Corrosion Resistance Of Alloy Research Articles

Effect of Citric Acid Hard Anodizing on the Mechanical Properties and Corrosion Resistance of Different Aluminum Alloys

Hard anodizing is used to improve the anodic films’ mechanical qualities and aluminum alloys’ corrosion resistance. Applications for anodic oxide coatings on aluminum alloys include the space environment. In this work, the aluminum alloys 2024-T3 (Al-Cu), 6061-T6 (Al-Mg-Si), and 7075-T6 (Al-Zn) were prepared by hard anodizing electrochemical treatment using citric and sulfur acid baths at different concentrations. The aim of the work is to observe the effect of citric acid on the microstructure of the substrate, the mechanical properties, the corrosion resistance, and the morphology of the hard anodic layers. Hard anodizing was performed on three different aluminum alloys using three citric–sulfuric acid mixtures for 60 min and using current densities of 3.0 and 4.5 A/dm2. Vickers microhardness (HV) measurements and scanning electron microscopy (SEM) were utilized to determine the mechanical characteristics and microstructure of the hard anodizing material, and electrochemical techniques to understand the corrosion kinetics. The result indicates that the aluminum alloy 6061-T6 (Al-Mg-Si) has the maximum hard-coat thickness and hardness. The oxidation of Zn and Mg during the anodizing process found in the 7075-T6 (Al-Zn) alloy promotes oxide formation. Because of the high copper concentration, the oxide layer that forms on the 2024-T6 (Al-Cu) Al alloy has the lowest thickness, hardness, and corrosion resistance. Citric and sulfuric acid solutions can be used to provide hard anodizing in a variety of aluminum alloys that have corrosion resistance and mechanical qualities on par with or better than traditional sulfuric acid anodizing.

Electrochemical stability of biodegradable Zn-Cu alloys through machine-learning accelerated high-throughput discovery.

Zn-Cu alloys have attracted great attention as biodegradable alloys owing to their excellent mechanical properties and biocompatibility, with corrosion characteristics being crucial for their suitability for biomedical applications. However, the unresolved identification of intermetallic compounds in Zn-Cu alloys affecting corrosion and the complexity of the application environment hamper the understanding of their electrochemical behavior. Utilizing high-throughput first-principles calculations and machine-learning accelerated evolutionary algorithms for screening the most stable compounds in Zn-Cu systems, a dataset encompassing the formation energy of 2033 compounds is generated. It reveals that most of the experimentally reported Zn-Cu compounds can be replicated, especially the structure of R32 CuZn5 is first discovered which possesses the lowest formation energy of -0.050 eV per atom. Furthermore, the simulated X-ray diffraction pattern matches perfectly with the experimental ones. By formulating 342 potential electrochemical reactions based on the binary compounds, the Pourbaix diagrams for Zn-Cu alloys are constructed to clarify the fundamental competition between different phases and ions. The calculated equilibrium potential of CuZn5 is higher than that of Zn through the forward reaction Zn + CuZn5 ⇌ CuZn5 + Zn2+ + 2e-, resulting in microcell formation owing to the stronger charge density localization in Zn compared to CuZn5. The presence of chlorine accelerates the corrosion of Zn through the reaction Zn + CuZn5 + 6Cl- + 6H2O ⇌ Cu + 6ZnOHCl + 6H+ + 12e-, where the formation of ZnOHCl disrupts the ZnO passive film and expands the corrosion pH range from 9.2 to 8.8. Our findings reveal an accurate quantitative corrosion mechanism for Zn-Cu alloys, providing an effective pathway to investigate the corrosion resistance of biodegradable alloys.

