Microstructural characterization and corrosion-resistance behavior of friction stir-welded A390/10 wt% SiC composites-AA2024 Al alloy joints

This study examined the effect of traverse speed on the mechanical properties, corrosion-resistance behavior, and microstructure of friction stir-welded A390/10 wt% SiC composites-AA2024 Al alloy joints. The laminar flow of both materials was found to diminish in the stir zone (SZ) when the traverse speed of the tool increased from 40 to 80 mm/min, lowering their mixing rate. Large aspect ratio Si particles are broken by the tool pin-induced applied plastic strain, which turns them into refined equiaxed particles. Their aspect ratio remains unchanged in the SZ, despite their decreasing size. SiC and Si particles progressively come into view when moving from the AA2024 alloy's SZ to the composite workpieces. These changes happen abruptly as traverse speed increases due to the lack of an interfacial layer structure. The advancing side (AS)'s SZ grain size drops from 4.2 ± 0.3 μm to 1.2 ± 0.2 μm as the traverse speed drops from 80 to 40 mm/min. Increased traverse speed from 40 to 80 mm/min will result in a 5.8% decrease in elongation percentage (EP) and 8.4%, 36%, and 10.3% increases in the ultimate tensile strength (UTS), corrosion resistance, and yield strength, respectively.

Tracing the impact of CO2 on the electrochemical and charge-discharge behavior for Al-Mg alloy in KOH and LiOH electrolytes for battery applications

For the first time, it has been found that the electrochemical performance of the Al-Mg alloy as an anode in alkaline batteries has been markedly enhanced in the presence of CO2 and LiOH as an electrolyte. This work compares the electrochemical performance of an Al-Mg alloy used as an anode in Al-air batteries in KOH and LiOH solutions, both with and without CO2. Potentiodynamic polarization (Tafel), charging-discharging (galvanostatic) experiments, and electrochemical impedance spectroscopy (EIS) are used. X-ray diffraction spectroscopy (XRD) and a scanning electron microscope (SEM) outfitted with an energetic-dispersive X-ray spectroscope (EDX) were utilized for the investigation of the products on the corroded surface of the electrode. Findings revealed that the examined electrode's density of corrosion current (icorr.) density in pure LiOH is significantly lower than in pure KOH (1 M). Nevertheless, in the two CO2-containing solutions investigated, icorr. significantly decreased. The corrosion rate of the examined alloy in the two studied basic solutions with and without CO2 drops in the following order: KOH > LiOH > KOH + CO2 > LiOH + CO2. The obtained results from galvanostatic charge-discharge measurements showed excellent performance of the battery in both LiOH and KOH containing CO2. The electrochemical findings and the XRD, SEM, and EDX results illustrations are in good accordance.

mori silk fibroin coatings on AZ31 biometals with enhanced corrosion resistance, adhesion and biocompatibility

Silk fibroin coatings on biomedical magnesium alloys have garnered significant attention due to their enhanced corrosion resistance and biocompatibility. However, the utilization of wild A. pernyi silk fibroin, known for its RGD sequence that facilitates tissue regeneration, presents a challenge for corrosion-resistant coatings on magnesium alloys due to its weak adhesion and high dissolution rate. In this study, we employed hexafluoroisopropanol as a solvent to blend A. pernyi silk fibroin with B. mori silk fibroin. The resulting blended fibroin coating at a 3:7 mass ratio exhibited a heterogeneous nucleation effect, enhancing β-sheet content (32.3 %) and crystallinity (28.6 %). This improved β-sheet promoted the "labyrinth effect" with an Icorr of 2.15 × 10-6 A cm-2, resulting in significantly improved corrosion resistance, which is two orders of magnitude lower than that of pure magnesium alloy. Meanwhile, the increased content of exposed serine in zigzag β-sheet contributes to a higher adhesion strength. Cell cytotoxicity evaluation confirmed the enhanced cell adhesion and bioactivity. This work provides a facile approach for wild A. pernyi silk fibroin coatings on magnesium alloys with enhanced corrosion resistance, adhesion and biocompatibility.

Design and preparation of Ti-xFe antibacterial titanium alloys based on micro-area potential difference

Fe was selected as an alloying element for the first time to prepare a new antibacterial titanium alloy based on micro-area potential difference (MAPD) antibacterial mechanism. The microstructure, the corrosion resistance, the mechanical properties, the antibacterial properties and the cell biocompatibility have been investigated in detail by optical microscopy, scanning electron microscopy, electrochemical testing, mechanical property test, plate count method and cell toxicity measurement. It was demonstrated that heat treatment had a significant on the compressive mechanical properties and the antibacterial properties. Ti-xFe (x = 3,5 and 9) alloys after 850 °C/3 h + 550 °C/62 h heat treatment exhibited strong antimicrobial properties with an antibacterial rate of more than 90% due to the MAPD caused by the redistribution of Fe element during the aging process. In addition, the Fe content and the heat treatment process had a significant influence on the mechanical properties of Ti-xFe alloy but had nearly no effect on the corrosion resistance. All Ti-xFe alloys showed non-toxicity to the MC3T3 cell line in comparison with cp-Ti, indicating that the microzone potential difference had no adverse effect on the corrosion resistance, cell proliferation, adhesion, and spreading. Strong antibacterial properties, good cell compatibility and good corrosion resistance demonstrated that Ti-xFe alloy might be a candidate titanium alloy for medical applications.

Surface reconstruction in amorphous CoFe-based hydroxides/crystalline phosphide heterostructure for accelerated saline water electrolysis

Developing electrocatalysts with high activity and robust performance for large-scale seawater electrolysis to produce hydrogen holds immense significance. Herein, a highly active bifunctional electrode composed of amorphous cobalt-iron layered double hydroxides (CoFeLDH) and crystalline nickel phosphide (Ni2P) (denoted as CoFeLDH@Ni2P), is employed to boost hydrogen production through seawater electrolysis. The strong interface coupling effectively modifies the electronic structure at active sites, thereby accelerating the catalytic reaction kinetics. Impressively, in situ Raman and post-stability analyses demonstrate a unique reconstruction behavior on the CoFeLDH@Ni2P electrode. Bimetal co-incorporated NiOOH (CoFe-NiOOH) and Ni(OH)2 species are formed during the oxygen evolution reaction (OER), while CoFeLDH@Ni2P can transform into Ni(OH)2 species during the hydrogen evolution reaction (HER) process. Furthermore, the highly negatively charged surface selectively rejects Cl- ions by formed PO43-, endowing CoFeLDH@Ni2P with excellent tolerance and promising durability in saline electrolytes. Consequently, the CoFeLDH@Ni2P electrode exhibits an overpotential of 106 mV for HER at 10 mA cm-2 and 308 mV for OER to achieve 100 mA cm-2 in 1.0 M KOH solution. Additionally, the CoFeLDH@Ni2P(+,-) electrolyzer requires a low cell voltage of 1.56 V to deliver 10 mA cm-2 in 1.0 M KOH + Seasalt. This work presents an appealing strategy for the rational design of advanced electrocatalysts with amorphous-crystalline interfaces, which reveals the source of the activity of transition-metal phosphating compounds in saline water electrolysis.

Effect of laser beam incidence angle on weld formation mechanism and corrosion resistance of T2 copper/304 stainless steel

Over the last 20 years, industry interest in copper has increased. Its application in the petrochemical, automotive, and nuclear power industries highlights the need for new research directions especially in the joining of copper to other metals. In this work, lap joint of 304 stainless steel and T2 copper precoated with Cu-Mn-Ni filler metal was performed by laser brazing. The aim of this study is to characterize the influence of laser beam incidence angle on the welded joint forming mode, microstructure, elements diffusion and corrosion resistance. According to the findings, the joint is classified as a welded joint when the laser beam incidence angle is 80°, and as a welded-brazed joint when it's 90°, 70°, or 60°. The microstructure is mainly composed of Cu-rich and Fe-rich phases, Mn in the Cu-rich phase aggregation and Cr in the Fe-rich phase aggregation. In the fusion zone (FZ) the content of less than 50% of the liquid will be in the form of supersaturated droplets in the matrix of the other side. The local corrosion pair that the copper steel matrix and liquid drop produce in the FZ speeds up the dissolution of the Cu-rich phase, which effected corrosion resistance of the joint.

