Self-corrosion Current Density Research Articles

Influence of added La2O3 on the microstructure, mechanical properties, and tribocorrosion resistance of TiB2–Ni plasma-sprayed coatings

To enhance the tribocorrosion resistance of 7075-T6 aluminum alloy in deep sea environments, TiB2–Ni coatings with varying La2O3 content were deposited on 7075-T6 aluminum alloy substrates using plasma spray technology. The effects of different La2O3 contents on the organization, structure, and properties of the coatings were analyzed. The results indicated that La2O3 incorporation suppressed brittle phase formation such as Ni3B; 1.0 wt% La2O3 addition reduced Ni3B by 16.9%. The coating's corrosion resistance significantly improved with La2O3 doping - the self-corrosion current density of the 1.0 wt% La2O3-doped coating decreased from 71.2 nA/cm2 to 30.2 nA/cm2.

Microstructure, corrosion resistance and high temperature oxidation properties of AlCrFeNiCu high-entropy alloy coating by high-speed laser cladding

AlCrFeNiCu high-entropy alloy (HEA) coating was prepared on Zirconium (Zr) rod by high-speed laser cladding (HSLC) technique. The effect of different laser power and scanning speed on the forming quality of the coating was studied. When the specific energy density was in the range of 3.0–3.2 J/mm2, the AlCrFeNiCu HEA coating with good adhesion to the substrate, low dilution rate (small heat affected zone) and no cracks were obtained. The phase structure, microstructure, microhardness, corrosion resistance and high temperature oxidation resistance of the coating were tested and analyzed. The results show that the AlCrFeNiCu HEA coating is composed of 76.9 % BCC phase and 23.1 % FCC phase, in which the BCC phase is mainly composed of disordered BCC phase rich in Cr and Fe elements and ordered B2 phase rich in Al and Ni elements, and the FCC phase is rich in Cu elements. Due to the rapid cooling of HSLC, the coating structure gradually changes from columnar crystal to equiaxial crystal from bottom to top. The hardness of the coating is as high as 805 HV, which may be caused by the solution strengthening effect, lattice distortion effect and slow diffusion effect of HEA. In 3.5 % NaCl solution and 0.1 mol/L KOH solution, the self-corrosion current density of the coating is 4.209 × 10−8 A/cm2 and 4.331 × 10−8 A/cm2, respectively. The passivation film on the surface of the coating is composed of a variety of oxides, and the oxygen vacancy density of the passivation film in the two solutions is 2.552 × 1020 cm−3 and 5.794 × 1020 cm−3, with fewer pitting pits on the surface. The structural integrity of the coating can be maintained after 60 min oxidation at 1200 °C. The oxidation process follows the growth kinetics curve, and the surface oxides mainly comprise FeAl2O4, Al2O3 and Cr2O3. AlCrFeNiCu HEA coating improves the corrosion resistance and high temperature oxidation resistance of the Zr-4 alloy.

Study on electrochemical polishing mechanism of TC4 titanium alloy

To achieve a high-quality and precise surface on TC4 titanium alloy for demanding engineering applications, electrochemical polishing (ECP) technology was employed to investigate the polishing process of TC4 titanium alloy in an ethylene glycol-sodium chloride green electrolyte. The macro and micro morphology, surface roughness, material removal rate, surface elements, surface corrosion resistance, and surface hardness of TC4 titanium alloy were measured before and after polishing. Single-factor experiments were conducted to explore the effects of processing gap, electrolyte temperature, polishing voltage, and polishing time on TC4 titanium alloy surface quality. Optimal polishing parameters were determined to be an electrode gap of 12 mm, a voltage of 20 V, a temperature of 40 °C, and a polishing time of 10 min. The experimental results indicated that after electrochemical polishing, the workpiece surface roughness Ra decreased from 256 nm to 25 nm, achieving a roughness reduction rate of 90.23%, the material removal rate was 3.348 μm min−1. The self-corrosion potential of the polished surface increased from −0.416 V to −0.375 V and the self-corrosion current density decreased from 4.447 × 10−7 A·cm−2 to 1.873 × 10−7 A·cm−2, the surface indentation hardness of the workpiece decreased from 5.8669 GPa to 4.6726 GPa. Based on the characterization of polished surface, the mechanism of electrochemical polishing of TC4 titanium alloy was proposed. The results demonstrate that electrochemical polishing of TC4 titanium alloy is highly efficient, involves no mechanical action, and causes no subsurface damage, making it a promising technology to meet medical requirements.

