Electrochemical Polarization Tests Research Articles

Tribological and electrochemical performances of HVOF sprayed NbC-NiCr coatings

A wide range of mechanical parts are protected against wear and corrosion by thermally sprayed WC- or Cr3C2-based hardmetals. However, little is known about the potential of other hardmetal coating formulations. Since promising results were obtained with bulk NbC-based hardmetal cutting tools, in this work we investigated NbC-based coatings, which have not been reported yet in the literature. NbC particles were homogeneously dispersed with volume fractions of 25 % and 40 % in a Ni-20wt.%Cr matrix by mechanical alloying, and the resulting powders were sprayed onto stainless steel substrates by the High-Velocity Oxygen Fuel (HVOF) process.Irrespective of the process parameters, the coatings exhibit low porosity (<1 vol%) and hardness values of about 900 HV0.3 (NbC-25NiCr) and 1000 HV0.3 (NbC-40NiCr). The composition with higher amount of NbC phase is less hard because its greater brittleness results in cracking during indentation.The sliding wear resistance of the NbC-based coatings, tested by ball-on-disc tribometry from room temperature up to 600 °C, is generally intermediate between that of WC-CoCr and Cr3C2-NiCr references, and it is usually comparable to that of TiC-NiCr, another type of alternative hardmetal coating, tested in our previous work. Though the NbC-NiCr coatings exhibited limited three-body abrasion resistance due to the occurrence of some brittle fracture together with ductile grooving, they offer a particularly interesting performance at 400 °C, with lower wear rates than Cr3C2-NiCr and TiC-NiCr.Additionally, the NbC-NiCr coatings tested in this work, especially the one with 40 vol% matrix phase, exhibit excellent corrosion resistance. Corrosion current densities (~0.1 μA/cm2) and passive current densities (<1 μA/cm2), both obtained by electrochemical polarization tests, were lower than the corresponding values found for all reference coatings (WC-CoCr, Cr3C2-NiCr and TiC-NiCr),Thus, the NbC-NiCr coatings are promising for applications where a good balance between corrosion resistance and wear resistance over a range of temperatures is required.

Third-generation biodegradable bone implants: A novel Mg-1Zn-0.5Sc alloy treated by laser shock peening to improve its characteristics

Magnesium (Mg) and its alloys are of much interest as promising third-generation bio-materials for bone implant applications; however, challenges remain for the alloy's mechanical integrity and bio-corrosion behaviour. Therefore, appropriate alloying elements and surface-modification techniques are required to overcome these limitations. Zinc and scandium were found to possess good biocompatibility and biodegradability, in addition to magnesium. This study aims to enhance the mechanical integrity and bio-corrosion resistance behaviour of a novel Mg-1wt% Zn-0.5wt% Sc cast alloy by laser shock peening surface treatment with multiple passes (LSP-2 pass and LSP-3 pass). The microstructural and texture evolution was investigated using various techniques, including field emission scanning electron microscopy with energy-dispersive spectroscopy (FESEM-EDS), optical microscopy (OM), X-ray diffraction (XRD) analysis, electron back-scattered diffraction analysis (EBSD), as well as the surface residual stress, wettability, microhardness, tensile strength, electrochemical polarization test, and biocompatibility were analysed on as-cast, LSP-2 pass and LSP-3 pass specimens. LSP induced beneficial compressive residual stress around the surface and sub-surface region of Mg-1Zn-0.5Sc alloy due to severe plastic deformation, which led to grain refinement through the twinning mechanism of the Mg alloy. Also, the dispersion of second-phase particles (β-ScZn) was observed while analysing the XRD profiles. Strain hardening, grain refinement, and precipitate strengthening have contributed to the structure and texture evolution, which enhanced the microhardness, tensile strength, ductility, and corrosion resistance of the Mg-1Zn-0.5Sc alloy. From in vitro studies, a low rate of corrosion in simulated body fluid and less cytotoxic behaviour were observed for the LSP-3 pass Mg-1Zn-0.5Sc alloy.

