Multi-component metallic alloys, such as high-entropy alloys (HEAs), have recently attracted scientific and industrial interest due to their capacity to be used in a variety of applications, especially as potential candidates for high-temperature services. In this study, the oxidation behavior of CrCoNiAlTi alloy was investigated at different temperatures and exposure times.

Oxidation tests were carried out in a tubular furnace in atmospheric air. Samples were tested at 800°C, 900°C and 1000°C and subjected to exposure times of 5 h, 24h and 48 h at each temperature. Microstructural characterization was performed by X-Ray Diffraction (XRD) scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS).

XRD revealed the presence of a hexagonal close-packed corundum-type phase, which might consist of both alumina and/or chromia, as both oxides present similar trigonal crystal structures. SEM analysis, supported by EDS, indicated the presence of an inner layer of Al2O3 and an external layer of Cr2O3. Mass gain calculations investigated the oxidation rate law. In this case, a parabolic rate law was observed in all tested samples, which suggests a diffusion-controlled process along the different time intervals and the possibility of formation of stable oxide scales. The observed mass gain for the 48 h time interval (which was the most significant oxide scale production interval), for example, included values ranging from 0,228 mg/cm² (at 800°C) to 0,679 mg/cm² (at 900°C) to 1,941mg/cm² (at 1000°C), showing a notable enhancement in scale production at the higher temperature of 1000°C. In fact, that significant increase in scale formation can be determined by the calculated equilibrium constant (Kp) when one compares the Kp at 800°C = 1,20 x 10^-3 mg²cm^-4h^-1 and the Kp at 1000°C = 4,59 x 10^-3 mg²cm^-4h^-1.

These results present a starting point for understanding the oxidation kinetics of CrCoNiAlTi multicomponent alloys.

Molten salt technology using nitrate salts in tubular external receivers is the current state-of-the-art in concentrated solar power (CSP) technology, but new molten salts chemistry, using carbonates and chloride salts, has been proposed in order to increase the TES temperature and improve the turbine block efficiency. The selection of a high-temperature molten salt chemistry is necessary, alongside the need to understand its impact on new containment materials, to achieve acceptable strength, durability, and cost targets at these high temperatures. In this direction, the aim of this work is to explore different high-entropy alloys (HEAs) to evaluate their corrosion resistance in contact with carbonate and chloride molten salts at 650 and 720ºC, respectively. HEAs exhibit a unique combination of properties attributed to four core effects: high mixing entropy, lattice distortion, sluggish diffusion, and cocktail effect. In particular, the equiatomic, single-phase, face-centered cubic (FCC) CrMnFeCoNi Cantor alloy has garnered significant attention for its exceptional thermodynamic stability and remarkable resistance to corrosive environments.

In this study, three cantor alloys with different Al additions and a Nickel base alloy (In702) were exposed to the eutectic ternary Li₂CO₃–K₂CO₃–Na₂CO₃ (32.1–34.5–33.4 wt%) salt mixture at 650 °C for 500 hours, as well as to ternary chloride salt, composed of 20.4 KCl + 55.1 MgCl₂ + 24.5 NaCl at 720ºC under inert atmosphere (N₂). A special setup was designed in order to integrate electrochemical electrodes into the corrosion reactor to carry out electrochemical impedance spectroscopy (EIS) tests and linear polarization resistance (LPR) during the isothermal immersion.

Lower corrosion rates (0.28mm/year) were obtained for Cantor C alloy with a higher addition of Al, improving the corrosion resistance of In702 in the molten salt selected. In this case, the addition of Al to CrMnFeCoNi alloy improves the corrosion resistance significantly due to the protective layers formed as NiAl₂O₄, MgFeAlO₄.