Research on the microstructure and properties of SiCp-SiO2/6061Al composites based on ball milling time

In this study, SiCp-SiO2/6061Al composites were synthesized by integrating SiC and SiO2 particulates into a 6061Al matrix, followed by ball milling and hot isostatic pressing sintering. The impact of ball milling duration on microstructure, mechanical properties, corrosion resistance, and thermal properties was evaluated. After 10h of ball milling, reinforcement particles were uniformly dispersed, achieving a material density of over 98%. Extending milling to 15h enhanced tensile strength to 253.53MPa and flexural strength to 433.56MPa, with a maximum elongation at break of 6.4%. Uniform SiO2 distribution improved corrosion resistance, evidenced by a self-corrosion potential of -1209 mV and a self-corrosion current density of 53.02µA·cm-2. After 20h, the lowest thermal expansion coefficient, 19.87×10-6·K-1, was achieved. However, agglomerated particles after 5h resulted in inferior thermal properties, including a thermal expansion coefficient of 20.45×10-6·K-1 and thermal conductivity of 94W·m-1·K-1. The optimal ball milling duration for these composites was determined to be 10h, balancing performance and cost-effectiveness.

Optimization of HVOF spraying parameters for enhanced Fe-based amorphous coatings: A taguchi approach

In this work, Fe57Cr15Mo8P10C7B3 amorphous coatings (ACs) were fabricated on 316L stainless steel (316L SS) substrate using high-velocity oxygen-fuel (HVOF) spraying technique. The Taguchi's method guided the design of L16 (43) orthogonal experiments to optimize the process parameters, including spraying distance, oxygen flow rate, and kerosene flow rate. Through statistical analyses, including signal-to-noise ratio analysis, analysis of variance (ANOVA), and response surface methodology (RSM), empirical relationships for evaluating the influence of these parameters on coating quality were established, with porosity as the primary metric. Our findings indicate a pronounced sensitivity of the porosity of the ACs to spraying conditions, in which oxygen flow rate has the most significant effect on the porosity of the ACs, while kerosene flow rate has the smallest impact. Meanwhile, it is predicted that a minimum coating porosity of 0.75 % can be achieved under the optimal deposition conditions of the spraying distance of 330 mm, the kerosene flow rate of 6.0 GPH, and an oxygen flow rate of 1900 SCF. Experimental validation confirmed these conditions, yielding coatings with superior coating quality and performance with a minimum coating porosity of 0.68 %, a microhardness of 826 ± 65 HV0.1, improved corrosion resistance in 3.5 wt% NaCl solution with a high self-corrosion potential of −0.37 V, a low self-corrosion current density of 1.08 × 10−6 A/cm2, and a low passivation current density of 1.16 × 10−5 A/cm2, and enhanced wear performance with a wear volume loss of only 4.00 × 10−5 mm3 N−1 m−1 and a friction coefficient of as low as 0.42 ± 0.022. The present study confirms the reliability of Taguchi's method in determining optimal HVOF processing parameters, evidenced by the consistency between theoretical predictions and experimental results.

Superhydrophobic Surfaces Prepared from Columnar Units by Convenient Electrodeposition with Excellent Mechanical Stability Impact and Corrosion Resistance.

