Characteristics of Thin High Entropy Alloy Films Grown by Pulsed Laser Deposition

Abstract

Starting from solid-solutions (SS) of AlCoCrFeNix high-entropy alloys (HEAs) that have been produced with high purity constituent elements by vacuum arc remelting (VAR) method varying the nickel molar ratio x from 0.2 to 2.0, we investigated the synthesis of protective thin films of HEAs and high-entropy nitrides (HENs) with the aid of the pulsed laser deposition (PLD) system. The structure of all ten available bulk targets have been examined by means of X-Ray Diffraction (XRD), as well as their elemental composition by means of energy dispersion X-ray spectroscopy (EDS). Three targets with nickel molar composition x = 0.4, 1.2 and 2.0 corresponding to BCC, mixed BCC and FCC, and finally FCC structures were used for thin film depositions using a KrF excimer laser. The depositions were performed in residual low vacuum (10−7 mbar) and under N2 (10−4 mbar) at room temperature (RT~25 °C) on Si and glass substrates. The deposited films’ structure was investigated using grazing incidence XRD, their surface morphology, thickness and elemental composition by scanning electron microscopy (SEM), EDS and X-ray photoelectron spectroscopy (XPS), respectively. A homemade four-point probe (4PP) set-up was applied to determine layers electrical resistance. Besides, a Nanoindentation (NI) was employed to test films’ mechanical properties. XRD results showed that all deposited films, regardless of the initial structure of targets, were a mixture of FCC and BCC structures. Additionally, the quantitative and qualitative EDS and XPS results showed that the elemental composition of films was rather close to that of the targets. The depositions under an N2 atmosphere resulted in the inclusion of several percentage nitrogen atoms in a metallic nitride type compound into films, which may explain their higher electrical resistivity. The Young’s modulus, nanohardness and friction coefficient values showed that the deposited films present good mechanical properties and could be used as protective coatings to prevent damage in harsh environments.

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

“…Increasing the Ni concentration, a second phase of face-centered cubic (fcc) material appeared, while the bcc phase content decreased. For the highest Ni concentration used in this study (x = 2.0), the structure was simple fcc [ 27 ]. Ni has a high valence electron concentration (VEC) value and its concentration in an HEA material will greatly influence the overall VEC value.…”

“…HEA and HEN thin films were deposited by magnetron sputtering [ 22 ] or pulsed laser deposition (PLD) [ 23 ]. Recently, we described the deposition of thin HEA and HEN films on Si substrates using the PLD technique starting from AlCoCrFeNi x alloys with a nominal Ni molar content, x, of 0.4, 1.2, and 2.0, respectively [ 27 ]. The PLD technique has the advantage that it requires small area targets and the optimization of the growth process is rather simple.…”

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

“…Oxide ceramics offer a wide range of properties due to their diverse and adjustable structure, including crystallography, microstructure, and electron density. , Recent advancements in oxide structure design have focused on engineering configurational entropy, enabling the creation of complex multicomponent oxides known as high-entropy oxides (HEOs). , These oxides, consisting of five or more oxide components with equimolar or near-equimolar compositions or an atomic concentration between 5 and 35%, form solid solutions with randomly distributed cations on a cation sublattice. , HEOs exhibit tolerance for cation multivalency and vacancies, allowing for tailored lattice distortion, oxygen stoichiometry, and superior properties . Additionally, there is increasing research on thin film deposition of high-entropy alloys (HEAs) and HEOs using techniques like DC and RF sputtering, focusing on mechanical, structural, electrical, and magnetic properties. − These materials find applications in high-tech industries, offering exceptional protection and properties such as improved wear resistance, corrosion resistance, and high hardness …”

“…Pulsed laser deposition (PLD) is a widely employed technique for the deposition of thin films, offering advantages such as compatibility with compounds and alloys, including low vapor pressure materials. , Briefly, during PLD, the pulsed laser source is focused on the HEA target, usually prepared through a mechanical alloying (MA)/sintering process at high temperatures and high pressures, causing the evaporation and subsequent condensation on the surface of the desired substrate . The PLD technique is intrinsically flexible and versatile and allows the deposition of high-quality films on low-temperature substrates .…”

“…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 .…”