Electrochemical and hot corrosion behaviour of annealed AlCoCrFeNi HEA coating over steel

The ability to endure extreme corrosion in challenging environments is reduced in stainless steel. This can be addressed by appropriate surface modification techniques to redefine the surface with the required properties. The characteristics of the atmospheric plasma sprayed AlCoCrFeNi High Entropy Alloy (HEA) on SS316l are presented in this study. The coating characterisation revealed uniform coating with homogeneous deposition of gas-atomized AlCoCrFeNi HEA spanning for 150 µm. The coated substrates were further annealed for 2 h at 400 °C, 550 °C, 700 °C and 850 °C and the annealing at 550 °C offered enhanced microstructure. Annealing the coated sample at 550 °C offered a 46% improvement in microhardness against the uncoated sample post-annealing. The electrochemical corrosion tests showcased improved corrosion resistance after annealing through the formation of a protective oxide layer and the influence of HEA. Hot corrosion tests at 900 °C resulted in 10.1%, 8.49%, and 10.36% improved corrosion resistance for the coated sample annealed at 550 °C than the coated sample pre annealing and 44.09%, 44.25%, and 42.09% than the uncoated sample pre annealing under three salt mixtures respectively. The microstructural analysis examines various corrosion modes and verifies the presence and formation of protective oxide layers.

Characterization, mechanical properties, corrosion behavior and bone-like apatite formation ability of fluorine substituted hydroxyapatite coating

Hydroxyapatite (HA) is a non-bioceramic commonly used in human implants in the form of coatings, which are limited in their application by mechanical and wear resistance properties, as well as biodegradability. In this study, fluorine substituted hydroxyapatite (FHA) coatings were prepared on Ti-6Al-4V surfaces by plasma spraying method using a mixture of calcium fluoride and hydroxyapatite powders. The prepared coatings were characterized by X-ray diffraction and fourier transform infrared (FTIR) spectroscopy at different levels of calcium fluoride (3 wt%, 6 wt%, 9 wt%, and 12 wt%). The biocompatibility of the coatings was evaluated by in vitro mineralization experiments. Experimental results showed that at 9 wt% of calcium fluoride, the prepared FHA coatings had better mechanical properties, with improved bond strength (28.2 MPa). The X-ray diffraction patterns of the coatings reflect the fluorine substitution during the spraying process and the 9FHA has the highest crystallinity according to the XRD analysis, which is closely related to the biological activity of the coating. In addition, Potentiodynamic polarisation showed that the sample coated with the 9FHA coating had the highest Ecorr and lowest Icorr, indicating the best corrosion resistance. The FHA coating exhibits faster apatite deposition in simulated body fluid, and the efficiency of apatite deposition increases with the increase of CaF2.

Enhanced mechanical properties and environmental stability of polymer-bonded magnets using three-step surface wet chemical modifications of Nd-Fe-B magnetic powder

This research focuses on the surface modification of Nd-Fe-B magnetic powder to enhance its thermal and oxidation resistance without compromising magnetic properties and to improve adhesion to the polymer binder for enhanced mechanical properties. A three-step surface modification process involving phosphatization treatment, tetraethyl orthosilicate (TEOS) application, and 3-aminopropyltriethoxysilane (APTES) grafting, was applied to the powder, which was then compounded with polyamide 12 and injection-moulded into cylinders and dog-bone-shaped tubes. The resulting magnets exhibited remanence (Br) of 487.6 mT, coercivity (Hci) of 727.7 kA/m, and energy product (BHmax) of 39.3 kJ/m3. The modified magnets demonstrated exceptional corrosion resistance and thermal stability, with less than 5% irreversible flux loss after exposure to hot water, temperature shock, and pressurised steam. Furthermore, the modified magnets displayed significantly higher tensile strength, elongation at break, and elastic modulus with improvements of 62%, 16.7%, and 19.9%, respectively, compared to the non-modified batch. Additionally, the modified batch showed a notable 52% increase in flexural stress during flexural testing. These findings underscore the potential of silane surface modifications in producing injection-moulded permanent magnets based on Nd-Fe-B alloy, extending their shelf life and enhancing their overall performance.

Advances in amelioration of plasma electrolytic oxidation coatings on biodegradable magnesium and alloys

Magnesium and its alloys are considered excellent materials for biodegradable implants because of their good biocompatibility and biodegradability as well as their mechanical properties. However, the rapid degradation rate severely limits their clinical applications. Plasma electrolytic oxidation (PEO), also known as micro-arc oxidation (MAO), is an effective surface modification technique. However, there are many pores and cracks on the coating surface under conventional PEO process. The corrosive products tend to penetrate deeply into the substrate, reducing its corrosion resistance and the biocompatibility, which makes PEO-coated Mg difficult to meet the long-term needs of in vivo implants. Hence, it is necessary to modify the PEO coating. This review discusses the formation mechanism and the influential parameters of PEO coatings on Mg. This is followed by a review of the latest research of the pretreatment and typical amelioration of PEO coating on biodegradable Mg alloys in the past 5 years, including calcium phosphate (Ca-P) coating, layered double hydroxide (LDH)-PEO coating, ZrO2 incorporated-PEO coating, antibacterial ingredients-PEO coating, drug-PEO coating, polymer-PEO composite coating, Plasma electrolytic fluorination (PEF) coating and self-healing coating. Meanwhile, the improvements of morphology, corrosion resistance, wear resistance, biocompatibility, antibacterial abilities, and drug loading abilities and the preparation methods of the modified PEO coatings are deeply discussed as well. Finally, the challenges and prospects of PEO coatings are discussed in detail for the purpose of promoting the clinical application of biodegradable Mg alloys.

Electrochemical behavior and surface stability of dental zirconia ceramics in acidic environments

Dental zirconia ceramics, widely employed in dentistry for their biocompatibility and mechanical properties, face challenges in long-term viability within the oral cavity. This study focuses on analyzing the electrochemical behavior of a commercial dental zirconia ceramic type in acidic environments. Through extensive electrochemical investigations, including Electrochemical Impedance Spectroscopy (EIS) and cyclic polarization resistance (Cpol), corrosion resistance was assessed. Despite indications of material dissolution, our results demonstrate significant corrosion resistance, as reflected in low corrosion current density (Icorr) values. Notably, the study reveals the development of a protective oxide layer at the ceramic-electrolyte interface, contributing to material stability. XRD analysis confirms the presence of stable crystallographic phases (t-ZrO2) even after exposure to acidic media. Surface characterizations utilizing scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) affirm minimal surface damage and maintained elemental composition. These findings illuminate the intricate electrochemical behavior of dental zirconia ceramics in challenging environments, underscoring their potential for durable dental restorations. This interdisciplinary research bridges dentistry and materials science, providing valuable insights for optimizing material properties and advancing dental materials and restorative techniques.

Ion-bombardment-driven surface modification of porous magnesium scaffolds: Enhancing biocompatibility and osteoimmunomodulation

Porous Mg scaffolds are promising for bone repair but are limited by high corrosion rates and challenges in preserving coating integrity. We used Directed Plasma Nanosynthesis (DPNS) at 400 eV and a fluence of 1 × 1018 cm-2 to augment the bioactivity and corrosion resistance of porous Mg scaffolds, maintaining their overall material integrity. DPNS creates nanostructures that increase surface area, promote apatite nucleation, and enhance osseointegration, improving the bioactivity and corrosion resistance of porous Mg scaffolds without compromising their structure. Our findings indicate a decrease in surface roughness, with pre-irradiated samples having Rq = 60.4 ± 5.3 nm andRa = 48.2 ± 3.1 nm, and post-DPNS samples showing Rq = 36.9 ± 0.3 nm andRa = 28.6 ± 0.8 nm. This suggests changes in topography and wettability, corroborated by the increased water contact angles (CA) of 129.2 ± 3.2 degrees. The complexity of the solution influences the CA: DMEM results in a CA of 120.4 ± 0.1 degrees, while DMEM + SBF decreases it to 103.6 ± 0.5 degrees, in contrast to the complete spreading observed in non-irradiated samples. DPNS-treated scaffolds exhibit significantly reduced corrosion rates at 5.7 × 10-3 ± 3.8 × 10-4 mg/cm²/day, compared to the control's 2.3 × 10-2 ± 3.2 × 10-4 mg/cm²/day over 14 days (P < 0.01). The treatment encourages the formation of a Ca-phosphate-rich phase, which facilitates cell spreading and the development of focal adhesion points in hBM-MSCs on the scaffolds. Additionally, J774A.1 murine macrophages show an enhanced immune response with diminished TNF-α cytokine expression. These results offer insights into nanoscale modifications of Mg-based biomaterials and their promise for bone substitutes or tissue engineering scaffolds.

Microstructure and properties analysis of Ni60-based/WC composite coatings prepared by laser cladding

In this study, Ni60-WCx coatings (x = 0, 2, 4, 6 %) on 316L stainless steel (316Lss) were prepared via laser cladding technology. We examined all specimens s for microstructure, phase composition, microhardness and electrochemistry using several characterization techniques. It shows that the microstructure of the Ni-based coatings can be changed with WC powder. When the WC ratio is 2 %, crystalline crystals and cellular crystals can be found in the coating. As the WC ratio increases, more cellular crystals and fewer spiny crystals appear in the coating. When the WC ratio changes to 6 %, only cellular crystals can be found in the coating. The microhardness resultsshow that the Ni-based overcoat with added WC has a better microhardness compared to the pure Ni coating, and its average value of the coating area reaches a maximum value of 822.8 HV at a WC ratio of 2 %. That is due to the addition of WC which can cause regime transition. In addition, the Ni-based coating has better corrosion properties due to its different microstructure. When the WC ratio is 2 %, the specimen possesses the maximum Ecorr and smaller icorr with the best corrosion resistance.