Regular array structures prepared by laser processing and three-dimensional printing have promising applications in building stable superhydrophobic structures. However, the size of the materials processed by these two methods is affected by the size of the processing equipment, which prevents the processing of large-size materials. In this paper, a columnar unit consisting of a spherical structure with similar mechanical stability to the array structure is designed and prepared for metal surface protection. A convenient electrodeposition method was used to deposit a layer of columnar micron-sized copper consisting of spheres on the surface of a 6061 aluminum alloy. Subsequently, modified ZrO2 nanoparticles and polytetrafluoroethylene (PTFE) were sprayed on the surface to form a superhydrophobic surface with synergistic columnar units and ZrO2 (CAZ). The structure was tested and found to have excellent mechanical stability, maintaining the superhydrophobic properties of the surface even after 200 abrasion cycles of 1000-grit sandpaper under a 500 g load. Moreover, the vertical deformation of the CAZ sample under normal pressure was increased by a factor of 4 compared to the original substrate. Importantly, in subsequent corrosion resistance tests, the CAZ samples showed a two-order-of-magnitude improvement in self-corrosion current density and impedance modulus at low frequencies compared to the original substrate. This strategy is an effective method for preparing mechanically stable superhydrophobic structures that are low-cost and large enough to provide long-term protection for metal surfaces. It is particularly suitable for surface protection of instruments and automotive chassis armor.

Effect of Ti3SiC2 concentration on corrosion resistance and ICR in bipolar plates composite ceramic coatings

Ti3SiC2, a MAX-phase ceramic, amalgamates metallic and ceramic traits, delivering exceptional electrical conductivity and corrosion resistance. In this research, Ti3SiC2 composite coatings were applied to 316 L stainless steel via low-power atmospheric plasma spraying (APS), aiming to bolster the electrical and corrosion resistance attributes of bipolar plates (BPPs). A power input of 15 kW notably enhanced coating density, yielding a Ti3SiC2 concentration of 19.2 wt% in the coating. Extremes in the spraying power led to either diminished deposition efficiency or a reduction of Ti3SiC2 mass fraction below 5 wt%. Tafel curves demonstrated that specimens with elevated Ti3SiC2 mass fractions exhibited robust corrosion resistance, characterized by a self-corrosion potential of −162.5 mV and a self-corrosion current density of 1.7217 × 10−6 A·cm−2. Moreover, the interfacial contact resistance (ICR) between the coating and the gas diffusion layer was remarkably low (down to 5.49 mΩ·cm−2), indicating enhanced surface electron transfer with increasing Ti3SiC2 mass fractions.

Cross-linked ZnAl-LDH/PEDOT:PSS/MoS2 coating in-situ grown on aluminum alloy for excellent protection against both corrosion and wear

In this study, a new Al-LPM composite coating was in-situ deposited on the Al alloy via a facile one-pot hydrothermal method. Morphological and compositional characterizations revealed a tri-layered structure of the Al-LPM coating, namely, zinc aluminum-layered double hydroxide (ZnAl-LDH)/poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS)/MoS2. ZnAL-LDH was deposited closest to the surface of Al alloy, and the metallic ion-cross-linking of PEDOT:PSS makes the 3D coating more robust. The unique structure endows the coating with superior protective properties against both corrosion and wear. For anti-corrosion, the Al-LPM coating showed very high self-corrosion potential (-0.092 V) and small self-corrosion current density (46.0 μA cm−2) (vs. Al substrate with -1.157 V and 354.8 μA cm−2, respectively), long-lasting high corrosion resistance (>57,000 Ω cm2) during the immersion test, and the almost intact surface morphology and composition after 360 h corrosion. For anti-wear, the friction coefficient of the Al-LPM coating was determined to be < 0.2, which was much smaller than for the Al substrate (> 0.4). Also, there were no serious wear marks and grooves left after the dry-friction test.

Study on the corrosion resistance of new reticulated organic polymerized film on copper foil surface

In response to the policy of energy saving and emission reduction, the field of new energy vehicles is booming, and along with it, the technical requirements for lithium-ion batteries are becoming more and more stringent. Electrolytic copper foil, as the anode collector material of lithium batteries, seriously affects the progress of lithium technology, and electrolytic copper foil with high corrosion and oxidation resistance is the key to ensuring its performance. Experimentally, the BTA-Si passivation film layer was constructed on the surface of electrolytic copper foil by compounding benzotriazole (BTA) and silane coupling agent (JH-M902) with an easy-to-operate chemical impregnation method. The results of electrochemical analysis and characterization showed that JH-M902 hydrolyzed to produce Si-OH and then dehydrated and polymerized with Cu-OH to form Si-O-Cu or partially dehydrated and polymerized with each other to form Si-O-Si, which formed an intertwined organic reticulation film on the electrolytic copper foil. At the same time, BTA and copper oxides form a BTA-Cu complex, which is adsorbed and perpendicular to the copper foil. The combination of the two can not only make up for the gap in the organic mesh layer but also anchor the mesh layer, thus inhibiting its desorption in harsh external environments. Immersed in 3.5 wt% NaCl, the self-corrosion current density (icorr) of BTA-Si passivation film is only 1.115 × 10−7 A/cm2, and the corrosion inhibition rate as high as 99.56 %, which is far better than that of the single BTA and Si passivation film. In addition, the BTA-Si passivation film is smooth, dense, and thin, which significantly improves the corrosion resistance of copper foil without changing its original structure.

