily alumina, and Y and Hf segregated to the alumina grain boundaries for both alloys. There was evidence of Ti-rich oxides in the outer part of the scale indicating that Ti had diffused through the coating into the thermally grown oxide but La was not found.

AB - To investigate the mechanisms by which Y and La dopants affect the oxidation behavior of Ni-base single-crystal superalloys, the oxide scales formed on two variants of a commercial X4 alloy, each with and without a MCrAlYHfSi coating were characterized. The alloy systems were oxidized for 100h at 1100°C and then examined using analytical transmission electron microscopy. Without a coating, a duplex scale was formed on the superalloy surface comprised of an outer Ni-rich spinel-type layer and an inner columnar α-Al2O3 layer. In this case, Hf and Ti were found segregated to the alumina grain boundaries in the outer part of the scale on both alloys but only Hf was detected near the metal-alumina interface. There was no evidence of Ta, Y or La segregation to the alumina scale grain boundaries after this exposure. The scale formed on the alloys with the thermally sprayed coating was primarily alumina, and Y and Hf segregated to the alumina grain boundaries for both alloys. There was evidence of Ti-rich oxides in the outer part of the scale indicating that Ti had diffused through the coating into the thermally grown oxide but La was not found.

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KW - HVOF

KW - Segregation

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Characterization of the alumina scale formed on coated and uncoated doped superalloys

Abstract

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Keywords

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