Eco-friendly approach for the fabrication of biо copper based superhydrophobic coating on steel metal and its corrosion resistance evaluation

This study presents an eco-friendly approach for constructing superhydrophobic (S.H.) coatings on steel surfaces. The biо Сu nanoparticles are synthesized using a biоgenic process. Two types of coatings, Ni-Ѕ.Α and Ni-biо Сu-Ѕ.Α, were developed and characterized. The EDX results confirm the successful fabrication of two distinct coatings on the steel substrate: one involving the modification of nickel with stearic acid, Ni-Ѕ.Α, and the other involving the modification of nickel with both bio-Cu and stearic acid, Ni-biо Сu-Ѕ.Α. The SEM results revealed that the S.H. coats exhibit circular microstructures which contribute to the surface roughness. The contact angles of water droplets on the Ni-Ѕ.Α and Ni-biо Сu-Ѕ.Α coatings were measured at 158° ± 0.9° and 162° ± 1.1°, respectively. Chemical stability tests demonstrated that the Ni-Ѕ.Α coating maintains its S.H. behaviour in a pH range of 3-11, whereas the Ni-biо Сu-Ѕ.Α coating exhibits excellent chemical stability in a broader range of pH (1-13). The coating's mechanical stability was evaluated through abrasion tests. The Ni-Ѕ.Α coating retained its S.H. properties even after an abrasion length equal 1100 mm, while the Ni-biо Сu-Ѕ.Α coating maintained its S.H. behaviour till an abrasion length equal 1900 mm. The corrosion behavior and protective properties of the S.H. coatings were studied via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques. The PDP and EIS findings demonstrated that both Ni-Ѕ.Α and Ni-biо Сu-Ѕ.Α coatings significantly reduced the corrosion rate compared to uncoated steel.

Corrosion, surface, and tribological behavior of electrophoretically deposited polyether ether ketone coatings on 316L stainless steel for orthopedic applications

Electrophoretic deposition (EPD) of polyether ether ketone (PEEK) coatings on metallic implants has recently attracted a great deal of interest; however, further investigation into their corrosion, surface, and tribological properties is required for their clinical application. Using Potentiodynamic polarization and Mott-Schottky analysis of PEEK coatings, we analyzed the electrochemical corrosion behavior of electrophoretically deposited PEEK coatings on 316L stainless steel (SS) substrates. In addition, the tribological behavior of the coatings was determined through pin-on-disc and scratch testing. Initially, the EPD parameters were optimized using a Taguchi Design of Experiment (DoE) approach. The coatings exhibited irregular shaped grains along with ∼66 μm of thickness. Fourier transform infrared spectroscopy confirmed the presence of functional groups ascribed with PEEK. The coatings were moderately hydrophobic and had an average roughness of ∼2 μm. The corrosion studies demonstrated promising features of current density and corrosion potential, indicating that corrosion resistance significantly improves with PEEK coating. Electrochemical impedance spectroscopy also confirmed the corrosion resistance of PEEK coating. The coatings exhibited a slightly lower wear resistance than SS samples, but still possessed adequate wear and scratch resistance for biomedical applications. The current study confirmed that the PEEK coatings on metallic implants is effective for orthopedic applications where corrosion and tribology are major concerns.

Gastric acid challenge of lithium disilicate-reinforced glass-ceramics and zirconia-reinforced lithium silicate glass-ceramic after polishing and glazing-impact on surface properties

OBJECTIVES

To investigate the impact of simulated gastric acid on the surface properties of lithium disilicate-reinforced glass-ceramics and zirconia-reinforced lithium silicate glass-ceramic after certain polishing and glazing procedures.

MATERIALS AND METHODS

Four different types of square-shaped specimens (10 × 10 × 2 mm3, n = 13) were manufactured: lithium disilicate-reinforced glass-ceramic milled and polished (LDS-P); milled, polished, and glazed (LDS-PG); milled, glazed, and no polishing (LDS-G); and milled and polished zirconia-reinforced lithium silicate glass-ceramic (ZR-LS). Specimens were immersed in hydrochloride acid (HCl 0.06 M, pH 1.2) to simulate gastric acid irritation and stored in the acid for 96 h in 37 °C. Specimen weight, surface gloss, Vickers surface microhardness and surface roughness (Ra, Rq, with optical profilometer), and surface roughness on nanometer level (Sq, Sal, Sq/Sal, Sdr, Sds with atomic force microscope) were measured before and after the acid immersion.

RESULTS

ZR-LS specimens lost significantly more weight after acid immersion (p = 0.001), also surface microhardness of ZR-LS was significantly reduced (p = 0.001). LDS-G and LDS-PG showed significantly lower surface roughness (Sa, Sq) values compared to LDS-P before (p ≤ 0.99) and after (p ≤ 0.99) acid immersion and ZR-LS after acid immersion (p ≤ 0.99).

CONCLUSIONS

Gastric acid challenge affects the surface properties of lithium disilicate-reinforced glass-ceramic and zirconia-reinforced lithium silicate glass-ceramic. Glazing layer provides lower surface roughness, and the glazed surface tends to smoothen after the gastric acid challenge.

CLINICAL RELEVANCE

Surface finish of lithium disilicate-reinforced glass-ceramic and zirconia-reinforced lithium silicate glass-ceramic has a clear impact on material's surface properties. Gastric acidic challenge changes surface properties but glazing seems to function as a protective barrier. Nevertheless, also glazing tends to smoothen after heavy gastric acid challenge. Glazing can be highly recommended to all glass-ceramic restorations but especially in patients with gastroesophageal reflux disease (GERD) and eating disorders like bulimia nervosa.

Corrosion behavior of SiC coated HX with MoSi2 interlayer to be utilized in iodine-sulfur cycle for hydrogen production

In this era, renewable energy technologies are suitable to meet the challenges of fossil fuel depletion and global warming. Thus, hydrogen is gaining attention as an alternative clean energy carrier that can be produced from various methods, one of them is the iodine-sulfur (I-S) cycle which is a thermochemical process. The I-S cycle requires a material that can withstand an extremely corrosive environment at high temperatures. Immersion tests were conducted on bare superalloy Hastelloy X (HX), MoSi2, and SiC-MoSi2 coated HX, deposited in physical vapor deposition (PVD) to evaluate their corrosion resistance. Bare HX exhibited a high corrosion rate of 208.1 mm yr-1 when exposed to 98 wt% sulfuric acid at 300 °C. In contrast, HX with MoSi2 coating showed a much lower corrosion rate of 23.5 mm yr-1, and HX with SiC-MoSi2 coating demonstrated the lowest corrosion rate at 6.5 mm yr-1 under the same conditions. The coated samples were analyzed via FESEM before and after corrosion testing. The FESEM images reveal the formation of coalescent particles on the surface of the coating. The elemental analysis illustrates an increased concentration of silicon and oxygen in the corroded samples. Elemental mapping of these samples show a uniform distribution of elements over the sample. These findings contribute not only to materials science understanding but also to practical applications in hydrogen production via the I-S cycle, where corrosion-resistant materials are critical.

In vitro and in vivo study on fine-grained Mg-Zn-RE-Zr alloy as a biodegradeable orthopedic implant produced by friction stir processing

Magnesium alloys containing biocompatible components show tremendous promise for applications as temporary biomedical devices. However, to ensure their safe use as biodegradeable implants, it is essential to control their corrosion rates. In concentrated Mg alloys, a microgalvanic coupling between the α-Mg matrix and secondary precipitates exists which results in increased corrosion rate. To address this challenge, we engineered the microstructure of a biodegradable Mg-Zn-RE-Zr alloy by friction stir processing (FSP), improving its corrosion resistance and mechanical properties simultaneously. The FS processed alloy with refined grains and broken and uniformly distributed secondary precipitates showed a relatively uniform corrosion morphology accompanied with the formation of a stable passive layer on the alloy surface. In vivo corrosion evaluation of the processed alloy in a small animal model showed that the material was well-tolerated with no signs of inflammation or harmful by-products. Remarkably, the processed alloy supported bone until it healed till eight weeks with a low in vivo corrosion rate of 0.7 mm/year. Moreover, we analyzed blood and histology of the critical organs such as liver and kidney, which showed normal functionality and consistent ion and enzyme levels, throughout the 12-week study period. These results demonstrate that the processed Mg-Zn-RE-Zr alloy offers promising potential for osseointegration in bone tissue healing while also exhibiting controlled biodegradability due to its engineered microstructure. The results from the present study will have profound benefit for bone fracture management, particularly in pediatric and elderly patients.