The increasing prevalence of implants is parallel to the global aging population. Titanium alloy Ti-6Al-4V (Ti 64) is widely utilized in biomedical applications; however, concerns regarding aluminium (Al) and vanadium (V) ion release and their potential long-term effects on human health are prompting the exploration of alternative materials. Among these, β-titanium alloys that are free of Al and V are being investigated. Ti 21S, a metastable β-titanium alloy, demonstrates a lower Young’s modulus that aligns more closely with the mechanical properties of human cortical bone, thereby mitigating the issue of stress shielding. In this study, Ti 64 and Ti 21S were fabricated using laser powder directed energy deposition (LP-DED), and their properties, including density, microstructure, hardness, and corrosion behaviour in a 0.9% NaCl solution, were assessed. Optimized LP-DED parameters for Ti 21S yielded over 99.9% of theoretical density, a fully β microstructure, uniform hardness, and stable passivation with low corrosion currents, indicating strong resistance to corrosive degradation. These findings confirm that Directed Energy Deposition can successfully produce high-quality Ti 21S while maintaining its advantageous properties. Overall, Ti 21S exhibits corrosion performance at least comparable to that of Ti 64 while offering a mechanical response characterized by a lower modulus closer to that of bone. In light of the increasing demand for durable implants in an aging population, Ti 21S presents a promising alternative to Ti 64 for future biomedical applications.

Orthopedic implant lifetime is a key health issue for patients. One in thirty Americans has an orthopedic prosthesis. In Europe, this number is not available but according to sales made by companies, this figure is likely on the same order of magnitude. Metals, stainless steels, titanium alloys, and Cobalt Chromium Molybdenum alloys used for implants must have the specificity to resist under liquid environments during usage, corrosion–friction–fretting, etc. It is worth noting that additive manufacturing is currently progressing but for implants, usual manufacturing processes are always used. Highlighting both the best mechanical and materials parameters in cases of degradation is the aim of this study, using the Point Defect Model. Contact mechanics between stainless steel and poly-mthylmetacrylate, PMMA, have been focused on. Two types of experiments were investigated: Free corrosion potential or open circuit potential and applied potential. Describing behaviors in terms of the wear and morphologies of the wear track area is the key point of this study. The authors paid attention to a synergistic approach, evaluating the contribution of wear to corrosion and vice versa. Theoretical and practical issues are related to understanding these phenomena and predicting passive film thickness. There were a few nanometers of oxides on the top surface and the material behavior depended on a few nanometers.

One of the key challenges confronting the use of implant materials is degradation, which occurs when the biomaterial interacts with the human body physiological fluids. This degradation is referred to as corrosion; hence, corrosion resistance is one of the vital properties the implant material should possess. Among the few biocompatible and most promising implant materials for long-term use is titanium (Ti) and its alloys, which have been extensively applied in various fields due to their excellent mechanical properties, and promising corrosion resistance. Alloying Ti with small amounts of copper (Cu) does not only increase the strength and corrosion resistance but also exhibits antibacterial properties which are beneficial to implants transplants. In this study, two Ti-Cu alloys containing 5 and 10 weight percent (wt.%) compositions of Cu were produced using an arc-melting process under a controlled inert atmosphere. The cast ingots were annealed at 900 ℃ and 1050 ℃ for 2h followed by furnace cooling. Samples were cut into thin plates of about 3mm thickness and undergone phase, microstructural and electrochemical analyses. Characterisation using XRD and SEM-EDX techniques revealed strong presence of the α-Ti(Cu) phase forming below the eutectoid point and hypereutectoid intermetallic Ti₂Cu phase. The size and volume fraction of intermetallic phase was found to increase with both Cu content and increase in the annealing temperature. In summary, this study demonstrates a correlation between phase, morphology and corrosion resistance. Particularly, the XRD, SEM-EDX and the corrosion tests showed that, as the Cu content and annealing temperature increased in the binary Ti-Cu alloys, the amount and size of intermetallic phase(s) increased, corresponding with significantly improved corrosion resistance performance. Current results validate our recent theoretically formulated mechanism that links the alloy oxidation state to corrosion resistance, an indication that both the α-Ti and intermetallic phases contribute towards the improved corrosion resistance.

