Thin Metal Oxide Coatings for Lightweight Alloys

Abstract

A new type of nanocomposite coating and its preparation technology was worked out1 and will be introduced in this presentation. The technology has two main steps – first, the working surface of substrate is anodized and second, the anodized base layer is covered with a thin toplayer, grown by atomic layer deposition method (ALD). Both steps of the coating preparation need special attention. The anodizing of a lightweight substrate, e.g. an aluminum alloy must result in a homogeneous by both thickness and composition anodic layer, and must consist as little as possible cracks and pores. It is well known that the anodic layer consist nanometric pores and at least part of them is reaching the substrate metal part and these are the weakest points of the anodized coating. Thus, the pores must be firmly sealed and even better filled up to the bottom with a corrosion resistant material. This can be achieved with the help of ALD that is a cyclic analogue of chemical vapor deposition method. In the presentation we will demonstrate how the new coating is prepared for Al2024 alloy, which is tending to pitting corrosion due to existing in it Cu-rich and other intermetallic particles, often with micrometer dimensions, part of them laying in near-surface region of the substrate.In the presentation we will go through the substrate surface pretreatment, anodizing and following ALD growth of nanolaminate of metal oxides as top part of the coating. The process gives micron thick composed coating with filled nanopores, see the scheme, and that coating withstand several thousand hours’ immersion in salt solution. Similar technique was used for protection Ti5 alloy substrates. In the presentation will be discussed surface pretreatment, anodizing and following ALD process, which gives micron thick composed coating with filled nanopores, see the scheme, and which withstand several thousand hours’ immersion in salt solution. Similar technique was used for protection Ti5 alloy substrates. In the presentation will be discussed surface pretreatment, anodizing and following ALD process, which gives micron thick composed coating with filled nanopores, see the scheme, and which withstand several thousand hours’ immersion in salt solution. Similar technique was used for protection Ti5 alloy substrates. L. A. thanks the European Social Funds of Doctoral Studies This work was also supported by the Estonian ME&S by projects IUT2-24, TK117 and TK141. Reference: V. Sammelselg, M. Merisalu, L. Aarik, Method of preparing corrosion resistant coatings, WO 2014102758 A1/GB2509335 A, Priority date 31.12.2012 (http://www.google.com/patents/WO2014102758A1?cl=en). Figure 1