Limitations of reuse for silver-palladium alloys -Evaluating post-recasting heat treatment impact on corrosion resistance

The aim of this study was to investigate the effect of repeated casting and heat treatment on the corrosion resistance of a commercial Ag-Pd-Cu-Au alloy as evaluated by electrochemical techniques. After repeated casting, the fifth cast of the Ag-Pd-Cu-Au alloy exhibited dramatic degradation of properties, although upon heat treatment, this corrosion resistance did improve. Despite the improvement by heat treatment, after five castings, this alloy may not have satisfactory hardness for clinical use. These results of this study demonstrate that, up to the fourth cast and heat treatment, the Ag-Pd-Cu-Au alloy has acceptable corrosion resistance and hardness.

Large improvement of the tensile strength of carbon nanotube films in harsh wet environments by carbon infiltration

Carbon nanotube (CNT) materials show large degradation in tensile strength when they are exposed in chemically active environments due to the loss of inter-tube bonding. Here, we report the suppression of such degradation by chemical vapor infiltration of amorphous carbon into CNT films. The amorphous carbon generated by the thermal decomposition of the gaseous hydrocarbon of acetylene is firmly bonded on the CNT sidewalls and intersections. Based on the improved inter-tube bonding and restriction of inter-tube sliding, the tensile strength of the film is improved to be 3 times of the original level. More importantly, the bonding is so strong and stable that the high tensile strength remains with little loss even in harsh wet environments such as boiling alcoholic, acidic, alkaline solutions and seawater. Such harsh environments-tolerant properties, which were rarely observed before, could open new windows for the CNT/C composite material to be applied from functional devices to structural components under extreme corrosive conditions.

Highly dispersed Co/Co9S8 nanoparticles encapsulated in S, N co-doped longan shell-derived hierarchical porous carbon for corrosion-resistant, waterproof high-performance microwave absorption

It is highly desirable, but challenging to develop multifunctional electromagnetic wave (EMW) absorbing material for practical applications in some harsh environments. Herein, we successfully embedded highly dispersed Co/Co₉S₈ nanoparticles into a three-dimensional (3D) honeycomb porous carbon skeleton (the carbon skeleton is derived from longan shell-derived S, N co-doped porous carbon) as a multifunctional material with outstanding EMW absorption properties, hydrophobicity and corrosion resistance. Its superior versatility is attributed to synergistic effects of the S and N dopants, large specific surface area, abundant carbon defects, and 3D porous characteristics. Minimal reflection loss (RL_min) and efficient absorption bandwidth (EAB) of the optimized material as EMW absorbers can achieve -59.9 dB and 6.8 GHz at a thickness of 2.7 mm, respectively, which are superior to most of the reported carbon-based absorbents. Meanwhile, theoretical simulations of the radar scattering cross section (RCS) further confirm that this multifunctional material has outstanding EMW attenuation performance and actual application potential. In addition, the material possesses strong hydrophobicity (124°) and anti-corrosion properties, expanding the scope of potential applications of microwave absorbers. Therefore, this work provides an effective development strategy for the design of anti-corrosion, super-hydrophobic, and high-performance EMW absorbing materials.

Investigation on the physical and electrochemical properties of typical Ni-based alloys used for the bipolar plates of proton exchange membrane fuel cells

The phase, mechanical properties, corrosion resistance, hydrophobicity, and interface contact resistance of three typical Ni-based alloys (Hastelloy B, Hastelloy C-276, and Monel 400) and 304 stainless steels were experimentally studied to evaluate their service performances as bipolar plate materials of proton exchange membrane fuel cells. All four alloys exhibit single-phase face-centered cubic structure, high strength, good ductility, and high hardness. Hastelloy C-276 has the best ductility with an uniform elongation of 72.5% and highest hardness of 363.7 HV. Hastelloy B has the highest ultimate tensile strength of 913.6 MPa. The hydrophobicity of all four alloys is not good, although Monel 400 has the highest water contact angle of 84.2°. Hastelloy B, Hastelloy C-276, and 304 stainless steel exhibit unsatisfying corrosion resistance in a simulated acidic work environment of proton exchange membrane fuel cell (0.5 M H₂SO₄+2 ppm HF, 80 °C, H₂) and high interface contact resistance. By contrast, Monel 400 demonstrates excellent corrosion resistance with a corrosion current density of 5.9 × 10^-7 A cm^-2 and a low interface contact resistance of 7.2 mΩ cm² at 140 N/cm². In terms of comprehensive performance, Monel 400 is the best uncoated material for the bipolar plates of proton exchange membrane fuel cells among typical Ni-based alloys.

Influence of TiO2 nanoparticles content as reinforce material to enhance the mechanical and corrosion resistance properties of Sn and Sn-Ag alloy for dental applications

This study evaluated the influence of the TiO₂ nanoparticles (NPs) on the mechanical and chemical performance of Sn and Sn-Ag alloys. The XRD (X-ray diffraction) and HR-TEM (high resolution-transmission electron microscopy) methods were used to characterize the NPs synthesized by the sol-gel microwave process. The chemical composition of the alloys was Sn, Sn+3TiO₂ NPs, Sn-5Ag+1.5TiO₂ NPs, Sn-10Ag, and Sn-10Ag+3TiO₂ NPs, obtained from an experimental factorial design (EFD). A statistical model was used to determine the mechanical and chemical properties, showing the Vickers hardness response surface, tensile strength, wear, and corrosion resistance. The wear and corrosion tests for the various alloy compositions were performed using human artificial saliva solution. The results indicated that the Sn-10Ag+3TiO₂ NPs exhibited the highest mechanical performance due to their increased hardness (380 HV), tensile strength (370 N), and wear resistance (0.34 × 10^-3 mm³ Nm^-1); in all the cases, the inclusion of TiO₂ NPs enhanced the corrosion resistance of the alloys. According to the American Dental Association (ADA), Sn-10Ag+3TiO₂ NPs alloy could be classified as a possible type IV restorative material.

Enhanced corrosion resistance properties of Fe-Al-Cr laser cladding coatings on 1045 carbon steel substrates

Fe-Al-Cr coatings with different content of Cr additive were prepared on 1045 carbon steel substrates by a laser cladding process. The incorporation of Cr atoms can effectively enhance the corrosion resistance of the coatings. In particular, the Fe-28Al-5Cr laser cladding coating exhibits the best film quality without phase segregation. In addition, the interfacial adhesion between the Fe-28Al-5Cr coating and the 1045 carbon steel substrate is improved. As a result, the Fe-28Al-5Cr laser cladding coating exhibits the best corrosion resistance in a 3.5 wt% NaCl solution under both immersion and electrochemical conditions. However, excessive Cr additive lead to the formation of Al₈Cr₅ in the grain boundaries, resulting in inferior corrosion resistance. Therefore, the new findings demonstrated in this work may inspire the design of high-quality coatings with excellent corrosion resistance.

S-modified NiFe-phosphate hierarchical hollow microspheres for efficient industrial-level seawater electrolysis

For sustained hydrogen generation from seawater electrolysis, an efficient and specialized catalyst must be designed to cope with the slow anode reaction and chloride ions (Cl^-) corrosion. In this work, an S-modified NiFe-phosphate with hierarchical and hollow microspheres was grown on the NiFe foam skeleton (S-NiFe-Pi/NFF), acting as a bifunctional catalyst to enable industrial-scale seawater electrolysis. The introduction of S distorted the lattice of NiFe-phosphate and regulated the local electronic environment around Ni/Fe active metal, both of which enhanced the electrocatalytic activity. Additionally, the existence of phosphate groups repelled Cl^- on the surface and enhanced corrosion resistance, enabling stable long-term operation in seawater. The double-electrode electrolyzer composed of the hollow-structured S-NiFe-Pi/NFF as both cathode and anode exhibited a potential of 1.68 V at 100 mA cm^-2 for seawater electrolysis. Particularly, to achieve industrial requirements of 500 mA cm^-2, it only required a low cell voltage of 1.8 V and demonstrated a consistent response over 100 h, which outperformed the pair of Pt/C || IrO₂. This study provides a feasible idea for the preparation of electrocatalysts that are with both highly activity and corrosion resistance, which is crucial for the implementation of industrial-scale seawater electrolysis.