Research on the mechanism of microbial corrosion in the subsurface layer of 7075 aluminum alloy under different corrosion environments with ultra low temperature double increase effect

Aluminum alloys exhibit a dual-enhancement effect, characterized by simultaneous increases in strength and ductility at ultra-low temperatures. This study investigates the effects of deep cooling time and corrosion time on the surface quality, elemental distribution, corrosion product films, and electrochemical properties of 7075 aluminum alloy using techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical testing. The research reveals that 7075 aluminum alloy surfaces are primarily covered with blocky corrosion products after microbiologically induced corrosion (MIC) in polar marine (PM) conditions, composed mainly of Al(OH)3, Al2O3, and AlCl3. In contrast, in boreal marine (BM) conditions, the surfaces mainly feature cluster-like corrosion products composed of Al(OH)3 and Al2O3. PM exhibits a lower self-corrosion potential compared to BM, and after 5 days of MIC, the self-corrosion potential of 7075 aluminum alloy in PM shifts positively by 0.612 V compared to BM. The BM-9 sample shows the lowest self-corrosion current density at 3.777 × 10^-7 A/cm2, reduced by 81.3 % compared to PM-9, with the BM-9 sample exhibiting the highest polarization resistance at 9.15 × 10^3 Ω cm2. In comparison to the PM MIC environment, BM MIC conditions result in better surface quality and electrochemical characteristics for 7075 aluminum alloy.

Effect of rare earth element Y content on microstructure, magnetic properties, and electrochemical properties of the as-annealed FeCoNiAl0.2Yx high-entropy alloys

FeCoNi high-entropy alloy (HEA) is widely used in the aerospace and chemical industry. However, the strength and corrosion resistance of the alloy still need to be improved. In this paper, FeCoNiAl0.2Yx (x = 0, 0.05, 0.1, 0.2, and 0.3 in mole ratio) high entropy alloys with different contents of rare earth (RE) element yttrium (Y) were prepared by the vacuum arc melting method, and then the alloys were subjected to annealing treatment at 800 °C/2h. The microstructure, hardness, magnetism, and corrosion performance of FeCoNiAl0.2Yx HEAs in the annealed state with different contents of element Y were analyzed. The results show that the annealed FeCoNiAl0.2Yx HEAs without the addition of element Y and after the addition of element Y both were composed of a face-centered cubic phase. The alloy showed a dendritic structure inside. The element Y was solidly dissolved in the alloys to refine the microstructure of the alloys, and the dendrites were gradually refined with the addition of Y. The Y element caused the phenomenon of lattice distortion inside the alloys, which led to the increase in the alloys’ hardness. The alloy with x = 0.2 showed the greatest exchange of magnetic atoms and the alloy with x = 0.05 showed the lowest coercivity. The alloy with x = 0.1 showed the lowest self-corrosion current density, the broadest passivation zone, the densest dendrites, the smallest grain spacing, and the weakest tendency for intergranular corrosion. The present study shows that the introduction of element Y improves the microstructural morphology, hardness, magnetism, and corrosion properties of FeCoNiAl0.2Yx HEAs in the annealed state.

