Nanostructured Coating for Aluminum Alloys Used in Aerospace Applications

The authors would like to acknowledge the Estonian Ministry of Education and Research by granting the projects IUT2–24, TLTFY14054T, PSG448, PRG4, SLTFY16134T and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-00). The atomic oxygen testing was performed in the framework of the “Announcement of opportunity for atomic oxygen in the ESTEC Materials and Electrical Components Laboratory/ESA-TECQE-AO-013375),” through a collaboration with Picosun Oy. The authors also thank Dr. Elo Kibena-Põldsepp for the electrodeposition of Ag onto the anodized substrates.A thin industrial corrosion-protection nanostructured coating for the Al alloy AA2024-T3 is demonstrated. The coating is prepared in a two-step process utilizing hard anodizing as a pre-treatment, followed by sealing and coating by atomic layer deposition (ALD). In the first step, anodizing in sulfuric acid at a low temperature converts the alloy surface into a low-porosity anodic oxide. In the second step, the pores are sealed and coated by low-temperature ALD using different metal oxides. The resulting nanostructured ceramic coatings are thoroughly characterized by cross-sectioning using a focused ion beam, followed by scanning electron microscopy, transmission electron microscopy, X-ray microanalysis, and nanoindentation and are tested via linear sweep voltammetry, electrochemical impedance spectroscopy, salt spray, and energetic atomic oxygen flow. The best thin corrosion protection coating, made by anodizing at 20 V, 1 °C and sealing and coating with amorphous Al2O3/TiO2 nanolaminate, exhibits no signs of corrosion after a 1000 h ISO 9227 salt spray test and demonstrates a maximum surface hardness of 5.5 GPa. The same coating also suffers negligible damage in an atomic oxygen test, which is comparable to 1 year of exposure to space in low Earth orbit. © 2022 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.Estonian Ministry of Education and Research by granting the projects IUT2–24, TLTFY14054T, PSG448, PRG4, SLTFY16134T; ERDF TK141 (2014-2020.4.01.15-00); Institute of Solid State Physics, University of Latvia as the Center of Excellence acknowledges funding from the European Union’s Horizon 2020 Framework Programme H2020- WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Tribological properties of PVD coatings with lubricating films

Abstract. This work reports on the tribological performance of three different commercial hard PVD coatings (TiN, TiCN and nACo) with lubricating extra films of Al 2 O 3 , Ni-WS 2 and diamondlike carbon (DLC). WC-Co hardmetal has been used as substrate material. Wear tests, employing two counter bodies of Al 2 O 3 and hardmetal WC-Co, were performed for the PVD coatings with and without the extra films. The results showed that the presence of DLC extra film reduces the coefficient of friction of the PVD hard coatings TiN and nACo. Furthermore, the wear of TiN coatings was reduced in the presence of an extra Ni-WS 2 lubricant film

Õhukeste kilede aatomkihtsadestamine, karakteriseerimine ja rakendamine kaitsekatetena