Mechanism of alteration in passivity of additively manufactured Ni-Fe-Cr Alloy 718 caused by minor carbon variation

Unlike conventional alloys, where carbon content typically promotes carbide compound formation and reduces localized corrosion resistance, the impact of carbon in additively manufactured materials remains largely unexplored due to rapid cooling rates inhibiting carbide formation. This study addresses the novel question of whether reducing carbon content benefits corrosion performance and its underlying mechanisms in Ni-Fe-Cr-based alloy 718. Employing high-resolution techniques and microcapillary electrochemical methods, it was revealed that higher carbon content increases dislocation density at cell boundaries. This increased dislocation density facilitates the enhanced ejection of nickel and iron from the protective chromium oxide layer on the surface, leading to the formation of a defective outer Ni-Fe oxide layer. This compromised layer subsequently diminishes the alloy's corrosion resistance, particularly under tensile stress conditions.

Role of scandium addition to microstructure, corrosion resistance, and mechanical properties of AA7085/ZrB2+Al2O3 composites

The effect of varying amounts of scandium (Sc) on the mechanical performance and corrosion resistance of aluminum alloy (AA7085) composites reinforced with Zirconium diboride (ZrB2) and Aluminum oxide (Al2O3) nanoparticles was investigated. The specimens were made using an in-situ process with varying amounts of Sc up to 0.5 wt%, and their microstructural behavior, corrosion, and mechanical properties were explored in detail. Phase structural analysis revealed the successful incorporation of ZrB2 and Al2O3 into the matrix through in-situ synthesis, ranging from 30 to 61.7 nm. In addition, HRTEM and XRD analysis displays the Al3Zr prominence observed with 0.1 wt% Sc content, transforming to Al3(Sc, Zr) in the 0.3 wt% Sc composite, and finally becoming Al3Sc with 0.5 wt% Sc. Corrosion analysis revealed that the 0.3 wt% Sc composite exhibited fine Al3(Sc, Zr) precipitate phases that enhanced corrosion properties. The Sc addition leads to a significant improvement in the mechanical properties of AA7085/ZrB2+Al2O3 composites. The ultimate tensile strength of 678 ± 5 MPa for 0.5 wt% Sc under the hot rolled and T6 aged condition was achieved. The optimum content of Sc in AA7085/ZrB2+Al2O3 composites has identified both corrosion and mechanical properties enhancement at 0.3 wt% and 0.5 wt%, respectively.

Design of ZIF-8-based PVB composite coating on AZ31B Mg alloy surface with superhydrophobic, wear, corrosion protection and durability

Magnesium (Mg) alloys are susceptible to being attacked by corrosive ions in practical application environments, which limits their widespread application as the most promising engineering material. Herein, the superhydrophobic composite coating PVB/STA/ZIF-8@SiO2 (PSZS) has been designed on the surface of Mg alloy by using a drop coating method to improve its corrosion resistance. In this study, we provide an approachable decoration strategy for hydrophobic and hierarchical modification of zeolite imidazolate frameworks (ZIF-8) with stearic acid (STA) and SiO2, and combined with polyvinyl butyral (PVB) to form a composite coating with excellent performance on the substrate surface. Notably, the PSZS composite coating exhibited superhydrophobic and the contact angle is greater than 150° after 300 cm of mechanical friction. The electrochemical testing of the PSZS composite coating indicated that it greatly protected the Mg alloys from corrosion. Moreover, the PSZS coating displayed highly effective corrosion resistance even after being immersed in 3.5 wt% NaCl aqueous solution for 7 days. Overall, the PSZS composite coating with the advantages of corrosion resistance, corrosion durability, superhydrophobic, abrasion resistance and simple preparation process broadens the horizons of Mg alloy corrosion resistance research.

Zinc-doped phosphate coatings for enhanced corrosion resistance, antibacterial properties, and biocompatibility of AZ91D Mg alloy

