Corrosion Resistance Of Alloy Research Articles

Effect of Ni on the corrosion resistance and passivation characteristics of Ni-Mn-Ga-Gd shape memory alloys in sodium chloride solutions

This paper investigates the effect of different Ni contents on the corrosion and passivation behavior of Ni54+xMn25Ga20.9-xGd0.1 (x = 0, 1, 2, 3, 4) shape memory alloy in a 3.5 wt% NaCl solution. Using scanning electron microscope, electrochemical workstation, and X-ray photoelectron spectroscopy. The results indicate that the corrosion resistance of single-phase alloys initially increases and then decreases as the Ni content ranges from x = 0 to 3, with the best corrosion resistance observed at x = 2. The passive film of the alloy mainly consists of NiO, Ni(OH)2, and Ga2O3. Both NiO and Ga2O3 positively affect the corrosion resistance of the passive film. In the range of 54 to 57 at% Ni content, the alloy remains a single-phase alloy. The elements Ni and Ga work together in the passivation film and at a Ni content of 56 at% to reach equilibrium, which provides the best corrosion resistance for single phase alloys. When the Ni content reaches 58 at%, the second phase appears in the form of a nickel-rich phase. Typically, intergranular corrosion preferentially corrodes the second phase, but in this study, the second phase is a nickel-rich phase with some corrosion resistance, which improves the overall corrosion resistance of the alloy.

Enhancing the corrosion properties and microhardness of titanium alloy by laser surface remelting

Laser surface remelting (LSR) was performed on the Ti80 alloy, and the effects of different laser powers with 50 W, 100 W and 200 W on the microstructure, microhardness and corrosion properties were systematically investigated. The results showed that after LSR treatment, the microstructure of the Ti80 alloy was significantly refined because of the rapid cooling effect of laser processing, and the microhardness of the remelted zone gradually increased with the increase of laser power. The electrochemical test results reveal that the corrosion resistance of the Ti80 alloy can be significantly improved after LSR treatment and the corrosion resistance in 3.5 wt% NaCl solution was as follows from high to low: 100 W>50 W>200 W>As-received. It was concluded that the content of Ti2O3 decreased and TiO2 increased after LSR, and the stability of the passive film exhibited a corresponding improvement. The LSR can improve the surface hardness and corrosion resistance of the Ti80 alloy, which can be attributed to the homogenization of the composition of the remelting zone and the reduction of the point defect density of passive film. It is believed that results documented in this study can provide an important reference for deepening understanding of the surface modification mechanisms of LSRed Ti80 alloys.

Influences of friction stir processing on the microstructure and properties of TC4 titanium alloy by laser metal deposition

To enhance the properties of TC4 titanium alloy samples prepared by Laser Metal Deposition (LMD), while minimizing metallurgical defects and increasing relative density of the samples, the advanced Friction Stir Processing (FSP) technology was employed to conduct a refined secondary modification on the LMD-deposited TC4 titanium alloy samples. The comprehensive influences of FSP on the microstructure and properties of the as-deposited TC4 titanium alloy were emphatically investigated. The results reveal that the as-deposited TC4 titanium alloy exhibits a microstructure characterized primarily by columnar grains interspersed with a minor amount of equiaxed grains in the vertical section. After FSP treatment, the microstructure transforms into a new morphology where more refined equiaxed grains coexist with bimodal structures. Meanwhile, on the horizontal plane, the existing equiaxed grains are further refined, and the microstructure gradually transitions from the original Widmanstätten and basketweave structures to a more uniform laminar structure. Accordingly, the transformation of the microstructure leads to enhanced mechanical properties of the TC4 titanium alloy. Compared to the untreated as-deposited titanium alloy, the hardness of the FSP-processed samples significantly increases by 46.9 HV1 on the horizontal plane and 33.8 HV1 on the vertical plane. Additionally, the reduction in friction coefficient (from 0.47 to 0.41), a substantial decrease in wear mass (3.7 mg), and a slight improvement in the corrosion resistance of the titanium alloy collectively demonstrate the effectiveness of the FSP process in enhancing the performance of as-deposited TC4 titanium alloy.

Effects of Mo Addition on Microstructure and Corrosion Resistance of Cr25-xCo25Ni25Fe25Mox High-Entropy Alloys via Directed Energy Deposition.

