Search Results (4)

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. Full article

Starting from solid-solutions (SS) of AlCoCrFeNi_x 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. Full article

In this work, a novel TiAlMoNbW high-entropy alloy (HEA) film and its corresponding nitrid (HEN) film were deposited on CSS-42L bearing steel by magnetron sputtering technology. The microstructure, microhardness, wear resistance, and corrosion resistance of the coated CSS-42L steel were systematically investigated. With the introduction of nitrogen, the crystal structure of TiAlMoNbW HEA film transformed from BCC into FCC. The microstructure of the deposited film became denser and was accompanied by lower surface roughness. The hardness of the nitride film was further increased from 11.43 to 25.7 GPa due to the formation of saturated metal nitride phases and the solid-solution strengthening of various elements. The tribological results showed that both TiAlMoNbW HEA and HEN films with excellent mechanical properties could improve the wear resistance of CSS-42L substrate, especially for the nitrid film, the mechanical properties of the film are significantly improved, resulting in a substantial reduction in the friction coefficient of about 22% and the wear rate of nearly 79%. In the electrochemical tests, both the TiAlMoNbW HEA and HEN-coated samples exhibited lower current densities and corrosion rates in 3.5 wt.% NaCl and 1 mol/L H₂SO₄ solutions. It was also noticed that the TiAlMoNbW nitrid film possessed a superior corrosion protection effect for CSS-42L steel. Full article

The interest in nitride coatings based on high-entropy alloys (HEAs) has increased rapidly in the last decade. According to a number of papers, such high-entropy nitride (HEN) coatings have a single-phase structure and properties that significantly exceed those of simpler nitride systems. These properties include high hardness, wear resistance, oxidation resistance and thermal stability. It is believed that these distinctive properties are due to the high entropy of mixing, which increases with an increase in the number of elements in the composition. However, comparison with various binary and ternary systems shows that better properties are not typical of each HEA-based coating, and the effect of the number of elements competes with other factors that can make even more pronounced contributions to the structure and properties of the coating. Because of fragmentation of data on the structure and properties of high-entropy coatings, a unified concept of alloying is needed. This review compares the methods for obtaining HEN coatings, describes their structural features and analyzes the main properties, such as hardness, wear resistance and oxidation resistance, in order to establish an understanding of the influence of the number of elements and their role in the composition of coatings. Full article