Magnesium and its alloys have been foreseen as promising bone-implant owing to good biocompatibility, high strength, mechanical properties, and biodegradability to replace the conventional bio-metals (Titanium, stainless-steel, Co-Cr alloys) in orthopedic applications. However, high corrosion rate and high degradation rates adversely effects like abrupt evolution of H2 gas and localized alkalization in a physiological environment limit its medical applications. To overcome these issues, phosphate-based surface coating is developed on Mg-alloy to resist the high biodegradation and corrosion rate utilizing magnesium substrate as source of magnesium ion through a single-step hydrothermal process. Controlling the fast corrosion rate and localized alkalization would reduce the antibacterial character of magnesium-based implants therefore, the simple phosphate-based coatings has been induced by doping it with zinc ions due to its physiological tolerance and excellent antibacterial efficacy. The doping of zinc ions may provide a sustained drug-free antibacterial characteristic for potential application in orthopedics. The synthesized phosphate-based coating was characterized using advanced techniques like Scanning Electron Microscopy, X-ray Diffraction, and wettability test, followed by comprehensive electrochemical testing to assess its corrosion behavior. The in vitro immersion test in simulated body fluid (SBF) indicates that deposition of phosphate and zinc doped phosphate coatings reduces the degradation rate consequently minimized the fast dissolution of Mg2+ ions and OH- in physiological environment. Additionally, cytotoxicity and biocompatibility were evaluated using Alamar Blue and live/dead assays on the MC3T3-E1 mouse osteoblast cell line. These assays demonstrated good cell viability, indicating the coatings possess favorable cytocompatibility and support cellular metabolic activity.

Enhancing corrosion resistance of AZ31B magnesium alloy substrate in 3.5 % NaCl solution with Al-Si coating prepared by cold metal transfer-based wire arc additive manufacturing

In this study, we explored an innovative approach to enhance the corrosion resistance of AZ31B magnesium alloy in 3.5 wt% NaCl solution by applying an Al-Si coating using cold metal transfer (CMT)-based wire arc additive manufacturing (WAAM) technology. The findings indicate that the Al-Si coating improved the alloy’s corrosion performance, with a more noble self-corrosion potential (- 0.97 VSCE) and lower self-corrosion current density (3.68 μA/cm2) compared to untreated AZ31B. Long-term immersion tests demonstrated that AZ31B suffered from severe localized corrosion, while Al-Si coating maintained a uniform corrosion profile. Analysis of the corrosion products showed that the Al-Si coating primarily comprised oxidized Mg and hydroxide Al, with minimal oxidized Al and Si, in contrast to the mainly metallic and hydroxide Mg on AZ31B. By reducing the electrochemical activity and enhancing the stability of corrosion products, the Al-Si coating significantly improved the corrosion resistance of AZ31B substrate. This study suggests a promising avenue for advancing the durability of magnesium alloys in corrosive environments.

Influence of Cu and Si on the microstructure and properties of CoCrFeNiCu1-xSix alloys

The effect of Cu and Si on the microstructure and properties of CoCrFeNiCu1-xSix alloys (x = 0, 0.2, 0.5, 0.8 and 1) was studied in this work. The results indicate that as the x value increased from 0 to 1, the phase compositions of CoCrFeNiCu1-xSix alloys evolved from FCC + Cu-rich phases to FCC + Cu-rich + NiSi-rich phases to FCC + BCC + NiSi-rich phases. Therefore, the decrease in Cu content led to the decreasing Cu-rich phase content, whereas Si addition not only favored the formation of intermetallic compounds, but also promoted the phase transition from FCC to BCC. Due to the competition between BCC phase suppressing corrosion and Cu-rich + NiSi-rich phases inducing galvanic corrosion, the corrosion resistance of CoCrFeNiCu1-xSix alloys improved with the increasing x value. The microstructure change also resulted in an improvement in hardness and wear resistance, and a deterioration in fracture toughness of CoCrFeNiCu1-xSix alloys. Moreover, the main wear mechanism evolved from adhesive wear and abrasive wear to slight abrasive wear. Comparison among five alloys indicates that Cu0.2Si0.8 alloy exhibited the excellent comprehensive properties, revealed by the corrosion current density of 4.81 × 10−8 A/cm2, the hardness value of 510.5 HV, the fracture toughness of 8.57 MPa·m1/2 and the wear rate of 0.88 mm3·N−1 · m−1.