Highly entropy alloys (HEAs) are novel materials that have great potential for application in aerospace and marine engineering due to their superior mechanical properties and benefits over conventional materials. NiCrCoFe, also referred to as Ni-based HEA, has exceptional low-temperature strength and microstructural stability. However, HEAs have limited corrosion resistance in some environments, such as a 3.5 wt% sodium chloride (NaCl) solution. Adding corrosion-resistant elements such as molybdenum (Mo) to HEAs is expected to increase their corrosion resistance in a variety of corrosive environments. Metal additive manufacturing reduces production times compared to casting and eliminates shrinkage issues, making it ideal for producing homogeneous HEA. This study used directed energy deposition (DED) to create Cr25-xCo25Ni25Fe25Mox (x = 0, 5, 10%) HEAs. Tensile strength and potentiodynamic polarization tests were used to assess the materials' mechanical properties and corrosion resistance. The mechanical tests revealed that adding 5% Mo increased yield strength (YS) by 20.1% and ultimate tensile strength (UTS) by 9.5% when compared to 0% Mo. Adding 10% Mo led to a 32.5% increase in YS and a 20.4% increase in UTS. Potentiodynamic polarization tests were used to assess corrosion resistance in a 3.5-weight percent NaCl solution. The results showed that adding Mo significantly increased initial corrosion resistance. The alloy with 5% Mo had a higher corrosion potential (Ecorr) and a lower current density (Icorr) than the alloy with 0% Mo, indicating improved initial corrosion resistance. The alloy containing 10% Mo had the highest corrosion potential and the lowest current density, indicating the slowest corrosion rate and the best initial corrosion resistance. Finally, Cr25-xCo25Ni25Fe25Mox (x = 0, 5, 10%) HEAs produced by DED exhibited excellent mechanical properties and corrosion resistance, which can be attributed to the presence of Mo.

Use of Pulsed Potentials for Electropolishing TA6V Parts Elaborated By Additive Manufacturing in Deep Eutectic Solvent

The Ti-6Al-4V alloy's high mechanical properties, low density, excellent biocompatibility, and corrosion resistance make it an ideal material for sectors such as aeronautics, astronautics and medical technology. The demand for increasingly complex part designs is speeding up the development of Additive Manufacturing (AM) technology, enabling the creation of shapes unachievable with traditional machining. However, the parts manufactured present significant surface roughness, thus reducing resistance to corrosion and mechanical stress. To mitigate these risks, homogeneous polishing of the entire shape is required. Electrochemical polishing is an all-round part treatment technique ideal for addressing AM challenges. Deep Eutectic Solvent (DES) electrolytes are well-suited for this application. The aim of this study is to develop electropolishing of Ti-6Al-4V parts in a DES solvent of ethylene glycol and choline chloride. The challenges posed by viscous layer thickness problems, as well as two methods to overcome them, are described, including agitation control and pulsed potentials.

Preparation of graphene/AlCoCrNiTiMox coatings by laser parameter optimization based on TRIZ theory and its application in extending the service life of surveying and mapping drones

During the use of surveying and mapping drones, their aluminum (Al) alloy body is prone to corrosion and has certain requirements for mechanical properties. In order to extend the service life of surveying and mapping drones, this study uses laser cladding technology to prepare graphene (Gr) reinforced AlCoCrNiTiMox high entropy alloys (HEAs) coatings on the Al alloy surface of the drone body. In order to optimize the laser preparation parameters, the Invention Problem Solving Theory (TRIZ) is introduced. By utilizing innovative tools such as physical contradictions, technical contradictions, and material field models of this theory, the preparation process parameters such as laser power, laser scanning speed, laser spot diameter were optimized. The microstructure of the coatings were analyzed using scanning electron microscope (SEM), transmission electron microscope (TEM), electron back scatter diffraction (EBSD), etc. The corrosion resistance, hardness and wear resistance of the coatings were tested. The experimental results show that the microstructure of Gr/AlCoCrNiTiMox alloy is mainly composed of equiaxed grains and molybdenum-chromium (Mo-Cr) precipitates. The Gr/AlCoCrNiTiMox HEAs exhibits excellent corrosion resistance in 0.5 mol/L H2SO4 solution. The corrosion resistance of alloys is related to their composition, the effects of Gr and Mo elements. Under the combined effects of solid solution strengthening, precipitation strengthening, Mo element and Gr, the mechanical properties of Gr/AlCoCrNiTiMox alloys are excellent. The hardness of Gr/AlCoCrNiTiMo0.1 and Gr/AlCoCrNiTiMo0.2 alloys are 685 HV and 736 HV, respectively, with average friction coefficients of 0.64 and 0.58, respectively. The effect of Mo element makes the grain size of Gr/AlCoCrNiTiMo0.2 alloy smaller than that of Gr/AlCoCrNiTiMo0.1 alloy, resulting in better mechanical properties and corrosion resistance. The research results indicate that laser cladding of Gr/AlCoCrNiTiMox coating on the Al alloy surface of drone fuselage provides assurance for extending its service life.

