Thermally induced solute migration in 2011 Al alloy implanted with Ti, Cr, or Al ions
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Thermally induced solute migration in 2011 Al alloy implanted with Ti, Cr, or Al ions J. W. Chua) and P. J. Evansb) Australian Nuclear Science and Technology Organisation, Private Mailbag 1, Menai, NSW 2234, Australia
D. K. Soodb) Royal Melbourne Institute of Technology, GPO Box 2746V, Melbourne, VIC 3001, Australia (Received 27 August 1994; accepted 21 March 1996)
A systematic experimental study of solute migration during thermal annealing and oxidation of type 2011 aluminum alloy is described. Specimens of this alloy were implanted with Ti, Cr, or Al ions to doses in the range 2 3 1015 –2 3 1017 ions cm22 . The implanted substrates were annealed at 500 ±C in vacuum or an oxygen atmosphere and analyzed with Rutherford backscattering and scanning electron microscopy. Changes to the alloy composition resulting from segregation of constituents in the near surface region occurred for both implanted and unimplanted specimens, though the effect was substantially more pronounced following implantation. In addition, segregation was affected by the type and dose of the implanted ion. For the Ti implants under oxidizing conditions, the Ti ions were found to diffuse toward the surface and form a thick oxide layer. Segregation of Cu and PbyBi then occurred below this oxide layer. In contrast, implanted Cr ions under similar conditions were observed to diffuse into the substrate with only a thin oxide layer being formed at the surface. Consequently, Cu and PbyBi segregated close to the surface.
I. INTRODUCTION
Oxidation is one of the major types of corrosion of pure metals and their alloys; a fact that is reflected in the extensive literature on the subject.1,2 Many studies have focused on the mechanisms of oxidation of metal alloys which, even for simple binary systems, can be quite complex. For instance, the oxidative process may result in oxides of constituent elements that are completely miscible, producing an oxide solid solution, or they may be immiscible or only partly miscible, thus forming a number of different phases. This leads to eight possible modes of oxidation in a simple binary alloy.3 Furthermore, different modes of oxidation may occur on a single specimen. In addition, surface properties, treatments, or coatings may affect the oxidation process and, in the case of the latter two, are frequently applied to protect metal components from premature degradation. It is for this reason that ion beam surface modification techniques, such as ion implantation, have been investigated as a means of improving the corrosion resistance of materials. The effects of ion implantation on the thermal oxidation of metals have formed the subject of a number of studies4–13 with those dealing with pure elements4–11 predominating relative to the few reports on alloys.12,13
a)Present
address: RMIT, GPO Box 2746V, Melbourne, VIC 3001, Australia. b) Authors to whom correspondence should be addressed. J. Mater. Res., Vol. 11, No. 7, Jul 1996
http://journals.cambridge.org
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