Improvement of corrosion resistance and electrical conductivity of a Cr–C coated heat-assisted forming stainless steel bipolar plate for proton exchange membrane fuel cell

Heat-assisted forming is gaining increasing attention for its potential in improving the formability and quality of metallic bipolar plate (BPP) of proton exchange membrane fuel cell (PEMFC). However, the effects of heat-assisted forming and the subsequent coating process on corrosion resistance and electrical conductivity of stainless steel BPP still remain unclear. This work proposes a way to improve simultaneously the corrosion resistance and electrical conductivity of heat-assisted forming stainless steel BPP by depositing a Cr–C coating directly on its surface without removing the oxide layer using the magnetron sputtering method. Potentiodynamic tests indicate that self-corrosion current density and corrosion current density at 1.0 V (vs. Ag/AgCl) of the Cr–C coated heat-assisted forming SS316L BPP prepared under 900 °C for 10 min are 0.021–0.040 μA cm−2 and 77.54 μA cm−2, respectively, both of which are smaller than those of coated SS316L BPP formed under room temperature. In addition, the contact resistance is close to that of the gold-plated copper plate under the same pressure. The corrosion resistant intermediate oxide layer and conductive network formed between Cr–C coating and metal substrate through defects of oxide layer may be the main reason for improvement of its corrosion resistance and electrical conductivity, respectively.

Corrosion Behavior of Q420qNH Plate and Welded Joint in Deicing Salt Medium by Cyclic Immersion + Infrared Drying

The corrosion behavior of Q420qNH steel plate and welded joint in deicing salt medium is investigated by cyclic immersion + infrared drying accelerated corrosion experiments. The results show that the corrosion products are mainly Fe2O3 and FeOCl under the influence of Cl− concentration differential corrosion microcells in the immersion corrosion anoxic stage, and the corrosion products are mainly β-FeOOH, γ-FeOOH, and Fe3O4 under the influence of oxygen concentration differential corrosion microcells catalyzed in the infrared drying stage. Throughout the corrosion process, the corrosion weight gain and average corrosion rate of the welded sample are always lower than that of the plate sample. The Iα-FeOOH/Iβ-FeOOH + FeOCl peak intensity ratio of the welded sample is always higher than that of the plate sample and the heat-affected zone (HAZ) sample. The corrosion types of the three samples are inhomogeneous total corrosion + pitting, and the depth of the pits in the plate is much larger than that in the weld and the HAZ. In the late stage of corrosion, the self-corrosion current density is: plate &amp;gt; HAZ &amp;gt; weld, and the resistance of the rust layer of the weld and HAZ samples is 1.66 times and 1.31 times that of the plate sample, respectively. This is because the microstructure of the weld and HAZ are composed of a large number of fine acicular ferrite and lath-shaped bainite generated inside the original austenite grains, and the small angle grain boundary is not conducive to the initiation and expansion of pitting corrosion. In addition, the higher content of Cu, Cr, Ni, and other elements in the weld can refine the rust layer products and effectively impede the intrusion of Cl−, contributing to corrosion resistance improvement. As the combined effect of Cl− and immersion anoxic environment inhibits the formation of α-FeOOH and promotes the formation of a large number of loose and unstable β-FeOOH and soluble FeOCl, the weathering steel is not well protected by the rust layer during cyclic immersion corrosion in deicing salt medium.

The Effects of Cl− and selected deoxidizers on the high temperature corrosion electrochemistry of alloy 690 in nuclear steam generator water

ABSTRACT The heat transfer tube in a steam generator serves as a critical heat exchange component in the primary and secondary loops of pressurized water reactor (PWR) nuclear power plants. The corrosion resistance of the heat transfer tube material directly influences the longevity of PWR nuclear power plants. This study investigated the electrochemical corrosion properties of 690 alloy (UNS N06690) in a simulated secondary water environment of PWR, focusing on different chloride ion concentrations and combinations of deoxidizers. The findings reveal a gradual decrease in the corrosion potential of 690 alloy, accompanied by an increase in self-corrosion current and a progressive reduction in the passivation range, ultimately leading to its disappearance as chloride ion concentration rises from 0 μg·L−1 to 500 μg·L−1. Moreover, the impedance value of the inner film exhibits a declining trend with increase of chloride ion concentration. Conversely, the resistance value of the outer film remains relatively stable while the size and spacing of oxide particles on the surface of the 690 alloy continuously increase. This observation suggests that chloride ions primarily influence the formation of the inner passivation film, which in turn determines the corrosion resistance of the 690 alloy. Notably, the performance of the 690 alloy is similar when the deoxidizer combination is ammonia(NH3)+erythorbic acid(ERA) or NH3+hydrazine(N2H4), demonstrating the ability to form a relatively complete passivation film and exhibit improved corrosion resistance compared to NH3+N-isopropyl hydroxylamine, additionally, when the deoxidizer combination is NH3+N2H4, the 690 alloy exhibits lower self-corrosion current density across different chloride ion concentrations, indicating enhanced corrosion resistance.