Realizing strength-ductility combination of Ni-12Mo-7Cr-2Nb based superalloy via nano-sized MC carbides at stacking faults and grain boundaries

Developing corrosion-resistant alloys with the outstanding strength-ductility combination at elevated temperatures are highly desirable for molten salt reactor (MSR) applications. In this study, by appropriate preaging process, the yield strength and elongation of one newly developed Ni-12Mo-7Cr-2Nb based superalloy at high temperatures respectively increase by ∼50 % and ∼100 % as compared with the solid-solution state. This preaged alloy exhibits the excellent strength and overcomes the intermediate temperature embrittlement problem as compared with other alloys. Microstructure observations indicate that the strengthening and ductility improvement are related to the formation of nano-sized MC carbides. After preaging process, the extrinsic stacking faults are formed along {111} close-packed planes and decorated with ultra-dense MC carbide particles, thus are called as stacking faults precipitates (SFPs). SFPs contribute to the precipitation strengthening by the complex interaction with dislocations. Surprisingly, the SFPs exhibits the better strengthening effect than the uniformly dispersed MC carbides with the same volume fraction and size. Furthermore, it was found that the “pseudo-continuous” intergranular MC carbide particles are beneficial to the high-temperature ductility, although the similar intergranular precipitates were widely regarded as harmful in other studies. Using crystal plasticity finite element method, it was proved that the strain concentration at the triple junctions would be obviously alleviated because the intergranular MC carbide particles can suppress grain boundary sliding. If tested at 750 °C, the intergranular MC carbide particles would trigger the particle-stimulated nucleation and lead to the local dynamic recrystallization at grain boundaries and crack tips. These small recrystallized grains can suppress crack propagation and bring about the improvement in ductility in the aged alloy.

Effects of Ti and Y on resistance to corrosion in Fe–Cr-X Alloys

The effect of Ti and Y on the corrosion behavior of the FeCr alloy was investigated in a 3.5% NaCl solution. Ti was found to inhibit the formation of the σ phase, significantly reducing the presence of pitting in the material. In addition, Ti acted indirectly on the oxide layer, increasing the concentrations of Cr and Fe, consequently generating a probable enrichment of Cr2O3 and FeOOH, which enabled the formation of a more stable passive film resistant to attack by chloride ions. On the other hand, Y caused the precipitation of a phase identified as Fe17Y2, which was accompanied by an elongated σ phase, both located at the grain boundaries, besides the formation of Cr23C6 and Y2O3. Its addition resulted in an improvement in the corrosion resistance of the FeCr alloy by reducing the precipitation of the σ phase. However, its effect was much less important than that of Ti, since the results showed that the FeCrY alloy was still highly susceptible to localized forms of corrosion.

Investigation of Mechanical and Corrosion Properties of New Mg-Zn-Ga Amorphous Alloys for Biomedical Applications.