Laser powder bed fusion (LPBF) is increasingly adopted for manufacturing Ti‑6Al‑4V biomedical alloy, yet the rapid solidification produces martensite that may influence corrosion, mechanical performance, and tribocorrosion in physiological environments. This study provides a comparison between wrought (WR) and LPBF Ti‑6Al‑4V alloys to assess the suitability of LPBF material for biomedical applications. Microstructural characterization revealed that WR Ti‑6Al‑4V exhibits a lamellar α+β structure with coarse grains, whereas LPBF consists of fine α′‑martensite and a 10-times smaller grain size. Nanoindentation testing showed that LPBF specimens possess a one-third higher hardness and significantly higher yield strength, while WR alloy demonstrates greater ductility. Electrochemical testing in simulated body fluid (SBF, 37 °C) confirmed very low corrosion rates (10⁻⁵ mA/cm²) and stable passivity for both alloys, with no localized corrosion; however, LPBF exhibited slightly higher passive currents and occasional metastable pitting, attributed to their martensitic structure and elevated defect density. Under dry sliding, LPBF Ti‑6Al‑4V demonstrated ~14% lower wear rate and marginally lower friction. In SBF, wear increased for both alloys, and their wear resistance converged due to tribocorrosion synergy. The LPBF alloy showed a stronger coupling between mechanical damage and electrochemical activity, more intensive wear‑accelerated corrosion, and faster depassivation–repassivation cycling within the wear track. These effects amplified material removal despite higher hardness, whereas the WR showed a more balanced interaction between mechanical wear and corrosion. Generally, LPBF Ti‑6Al‑4V combines high strength, good wear resistance, and excellent corrosion performance, confirming its suitability for implants, while post‑processing heat treatments may further optimize its tribocorrosion response.

Recent advances in biomedical engineering have highlighted the potential of biocompatible metals, particularly magnesium alloys, for temporary implant applications. These materials are designed to degrade in physiological environments, eliminating the need for secondary surgical removal. However, their corrosion rate often exceeds the rate of tissue healing, limiting clinical applicability and requiring effective strategies to better control degradation [1].

This study presents the development of a Zr–Si hybrid sol–gel coating aimed at enhancing corrosion resistance and regulating the degradation behaviour of AZ31 magnesium alloy. The coatings were synthesised from tetraethyl orthosilicate (TEOS) and the organically modified silane 3-methacryloxypropyltrimethoxysilane (MAPTMS). Zirconium(IV) propoxide (ZTP), chelated with methacrylic acid (MAA), was incorporated to tailor the inorganic–organic network structure and optimise protective performance [2]. The evolution of the sol–gel system was monitored by in situ Fourier transform infrared spectroscopy (FTIR), while surface morphology and elemental composition were characterised using scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS).

Corrosion performance was evaluated in simulated body fluid (SBF) using potentiodynamic polarisation and electrochemical impedance spectroscopy. Degradation kinetics in SBF were further assessed by hydrogen evolution during immersion.

The developed hybrid coatings improved corrosion resistance and effectively moderated magnesium degradation in simulated physiological conditions, demonstrating the potential of Zr–Si hybrid sol–gel systems for controlled resorption of magnesium-based implants.

References
[1] L. Xu et al., Materials 15 (2022) 2613. https://doi.org/10.3390/ma15072613.
[2] P. Rodič et al., Prog. Org. Coat. 124 (2018) 286–295. https://doi.org/10.1016/j.porgcoat.2018.02.025.

Acknowledgements
This work was supported by the Slovenian Research and Innovation Agency (ARIS) under research core funding P1-0134, P2-0393, P2-0089, and P2-0223, and through project J2-60047

