A microellipsometric study of the passive film formation on Al-Ta alloys; 2: The role of Al[sub 3]Ta precipitates in breakdown

Journal Article · Sun May 01 04:00:00 EDT 1994 · Journal of the Electrochemical Society; (United States)

DOI:https://doi.org/10.1149/1.2054885· OSTI ID:7198713

Streinz, C C; Moran, P J ^[1]; Wagner, J W; Kruger, J ^[2]

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1. Naval Academy, Annapolis, MD (United States). Dept. of Mechanical Engineering
2. Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Materials Science and Engineering

Al[sub 3]Ta precipitates act as sites for pit initiation and propagation in Al-Ta alloys. Dynamic imaging microellipsometry was used to measure the change in oxide film thickness and the refractive indexes of the films that form on the precipitates and matrix to examine the role of the precipitates in breakdown. Film formation was measured on an Al-1.5 a/o Ta alloy, containing Al[sub 3]Ta precipitates approximately 50 [mu]m in diameter at applied potentials of 0.0, 1.0, 2.0, and 5.0 V SCE in a pH 7.2 borate buffer solution. At 0.0 V SCE the change in passive film thickness on the precipitate was greater than that on the Al matrix. The changes in film thicknesses at 1.0 V SCE were approximately equal and at higher potentials (2.0 and 5.0 V SCE) the matrix film thickened more than the film on the precipitate. SEM observations demonstrate that the precipitate-matrix interface is highly susceptible to localized attack when the passive film on the Al[sub 3]Ta is thicker than on the matrix (at 0.0 V SCE). The authors propose that pit initiation occurs at both the interface of the Al[sub 3]Ta precipitation and in the dealloyed region around its periphery.

• OSTI ID: 7198713
• Journal Information: Journal of the Electrochemical Society; (United States), Journal Name: Journal of the Electrochemical Society; (United States) Vol. 141:5; ISSN JESOAN; ISSN 0013-4651
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM BASE ALLOYS
CHEMICAL REACTIONS
COATINGS
CORROSION
ELLIPSOMETRY
INTERMETALLIC COMPOUNDS
MEASURING METHODS
MICROANALYSIS
PASSIVATION
PITTING CORROSION
PROTECTIVE COATINGS
TANTALUM ALLOYS