Magnesium alloys are considered as promising materials for use as biodegradable implants due to their biocompatibility and similarity to human bone properties. However, their high corrosion rate in bodily fluids limits their use. To address this issue, amorphization can be used to inhibit microgalvanic corrosion and increase corrosion resistance. The Mg-Zn-Ga metallic glass system was investigated in this study, which shows potential for improving the corrosion resistance of magnesium alloys for biodegradable implants. According to clinical tests, it has been demonstrated that Ga ions are effective in the regeneration of bone tissue. The microstructure, phase composition, and phase transition temperatures of sixteen Mg-Zn-Ga alloys were analyzed. In addition, a liquidus projection of the Mg-Zn-Ga system was constructed and validated through the thermodynamic calculations based on the CALPHAD-type database. Furthermore, amorphous ribbons were prepared by rapid solidification of the melt for prospective alloys. XRD and DSC analysis indicate that the alloys with the most potential possess an amorphous structure. The ribbons exhibit an ultimate tensile strength of up to 524 MPa and a low corrosion rate of 0.1-0.3 mm/year in Hanks' solution. Therefore, it appears that Mg-Zn-Ga metallic glass alloys could be suitable for biodegradable applications.

Enhancing the mechanical properties and corrosion resistance of biomedical Ti15Mo alloy with ultra-finer {332} twins via cyclic deformation

Mechanical properties, passivation behaviors and corrosion resistance of biomedical Ti15Mo alloy with ultra-finer twins were investigated. Cyclic deformation was conducted to activating more {332} twin variants via periodic changes of tension and compression. Microstructural refinement via numerous twins with the stable boundaries is different from other mechanisms, resulting in a higher hardness and maintaining the low elastic modulus after deformation and annealing. The results of electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy tests, revealed that twin boundaries are beneficial to enhancing passivation behaviors via forming a thicker oxide film in PBS solution. The alloy with ultra-finer {332} twins exhibit a better corrosion resistance due to a lower passivation current. The expected biomedical performance was obtained in the alloy after ±3 % amplitude cyclic deformation and 730 °C/7 min annealing, in contrast to the initial alloy with coarse grains, increasing 8.8 % of the hardness, decreasing 46 % of the corrosion current and maintaining the low elastic modulus.

Role of Mn in improving the corrosion resistance and cytocompatibility of antibacterial Mg-Ag-Mn alloy

To improve corrosion resistance and cytocompatibility of biodegradable Mg-Ag alloy, the non-toxic Mn was added to produce Mg-Ag-xMn (x=0, 0.5, 1, 2 and 3 wt%) alloys. It was revealed that Mg-Ag-2Mn alloy exhibits an optimized comprehensive property after post-casting heat treatment (PCHT). Microstructural factors for the improved performances are then determined. It is revealed that the addition of Mn promotes the precipitation of the Fe-containing α-Mn phase and alters the configuration of the corrosion product after PCHT, which enhances the corrosion resistance of the alloy and thus optimises the ionic release kinetics for improved biological performance.

Investigation on corrosion behaviour of metal oxide nanoparticles reinforced magnesium composites by salt spray and immersion corrosion test methods

ABSTRACT This study explores the increasing utilisation of lightweight materials, particularly magnesium (Mg) alloy, in sectors such as automobile, aerospace, and marine due to its notable advantages such as high strength-to-weight ratio, good castability, and excellent damping capacity. Despite these merits, Mg alloy faces challenges, notably in wear and corrosion resistance. The research focuses on enhancing the corrosion resistance of Mg alloy by incorporating Zinc Oxide (ZnO), Manganese Oxide (MnO), and Titanium Oxide (TiO2) nanoparticles. The alloy AZ91D and three nanocomposites, namely AZ91D + 1% ZnO, AZ91D + 1% MnO, and AZ91D + 1% TiO2, were manufactured using a stir squeeze casting technique combined with an ultrasonication process. To confirm the even distribution of reinforcement particles, Optical Microscope (OM), Scanning Electron Microscope (SEM) and High-Resolution Scanning Electron Microscope (HR-SEM) were employed. X-ray Diffraction (XRD) analysis revealed the presence of matrix and reinforcement material with intermetallic precipitates around the grain boundaries. Corrosion properties were assessed following ASTM standards and utilising a 3.5% NaCl concentration. The study found that AZ91D + 1% TiO2 nanocomposites exhibited superior corrosion resistance compared to the AZ91D alloy, showing a remarkable 77.78% and 69.89% improvement in corrosion behaviour under salt spray and immersion environments, respectively, after 48 hours.

