High-temperature oxidation of two-phase nanocrystalline Ag-Cr alloys in 1 atm O-2

Citation
Y. Niu et al., High-temperature oxidation of two-phase nanocrystalline Ag-Cr alloys in 1 atm O-2, OXID METAL, 55(3-4), 2001, pp. 291-305
Citations number
46
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Metallurgy
Journal title
OXIDATION OF METALS
ISSN journal
0030-770X → ACNP
Volume
55
Issue
3-4
Year of publication
2001
Pages
291 - 305
Database
ISI
SICI code
0030-770X(200104)55:3-4<291:HOOTNA>2.0.ZU;2-A
Abstract
Two nanocystalline two-phase Ag-Cr alloys prepared bq: mechanical alloying and containing approximately 30 and 50 wt.% Cr were oxidized in I atm OZ at 700 and 800 degreesC. Under all conditions, a continuous layer of chromia formed at the surface of the alloys, in spite of the very low solubility of Cr in Ag. A laver of AgCrO2 also formed externally to the chromia layer. I n the case of the Ag-30 Cr alloy, some Ag particles were also present on th e scale, directly in contact with the gas phase. Moreover, Cr particles dis solved in the subsurface region of the alloy, while internal oxidation of C r, was absent. Ag-Cr alloys prepared by powder metallurgy with coarse grain si-es were able to form an irregular thin chromia layer only at a Cr conte nt of 69 wt.%, while an alloy containing 35 wt.% Cr corroded much more rapi dly than the nanocrystalline Ag-30Cr alloy. This difference in the scaling behavior is attributed to the large reduction in the alloy grain size, whic h favors the dissolution of tile Cr-rich particles in a Cr-depleted silver matrix and thus provides a faster supply of chromium from the alloy to the scale.