Combined PEO and Spray Pyrolysis Coatings of Phosphate and ZnO for Enhancing Corrosion Resistance in AZ31 Mg Alloy

Oxide films produced from plasma electrolytic oxidation are porous in structure. While they have some passivating effect in Mg alloys, the pores still lead to corrosion over long periods of exposure. In this study, spray pyrolysis was used to seal the porous oxide layer developed through the plasma electrolytic oxidation method on Mg alloy AZ31. The PEO coating acted as a good base for the application of spray pyrolysis due to its morphology. Three different kinds of coatings were obtained using different precursors: zinc acetate for ZnO, phosphoric acid for phosphate (P), and a mixture of zinc acetate and sodium phosphate for ZnO+P. The corrosion performance of all three coatings was studied by performing electrochemical impedance and polarization tests on the samples. Mass loss over a duration of 1 week was measured in 3% NaCl solution using immersion gravimetry. The coating with only phosphate (P) was found to be most corrosion-resistant with 52 times lower rate of corrosion and 50 times more polarization potential. The chemical composition of the corrosion products was studied using XRD and SEM-EDS analysis. Mass loss in ZnO+P was the highest, at up to 1.4 and 5.1 times higher than ZnO and P, respectively.

Combined electrochemical, DFT/MD-simulation and hybrid machine learning based on ANN-ANFIS models for prediction of doxorubicin drug as corrosion inhibitor for mild steel in 0.5 M H2SO4 solution

In this work, Doxorubicin drug was used as mild steel corrosion inhibitor in 0.5 M H2SO4 solution. Herein, standard techniques like gravimetric, electrochemical measurement, density functional theory via DFT/ molecular dynamic simulation (MDS), Scanning electron microscopic (SEM), were used for proper evaluation of Doxorubicin drug as anticorrosive agent. According to the experimental findings, Doxorubicin drug significantly inhibits mild steel corrosion, and its effectiveness increases with an increase in the drug concentration. Maximum inhibition efficiency at 100 ppm was 93.3 %, 91.3 % and 96.8 % for electrochemical impedance (EIS), polarization test (PDP) and gravimetric techniques respectively. The electrochemical study indicates that Doxorubicin is a mixed-type inhibitor. Close scrutiny of the corroded and inhibited metals evidenced that Doxorubicin drug produced a better and more uniform coating on the surface of mild steel. The molecular structure of the drug and its contribution to the inhibition mechanism was further understood using simulations based on density functional theory (DFT) and molecular dynamics simulation (MDS). In addition, artificial neural networks (ANN) and adaptive neuro-fuzzy inference system (ANFIS) were used to predict and model the interactive effects affecting the response. Also, statistical parameters like coefficient of determination (R2), root mean square error (RMSE), mean absolute percentage error (MAPE), and mean absolute deviation (MAD) were used to assess the models' performance. The results demonstrate that the FCM-clustered ANFIS model with 15 clusters perform better than ANN model with RMSE, MAD, MAPE, and R2values of 0.978, 0.642, 4.823, and 0.9925 at the testing phase, and 0.6435, 0.4248, 2.8151, and 0.9998 at the training phase respectively. The best prediction was made using complete FCM-ANFIS model, which had accuracy of 98.4 %. Hence, a robust system prediction can be achieved via ANN and ANFIS algorithms to predict corrosion inhibition of mild steel in acidic environment using drug based corrosion inhibitors.

Doped Multiple Nanoparticles with Hydroxyapatite Coating Show Diverse Health Effects in vivo.

