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Harkonen E.,University of Helsinki | Diaz B.,École Nationale Supérieure de Chimie de Paris | Swiatowska J.,École Nationale Supérieure de Chimie de Paris | Maurice V.,École Nationale Supérieure de Chimie de Paris | And 6 more authors.
Chemical Vapor Deposition | Year: 2013

Atomic layer deposited (ALD) 50 nm AlxTayO z mixture coatings are grown on steel for corrosion protection. In morphological and compositional analyses the coatings are found to be uniform, conformal, well-adhered, and low in defect density. Corrosion protection properties are evaluated with polarization measurements and neutral salt spray (NSS) testing. The sealing properties of the mixtures improve with increasing aluminum oxide content, whereas the protection durability improves with increasing tantalum oxide content. In comparison to single-layer and nano-laminate ALD Al2O3 and Ta2O5 coatings, all mixtures are found to have better protective properties. Corrosion protection of steel with 50 nm AlxTayOz mixture coatings of varying composition, produced using atomic layer deposition (ALD), is studied. Analysis of the morphology, composition, and protective properties of the coatings shows that the coatings are conformal, uniform, and very low in defect density. The corrosion durability of steel is significantly improved with all mixture coatings. Furthermore, the mixtures are found to be superior to ALD-produced Al2O3, Ta2O 5, and Al2O3/Ta2O5 nano-laminate coatings Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Harkonen E.,University of Helsinki | Kolev I.,Hauzer Techno Coating BV | Diaz B.,Chimie Paristech | Swiatowska J.,Chimie Paristech | And 8 more authors.
ACS Applied Materials and Interfaces | Year: 2014

Atomic layer deposition (ALD) is a thin film deposition technique that is based on alternating and saturating surface reactions of two or more gaseous precursors. The excellent conformality of ALD thin films can be exploited for sealing defects in coatings made by other techniques. Here the corrosion protection properties of hard CrN and diamond-like carbon (DLC) coatings on low alloy steel were improved by ALD sealing with 50 nm thick layers consisting of Al2O3 and Ta2O5 nanolaminates or mixtures. In cross sectional images the ALD layers were found to follow the surface morphology of the CrN coatings uniformly. Furthermore, ALD growth into the pinholes of the CrN coating was verified. In electrochemical measurements the ALD sealing was found to decrease the current density of the CrN coated steel by over 2 orders of magnitude. The neutral salt spray (NSS) durability was also improved: on the best samples the appearance of corrosion spots was delayed from 2 to 168 h. On DLC coatings the adhesion of the ALD sealing layers was weaker, but still clear improvement in NSS durability was achieved indicating sealing of the pinholes. © 2014 American Chemical Society.

Harkonen E.,University of Helsinki | Tervakangas S.,DIARC Technology Inc. | Kolehmainen J.,DIARC Technology Inc. | Diaz B.,Chimie Paristech | And 8 more authors.
Materials Chemistry and Physics | Year: 2014

Sublayers grown with filtered cathodic arc deposition (FCAD) were added under atomic layer deposited (ALD) oxide coatings for interface control and improved corrosion protection of low alloy steel. The FCAD sublayer was either Ta:O or Cr:O-Ta:O nanolaminate, and the ALD layer was Al2O 3-Ta2O5 nanolaminate, AlxTa yOz mixture or graded mixture. The total thicknesses of the FCAD/ALD duplex coatings were between 65 and 120 nm. Thorough analysis of the coatings was conducted to gain insight into the influence of the FCAD sublayer on the overall coating performance. Similar characteristics as with single FCAD and ALD coatings on steel were found in the morphology and composition of the duplex coatings. However, the FCAD process allowed better control of the interface with the steel by reducing the native oxide and preventing its regrowth during the initial stages of the ALD process. Residual hydrocarbon impurities were buried in the interface between the FCAD layer and steel. This enabled growth of ALD layers with improved electrochemical sealing properties, inhibiting the development of localized corrosion by pitting during immersion in acidic NaCl and enhancing durability in neutral salt spray testing. © 2014 Elsevier B.V. All rights reserved.

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