Zn doped CaP coatings used for controlling the degradation rate of MgCa1 alloy: In vitro anticorrosive properties, sterilization and bacteria/cell-material interactions

The purpose of this study was to investigate the effect of Zn doped CaP coatings prepared by micro-arc oxidation method, as a possible approach to control MgCa1 alloy degradation. All the prepared coatings comprised a calcium deficient CaP phase. The control in this evaluation was performed with undoped CaP coating in SBF solution at body temperature (37 ± 0.5⁰C). The investigation involved determination of microchemical, mechanical, morphological, properties along with anticorrosive, cytocompatibility and antibacterial efficacy. The effect of sterilization process on the properties of the surfaces was also investigated. The results showed that the addition of Zn into CaP increased the corrosion resistance of MgCa1 alloy. Moreover, the adhesion strength of the coatings to MgCa1 alloy was enhanced by Zn addition. In cytotoxicity testing of the samples, extracts of the samples in MEM were incubated with L929 cells and malformation, degeneration and lysis of the cells were examined microscopically after 72 h. The results showed that all samples were cytocompatible. The degradation of MgCa1 alloy in the simulated body fluids (SBF) or DMEM was decreased by coating with CaP. Moreover, the degradation rate of CaP was further decreased by adding a small amount of Zn into the CaP matrix. The samples having CaP coatings and Zn doped CaP coating demonstrated antibacterial efficacy against E.coli. As a result, coating of magnesium alloy with Zn-doped CaP decreased the degradation rate, increased the corrosion resistance, cytocompatibility and the antibacterial effects of the alloys.

Recovery of Al2O3 from hazardous Al waste as a reinforcement particle for high-performance Ni/Al2O3 corrosion resistance coating via ultrasonic-aided supercritical-CO2 electrodeposition

The unprocessed dumping of aluminium wastes in the landscape leads to generation of heat and toxic gases, which are detrimental to the ecosystem. Motivated by the waste-to-wealth notion, we demonstrated the recovery of aluminium oxide nanoparticles (Al₂O₃NPs) from domestic aluminium wastes via a sonochemical approach and synthesis of nickel/aluminium oxide (Ni/Al₂O₃) coating via ultrasonic-coupled supercritical carbon dioxide (US-SC-CO₂) electrodeposition method for higher corrosion resistance performance. The physical characterization and material confirmation of prepared films were examined by microscopic and various spectroscopic techniques. The electrochemical corrosion resistance studies were explored via potentiodynamic polarization and electrochemical impedance spectroscopy techniques. Based on the results, the US-SC-CO₂ strategy exposed an improved distribution of Al₂O₃ NPs assimilation in Ni matrix, higher corrosion resistance, and microhardness. The integration of ultrasonic irradiation into the SC-CO₂ process promises an enhanced coating quality. Thereby, the novel US-SC-CO₂ approach for Ni/Al₂O₃ synthesis is expected to achieve a sustainable green impact in real-world applications.

Microstructures, mechanical and corrosion properties of graphene nanoplatelet-reinforced zinc matrix composites for implant applications

Zinc (Zn)-based alloys and composites are gaining increasing interest as promising biodegradable implant materials due to their appropriate biodegradation rates and biological functionalities. However, the inadequate mechanical strength and ductility of pure Zn have restricted its application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4 wt.% graphene nanoplatelets (GNP) fabricated via powder metallurgy were investigated as potential biodegradable implant materials. The microstructures, mechanical properties, and corrosion behaviors of the GNP-reinforced ZMCs were characterized using optical microscopy, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, Raman spectroscopy, compression testing, and electrochemical and immersion testing in Hanks' balanced salt solution (HBSS). The microstructural study revealed that the GNP was uniformly dispersed in the ZMCs after ball milling and sintering at 420°C for 6 h. The microhardness, compressive yield strength, ultimate compressive strength, and compressive strain of the ZMC-0.2GNP were 69 HV, 123 MPa, 247 MPa, and 23 %, respectively, improvements of ∼ 18 %, 50%, ∼ 28%, and ∼ 15% compared to pure Zn. The corrosion rate of the ZMCs were lower than that of the pure Zn in HBSS, and the ZMC-0.2GNP composite exhibited the lowest corrosion rate of 0.09 mm/y as measured by electrochemical testing. Biocompatibility assessment indicated that the diluted extracts of pure Zn and GNP-reinforced ZMCs with concentrations of 12.5% and 6.25% exhibited no cytotoxicity after cell culturing for up to 5 days, and the diluted extracts of ZMC-0.2 GNP composite revealed more than 90% cell viability after cell culturing of 3 days, showing the satisfying cytocompatibility. STATEMENT OF SIGNIFICANCE: Biodegradable Zn is a promising candidate material for orthopedic implant applications. Nonetheless, the inadequate mechanical strength and ductility of pure Zn limited its clinical application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4 wt.% graphene nanoplatelets (GNP) were developed via powder metallurgy, and the reinforcing efficacy of GNP on their mechanical properties was investigated. The addition of GNP significantly improved the compressive properties of ZMCs, with the Zn-0.2GNP composite exhibiting the best compressive properties, including 123 MPa compressive yield strength, 247 MPa ultimate compressive strength, and 22.9% compressive strain. Further, the 12.5% concentration extract of the ZMCs exhibited no cytotoxicity after cell culturing for 5 d toward SaOS2 cells.

In-vivo bone remodeling potential of Sr-d-Ca-P /PLLA-HAp coated biodegradable ZK60 alloy bone plate

Magnesium and its alloys are widely applied biomaterials due to their biodegradability and biocompatibility. However, rapid degradation and hydrogen gas evolution hinder its applicability on a commercial scale. In this study, we developed an Mg alloy bone plate for bone remodeling and support after a fracture. We further coated the Mg alloy plate with Sr-D-Ca-P (Sr dopped Ca-P coating) and Sr-D-Ca-P/PLLA-HAp to evaluate and compare their biodegradability and biocompatibility in both in vitro and in vivo experiments. Chemical immersion and dip coating were employed for the formation of Sr-D-Ca-P and PLLA-HAp layers, respectively. In vitro evaluation depicted that both coatings delayed the degradation process and exhibited excellent biocompatibility. MC3T3-E1cells proliferation and osteogenic markers expression were also promoted. In vivo results showed that both Sr-D-Ca-P and Sr-D-Ca-P/PLLA-HAp coated bone plates had slower degradation rate as compared to Mg alloy. Remarkable bone remodeling was observed around the Sr-D-Ca-P/PLLA-HAp coated bone plate than bare Mg alloy and Sr-D-Ca-P coated bone plate. These results suggest that Sr-D-Ca-P/PLLA-HAp coated Mg alloy bone plate with lower degradation and enhanced biocompatibility can be applied as an orthopedic implant.

Corrosion in seawater desalination industry: A critical analysis of impacts and mitigation strategies

In the current world, freshwater production by clean energy sources with minimum environmental footprints is the main challenge for humankind which is dramatically deteriorating by overexploitation of available water resources. Seawater desalination technology greatly contributes to the mitigation of these serious conditions to produce potable water. However, because desalination plants handle extremely aggressive seawater under stringent operational conditions, they are highly vulnerable to insidious effects of corrosion primarily in the form of general and localized corrosion. Moreover, mineral scaling and bio-fouling are major challenges that further exacerbate corrosion phenomena. So, to ensure the continual operation and curbing corrosion in seawater desalination systems, strict monitoring and selection of highly corrosion-resistance materials are of prime concern. The present paper briefly explores fundamental concepts of corrosion in the desalination industry besides discussing different mitigation strategies for reducing the pernicious effects of corrosion which gravely impair environment quality and durability of desalination infrastructures. Moreover, the authors propose the knowledge gaps and perspectives to delineate the future research direction. Effective solutions for avoiding seawater stagnation, developing highly sophisticated coatings and surface modification technologies, application of advanced computational programs for accurate prediction of possible corrosion failure in desalination plants, and using quantum technology and magnetic corrosion inhibitor in seawater desalination are recommended as an urgent future research focus to combat against corrosion. On the whole, despite outstanding breakthroughs in the field of corrosion control in the desalination industry, the long-term performance of current materials is highly controversial as still many cases of corrosion failures have been reported which indicates the necessity of intensive research work.

Copper-doped zeolitic imidazolate frameworks-8/hydroxyapatite composite coating endows magnesium alloy with excellent corrosion resistance, antibacterial ability and biocompatibility

Magnesium (Mg) and its alloys exhibit an excellent prospect for orthopedic clinical application due to their outstanding biodegradability and mechanical adaptability. However, the rapid corrosion rate/latent device-associated infections may lead to a failed internal fixation of Mg-based implants. Herein, a novel composite coating consisted of outer copper-doped zeolitic imidazolate frameworks-8 and inner hydroxyapatite (Cu@ZIF-8/HA) was in situ constructed on AZ31B Mg alloy via a two-step approach of hydrothermal treatment and seeded solvothermal method. The results verified that the electrochemical impedance of the obtained Cu45@ZIF-8/HA composite coating increased by two orders of magnitude to 6.6013 × 104 Ω·cm2 compared to that of bare Mg alloy. This was attributed to the reduced particle size of ZIF-8 nanoparticles due to the doped copper ions, which could be effectively grown in situ on the micro-nano flower-like structure of the HA-coated Mg alloy. Meanwhile, the Cu@ZIF-8/HA coating exhibited excellent antibacterial properties due to the release of copper ions and zinc ions from Cu@ZIF-8 dissolved in bacterial culture solution. The ICP results unraveled that the released concentration of copper and zinc ions could enhance the activity of alkaline phosphatase in the appropriate range during MC3T3-E1 cell culture in vitro for 7 days. This research revealed that the preparation of multifunctional metal-organic frameworks coating doped with antimicrobial metal ions via the seed layer solvothermal method was significant for studying the antimicrobial properties, osteogenic performance and corrosion resistance of Mg-based bioactive coatings.