Corrosion property investigation of laser-cladding copper coating in the simulated nuclear waste disposal solution

To explore the efficient corrosion protection for the nuclear waste storage containers, pure copper coatings were successfully prepared on the 20# steel pipe surface using an infrared laser system under different laser powers. The study was conducted on the copper coatings, encompassing the surface quality, defects, microstructure, elemental distribution, phase composition, and corrosion products. The electrochemical and immersion corrosion behavior of the copper coatings in simulated nuclear waste disposal solutions was analyzed. The pure copper coating prepared by 2800 W laser power has fewer amounts and smaller sizes of defects inside the coating with only a slight fusion of Cu and Fe elements at the interface, which exhibits the highest corrosion potential and the smallest self-corrosion current density. During the immersion corrosion process, pores and unfused defects inside the coating, as well as the pits formed by galvanic coupling corrosion, lead to enhanced acidity inside these defects, resulting in a higher corrosion rate. As the immersion time proceeds, the corrosion rate slows down gradually and the content of Cu2+ corrosion product increases significantly.

The growth behavior and performance of microarc oxidation coating on AZ91/Ti composite: Influence of Ti-reinforcement phase and electrolyte

Magnesium matrix composites with both high strength and ductility have been achieved by introducing pure Ti particles. However, the properties of the surfaces of the composites need to be improved by surface technology, such as micro-arc oxidation (MAO). In this study, we investigated the influence of the Ti-reinforcement phase on coating growth and evolution by subjecting both AZ91 alloy and AZ91/Ti composite to MAO treatment using silicate-based and phosphate-based electrolytes. Results revealed that the Ti-reinforcement phase influenced the MAO process, altering discharge behavior, and leading to a decreased cell voltage. The vigorous discharge of the Ti-reinforcement phase induced the formation of coating discharge channels, concurrently dissolving and oxidizing Ti-reinforcement to produce a composite ceramic coating with TiO2. The MAO coating on the AZ91/Ti composite exhibited a dark blue macromorphology and distinctive local micromorphological anomalies. In silicate electrolyte, a “volcano-like” localized morphology centered on the discharge channel emerged. In contrast, treatment in phosphate-based electrolyte resulted in a coating morphology similar to typical porous ceramic coatings, with visible radial discharge micropores at the reinforcement phase location. Compared to the AZ91 alloy, the coating on the AZ91/Ti composite exhibited lower thickness and higher porosity. MAO treatment reduced the self-corrosion current density of the AZ91/Ti surface by two orders of magnitude. The silicate coating demonstrated better corrosion resistance than the phosphate coating, attributed to its lower porosity. The formation mechanism of MAO coatings on AZ91/Ti composites in phosphate-based and silicate-based electrolytes was proposed.

Effect of laser shock peening on stress corrosion cracking of TC4/2A14 dissimilar metal friction stir welding joints

Stress corrosion cracking (SCC) of welded joints is a significant issue that affects the widespread application of multimetal welded structures in aerospace, transportation, and other fields. This paper investigates the effect of laser shock peening (LSP) on the SCC of TC4/2A14 friction stir welded (FSW) joints with dissimilar metals. The microstructural evolution, mechanical properties, and corrosion behavior with and without LSP treatment were investigated using optical microscopy, transmission electron microscopy, X-ray analysis, electrochemical testing, and slow strain rate tensile testing (SSRT). The results showed that the LSP significantly refined the grains and induced work-hardening on the near-surface of the material. After LSP, the compressive residual stresses on the surface of the titanium and aluminium sides were −817.6 MPa and −153.6 MPa for the joint, respectively. Corrosion resistance was also improved, with the self-corrosion current density on the Al side of the joints reduced by 77% and the SCC susceptibility index (Issrt) reduced from 0.140 to 0.121. The enhanced SCC resistance of the LSP-treated TC4/2A14 dissimilar metal FSW joints is primarily due to grain refinement, work-hardening effect, and high-level compressive residual stress. These factors not only enhance the material strength and improve the pitting resistance of the joints but also prevent the initiation and propagation of SCC.

