The high temperature oxidation of a two-phase Ag-Y alloy under 1 and 10(-20) atm O-2

Citation
Y. Niu et al., The high temperature oxidation of a two-phase Ag-Y alloy under 1 and 10(-20) atm O-2, J ALLOY COM, 317, 2001, pp. 573-577
Citations number
30
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
JOURNAL OF ALLOYS AND COMPOUNDS
ISSN journal
0925-8388 → ACNP
Volume
317
Year of publication
2001
Pages
573 - 577
Database
ISI
SICI code
0925-8388(20010412)317:<573:THTOOA>2.0.ZU;2-B
Abstract
A silver-based alloy containing about 8 wt% Y (Ag-8Y) has been oxidized und er 1 atm and 10(-20) atm O-2 at 700 degreesC. The alloy contains a mixture of a solid solution of Y in Ag (alpha phase) with an eutectic mixture of th e alpha phase with the intermetallic compound Ag51Y14 (beta phase). The oxi dation rate in 1 atm O-2 is very fast and follows the parabolic rate law to a good approximation. Oxidation under low P(O-2) is much slower and quite- irregular with large deviations from an average parabolic behavior. Under 1 atm O-2 the alloy undergoes only an internal oxidation of Y without any s ignificant outward Y diffusion. as a result of a fast oxygen penetration. U nder low P(O-2) the alloy forms an almost continuous Y2O3 layer containing Ag particles, plus a region of internal oxidation of Y much thinner than in 1 atm O-2. In bath cases the alloy forms also an external layer of pure Ag metal, more continuous for the oxidation under 1 atm O-2. The Y2O3 particl es within the alloy change shape with depth, being small and globular close to the alloy surface but larger and acicular, elongated nearly perpendicul arly to the alloy surface, ai larger depths. For samples oxidized under 10( -20) atm O-2 the volume fraction of internal oxide increases with depth in the alloy, tending to form an almost continuous oxide layer close to the fr ont of internal oxidation, except over regions very rich in Ag. (C) 2001 El sevier Science B.V. All rights reserved.