The lack of osteoinductive, angiogenic and antimicrobial properties of hydroxyapatite coatings (HA) on titanium surfaces severely limits their use in orthopedic and dental implants. Therefore, we doped SiO2, Gd2O3 and CeO2 nanoparticles into HA to fabricate a HASiGdCe coating with a combination of decent antibacterial, angiogenic and osteogenic properties by the plasma spraying technique. The HASiGdCe coating was analyzed by SEM (EDS), surface roughness tests, contact angle tests, XRD, FTIR spectroscopy, tensile tests and electrochemical dynamic polarization tests. Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO-1) were used as representative bacteria to verify the antibacterial properties of the HASiGdCe coating. We evaluated the cytocompatibility and in vitro osteoinductivity of the HASiGdCe coating by investigating its effect on the cell viability and osteogenic differentiation of MC3T3-E1 cells. We assessed the in vitro angiogenic activity of the HASiGdCe coating by migration assay, tube formation assay, and RT‒PCR analysis of angiogenic genes in HUVECs. Finally, we used infected animal femur models to investigate the biosafety, antimicrobial and osteointegration properties of the HASiGdCe coating in vivo. Through various characterization experiments, we demonstrated that the HASiGdCe coating has suitable microscopic morphology, physical phase characteristics, bonding strength and bioactivity to meet the coating criteria for orthopedic implants. The HASiGdCe coating can release Gd3+ and Ce4+, showing strong antibacterial properties against MRSA and PAO-1. The HASiGdCe coating has been shown to have superior osteogenic and angiogenic properties compared to the HA coating in in vitro cellular experiments. Animal implantation experiments have shown that the HASiGdCe coating also has excellent biosafety, antimicrobial and osteogenic properties in vivo. The HASiGdCe coating confers excellent antibacterial, angiogenic and osteogenic properties on titanium implants, which can effectively enhance implant osseointegration and prevent bacterial infections, and it accordingly has promising applications in the treatment of bone defects related to orthopedic and dental sciences.

Clean fabrication strategy of diamond crystals containing nanocomposite films for corrosion and wear protection of AISI-321 alloy

This study focused on the synthesis of Niobium/Hexagonal-Diamond/Amorphous-Carbon (Nb/H-D: a-C) films on AISI-321 alloy. The substrate heating used as a vital deposition parameter to tailor structure of the films in an unbalanced magnetron (UB-M) sputtering system for the first time. The substrate heater temperature (Th) ranged between (RT) to 150 °C. The results indicated that increasing the substrate heater temperature promoted the abundance of hexagonal diamond (H-Diamond) crystals through the solid phase separation. Therefore, the film deposited at the highest temperature (150 °C) demonstrated the highest plenty of H-Diamond. Electrochemical impedance spectroscopy (EIS) measurements (after 2, 8, 24, 72, and 168 h immersion) and polarization tests (after 168 h immersion) disclosed that increasing the substrate heater temperature positively affects the corrosion resistance of (Nb/H-D: a-C) films. The results proved that the film deposited at the highest temperature of 150 °C, demonstrated the exceptional corrosion protection efficiency of 99.69 %. Moreover, this film presented acceptable low-frequency impedance (|Z|10KHz) and total resistance (Rt) values of >108 Ω·cm2 and >117 MΩ·cm2 at all immersion times in 3.5 wt% NaCl solution. The highest abundance of the H-Diamond phase, with remarkable chemical inertness at higher substrate heater temperatures, can be an effective reason for elevating anti-corrosion performance of the films. Additionally, as the substrate heater temperature enhanced from RT to 150 °C, mechanical properties illustrated an remarkable increment trend (increasing hardness from 20 to 32.7 GPa and the elasticity modulus from 407 to 470 GPa). Moreover, the anti-wear performances of the films significantly improved with increasing substrate heater temperature, reducing the wear rate from 9.4 × 10−6 to 9 × 10−7 mm3/N·m. These results are mainly attributed to the highest abundance of the superhard H-Diamond phase in the film deposited at higher substrate heater temperature. In conclusion, the (Nb/H-D: a-C) film synthesized at 150 °C represented a promising candidate for tailoring the electrochemical and anti-wear performances of AISI-321 alloy.

Effect of MBF-20 Interlayer on the Microstructure and Corrosion Behaviour of Inconel 625 Super Alloy after Diffusion Brazing.

The joining zone includes three main parts, which comprise an isothermal solidification zone (ISZ), the athermal solidification zone (ASZ), and a diffusion affected zone (DAZ). Field emission scanning electron microscopy (FESEM) was used here to observe the microstructure equipped with ultra-thin window energy dispersive X-ray spectrometer (EDS) system. Additionally, electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization tests were conducted to evaluate the effect of the DB process on the corrosion resistance of the Inconel 625 superalloy. In the bonding time period, some Mo- and Cr-rich boride precipitations and Ni-rich γ-solid solution phases with hardened alloy elements, such as Mo and Cr, formed in DAZ and ASZ, respectively, because of the inter-diffusion of melting point depressants (MPD). Moreover, during cooling cycles, Ni-Cr-B, Ni-Mo-B, Ni-Si-B, and Ni-Si phase compounds were formed in the ASZ area at 1110-850 °C. The DAZ area developed by borides compound with cubic, needle, and grain boundary morphologies. The corrosion tests indicated that the DB process led to a reduction in the passive region and increased the sensitivity to pitting corrosion.