Design of single-phased magnesium alloys with typically high solubility rare earth elements for biomedical applications: Concept and proof

Rare earth elements (REEs) have been long applied in magnesium alloys, among which the mischmetal-containing WE43 alloy has already got the CE mark approval for clinical application. A considerable amount of REEs (7 wt%) is needed in that multi-phased alloy to achieve a good combination of mechanical strength and corrosion resistance. However, the high complex RE addition accompanied with multiple second phases may bring the concern of biological hazards. Single-phased Mg-RE alloys with simpler compositions were proposed to improve the overall performance, i.e., “Simpler alloy, better performance”. The single-phased microstructure can be successfully obtained with typical high-solubility REEs (Ho, Er or Lu) through traditional smelting, casting and extrusion in a wide compositional range. A good corrosion resistance with a macroscopically uniform corrosion mode was guaranteed by the homogeneously single-phased microstructure. The bimodal-grained structure with plenty of sub-grain microstructures allow us to minimize the RE addition to <1 wt%, without losing mechanical properties. The single-phased Mg-RE alloys show comparable mechanical properties to the clinically-proven Mg-based implants. They exhibited similar in-vitro and in-vivo performances (without local or systematic toxicity in SD-rats) compared to a high purity magnesium. In addition, metal elements in our single-phased alloys can be gradually excreted through the urinary system and digestive system, showing no consistent accumulation of RE in main organs, i.e., less burden on organs. The novel concept in this study focuses on the simplification of Mg-RE based alloys for biomedical purpose, and other biodegradable metals with single-phased microstructures are expected to be explored.

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A concept of developing single-phased biodegradable magnesium alloys was proposed.

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Single-phased magnesium alloys with bimodal-grained structures were obtained.

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Good strength and corrosion resistance synergy was achieved in the alloys.

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Significantly reduced rare earth addition is beneficial to the biocompatibility.

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Simpler alloy helps to lower the possible biological risks of Mg related implants.

Optimization of the clinically approved mg-Zn alloy system through the addition of ca

Background

Although several studies on the Mg-Zn-Ca system have focused on alloy compositions that are restricted to solid solutions, the influence of the solid solution component of Ca on Mg-Zn alloys is unknown. Therefore, to broaden its utility in orthopedic applications, studies on the influence of the addition of Ca on the microstructural, mechanical, and corrosion properties of Mg-Zn alloys should be conducted. In this study, an in-depth investigation of the effect of Ca on the mechanical and bio-corrosion characteristics of the Mg-Zn alloy was performed for the optimization of a clinically approved Mg alloy system comprising Ca and Zn.

Methods

The Mg alloy was fabricated by gravitational melting of high purity Mg, Ca, and Zn metal grains under an Ar gas environment. The surface and cross-section were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to analyze their crystallographic structures. Electrochemical and immersion tests in Hank’s balanced salt solution were used to analyze their corrosion resistance. Tensile testing was performed with universal testing equipment to investigate the impact of Ca addition. The examination of cytotoxicity for biometric determination was in line with the ISO10993 standard.

Results

In this study, the 0.1% Ca alloy had significantly retarded grain growth due to the formation of the tiny and well-dispersed Ca₂Mg₆Zn₃ phase. In addition, the yield strength and elongation of the 0.1% Ca alloy were more than 50% greater than the 2% Zn alloy. The limited cell viability of the 0.3% Ca alloy could be attributed to its high corrosion rate, whereas the 0.1% Ca alloy demonstrated cell viability of greater than 80% during the entire experimental period.

Conclusion

The effect of the addition of Ca on the microstructure, mechanical, and corrosion characteristics of Mg-Zn alloys was analyzed in this work. The findings imply that the Mg-Zn alloy system could be optimized by adding a small amount of Ca, improving mechanical properties while maintaining corrosion rate, thus opening the door to a wide range of applications in orthopedic surgery.

Enhanced anti-corrosion and biocompatibility of a functionalized layer formed on ZK60 Mg alloy via hydroxyl (OH-) ion implantation

Magnesium and its alloys have piqued the interest of researchers due to their promising mechanical properties and biocompatibility. Moreover, the excessively fast corrosion rate of Mg alloys impedes their development in biomedical fields. Inspired by conventional ion implantation, a less-toxic functional group (hydroxyl) is used as the ion source to bombard the ZK60 Mg alloy surface to form a functionalized oxide layer. The surface characterization, corrosion resistance, and biocompatibility are systematically investigated before and after hydroxyl ion implantation. A smoother surface mainly constituted of hydroxide/oxide is formed for the treated samples. The formed functionalized layer significantly improves the corrosion resistance of the ZK60 Mg alloy substrate and the proliferation of MC3T3-E1 cells, as demonstrated by electrochemical, immersion, and in vitro cytocompatibility tests. In summary, less-toxic functional ion implantation can be an effective strategy for preventing corrosion of Mg alloy implants and promoting their biocompatibility.

Enhanced antibacterial behavior of a novel Cu-bearing high-entropy alloy

Contact infection of bacteria and viruses has been a critical threat to human health. The worldwide outbreak of COVID-19 put forward urgent requirements for the research and development of the self-antibacterial materials, especially the antibacterial alloys. Based on the concept of high-entropy alloys, the present work designed and prepared a novel Co_0.4FeCr_0.9Cu_0.3 antibacterial high-entropy alloy with superior antibacterial properties without intricate or rigorous annealing processes, which outperform the antibacterial stainless steels. The antibacterial tests presented a 99.97% antibacterial rate against Escherichia coli and a 99.96% antibacterial rate against Staphylococcus aureus after 24 h. In contrast, the classic antibacterial copper-bearing stainless steel only performed the 71.50% and 80.84% antibacterial rate, respectively. The results of the reactive oxygen species analysis indicated that the copper ion release and the immediate contact with copper-rich phase had a synergistic effect in enhancing antibacterial properties. Moreover, this alloy exhibited excellent corrosion resistance when compared with the classic antibacterial stainless steels, and the compression test indicated the yield strength of the alloy was 1015 MPa. These findings generate fresh insights into guiding the designs of structure-function-integrated antibacterial alloys.

Microstructure Design of High-Entropy Alloys Through a Multistage Mechanical Alloying Strategy for Temperature-Stable Megahertz Electromagnetic Absorption

Developing megahertz (MHz) electromagnetic wave (EMW) absorption materials with broadband absorption, multi-temperature adaptability, and facile preparation method remains a challenge. Herein, nanocrystalline FeCoNiCr_0.4Cu_0.2 high-entropy alloy powders (HEAs) with both large aspect ratios and thin intergranular amorphous layers are constructed by a multistage mechanical alloying strategy, aiming to achieve excellent and temperature-stable permeability and EMW absorption. A single-phase face-centered cubic structure with good ductility and high crystallinity is obtained as wet milling precursors, via precisely controlling dry milling time. Then, HEAs are flattened to improve aspect ratios by synergistically regulating wet milling time. FeCoNiCr_0.4Cu_0.2 HEAs with dry milling 20 h and wet milling 5 h (D20) exhibit higher and more stable permeability because of larger aspect ratios and thinner intergranular amorphous layers. The maximum reflection loss (RL) of D20/SiO₂ composites is greater than - 7 dB with 5 mm thickness, and EMW absorption bandwidth (RL < - 7 dB) can maintain between 523 and 600 MHz from - 50 to 150 °C. Furthermore, relying on the "cocktail effect" of HEAs, D20 sample also exhibits excellent corrosion resistance and high Curie temperature. This work provides a facile and tunable strategy to design MHz electromagnetic absorbers with temperature stability, broadband, and resistance to harsh environments.

Fabrication of Zirconium Silicate Reinforced Superhydrophobic Coating for the Evaluation of Corrosion-Resistance

The present work investigates on anodisation of aluminium in 1.0 M sodium oxalate and methodically evaluates the influence of zirconium silicate as an additive. The effect of additive upon structure, morphology, micro hardness and composition of the coating formed under various anodising conditions has been examined comprehensively. The surface of the coating was modified by stearic acid and its immersion time was optimized. The dependence of surface morphology, kinetic parameters, and microstructural characteristics of the coating on electrolyte /additive concentration, anodising time, and the temperature has also been inspected. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) combined with EDAX studies indicates the beneficial role of zirconium silicate towards the formation of crystalline coating with improved corrosion-resistant characteristics. The static water contact angle on the surface-modified coatings was 122° ± 0.4°. This contact angle of super hydrophobic coating has been improved by KOH treatment (152.76o ± 0.4°) which is obtained under optimized conditions exhibit the corrosion resistance (1.68 × 108 Ω cm-1)which is nearly 8 times higher than that of bare aluminium (8.36 × 101 Ω cm-1). The efficacies of the surface-modified coatings against bacteria that are commonly encountered in marine (Desulfovibrio desulfuricans) and medical applications (Staphylococcus aureus and Escherichia coli) are also demonstrated.

