Structural Parameters and Behavior in Simulated Body Fluid of High Entropy Alloy Thin Films

Author:

Craciun Doina1,Laszlo Edwin A.2ORCID,Mirza-Rosca Julia C.34ORCID,Dorcioman Gabriela1ORCID,Geanta Victor5,Voiculescu Ionelia5ORCID,Craciun Gabriel6ORCID,Badea Liviu27,Craciun Valentin18

Affiliation:

1. National Institute for Laser, Plasma and Radiation Physics, 077125 Măgurele, Romania

2. Faculty of Physics, Doctoral School of Physics, University of Bucharest, 077125 Măgurele, Romania

3. Mechanical Engineering Department, University of Las Palmas de Gran Canaria, 35017 Las Palmas de Gran Canaria, Spain

4. Materials Engineering and Welding Department, Transilvania University of Brasov, 500036 Brasov, Romania

5. Faculty of Material Science and Engineering, National University of Science and Technology Politehnica of Bucharest, 060042 Bucharest, Romania

6. Institute for Microtechnology, 077190 Voluntari, Romania

7. National R&D Institute for Non-Ferrous and Rare Metals, 077145 Pantelimon, Romania

8. Extreme Light Infrastructure for Nuclear Physics, IFIN-HH, 077125 Măgurele, Romania

Abstract

The structure, composition and corrosion properties of thin films synthesized using the Pulsed Laser Deposition (PLD) technique starting from a three high entropy alloy (HEA) AlCoCrFeNix produced by vacuum arc remelting (VAR) method were investigated. The depositions were performed at room temperature on Si and mirror-like polished Ti substrates either under residual vacuum (low 10−7 mbar, films denoted HEA2, HEA6, and HEA10, which were grown from targets with Ni concentration molar ratio, x, equal to 0.4, 1.2, and 2.0, respectively) or under N2 (10−4 mbar, films denoted HEN2, HEN6, and HEN10 for the same Ni concentration molar ratios). The deposited films’ structures, investigated using Grazing Incidence X-ray Diffraction, showed the presence of face-centered cubic and body-centered cubic phases, while their surface morphology, investigated using scanning electron microscopy, exhibited a smooth surface with micrometer size droplets. The mass density and thickness were obtained from simulations of acquired X-ray reflectivity curves. The films’ elemental composition, estimated using the energy dispersion X-ray spectroscopy, was quite close to that of the targets used. X-ray Photoelectron Spectroscopy investigation showed that films deposited under a N2 atmosphere contained several percentages of N atoms in metallic nitride compounds. The electrochemical behavior of films under simulated body fluid (SBF) conditions was investigated by Open Circuit Potential (OCP) and Electrochemical Impedance Spectroscopy measurements. The measured OCP values increased over time, implying that a passive layer was formed on the surface of the films. It was observed that all films started to passivate in SBF solution, with the HEN6 film exhibiting the highest increase. The highest repassivation potential was exhibited by the same film, implying that it had the highest stability range of all analyzed films. Impedance measurements indicated high corrosion resistance values for HEA2, HEA6, and HEN6 samples. Much lower resistances were found for HEN10 and HEN2. Overall, HEN6 films exhibited the best corrosion behavior among the investigated films. It was noticed that for 24 h of immersion in SBF solution, this film was also a physical barrier to the corrosion process, not only a chemical one.

Funder

Romanian Ministry of Research, Innovation and Digitalization, UEFISCDI

Project NUCLEU LAPLAS VII

IOSIN funds for research infrastructures of national interest

European Regional Development Fund and the Competitiveness Operational Programme

Publisher

MDPI AG

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