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

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.

Optimization of Laser-Wavelength Dependence for Open-Air Atmospheric Pressure Pulsed Laser Deposition of AlCrFeMnTi High-Entropy Alloy for Tailored Surface Properties

“…Guo et al developed a nanoporous HEO with a composition of (Co 0.2 Ni 0.2 Cu 0.2 Mg 0.2 Zn 0.2 )O and, by varying the laser energy fluence, investigating the morphology of the HEO thin film . Laszlo et al studied the mechanical properties of pulsed laser-deposited AlCoCrFeNi x HEAs and nitrides and also explored the biocorrosion behavior of the thin-film alloys in simulated body fluid . In another work, Jung et al employed PLD for the fabrication of superconductive thin films of TaNbHfZrTi HEA on c-cut Al 2 O 3 substrates over a wide range of temperatures .…”

“… 16 Laszlo et al studied the mechanical properties of pulsed laser-deposited AlCoCrFeNi x HEAs and nitrides 11 and also explored the biocorrosion behavior of the thin-film alloys in simulated body fluid. 17 In another work, Jung et al employed PLD for the fabrication of superconductive thin films of TaNbHfZrTi HEA on c-cut Al 2 O 3 substrates over a wide range of temperatures. 18 Laser deposition in open air at atmospheric pressure is a low-cost and facile method of thin-film fabrication because as opposed to the conventional PLD technique, there is no requirement for the use of a vacuum chamber.…”