In-situ N-doping to improve wear and corrosion resistance of a complex-concentrated alloy manufactured by directed energy deposition

In this study, the effects of in-situ N-doping on wear and corrosion resistance of a complex-concentrated alloy (CCA) prepared by directed energy deposition have been studied. After the addition of N, the wear resistance of the CCA is significantly improved (wear rate: decreasing from ∼2.92 × 10−4 mm3/N•m to ∼0.68 × 10−4 mm3/N•m). Attributed to grain refinement and solution strengthening brought by N-doping, the resistance of the matrix to plastic deformation and delamination is enhanced effectively. Besides, the in-situ N-doping helps to reduce corrosion sites and promote the formation of protective films to improve electrochemical corrosion resistance. Therefore, in-situ N-doping is an effective method to improve the wear resistance and corrosion resistance of superalloy.

Exploring the Kinetics of Oxygen Reduction Reaction in Relation to Pitting Corrosion Resistance in Fe-Cr Alloys

Pitting corrosion, a major concern in materials science and engineering, threatens critical metallic structures and components. Its implications reach across daily life and industries such as energy, transportation, and infrastructure, potentially causing environmental harm, economic losses, and even loss of life. This complex process is influenced by factors including material composition, local environment, and mechanical stresses.1 Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film.2 In Fe-Cr alloys, the ORR occurs on this film, undergoing a mixed diffusion and kinetic-controlled process. The number of electrons involved and the corrosion rate are determined by the thermodynamically stable state of the passive film.This research studies the ORR kinetics on FeCr alloys fabricated by arc-melting, using both computational and experimental methods. The rotating disc electrode technique was employed across various Fe:Cr alloys in alkaline and neutral electrolytes. The Koutecky-Levich analysis showed a dominant four-electron ORR pathway in all tested Fe-Cr alloys, with the ORR significantly inhibited by higher proportions of Cr2O3 in the film, suggesting a correlation with high chromium content. Experimental ORR overpotentials, when combined with theoretical potential-pH (Pourbaix) diagrams, helped discern the likely characteristics of the passive films on the alloys. It was deduced that the catalytic properties of potential passive films increased in the order Cr2O3 < Fe3O4 < Fe2O3 < FeCr2O4. These findings, excellently aligned with density functional theory (DFT) modelling, underscore the role of increased chromium levels in slowing pitting progression by suppressing the ORR.In summary, this research offers distinctive insights into the correlation between the kinetics of the ORR and the resistance to localized corrosion in Fe-Cr alloys, which enhances our understanding of the underlying mechanisms of pitting corrosion. Keywords FeCr alloy, pitting corrosion, ORR, rotating disc electrode, DFT Reference [1] B. Zhang, J. Wang, B. Wu, X. W. Guo, Y. J. Wang, D. Chen, Y. C. Zhang, K. Du, E. E. Oguzie, and X. L. Ma, Nat. Commun. (2018) 9, 2559.[2] G. T. Burstein, P. C. Pistorius, and S. P. Mattin, Corros. Sci. (1993) 35, 57.