Väitekirja elektrooniline versioon ei sisalda publikatsiooneErinevates toodetes kasutatavate materjalide eluea pikendamine ja koguste vähendamine on kaks tähtsat ülesannet, mille lahendamine võimaldab muuta väiksemaks ühiskonna ökoloogilist jalajälge. Kuna materjalid korrodeeruvad peaaegu kõigis keskkondades, siis selle tulemusena nende vastupidavus ning kasutusaeg vähenevad. See omakorda muudab lihtsalt kättesaadavate ja odavate materjalide kasutamise mõnede rakenduste puhul võimatuks. Üheks võimaluseks selliste materjalide eluiga pikendada ja neid seejuures ikkagi korrodeerivate keskkondades kasutada, on nende kaitsmine vastupidavamast materjalist katetega, mis isoleerivad kaitstavad materjalid neid hävitavast keskkonnast. Tänu tänapäevaste kõrgtehnoloogiliste seadmete üha keerukamale ehitusele ja detailide rangematele täpsusnõuetele on nende kaitsekatetega katmine traditsiooniliste meetoditega järjest keerulisem. Sellest tulenevalt on kasvanud vajadus uute senisest täpsemate tehnoloogiate järele. Käesolevas töös uuriti üliõhukeste kaitsekatete valmistamise võimalusi, kasutades selleks aatomkihtsadestamise meetodit, mis võimaldab kaitsekihi paksust ülitäpselt kontrollida. Uuringute käigus pandi kokku ja katsetati seadet, millega on võimalik sadestada kaitsekatteid ballooni-tüüpi kinniste anumate sisepinnale. Et arendada vastavaid sadestamismetoodeid ja parandada kaitsekatete omadusi, töötati välja uudsed lahendused TiO2 ja Al2O3 aatomkihtsadestamiseks tehnoloogilistes protsessides, milles lähteainesüsteemideks on vastavalt TiCl4-O3 ja AlCl3-O3. Töö käigus uuriti eelnimetatud meetoditega sadestatud kaitsekatete füüsikalisi ja keemilisi omadusi ning demontreeriti nende häid kaitseomadusi laialt kasutatava roostevaba terase pinnal.Prolonging the lifetime and reducing the amount and cost of materials, used in different kind of products, are two big problems that have to be solved to decrease the ecological footprint of contemporary society. Corrosion is a process, which takes place in almost all environments and reduces the durability of materials, and sometimes makes impossible application of cheap and easily accessible materials. One of the possibilities to protect materials against corrosion is to add a barrier layer of a durable material on the top of a product to isolate it from environment and thereby increases its lifetime or make possible its application in more aggressive environments. However, due to and construction complexity of high-technology production, novel high-precision techniques are needed also for preparation of appropriate protective coatings. Therefore, need for corresponding studies is growing day by day. In this study, application of the atomic layer deposition method for deposition of thin precisely controlled protective coatings was investigated. During the studies novel atomic layer deposition equipment, which made possible deposition of protective coatings onto the inner surface of hermetic containers, was constructed and tested. Secondly, to advance the preparation methods and improve the properties of the protective coatings, atomic layer deposition processes based on new precursor combinations, TiCl4-O3 for deposition of TiO2 and AlCl3-O3 for deposition of Al2O, were developed and physical as well as chemical properties of coatings obtained in these processes were investigated. In the experiments, the potential of these coatings to protect surface of stainless steel was demonstrated

Influence of α-Al2O3 Template and Process Parameters on Atomic Layer Deposition and Properties of Thin Films Containing High-Density TiO2 Phases

High-density phases of TiO2, such as rutile and high-pressure TiO2-II, have attracted interest as materials with high dielectric constant and refractive index values, while combinations of TiO2-II with anatase and rutile have been considered promising materials for catalytic applications. In this work, the atomic layer deposition of TiO2 on α-Al2O3 (0 0 0 1) (c-sapphire) was used to grow thin films containing different combinations of TiO2-II, anatase, and rutile, and to investigate the properties of the films. The results obtained demonstrate that in a temperature range of 300–400 °C, where transition from anatase to TiO2-II and rutile growth occurs in the films deposited on c-sapphire, the phase composition and other properties of a film depend significantly on the film thickness and ALD process time parameters. The changes in the phase composition, related to formation of the TiO2-II phase, caused an increase in the density and refractive index, minor narrowing of the optical bandgap, and an increase in the hardness of the films deposited on c-sapphire at TG ≥ 400 °C. These properties, together with high catalytic efficiency of mixed TiO2-II and anatase phases, as reported earlier, make the films promising for application in various functional coatings

Structure and Electrical Behavior of Hafnium-Praseodymium Oxide Thin Films Grown by Atomic Layer Deposition

Crystal structure and electrical properties of hafnium-praseodymium oxide thin films grown by atomic layer deposition on ruthenium substrate electrodes were characterized and compared with those of undoped HfO2 films. The HfO2 reference films crystallized in the stable monoclinic phase of HfO2. Mixing HfO2 and PrOx resulted in the growth of nanocrystalline metastable tetragonal HfO2. The highest relative permittivities reaching 37–40 were measured for the films with tetragonal structures that were grown using HfO2:PrOx cycle ratio of 5:1 and possessed Pr/(Pr + Hf) atomic ratios of 0.09–0.10. All the HfO2:PrOx films exhibited resistive switching behavior. Lower commutation voltages and current values, promising in terms of reduced power consumption, were achieved for the films grown with HfO2:PrOx cycle ratios of 3:1 and 2:1 and showing Pr/(Pr + Hf) atomic ratios of 0.16–0.23. Differently from the undoped HfO2 films, the Pr-doped films showed low variability of resistance state currents and stable endurance behavior, extending over 104 switching cycles