Analysis of passive film growth on Al-Ta and Al-W alloys by dynamic imaging microellipsometry
- Dept. of Materials Science and Engineering, Johns Hopkins Univ., Baltimore, MD (US)
This paper reports that aluminum alloys containing super-saturated solid solution additions of tantalum or tungsten exhibit a markedly increased resistance to pitting corrosion. These alloys are prepared by nonequilibrium method such as sputter deposition. The addition of 8 atom percent (a/0) Ta to Al has been demonstrated to increase the pitting potential by 700 mV. Ex situ x-ray photoelectron spectroscopy (XPS) analysis has shown that the passive film in that system is thin and rich in Ta{sub 2}O{sub 5}. It is proposed that the Ta{sub 2}O{sub 5} provides a barrier layer that impedes Cl{sup {minus}} ingress and subsequent breakdown. The addition of 9 a/o W to Al has been demonstrated to increase the pitting potential by up to 2600 mV. Ex situ analysis demonstrated that the concentration of WO{sub 2} and WO{sub 3} in the passive film is less than 0.5 a/o. As a result it was proposed that the W additions stabilized the structure of the oxide film, enhancing its resistance to localized attack. Heat-treatment of these alloys results in the precipitation of a second phase that has been shown to be detrimental to the improved pitting resistance. This is not surprising since these alloys are nonequilibrium alloys and the solubility limit for W or Ta in aluminum is less than 0.2%.
- OSTI ID:
- 5325632
- Journal Information:
- Journal of the Electrochemical Society; (United States), Journal Name: Journal of the Electrochemical Society; (United States) Vol. 139:2; ISSN JESOA; ISSN 0013-4651
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102 -- Metals & Alloys-- Structure & Phase Studies
360105* -- Metals & Alloys-- Corrosion & Erosion
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400101 -- Activation
Nuclear Reaction
Radiometric & Radiochemical Procedures
664200 -- Spectra of Atoms & Molecules & their Interactions with Photons-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ALLOYS
ALUMINIUM ALLOYS
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMICAL PREPARATION
CHEMICAL REACTIONS
CORROSION
CORROSION RESISTANCE
CORROSION RESISTANT ALLOYS
DISPERSIONS
ELECTRON SPECTROSCOPY
ELLIPSOMETRY
FILMS
MEASURING METHODS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
PASSIVATION
PHOTOELECTRON SPECTROSCOPY
PITTING CORROSION
REFRACTORY METAL COMPOUNDS
SOLID SOLUTIONS
SOLUTIONS
SPECTROSCOPY
SPUTTERING
SYNTHESIS
TANTALUM ALLOYS
TANTALUM COMPOUNDS
TANTALUM OXIDES
THIN FILMS
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN ADDITIONS
TUNGSTEN ALLOYS