EIS Investigation of a Single Pit on Cantor Alloy in Acidic Environment

High-entropy alloys (HEA) are an emerging class of materials with promising properties such as high strength and ductility, improved fatigue resistance, fracture toughness, and thermal stability. They show considerable potential for use as corrosion resistant alloys to support our infrastructure especially for use in extreme environments. In this work, we mainly focused on the typical Cantor alloy, which consists in a mixture of 5 elements CrMnFeCoNi in equimolar proportion. A huge amount of works has already been devoted to the study corrosion resistance of alloys in sulfuric acid [1] or in chloride containing solutions [2,3]. For the latter, the study of the pitting propagation remains challenging since this kind of corrosion initiates as a stochastic process.Electrochemical impedance spectroscopy (EIS) is intensively used as a tool for corrosion research and is well suited for the identification of complex mechanisms. However, data analysis remains difficult in the case of pitting studies, which can be described schematically as n anodic sites in parallel at different states of evolution. In this work we report on EIS analysis performed on a single pit (Fig. 1a) in order to describe the various step of its evolution as a function of time, but also as a function of various parameters such as the chloride ion concentration or the corrosion potential. Single pits were obtained by studying the breakdown of the passive film using the pumped-micropipette delivery/substrate collection (Pumped-MD/SC) mode of scanning electrochemical microscopy (SECM). A detailed mechanism is proposed to account for EIS results obtained on a single pit (Fig. 1b) in order to explain results on usuals EIS measurements.[1] J. Yang, J. Wu, C. Y. Zhang, S. D. Zhang, B. J. Yang, W. Emori et J. Q. Wang, « Effects of Mn on the electrochemical corrosion and passivation behavior of CoFeNiMnCr high-entropy alloy system in H2SO4 solution », Journal of Alloys and Compounds, 819, avril 2020, p. 152943, https://doi.org/10.1016/j.jallcom.2019.152943[2] Camila Boldrini Nascimento, Uyime Donatus, Carlos Triveño Ríos et Renato Altobelli Antunes, « Electronic properties of the passive films formed on CoCrFeNi and CoCrFeNiAl high entropy alloys in sodium chloride solution », Journal of Materials Research and Technology, 9, no 6, novembre 2020, p. 13879-92, https://doi.org/10.1016/j.jmrt.2020.10.002[3] Mengjiao Li, Qingjun Chen, Xia Cui, Xinyuan Peng et Guosheng Huang, « Evaluation of corrosion resistance of the single-phase light refractory high entropy alloy TiCrVNb0.5Al0.5 in chloride environment », Journal of Alloys and Compounds, 857, mars 2021, p. 158278, https://doi.org/10.1016/j.jallcom.2020.158278 Figure 1

Mechanism for corrosion protection of β-TCP reinforced ZK60 via laser rapid solidification

It remains the primary issue to enhance the corrosion resistance of Mg alloys for their clinical applications. In this study, β-tricalcium phosphate (β-TCP) was composited with Mg-6Zn-1Zr (ZK60) using laser rapid solidification to improve the degradation behavior. Results revealed rapid solidification effectively restrained the aggregation of β-TCP, which thus homogenously distributed along grain boundaries of α-Mg. Significantly, the uniformly distributed β-TCP in the matrix promoted the formation of apatite layer on the surface, which contributed to the formation of a compact corrosion product layer, hence retarding the further degradation. Furthermore, ZK60/8β-TCP (wt. %) composite showed improved mechanical strength, as well as improved cytocompatibility. It was suggested that laser rapidly solidified ZK60/8β-TCP composite might be a potential materials for tissue engineering.

Corrosion Resistance of Coatings Based on Chromium and Aluminum of Titanium Alloy Ti-6Al-4V.

Improvement of wear, corrosion, and heat-resistant properties of coatings to expand the operational capabilities of metals and alloys is an urgent problem for modern enterprises. Diffusion titanium, chromium, and aluminum-based coatings are widely used to solve this challenge. The article aims to obtain the corrosion-electrochemical properties and increase the microhardness of the obtained coatings compared with the initial Ti-6Al-4V alloy. For this purpose, corrosion resistance, massometric tests, and microstructural analysis were applied, considering various aggressive environments (acids, sodium carbonate, and hydrogen peroxide) at different concentrations, treatment temperatures, and saturation times. As a result, corrosion rates, polarization curves, and X-ray microstructures of the uncoated and coated Ti-6Al-4V titanium alloy samples were obtained. Histograms of corrosion inhibition ratio for the chromium-aluminum coatings in various environments were discussed. Overall, the microhardness of the obtained coatings was increased 2.3 times compared with the initial Ti-6Al-4V alloy. The corrosion-resistant chromaluminizing alloy in aqueous solutions of organic acids and hydrogen peroxide was recommended for practical application in conditions of exposure to titanium products.