The effect of high temperature aging on the corrosion resistance, mechanical property and antibacterial activity of Cu-2205 DSS

The effects of high temperature aging on the corrosion resistance, mechanical property and antibacterial activity of a copper-bearing 2205 duplex stainless steel (Cu-2205 DSS) were investigated. The results from scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and EDS analysis showed that after aging the proportion of γ phase in microstructure was increased and new σ phase and copper-rich precipitates were formed. The mechanical properties including hardness and tensile and yield strengths of the aged Cu-2205 DSS were significantly enhanced compared to the solution-treated Cu-2205 DSS as well as the 2205 DSS. Electrochemical measurements including electrochemical impedance spectroscopy, potentiodynamic polarization curves and potentiostatic polarization scan were performed to evaluate the corrosion behavior of the Cu-2205 DSS. It was found that aging increased the uniform corrosion resistance but had slightly adverse effect on the pitting corrosion resistance. Additionally, the antibacterial performance of aged Cu-2205 DSS was significantly improved compared to the solution treated Cu-2205 DSS, which was attributed to the more release of copper ions from the matrix that killed the bacteria cells and inhibited the biofilm formation on the surface. The above results suggest that Cu-2205 DSS after high temperature aging revealed good mechanical property, antibacterial performance, and corrosion resistance, which will further expand the application of duplex stainless steel in marine engineering fields.

Bioinspired micro/nano structured aluminum with multifaceted applications

Inspired by many biological systems such as lotus leaves, insect wings and rose petals, great attention has been devoted to the study and fabrication of artificial superhydrophobic surfaces with multiple functionalities. In the present study, a simple and ecological synthesis route has been employed for large scale fabrication of self-assembled, sustainable nanostructures on unprocessed and micro imprinted aluminum surfaces named 'Nano' and 'Hierarchy'. The processed samples show extreme wettability ranging from superhydrophilicity to superhydrophobicity depending on post-processing conditions. The densely packed ellipsoidal nanostructures exhibited superhydrophobicity with excellent water, bacterial and dust repellency when modified by low surface energy material 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FOTES), characterized by a static contact angle of 163 ± 1° and contact angle hysteresis (CAH) ~3°. These coated surfaces show significant corrosion resistance with current density of 6 nA/cm² which is 40 times lower than unprocessed counterpart and retain chemical stability after prolonged immersion in corrosive media. These surfaces show excellent self-cleaning ability with significantly low water consumption (< 0.1 µl/mm²-mg) and prevent biofouling which ensures its applicability in biological environment and marine components. The nanostructured superhydrophilic aluminum shows maximum antibacterial activity due to disruption of cell membrane. This work can offer a simple strategy to large scale fabrication of multifunctional biomimetic metallic surfaces.

Synthesis of enhanced corrosion resistant Fe-B-C-Ti amorphous ribbons and evaluation of their photodegradation efficiency under light irradiation

Fe-based amorphous alloys have been found to be very efficient in the degradation of water pollutants due to their unique atomic arrangements with long-range disordered structure. In this work, Fe-B-C-Ti amorphous ribbons were successfully synthesized and showed high catalytic efficiency in the degradation of methylene blue (MB) under simulated sunlight and across a wide pH range. The catalytic efficiency was evaluated under different conditions to optimize the degradation performance. The amorphous ribbon Fe₇₅B₁₀C₁₀Ti₅ was found to exhibit the highest photocatalytic activity as explained by its optical and photoelectrochemical properties. It can degrade MB completely with low Fe-leaching and significant recyclability at pH close to a neutral range (pH 5). The degradation mechanisms can be explained in terms of photocatalytic activity along with the galvanic cell effect which contributed to the efficient MB degradation. This work provides a comprehensive idea for the synthesis of amorphous alloys by optimizing their elemental composition and also explains the catalytic activity of partially crystallized regions on the ribbon surface. The significant corrosion resistance and the quick degradation of MB in a wide pH range in a recyclable manner by these easily separable and highly efficient catalysts indicate great potential for their practical application.

Antibacterial mechanism of Cu-bearing 430 ferritic stainless steel

Copper (Cu)-bearing stainless steel has testified its effectiveness to reduce the risk of bacterial infections. However, its antibacterial mechanism is still controversial. Therefore, three 430 ferritic stainless steels with different Cu contents are selected to conduct deeper research by the way of bacterial inactivation from two aspects of material and biology. Hereinto, electrochemical and antibacterial results show that the increase in Cu content simultaneously improves the corrosion resistance and antibacterial property of 430 stainless steel. In addition, it is found that Escherichia coli (E. coli) on the surface 430 Cu-bearing stainless steel by the dry method of inoculation possesses a rapid inactivation ability. X-ray photoelectron spectroscopy (XPS) aids with ion chelation experiments prove that Cu (I) plays a more crucial role in the contact-killing efficiency than Cu (II), resulting from more production of reactive oxygen species (ROS).

In situ growth of corrosion resistant Mg-Fe layered double hydroxide film on Q235 steel

HYPOTHESIS

In situ grown layered double hydroxide (LDH) is commonly used one of the anticorrosion ways for metal materials; Due to the dense growth of LDH on the metal surface, its special layered structure can effectively delay the corrosion rate of metal.

METHODS

In this study, we use a hydrothermal method to successfully grow Mg-Fe LDH film on steel substrates based on self-supplied Fe³⁺ ions. The films were characterized by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectrometry. The potential corrosion resistance of the obtained Mg-Fe LDH film was confirmed using electrochemical impedance spectroscopy and polarization curves.

FINDINGS

After systematic adjustment and parameter optimization, it was found that Mg-Fe LDH film exhibited the best growth morphology and comprehensive performance with an initial pH value of 10, Mg²⁺/urea ratio of 1:4 and reaction time of 12 h. The SEM and electrochemical results further demonstrated that Mg-Fe LDH film play a good protection effect on carbon steel surface. This study provides an important reference for the processing of anticorrosion LDHs film.

Micro-arc oxidation-assisted sol-gel preparation of calcium metaphosphate coatings on magnesium alloys for bone repair

Calcium phosphate coating is an attractive surface modification strategy for magnesium alloys, since it can increase their corrosion resistance and endow them with osteogenic function simultaneously. Herein, a calcium metaphosphate (CMP) coating was fabricated on magnesium alloy by using sol-gel approach assisted with micro-arc oxidation pre-treatment. Scanning electron microscopy showed that the micro-pores and cracks in micro-arc oxidation inner layer generated during the pre-treatment process were sealed by the grainy sol-gel outer layer. Energy dispersive spectrometry and X-ray diffraction results demonstrated the identity of the coating as CMP. The cross-cut test showed that the adhesion of CMP coating was strong. Applying bare magnesium alloy substrate as a control, the CMP coating surface was rougher and more hydrophilic. The potentiodynamic polarization test demonstrated that the corrosion resistance was significantly improved by using CMP coating. Hydrogen evolution in immersion test further confirmed that the degradation rate was decelerated within 14 days. Moreover, CMP coating facilitated the adhesion speed, spreading area, and focal adhesion formation of bone marrow stem cells. The number of cells in the active proliferating state and proliferated cells present on the CMP coating also increased. Additionally, CMP coating upregulated alkaline phosphatase activity and osteogenic gene expression in cells. In summary, the micro-arc oxidation assisted sol-gel CMP coatings increased the corrosion resistance and promoted the interfacial cell behavior for magnesium alloy implants, which might inform the further development of surface modifications on magnesium alloys for bone related applications.

Improving in vitro and in vivo corrosion resistance and biocompatibility of Mg-1Zn-1Sn alloys by microalloying with Sr

Magnesium (Mg) and its alloys have attracted attention as potential biodegradable materials in orthopedics due to their mechanical and physical properties, which are compatible with those of human bone. However, the effect of the mismatch between the rapid material degradation and fracture healing caused by the adverse effect of hydrogen (H2), which is generated during degradation, on surrounding bone tissue has severely restricted the application of Mg and its alloys. Thus, the development of new Mg alloys to achieve ideal degradation rates, H2 evolution and mechanical properties is necessary. Herein, a novel Mg-1Zn-1Sn-xSr (x = 0, 0.2, 0.4, and 0.6 wt%) quaternary alloy was developed, and the microstructure, mechanical properties, corrosion behavior and biocompatibility in vitro/vivo were investigated. The results demonstrated that a minor amount of strontium (Sr) (0.2 wt %) enhanced the corrosion resistance and mechanical properties of Mg-1Zn-1Sn alloy through grain refinement and second phase strengthening. Simultaneously, due to the high hydrogen overpotential of tin (Sn), the H2 release of the alloys was significantly reduced. Furthermore, Sr-containing Mg-1Zn-1Sn-based alloys significantly enhanced the viability, adhesion and spreading of MC3T3-E1 cells in vitro due to their unique biological activity and the ability to spontaneously form a network structure layer with micro/nanotopography. A low corrosion rate and improved biocompatibility were also maintained in a rat subcutaneous implantation model. However, excessive Sr (>0.2 wt %) led to a microgalvanic reaction and accelerated corrosion and H2 evolution. Considering the corrosion resistance, H2 evolution, mechanical properties and biocompatibility in vitro and in vivo, Mg-1Zn-1Sn-0.2Sr alloy has tremendous potential for clinical applications.