After numerous surgeries in the urinary system, stenting is often required to ensure complete urine discharge, prevent urine from flowing back into the kidneys, and maintain proper urine flow to avoid renal failure. The stents currently used in medical centers are primarily polymeric. Over time, the surface of these stents becomes covered with a crystalline layer and bacterial colonies, which, without secondary care, leads to reduced mechanical properties and potential infection. To address these issues, biodegradable stents have been introduced as an alternative. This research investigates the magnesium alloy, specifically the Mg-Ca-Mn alloy, as a biodegradable material for this purpose. Given the limited formability of magnesium alloys, rolling was selected as the fabrication method for the stents. Samples were rolled from an initial thickness of 5.0 mm down to 0.4 mm with a preheating duration of 10 minutes. The grain size of the specimens after rolling was significantly reduced from 200 ± 30 µm to 17 ± 5 µm. This reduction in grain size resulted in a notable increase in yield and ultimate tensile strength, from 108.30 ± 3.60 MPa to 231.45 ± 17.17 MPa. The microstructure and texture of the material were evaluated using optical microscopy, X-ray diffraction, and electron backscatter diffraction. The results indicate a significant reduction in grain size following rolling, along with changes in dislocation density and texture, as revealed by EBSD data. These factors contribute to a higher surface potential, leading to a higher corrosion rate in the initial seconds of the corrosion process. Nevertheless, a protective layer forms rapidly, thereby controlling the corrosion rate sooner and resulting in lower rates over time. The average corrosion rates calculated from hydrogen evolution and weight loss studies in artificial urine over 14 days, and from polarization assessments, were 0.889 mm/y, 1.616 mm/y, and 2.402 mm/y, respectively. Consequently, the stent produced through this process is expected to fully degrade within 10-12 weeks.

Magnesium–calcium (Mg-Ca) alloys have emerged as promising candidates for temporary bio-implant applications due to some notable mechanical, biodegradability and biocompatibility properties. However, the corrosion behavior of Mg-Ca alloy, especially in protein-containing physiological environments, remains insufficiently understood. This study investigates the effect of bovine serum albumin (BSA) addition to Hank's Balanced Salt Solution (HBSS) on the corrosion and stress corrosion cracking (SCC) behavior of Mg-Ca alloy. A combination of potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and surface characterization techniques—optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR)—were employed. The results indicate that BSA adsorption on the alloy surface initially inhibits dissolution, reducing corrosion rates during the first 24 hours. However, prolonged immersion leads to enhanced corrosion, driven by the chelation of BSA with Ca²⁺ ions, which induces cracks in the surface film and promotes alloy dissolution. Furthermore, the fractography reveals that the Mg-Ca alloy is susceptible to SCC in an HBSS environment. However, no evidence of SCC was observed in the HBSS+BSA environment. These findings provide new insights into the complex interactions between proteins and Mg-based implants, contributing to the design of more reliable temporary bio-implant materials.

Critical petrochemical industry plant equipment exposed to corrosive chemicals remains susceptible to metal dusting (MD) corrosion, resulting in infrastructure degradation, significant financial losses and huge safety risks. Metal coating is one approach used to inhibit metal dusting. Firstly, this is achieved by adding elements inhibiting the catalytic activity of iron (Fe) and nickel (Ni), such as tin (Sn) or copper (Cu). Secondly, high amounts of chromium (Cr), aluminium (Al) and silicon (Si) can be added to establish a stable protective oxide scale. NiCr-based alloys are well-known multicomponent alloys with a carefully balanced composition that provide the desired properties for various industrial applications. Although these alloys can resist corrosion to a certain extent, MD can still occur under severe conditions, resulting in serious damage to a system in operation. The composition of nickel-based alloys can be tailored to specific operating conditions to improve their reliability. This stems from the fact that alloying the Ni-Cr alloy with transition elements such as molybdenum (Mo), iron and copper can improve the corrosion resistance by promoting the oxide formation process, which contributes to oxide passivity. This study is focused on investigating the effect of adding small amounts of Fe to austenitic Ni-Cr-based alloys in the process of developing a coating material that can form stable protective phases on the surface when reacting with the process environment. The current work reports the results of the initial plan of undertaking low-temperature corrosion simulation tests (electrochemical), with the aim of exposing the coating alloys to metal-dusting environments in the near future. An arc-melting furnace was used to produce the coating alloys, followed by subsequent heat treatment in a tube furnace. Phase and microstructural analyses were conducted using an X-ray diffractometer (XRD) and optical microscopy (OM), respectively. Using an electrochemical potentiostat, corrosion resistance trends at various Fe contents were established.