Development of high corrosion resistant (Ni-Fe) alloy coatings from a low concentration bath through multilayer approach

Development of high corrosion resistant (Ni-Fe) alloy coatings from a low concentration bath through multilayer approach

Corrosion resistance of FeCrMnxAlCu high-entropy alloys in 0.5M H2SO4 solution

In this study, FeCrMnxAlCu high-entropy alloys with varying Mn contents (x = 2.0, 1.5, 1.0, 0.5, and 0) were prepared using a vacuum arc melting furnace. The phase structure and microstructure of the alloys before and after corrosion were characterized via X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion resistance of the alloys in a 0.5 M H2SO4 solution was comprehensively evaluated through potentiodynamic polarization, electrochemical impedance spectroscopy, immersion tests, white light interferometry, and X-ray photoelectron spectroscopy. Microstructural characterization results revealed that the FeCrMnxAlCu high-entropy alloys exhibited mixed FCC and BCC phase structures and featured typical dendritic and interdendritic regions. Corrosion tests indicated that as the Mn content decreased, the corrosion resistance of the high-entropy alloys improved, and the corrosion type transitioned from dendritic to interdendritic. Among these alloys, the FeCrAlCu high-entropy alloy exhibited the highest corrosion resistance, with the highest positive corrosion potential (Ecorr = −0.11 V), the lowest corrosion current density (Icorr = 1.02 × 10−5 A∙cm2), minimal corrosion depth, and the lowest corrosion rate (0.1592 mm/y). After corrosion, a composite oxide protective film was formed on the alloy surface, effectively hindering further penetration of the H2SO4 solution and exhibiting excellent corrosion resistance.

Preparation and corrosion behavior of MAO based MOFs coatings with excellent film-forming and adhesion properties

Magnesium (Mg) alloys can be applied in many fields, but their poor corrosion resistance limits their widespread applications. Metal-organic frameworks (MOFs) are often used as fillers in the field of corrosion protection due to their poor adhesion. In order to improve the film-forming performance and adhesion of MOFs coatings, and enhance the corrosion resistance of AZ31 Mg alloys, various MOFs coatings were prepared on the Mg alloy micro-arc oxidation (MAO) coating. The results demonstrated that the MAO facilitated film-forming of MOFs and enhanced their adhesion. Moreover, MOFs crystals can seal the pores of MAO, capture corrosive ions, and form insoluble chelates, significantly improving the corrosion resistance of Mg alloys. Among them, the Ce-MOF exhibited the highest corrosion resistance and the lowest corrosion rate, with a corrosion current density of 8.68 × 10−8 A/cm2 after immersing for 30 min. Moreover, MOFs coatings exhibited good stability and durability, and even after immersing in 3.5 wt% NaCl solution for 14 days, their corrosion protection effects were still superior than MAO.

Comparison of microstructure, mechanical properties and corrosion resistance of Ti6321 alloy by wire-arc directed energy deposition versus rolling

Ti-6Al-3Nb-2Zr-1Mo (Ti6321) alloy, as a new type of marine metal, has excellent corrosion resistance and mechanical properties, but its application is restricted by the traditional manufacturing processes. Wire-arc directed energy deposition (DED) has some incomparable advantages in the efficient and customized fabrication of large/extra-large components, which makes it become a potential manufacturing process for the fabrication of Ti6321 alloy components. However, the formability and corresponding performance evaluation of wire-arc DEDed Ti6321 alloy remains unknown. Here, for the first time, the microstructure, mechanical properties and corrosion resistance of wire-arc DEDed Ti6321 alloy was characterized and compared with rolling, and the relationship between process-microstructure-properties was established. Results show that the full lamellar α+β structure of the DEDed specimens demonstrated better corrosion resistance than the near equiaxed αp + lamellar αs/β structure of rolled specimens. This is owed to the higher grain boundary density, more content of β phase and slighter element segregation of the DEDed specimens, resulting in a more uniform and stable passivation film on its surface. Meanwhile, the grain morphology and low dislocation density of the DEDed specimens causing in lower tensile strength (decrease by ~15.6%) but higher elongation (increase by ~41.5%) than the rolled specimens. Due to the presence of coarse prior-β grains, the DEDed specimens show expected anisotropy in building direction and traveling direction, but overall exhibits sufficient mechanical properties, which exceed the execution standard. This study verified the feasibility of fabricating Ti6321 alloy with idea properties by wire-arc DED, and provides a potential strategy for the production and practical application of large-size Ti6321 alloy components.

