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Toward a Comprehensive Mechanistic Understanding of Hydrogen Uptake in Zirconium Alloys by Combining Atom Probe Analysis With Electronic Structure Calculations

Mikaela Lindgren (Institutionen för kemi och kemiteknik, Oorganisk miljökemi) ; Gustav Sundell (Institutionen för teknisk fysik, Materialens mikrostruktur ) ; Itai Panas (Institutionen för kemi och kemiteknik, Oorganisk miljökemi) ; Lars Hallstadius ; Mattias Thuvander (Institutionen för teknisk fysik, Materialens mikrostruktur ) ; Hans-Olof Andrén (Institutionen för teknisk fysik, Materialens mikrostruktur )
ASTM 17th International Symposium on Zirconium in the Nuclear Industry, Hyderabad, Andhra Pradesh, India, 3-7 February 2013 (0066-0558). Vol. STP 1543 (2015), p. 515-539.
[Konferensbidrag, refereegranskat]

The ability of a zirconium alloy to resist corrosion relies on a compromise between two opposing strategies. Minimizing the hydrogen pickup fraction (HPUF) by invoking metallic electron conduction in the barrier oxide results in rapid parabolic oxide growth. On the other hand, slow sub-parabolic barrier oxide growth, as reflected in rate limiting electron transport, may result in a high HPUF. The objective of the present study is to offer mechanistic insights as to how low concentrations of different alloying elements become decisive for the overall corrosion behavior. Combining atomistic microanalysis with first principles modeling by means of density functional theory, the speciation and redox properties of Fe and Ni towards hydrogen evolution are firstly explored. Complementary atom probe microanalysis at the metal–oxide interface provides evidence for Fe and Ni segregation to grain boundaries in Zircaloy-2 that propagates into the ZrO2 scale. Descriptors for how alloying elements in ZrO2 control electron transport as well as catalytic electron-proton recombination in grain boundaries to form H2 are determined by means of theory. The findings are generalized by further atomistic modeling, and are thus put in the context of early reports from autoclave experiments on HPUFs of zirconium with the alloying elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Nb. A shunting mechanism which combines inner and outer hydrogen evolution mechanisms is proposed. Properties of the transient zirconium sub-oxide are discussed. A plausible atomistic overall understanding emerges.

Nyckelord: corrosion, hydrogen pickup, density functional theory, atom probe tomography, zirconium, alloys, suboxide, hydride, HPU, HPUF



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Denna post skapades 2014-10-23. Senast ändrad 2016-05-26.
CPL Pubid: 204781

 

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