A comprehensive study on microstructure, in-vitro biodegradability, bacterial sensitivity, and cellular interactions of novel ternary Zn-Cu-xAg alloys for urological applications

Novel ternary Zn-Cu-xAg alloys are designed and fabricated by the casting method under a vacuum atmosphere and then homogenized at 350 °C for 15 h. The effect of Ag concentration (x: 0, 1, 2, 3, and 4 wt%) on microstructure, hardness, in vitro corrosion, biodegradability, and bacterial sensitivity was studied systematically. The structural analysis of the alloys was investigated by using a scanning electron microscope (SEM-EDS), and an optical microscope (OM). Besides, phase characterization of the samples was conducted using X-ray diffraction (XRD). The degradation behaviors of the alloys were determined under in vitro conditions, electrochemical polarization, and immersion tests (up to 21 days) in artificial urine (AU) solution. The maximum hardness value for Zn-1Cu-4Ag alloy was about 2.38 times higher than pure Zn due to solid-solution strengthening and precipitation hardening of (Ag, Cu)Zn4 phases. The highest and lowest Icorr values, reference also corrosion rate, were calculated in Zn-1Cu and Zn-1Cu-3Ag alloys as 17.13 and 1.318 mA·cm−2, respectively. The alloys' bacterial sensitivities were evaluated with the disc diffusion test for E. coli and S. aureus. The inhibition ratio of the Zn-1Cu-1Ag was higher than the inhibition rates of the other alloys on E. coli and S. aureus. In addition, the biological properties of the generated material were promising by altering cell survival/death ratio in both prostate epithelial and bladder cancer cells related to their use potential in urology.

Enhancing Self-Healing and Adhesion Bonding Properties: Investigating the Promising Potential of Ce-ZIF8 MOF Hybrid Thin Films as pH-Responsive Nanocoatings.

Further modification of the pre-treated steel surface with cerium conversion coating was performed using a novel porous coordination polymer (PCP) based on zeolitic imidazole framework-8 (ZIF8) in order to reduce the defect and disorders of the surface. The treated mild steels (MS) with Ce (MS/Ce) and Ce-ZIF8 (MS/Ce-ZIF8) were characterized by the GIXRD, Raman, and FT-IR, and via contact angle and FE-SEM, their surface features were investigated. The protection performance of the samples against corrosion was evaluated in the saline solution media using electrochemical impedance spectroscopy (EIS, in the long term) and polarization tests. The results evidenced that applying the ZIF8 nanoparticles onto the Ce-treated steel surface increased the total resistance value after 24 h of immersion (49.47%). Afterward, the ZIF8-modified coating (MS/Ce and MS/Ce-ZIF8) impact on the epoxy coating protection function was characterized by EIS (in the scratched form), salt spray (5 wt % salts), cathodic disbonding (at 25 °C), and pull-off tests. The EIS outcomes of the scratched coatings proved approximately a 51.29% increase in Rt of the MS/Ce-ZIF8/EC sample compared with the MS/EC sample after 24 h of immersion. The cathodic disbonding test results after 24 h of exposure revealed that the delamination area of the coating decreased in the modified sample, and the delamination radius of the epoxy coating was about 4.78, 2.96, and 2.0 mm for the MS/EC, MS/Ce/EC, and MS/Ce-ZIF8/EC samples, respectively.

Microstructural, Biomechanical, and In Vitro Studies of Ti-Nb-Zr Alloys Fabricated by Powder Metallurgy.