Improved corrosion resistance of hydroxyapatite-reinforced plasma electrolytic oxide coatings on AZ31 alloy from one-step and two-step fabrications

The improved corrosion resistance of AZ31 alloy by plasma electrolytic oxidation (PEO) counteracts its apatite-forming ability. To overcome the issue, apatite-containing coatings were fabricated. One-step and two-step fabrications were compared to incorporate the nanoparticle hydroxyapatite (HA) in the coating and to evaluate their effect on the corrosion resistance. The corrosion resistance was evaluated by polarization test and EIS measurement in 0.9% NaCl solution. The electron microscopy and chemical analysis revealed that the HA particles were dispersed in the one-step coatings, while an interspersed HA distribution was observed in the two-step coatings. The dispersed particles enhanced the coating’s hardness from 490 to 554 HV. In the two-step coatings, the HA particles mainly accumulated inside the pores, reducing the coating porosity down to 3.9%. The one-step coatings were more stable in the corrosive solution, offering a remarkably higher corrosion resistance, than the two-step coatings. Moreover, the one-step coating required a shorter (half) processing time (10 min) than the two-step process (20 min) to achieve a similar order of corrosion current density of 10−7 A cm−2. The results demonstrated that the arrangement of reinforcement in the PEO coatings and its effect on the corrosion resistance can be adjusted.

Effect of annealing treatment on the mechanical properties and corrosion behaviour of Co40Cr20Ni30Al4.5Ti5Mo0.5 high-entropy alloy

Cast high-entropy alloys are frequently found to have large internal tensions, compositional segregation, and shrinkage defects, which can directly prevent them from performing as intended. Proper heat treatment can modify the internal structure of an alloy and enhance its overall performance. This study describes a new nonequiatomic proportional cast Co40Cr20Ni30Al4.5Ti5Mo0.5 high-entropy alloy prepared by a vacuum induction melting technique. The impacts of different annealing temperatures (700, 800, 900, and 1000 °C) on the microstructure evolution mechanism, mechanical properties and corrosion behaviour of the alloy are systematically examined. The results show that the heat treatment can successfully improve the overall mechanical properties and corrosion resistance of high-entropy alloys while suppressing casting defects. The alloy exhibits the best overall mechanical properties after annealing at 700 °C, with a yield strength of 923MPa and a tensile strength of 1090MPa. After annealing at a temperature of 800 °C, the alloy demonstrates excellent corrosion resistance, characterized by a low passivation current density, a large passivation range, and a high corrosion potential. Specifically, ipass is measured to be 4.59 × 10-7A/cm2, and Ecorr is -319 mV. Furthermore, the maximum Cr2O3 oxide content in the alloy passivation film formed at 800 °C contributes to the passivation film stability.

Corrosion performance of a high-strength FeNiCrAl medium-entropy alloy compared with 304 stainless steel in KOH solution

The corrosion performance of high-strength FeNiCrAl medium-entropy alloy compared with that of 304 stainless steel was investigated in 1 mol/L KOH solution. The electrochemical results indicated that the FeNiCrAl medium-entropy alloy has a better corrosion resistance and lower corrosion rate. The immersion tests confirmed that the degree of corrosion of the FeNiCrAl medium-entropy alloy was less severe than that of 304 stainless steel. X-ray photoelectron spectroscopy results revealed that the higher corrosion resistance of the FeNiCrAl medium-entropy alloy results from the difference in composition of the passive films. The FeNiCrAl medium-entropy alloy promotes the enrichment of Al and Ni with an oxidation state on the surface, and it suppresses the formation of iron oxidation, inducing effective passive films with increased compactness, higher charge transfer resistance, and lower defect density. Our results are meaningful for designing and applying medium-entropy alloys with excellent corrosion resistance in alkaline media.