Improved mechanical properties and corrosion resistance of Zr-Cu-Al-Ni-Ti bulk metallic glasses by Co addition

Zr-based bulk metallic glasses (BMGs) are considered very promising medical materials because of their high strength and good corrosion resistance. However, poor room temperature plasticity severely hinders their development. In this work, a series of Zr61Cu18Al9Ni7-xTi5Cox (x = 0,1,3,5,7 at.%) BMGs are manufactured using vacuum arc melting technology. The effect of the Co addition on the glass forming ability, mechanical properties, and corrosion resistance is investigated. The results show that the appropriate Co addition can improve the room temperature plasticity and corrosion resistance. Compression tests show that when 1 at.% of Co element is added, the compressive strength is 1769.0 MPa, and the plasticity is 11.5 %, higher than the base alloy Zr61Cu18Al9Ni7Ti5 with 1607.9 MPa and 3.4 %. Corrosion tests show that the passivation interval of all Zr-based BMGs increases with the addition of Co. In particular, the maximum passivation interval of 1.320 V and the minimum self-corrosion current density are exhibited at 5 at.% Co addition. Overall, the effects of Co addition in terms of mechanical and corrosion aspects provide new guidance for the study of Zr-based alloys in the medical field.

Corrosion Behavior of the 2024 Aluminum Alloy in the Atmospheric Environment of the South China Sea Islands

The 2024 aluminum alloy, a structural material commonly used in aviation aircraft bodies, is susceptible to serious corrosion in marine atmospheric environments. This paper comprehensively studies the corrosion behavior of the 2024 aluminum alloy in the South China Sea atmosphere. Weighing, morphology observation, phase analysis, electrochemical testing, and other methods were used to study the corrosion law and corrosion mechanism of the 2024 aluminum alloy. The main conclusions are as follows: At the initial stage of exposure, pitting corrosion occurred on the surface of the 2024 aluminum alloy. After 3 months of exposure, the self-corrosion current density increased from 0.456 μA·cm−2 to 8.338 μA·cm−2. After 6 months of exposure, the corrosion developed into general corrosion. The main component of the corrosion product was Al2O3·3H2O. The product covered the surface to form a loose corrosion product layer, which had an inhibitory effect on corrosion. The self-corrosion current density was reduced to 2.359 μA·cm−2. After 12 months of exposure, the corrosion product layer fell off and became thinner, and the self-corrosion current density increased to 2.849 μA·cm−2. The corrosion kinetics conformed to the functional equation W = 0.00346t0.73891, indicating that the corrosion products have a certain protective effect on the matrix.

High stability and high corrosion resistance of a class of Co–Cr–Mo–Nb–B high-entropy metallic glasses

In this study, we have developed a class of new Co–Cr–Mo–Nb–B high-entropy metallic glass alloys with high stability and high corrosion resistance. It was found that for Co26Cr26Mo26Nb7B15 metallic glass, the glass transition temperature reached to 1058 K, and the initial crystallization temperature of Co24.5Cr26.5Mo26.5Nb7.5B15 metallic glass was as high as 1132 K. There is a large hardness of 18.1 GPa and Young's modulus of 267 GPa of Co27.5Cr27.5Mo26.5Nb3.5B15 metallic glass. The excellent thermodynamic property and mechanical properties were proved to be related to the covalence bond and hybridization of metal-metalloid bonds. The Co–Cr–Mo–Nb–B metallic glasses exhibited a lower self-corrosion current density and higher self-corrosion voltage compared with 316 in 1 M hydrochloric acid solution, and the high corrosion resistance could be attributed to passive films enriched with Cr3+ and Mo4+. These findings provide a new and effective way to design high-entropy metallic glasses with excellent comprehensive properties and suitable for high stability applications.