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Grain Boundary Chemistry and Transport Through Alumina Scales on NiAl Alloys

Torben Boll (Institutionen för fysik, Materialens mikrostruktur (Chalmers)) ; Kinga A. Unocic ; Bruce A. Pint ; Anders Mårtensson (Institutionen för kemi och kemiteknik, Polymerteknologi) ; Krystyna Stiller (Institutionen för fysik, Materialens mikrostruktur (Chalmers))
Oxidation of Metals (0030-770X). Vol. 88 (2017), 3-4, p. 469-479.
[Artikel, refereegranskad vetenskaplig]

It is widely accepted that the growth of protective ?-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.

Nyckelord: Atom probe tomography, Diffusion, Grain boundaries, Oxidation, Reactive elements



Denna post skapades 2017-10-04. Senast ändrad 2017-10-05.
CPL Pubid: 252240

 

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