ISSN: 1546-962X
CODEN: JAIOAD
Published Online: 11 July 2011
Page Count: 16

Detailed Analysis of the Microstructure of the Metal/Oxide Interface Region in Zircaloy-2 after Autoclave Corrosion Testing

Tejland, Pia
Chalmers University of Technology,

Thuvander, Mattias
Chalmers University of Technology,

Andrén, Hans-Olof
Chalmers University of Technology,

Ciurea, Sorina
Sandvik Materials Technology,

Andersson, Thomas
Sandvik Materials Technology,

Dahlbäck, Mats
Westinghouse Electric Sweden,

Hallstadius, Lars
Westinghouse Electric Sweden,

(Received 28 January 2010; accepted 22 April 2011)

Abstract

Two varieties of Zircaloy-2, with different second phase particle (SPP) size distributions and different corrosion resistance, were oxidized in a steam autoclave. Transmission electron microscopy (TEM) of large thin-foil cross-sections of the oxide and the adjacent metal shows an undulating metal/oxide interface in both materials with a periodicity of slightly less than 1 μm and an amplitude of around 100 nm. The SPPs oxidize slower than the surrounding metal, and the absence of volume increase leads to void and crack formation as the SPPs become embedded in the oxide. On SPP oxidation, iron diffuses out of the particles into the surrounding oxide. A sub-oxide with an oxygen content of approximately 50 at. % and a layer thickness of about 200 nm was observed close to the metal/oxide interface. There is a 200 nm oxygen concentration gradient into the metal, from the level close to the sub-oxide of about 30 at. % down to a few atomic percent. All tin in the matrix is incorporated in the sub-oxide, and no segregation to the metal/oxide interface was found.

Keywords:
Zircaloy-2, sub-oxide, SPP, oxide crack, oxide void, atom probe, HAADF, TEM

Paper ID: JAI102956
DOI: 10.1520/JAI102956
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