This study investigated the microstructures, mechanical performances, corrosion resistances, and in vitro studies of porous Ti-xNb-10Zr (x: 10 and 20; at. %) alloys. The alloys were fabricated by powder metallurgy with two categories of porosities, i.e., 21-25% and 50-56%, respectively. The space holder technique was employed to generate the high porosities. Microstructural analysis was performed by using various methods including scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, and x-ray diffraction. Corrosion resistance was assessed via electrochemical polarisation tests, while mechanical behavior was determined by uniaxial compressive tests. In vitro studies, such as cell viability and proliferation, adhesion potential, and genotoxicity, were examined by performing an MTT assay, fibronectin adsorption, and plasmid-DNA interaction assay. Experimental results showed that the alloys had a dual-phase microstructure composed of finely dispersed acicular hcp α-Ti needles in the bcc β-Ti matrix. The ultimate compressive strength ranged from 1019 MPa to 767 MPa for alloys with 21-25% porosities and from 173 MPa to 78 MPa for alloys with 50-56% porosities. Noted that adding a space holder agent played a more critical role in the mechanical behaviors of the alloys compared to adding niobium. The pores were largely open and exhibited irregular shapes, with uniform size distribution, allowing for cell ingrowth. Histological analysis showed that the alloys studied met the biocompatibility criteria required for orthopaedic biomaterial use.

Electrophoretic Deposition, Microstructure, and Selected Properties of Poly(lactic-co-glycolic) Acid-Based Antibacterial Coatings on Mg Substrate.

There is an urgent need to develop biodegradable implants that can degrade once they have fulfilled their function. Commercially pure magnesium (Mg) and its alloys have the potential to surpass traditional orthopedic implants due to their good biocompatibility and mechanical properties, and most critically, biodegradability. The present work focuses on the synthesis and characterization (microstructural, antibacterial, surface, and biological properties) of poly(lactic-co-glycolic) acid (PLGA)/henna (Lawsonia inermis)/Cu-doped mesoporous bioactive glass nanoparticles (Cu-MBGNs) composite coatings deposited via electrophoretic deposition (EPD) on Mg substrates. PLGA/henna/Cu-MBGNs composite coatings were robustly deposited on Mg substrates using EPD, and their adhesive strength, bioactivity, antibacterial activity, corrosion resistance, and biodegradability were thoroughly investigated. Scanning electron microscopy and Fourier transform infrared spectroscopy studies confirmed the uniformity of the coatings' morphology and the presence of functional groups that were attributable to PLGA, henna, and Cu-MBGNs, respectively. The composites exhibited good hydrophilicity with an average roughness of 2.6 μm, indicating desirable properties for bone forming cell attachment, proliferation, and growth. Crosshatch and bend tests confirmed that the adhesion of the coatings to Mg substrates and their deformability were adequate. Electrochemical Tafel polarization tests revealed that the composite coating adjusted the degradation rate of Mg substrate in a human physiological environment. Incorporating henna into PLGA/Cu-MBGNs composite coatings resulted in antibacterial activity against Escherichia coli and Staphylococcus aureus. The coatings stimulated the proliferation and growth of osteosarcoma MG-63 cells during the initial incubation period of 48 h (determined by the WST-8 assay).

Biocompatible superhydrophobic surface on Zr-based bulk metallic glass: Fabrication, characterization, and biocompatibility investigations

Superhydrophobic metal materials are promising candidates for preparing the precision blood-contacting medical devices. Finding a metal material with excellent biocompatibility and superplastic forming ability to fabricate superhydrophobic surface is of great practical significance. Zr-based bulk metallic glass with high glass-forming ability was selected as the experimental sample. Micro-nano hierarchical structure was etched by electrochemical method in the ultrasonic environment, and the superhydrophobic surface with good biocompatibility was obtained after further modification. Electrochemical polarization tests show that the superhydrophobic surface can maintain long-term corrosion resistance in simulated body fluids. Blood and cell tests indicate that the superhydrophobic sample has an extremely rate of hemolysis and exhibits the ability to effectively inhibit the adhesion of platelets and smooth muscle cells. In addition, the superhydrophobic sample surface also exhibits good mechanical durability and chemical stability. This study offers a new perspective on the application of Zr-based bulk metallic glass in blood-contacting medical devices.