In situ evaluation of sensitization in the heat affected zone of supermartensitic stainless steel welded with superduplex filler metal

Supermartensitic stainless steels (SMSS) are high strength corrosion resistant alloys used in oil and gas production in deep water. Failures related to sensitization and excessive hardness in the heat affected zone (HAZ) are prone to happen in harsh environments, such as those found in oil production. To avoid dangerous types of failure, post weld heat treatments (PWHT) are necessary. Temperature and duration of PWHTs are fundamental parameters to be adjusted. In the present work, a minicell was developed to perform DL-EPR tests in different regions of a multipass welded joint of SMSS with superduplex stainless steel as filler metal. The welded joint was submitted to PWHT at 650 °C for 5 and 15 min. The effects of these short duration PWHT on the HAZ and base metal were analyzed using a minicell for double loop electrochemical tests (DL-EPR), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results indicate that both PWHTs (5 and 15 min) caused the increase in the degree of sensitization of HAZ without the reduction of hardness to acceptable values.

Corrosion behaviour of superaustenitic stainless steel N08029 in harsh acidizing environment

It is vital to examine the resistance to corrosion of corrosion resistant alloys (CRAs) in severe oilfield corrosive environments such as acidizing to validate their performance. Super austenitic stainless steel (SASS) UNS N08029 was recently developed to offer competitive and improved corrosion resistance in extreme and aggressive environments. However, no systematic studies have evaluated the N08029 performance in acidizing conditions. In this study, N08029 was investigated in harsh acidizing conditions of different HCl concentrations (up to 25 % HCl), long immersion duration (up to 48 h), and at elevated temperatures (up to 80 °C) using both weight loss and electrochemical measurement techniques. Interestingly, all the test methods show that the corrosion resistance of the SASS increases with increasing the concentration of HCl acid. This may be due to the formation of ferric chloride protective layer on the steel surface after the dissolution of the formed chromium oxide layer by the increasing acid concentration. The decrease in the corrosion rate observed at higher HCl concentrations is because the higher concentration of HCl causes the more ferric chloride layer to form on the metal's surface. This layer protects the metal from further acid attack. Also, after 24 h immersion duration, a decrease in corrosion rate with further increase immersion duration was observed which may is also due to the formation of more ferric chloride protective layer. However, the corrosion resistant of the SASS was observed to decrease with increase in temperature of the test solution. The decreased resistance of the SASS to corrosion with increase in temperature is associated with the instability or damage of the passive/protective film on the surface of the SASS at elevated temperatures.

Unveiling the novel anti-corrosion and anti-bacterial biofilm forming characteristics of eco-safe MWCNT-AZ91E alloy for food-processing surfaces

This study explores the eco-friendly modification of AZ91E alloy with MWCNT casting to enhance surfaces crucial for food processing, storage, and transportation, with a specific focus on reducing bacterial biofilm formation and preventing corrosion. Incorporating nanomaterials like MWCNT into magnesium alloys offers promising prospects for improving the surfaces of equipment and structures used in food-related industries. The advanced mechanical properties observed in MWCNT-doped alloys can lead to the development of lightweight yet durable surfaces essential for maintaining hygiene standards and ensuring food safety during processing, storage, and transportation. Employing sophisticated systematic practices such as XRD, FTIR, and Vickers hardness testing allows for comprehensive evaluation of surface modifications and mechanical enhancements. Furthermore, the demonstrated corrosion resistance of MWCNT-doped magnesium alloys is crucial for protecting surfaces from degradation caused by exposure to corrosive environments commonly encountered in food processing facilities and transportation systems. Additionally, the remarkable antibacterial properties exhibited by MWCNT-doped alloys hold promise for mitigating bacterial biofilm formation on surfaces, thereby contributing to enhanced sanitation and hygiene practices in food-related industries. KEY WORDS: Multiwalled carbon nanotube, Magnesium alloys, Anticorrosion, Squeeze casting, Antibacterial, Biofouling Bull. Chem. Soc. Ethiop. 2024, 38(6), 1897-1914. DOI: https://dx.doi.org/10.4314/bcse.v38i6.30

Study of the Synergistic Influence of Plasma Electrolytic Oxidation and Wet Post-Treatment on the Surface of AA7075.