Laser machined micropatterns as corrosion protection of both hydrophobic and hydrophilic magnesium

Magnesium and its alloys are promising candidate materials for medical implants because they possess excellent biocompatibility and mechanical properties comparable to bone. Furthermore, secondary surgical operations for removal could be eliminated due to magnesium's biodegradability. However, magnesium's degradation rate in aqueous environments is too high for most applications. It has been reported that hydrophobic textured surfaces can trap a surface gas layer which acts as a protective barrier against corrosion. However, prior studies have not investigated separately the role of the texture and hydrophobic treatments on magnesium corrosion rates. In this study, pillar-shaped microstructure patterns were fabricated on polished high purity magnesium surfaces by ablation with a picosecond laser. Some micropatterned samples were further processed by stearic acid modification (SAM). Micropatterned surfaces with SAM had hydrophobic properties with water droplet contact angles greater than 130°, while the micropatterned surfaces without SAM remained hydrophilic. The corrosion properties of textured and smooth magnesium surfaces in saline solution were investigated using electrochemical impedance spectroscopy (EIS) and optical microscopy. Corrosion rates on both hydrophobic and hydrophilic laser machined surfaces were reduced ∼90% relative to polished surfaces. Surprisingly, corrosion rates were similar for both hydrophobic and hydrophilic surfaces. Indirect evidence of local alkalization near microstructures was found and was hypothesized to stabilize the Mg(OH)₂ layer, thereby inhibiting corrosion on hydrophilic surfaces. This is different than the corrosion resistance mechanism for superhydrophobic surfaces which makes use of gas adhesion at the liquid solid interface. These results suggest additional processing to render the magnesium hydrophobic is not necessary since it does not significantly enhance the corrosion resistance beyond what is conferred by micropatterned textures.

Effect of titanium dioxide intermediate layer on scratch and corrosion resistance of sol-gel-derived HA coating applied on Ti-6Al-4V substrate

Modification of dental and orthopedic implants' surface by coating them with bioactive materials, such as hydroxyapatite (HA), diminishes the implants' fixation time. Appropriate adhesion to the substrate and stability in biological conditions are essential requirements for these coatings. In this study, sol-gel-derived HA coating was applied on the Ti-6Al-4 V substrate, which is a high-performance alloy for manufacturing bone implants. Also, titanium dioxide (TiO₂) which was prepared by the sol-gel method was used as an intermediate layer between HA coating and the substrate. The nano-scratch and potentiodynamic polarization tests were employed to evaluate the effectiveness of TiO₂ intermediate layer on improving the scratch resistance, as an indicator of coating adhesion strength, and the corrosion resistance of the coated samples. The quality of the coating bonded to the substrate was studied by cross-sectional SEM images. The XRD tests indicated that HA and TiO₂ coatings were formed with predetermined phase compositions. The biocompatibility of sol-gel-derived HA coating was established by simulated body fluid (SBF) immersion tests. The SEM images, along with the results of electrochemical and nano-scratch tests, proved the significant effect of a TiO₂ intermediate layer on improving the scratch resistance and stability of HA coating on titanium alloy substrate.

Corrosion resistance and antibacterial activity of procyanidin B2 as a novel environment-friendly inhibitor for Q235 steel in 1 M HCl solution

Flavonoids, alkaloids, glucosides and tannins with good corrosion inhibition are the main natural components in plants. In this work, procyanidin B2 (PCB2), a natural flavonoid, was firstly isolated from Uncaria laevigata. Corrosion inhibition, chemical reactivity and adsorption of PCB2 on Q235 carbon steel were described by experimental and theoretical studies. The inhibition performance of PCB2 as a green corrosion inhibitor was evaluated by electrochemical and gravimetric tests. The binding active sites and activities thereof on the steel surface were illustrated by quantum chemistry, and the equilibrium configuration was predicted by molecular dynamics simulation. PCB2 exhibits good corrosion inhibition on Q235 steel over a wide temperature range. The electrochemical results show that PCB2 is a mixed inhibitor, and its inhibition efficiency increases with the addition of PCB2 concentration. Moreover, the protective film is formed on the steel and the active corrosion sites are blocked significantly by surface analysis. Additionally, the theoretical calculation proves a strong interaction between PCB2 molecule and carbon steel. Besides, the antimicrobial activity was also preliminarily studied. This suggests that PCB2 exhibits better antimicrobial activity against many Gram-positive and Gram-negative bacteria. As a novel green corrosion inhibitor and antimicrobial agent, PCB2 is worthy of further exploitation.

Corrosion behavior of high nitrogen nickel-free austenitic stainless steel in the presence of artificial saliva and Streptococcus mutans

High nitrogen nickel-free austenitic stainless steels (HNSs) have great potentials to be used in dentistry owing to its exceptional mechanical properties, high corrosion resistance, and biocompatibility. In this study, HNSs with nitrogen of 0.88 wt% and 1.08 wt% displayed much lower maximum pit depths than 316L stainless steel (SS) after 21 d of immersion in abiotic artificial saliva (2.2 μm and 1.7 μm vs. 4.5 μm). Microbiologically influenced corrosion (MIC) evaluations revealed that Streptococcus mutans biofilms led to much severer corrosion of 316L SS than HNSs. Corrosion current densities of HNSs were two orders of magnitude lower than that of 316L SS after incubation of 7 d (37.5 nA/cm² and 29.9 nA/cm² vs. 5.63 μA/cm²). The pitting potentials of HNSs were at least 550 mV higher than that of 316L SS in the presence of S. mutans, confirming the better MIC resistance of HNSs. Cytotoxicity assay confirmed that HNSs were not toxic to MC3T3-E1 cells and allowed better sessile cell growth on them than on 316L SS. It can be concluded that HNSs are more suitable dental materials than the conventional 316L SS.

Stable, superfast and self-healing fluid coating with active corrosion resistance

Fluid material can recover from damage rapidly with no demand of external triggering in contrast with the traditional self-healing material which presents low healing efficiency and demands external triggering, such as heat, light, moisture, electricity, etc. However, due to its low viscosity, fluid material is easy to flow away from the surface and thus it is difficult to form a stable coating on the surface to provide practical corrosion resistance to the substrate. Herein, a stable and superfast self-healing coating on steel substrate has been obtained by incorporating carbon nanotube (CNT) into the fluid matrix of epoxy resin (EP) or silicone oil (OIL). To further achieve the active corrosion resistance, 1H, 1H, 2H, 2H- perfluorooctyltriethoxysilane (PTES) which can react with the water inside the coating is added. The coating possesses superfast (tens of seconds) self-healing properties against millimeter-scale scratch repeatedly and excellent corrosion resistance in the aqueous solution of HCl (1 M) and NaOH (1 M). In-situ self-healing and electrochemical behavior in scanning vibrating electrode technique (SVET) measurement indicate the fluid coating possesses infinite self-healing capacity theoretically. Due to its excellent durability and infinite self-healing capacity with short responding time, the optimized fluid coating can be a smart corrosion barrier coating for metals.

The microstructure, mechanical properties, corrosion performance and biocompatibility of hydroxyapatite reinforced ZK61 magnesium-matrix biological composite

Magnesium (Mg)-based composites, as biomaterials, have attracted widespread attention due to their adjustable mechanical properties like elastic modulus, ductility, ultimate tensile strength, and corrosion resistance. In this study, hydroxyapatite (HA) reinforced ZK61 Mg-matrix composites were prepared by powder metallurgy and hot extrusion methods. The influence of the content of HA (10 wt%, 20 wt%, and 30 wt%) on the microstructure, density, mechanical properties, corrosion property and biocompatibility were investigated. The results showed that the density and yield strength of the composites match those of natural bone. Moreover, the composite with 10 % HA (ZK61-10HA) exhibited the best corrosion resistance, as determined by the electrochemical measurement and immersion test in simulated body fluid (SBF) at 37 °C. In addition, the ZK61-10HA composite significantly enhanced the cell viability (≥78 %) compared with ZK61 alloy in vitro testing. It is demonstrated that the mechanical properties, corrosion resistance and biocompatibility of Mg alloy can be effectively controlled by adjusting the content of HA, which suggested that the ZK61-HA composites were promising candidates for degradable implant materials.