Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

Torben Boll; Kinga A. Unocic; Bruce A. Pint; Anders Mårtensson; Krystyna Stiller

doi:10.1007/s11085-016-9697-x

Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

Torben Boll, Kinga A. Unocic, Bruce A. Pint, Anders Mårtensson, Krystyna Stiller

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

13 Scopus citations

Abstract

It is widely accepted that the growth of protective α-Al₂O₃ scales on Ni-based alloys is governed by the inward diffusion of oxygen through the oxide grain boundaries (GB). However, there is also some outward diffusion of metal ions to the surface, but it is difficult to quantify. In this work we apply atomic force microscopy, scanning electron microscopy and transmission electron microscopy to investigate the outward flux of Al, which manifests as the growth of small ridges along the alumina GBs after the removal of the outermost oxide layer by mechanical polishing or focused ion beam techniques followed by additional oxidation. As a model alumina-former, NiAl with Hf and Zr additions was investigated. In comparison to Zr, Hf was found to reduce the outward Al diffusion. This outward diffusion was six orders of magnitude smaller than the O inward diffusion.

Original language	English
Pages (from-to)	469-479
Number of pages	11
Journal	Oxidation of Metals
Volume	88
Issue number	3-4
DOIs	https://doi.org/10.1007/s11085-016-9697-x
State	Published - Oct 1 2017

Funding

The authors would like to thank Patrik Alnegren and Kristina Hellström from Chalmers for help with the oxidations exposures and Tracie Lowe, Adam W. Willoughby, Michael S. Stephens from ORNL for assistance with experimental work. This research is supported by Swedish Energy Agency.

Funders	Funder number
Energimyndigheten

Keywords

Atom probe tomography
Diffusion
Grain boundaries
Oxidation
Reactive elements

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abstract = "It is widely accepted that the growth of protective α-Al2O3 scales on Ni-based alloys is governed by the inward diffusion of oxygen through the oxide grain boundaries (GB). However, there is also some outward diffusion of metal ions to the surface, but it is difficult to quantify. In this work we apply atomic force microscopy, scanning electron microscopy and transmission electron microscopy to investigate the outward flux of Al, which manifests as the growth of small ridges along the alumina GBs after the removal of the outermost oxide layer by mechanical polishing or focused ion beam techniques followed by additional oxidation. As a model alumina-former, NiAl with Hf and Zr additions was investigated. In comparison to Zr, Hf was found to reduce the outward Al diffusion. This outward diffusion was six orders of magnitude smaller than the O inward diffusion.",

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Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

Abstract

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Keywords

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