In this study, we enhanced the corrosion and microbial resistance of aluminum 7075 alloys by applying a thin layer of alumina through plasma electrolytic oxidation (PEO) in an alkali-silicate electrolyte. In addition, the influence of film sealing on coated aluminum alloy 7075 was studied in detail, specifically in oil and water at 100 °C after treatment. The surface and cross-sectional morphology, element composition, and phase composition of the PEO coatings were characterized by using scanning electron microscopy (SEM) assisted with energy-dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD), respectively. The corrosion resistance of the coating on AA7075 PEO was evaluated before and after post-treatment using hot water and hump oil at 100 °C. This assessment was conducted by using various electrochemical techniques, including open-circuit potential (OCP), linear polarization resistance (LPR), potentiodynamic polarization scan (PD), electrochemical impedance spectroscopy (EIS), and cyclic potentiodynamic scan (CPS). The results showed that the corrosion resistance of the AA7075 alloy was significantly improved after the PEO coating. The AA7075 + SF, among all of the examined alloys, exhibited superior corrosion properties, due to its fat sealing. This is probably due to the formation of a mixed fatty acid layer from oil on the surface of the AA7075 PEO, which synthesizes a hydrophobic layer. Interestingly, the samples treated with PEO showed a great resistance to microbial growth.

Enhancing Corrosion Resistance and Antibacterial Properties of ZK60 Magnesium Alloy Using Micro-Arc Oxidation Coating Containing Nano-Zinc Oxide

Enhancing Corrosion Resistance and Antibacterial Properties of ZK60 Magnesium Alloy Using Micro-Arc Oxidation Coating Containing Nano-Zinc Oxide

Boosting corrosion resistance of Mg-Li alloy: Implanting bioinspired superhydrophobic surfaces into MAO matrix for enhanced protection

The corrosion problem has significantly impeded the practical application of Mg-Li alloys. In this report, a method that combines micro-arc oxidation (MAO) with electrochemical deposition is developed to create a superhydrophobic matrix on Mg-Li substrate. The combination approach harnesses the superiority of both coverages, including MAO as the dense, firmly bonded ceramic oxide layer on the metal substrate and the superhydrophobic surface (SHS) implanted into MAO matrix. The MAO-SHS coating exhibits high mechanical stability, maintaining the superhydrophobicity due to the “implanting effect” even after a long distance of friction effect. For corrosion inhibition, compared to the bare Mg-Li with icorr of 9.26 × 10−5 A/cm2, the icorr for MAO and MAO-SHS is 7.83 × 10−6 A/cm2 and 7.50 × 10−9 A/cm2, respectively, representing the reduction of approximately one and four orders of magnitude. Focusing the atmospheric corrosion inhibition, MAO-SHS proves to manipulate the dynamic evolution of saline solution evaporation and salt particle deliquation. The salt particle crystalized from saline solution on MAO-SHS is found to have significantly smaller contact area than that of the bare Mg-Li and MAO. By employing atomic force microscopy, the adhesion force of salt particle is revealed as ca. 45 nN, 13 nN, and 2 nN for salt particle on Mg-Li, MAO, and MAO-SHS, respectively. This suggests that the salt can be more easily removed from the MAO-SHS surface, thereby reducing the susceptibility to corrosion. The in situ deliquation is conducted to understand the formation of the droplet on different surfaces. The air in the SHS layer hinders chloride ingress and the SHS layer seals the pores in MAO layer, proving the synergistic effect afforded by MAO-SHS to achieve superior corrosion resistance.

Microstructure evolution and properties of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloy prepared by SIMA

The semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were prepared by strain induced melting activation method (SIMA), and the microstructure evolution, mechanical properties and corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were investigated. The results indicate that the ideal globular or near-globular microstructures with an average grain size of 29.1 μm and a shape factor of 0.86 can be obtained when the Al80Mg5Li5Zn5Cu5 light weight high entropy alloys with 20% deformation held at 500 °C for 15 min. The coarsening coefficient is 35.8 μm3/s when the temperature is 500 °C, which is lower than the traditional single major element alloys due to the sluggish diffusion effect of high entropy alloys. The compression strength of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is 558.4 MPa, which is 11% higher than that of as-cast state. The corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is also significantly improved.

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.