Surface Modification of Pure Mg for Enhanced Biocompatibility and Controlled Biodegradation: A Study on Graphene Oxide (GO)/Strontium Apatite (SrAp) Biocomposite Coatings

Magnesium alloys have excellent biodegradability but suffer from high corrosion rates and unfavorable biological responses. Thus, a surface modification strategy to regulate the corrosion rate and enhance biocompatibility is required. In this study, pure Mg substrate surfaces were coated with strontium apatite (SrAp) and graphene oxide (GO) biocomposite structures using the hydrothermal method to increase the biocompatibility of the surface of the Mg and obtain a moderate biodegradation rate. The effect of the GO concentration (0, 2, 4, and 6 wt.%) on the surface microstructure and its corrosion behavior were systematically studied. The corrosion behavior of the coatings was characterized in-vitro using the electrochemical polarization method in Hank’s solution. An EDS-connected SEM was used to examine the coatings’ surface properties. The functional groups of the coatings were identified using ATR-IR spectroscopy. To determine the degree of crystallization and examine the elemental distribution of the coatings, an XRD was used with a grazing incidence attachment. The XRD and SEM-EDS results showed that increasing the GO ratio in the SrAp-based coatings significantly enhanced the homogeneity and crystallinity, and the ATR-IR spectroscopy revealed that the SrAp/GO coatings were rich in functional groups, including hydroxyl, phosphate, and carbonate groups, that are known to promote bone formation and regeneration. The results of the electrochemical polarization tests demonstrated a considerable decrease in the corrosion rates for the samples with SrAp matrix and GO coatings. Additionally, the coatings containing GO exhibited higher polarization resistance (Rp) values, indicating their potential as a promising surface modification technique for biodegradable implants. These findings suggest that incorporating GO into the SrAp coatings could enhance their biocompatibility and provide a moderate biodegradation rate, which is desirable for biomedical applications.

Corrosion protection studies of different alloys in 1 M HCl by benzimidazole derivative: Combined molecular dynamic simulations/DFT

Corrosion prevention of metals like Steel, Aluminum, and Copper is an interesting problem in industries, to solve this problem corrosion inhibitors are one of the most effective applications for metal protection against corrosion in aggressive media. The effect of (2E)-3-(6-phenylimidazo[2,1-b][1,3]thiazol-5-yl)-1-(2,4,6-trimethylphenyl)prop-2-en- 1-one (KO38) on the protection of steel, aluminum, and copper in 1 M HCl medium was examined using electrochemical polarization tests to assess inhibition efficiency, also scanning electron microscopy (SEM) to analyze the surface of metals. The maximum protection capacity of KO38 by the method of polarization is between 96% and 97% for the three metals exposed in an acid solution containing 10−4 M. The organic inhibitors can be classified as mixed-type inhibitors since they inhibited both anodic corrosion and cathodic corrosion. The study of the dynamic simulation (DM) helped to visualize the energies of adsorption of the molecule (KO38) on the interfaces of Iron (110), Aluminum (111), and Copper (111), the calculations of quantum chemistry were analyzed by (DFT) at B-3LYP /6–311 G (d, p). The experimental results are in good agreement with the theoretical studies.

Effects of Applied Cathodic Current on Hydrogen Infusion, Embrittlement, and Corrosion-Induced Hydrogen Embrittlement Behaviors of Ultra-High Strength Steel for Automotive Applications

The effects of the electrogalvanizing conditions (a combination of plating current and time) on hydrogen infusion, embrittlement, and corrosion-induced hydrogen embrittlement (HE) behaviors of ultra-high strength steel were examined. A range of experimental and analytical methods, including electrochemical impedance spectroscopy, hydrogen permeation, polarization, and slow strain rate test, were employed. The results showed that the applied cathodic current density during electrogalvanizing had an inverse relationship with the Zn crystalline size. A smaller cathodic current density and longer plating time led to a larger crystalline size, resulting in a higher infusion rate of hydrogen atoms, and HE-sensitivity (i.e., mechanical degradation with larger density of secondary crack in fracture surface). On the other hand, a larger cathodic current density and shorter plating time caused a higher anodic dissolution rate and smaller polarization resistance of the coating when exposed to neutral aqueous environments. Hence, a higher rate of galvanic corrosion between the coating and exposed steel substrate (e.g., locally damaged areas around coating layer) resulted in a higher infusion rate of hydrogen atoms and HE-sensitivity. This study provides insight into the desirable plating conditions for electro-Zn plating on ultra-high strength steels with enhanced resistance to hydrogen infusion and embrittlement, induced by aqueous corrosion.

Magnesium-zinc-graphene oxide nanocomposite scaffolds for bone tissue engineering

The aim of this study was to fabricate and evaluate magnesium-zinc-graphene oxide nanocomposite scaffolds for bone tissue engineering. For this reason, Mg-6Zn, Mg-6Zn-1GO, and Mg-6Zn-2GO scaffolds were fabricated by the powder metallurgy method. The porosity level and also the pore size of the scaffolds were evaluated by SEM which varied from 40 to 46% and 200 to 500 μm, respectively. The chemical composition and microstructure of the scaffolds were characterized by XRD and SEM equipped with EDS; the presence of Mg, Zn, C, and O elements in the structure of the scaffolds was shown. Also, the elemental map confirmed the existence of magnesium, zinc, carbon, and oxygen in the structure of the scaffold. The mechanical properties of the scaffolds were investigated by the compression test; the results showed that by the addition of graphene oxide to the structure, the compressive strength of the samples increased from 5 to 8 MPa. Electrochemical corrosion polarization tests were conducted to evaluate the corrosion resistance of the samples immersed in simulated body fluid (SBF). Furthermore, the biodegradability of the scaffolds was determined by immersion of the samples in phosphate-buffered saline (PBS). The results demonstrated that the polarization resistance value and the corrosion rate for different formulations including Mg-6Zn, Mg-6Zn-1GO, and Mg-6Zn-2GO were 41.58, 35.48, and 55.40 Ω.cm2 followed by 10.60, 14.83, and 9.06 mm.year−1, respectively. Based on the results, the Mg-6Zn-2GO formulation presented the best corrosion resistance among the samples were investigated, which confirmed the results of the immersion test. Moreover, the MTT assay proved that the extract of Mg-6Zn-2GO scaffolds was not cytotoxic in contact with L-929 cells which validated the studied scaffolds for bone tissue applications.

The effect of microstructural and texture evolutions during thermomechanical treatment on corrosion resistance of 310s austenitic stainless steel

In this study, the evolution of the microstructure and texture during thermomechanical treatment and its effect on corrosion properties of 310s austenitic stainless steel were investigated. This stainless steel was cryo-rolled at 50 and 90% thickness reductions, and then the 90% cryo-rolled sample was annealed at 750 °C for 5 and 30 min. SEM and optical microscope images were used to examine the microstructure of the samples. Fritoscopy test was also used to calculate the volume fraction of the martensite phase. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and cyclic potentiodynamic polarization tests were performed in the 3.5 wt.% NaCl solution to investigate the corrosion behavior of the studied steel. The results showed that the cryo-rolling process caused the reduction of grain size, texture strengthening and transformation of austenite to strain-induced αʹ-martensite phase. Decreasing grain size and increasing texture components containing dense planes are beneficial factors and the formation of the αʹ-martensite phase is a harmful factor for corrosion resistance. It was observed that annealing at 750 °C for 30 min caused the grain growth and texture weakening, while a favorable condition is developed in the annealed sample for 5 min. After 90% cryo-rolling and subsequent annealing at 750 °C for 5 min, the corrosion resistance was significantly improved compared to the as-received sample and reached 37 kΩ.cm2. Formation of the sub-micron microstructure along with the high volume fraction of Brass and Goss texture components were the main reasons for improving corrosion resistance at 750 °C–5 min.

In vitro degradation and multi-antibacterial mechanisms of β-cyclodextrin@curcumin embodied Mg(OH)2/MAO coating on AZ31 magnesium alloy

It is a challenging task to prepare a coating on Mg alloys for desirable corrosion resistance, good antibacterial ability and biocompatibility. In this research work, an in-situ Mg(OH)2 coating incorporated with sodium alginate (SA) and β-cyclodextrin (β-CD)@curcumin (Cur) was formed on the surface of micro arc oxidation (MAO) coated AZ31 alloy via a low temperature hydrothermal method. Characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR) and scanning electron microscope (SEM) were employed to characterize the chemical composition and surface morphology of the coatings. The corrosion protection ability of the coatings was monitored via electrochemical polarization, hydrogen evolution and immersion tests. Photothermal antibacterial ability and cytocompatibility of the coatings were evaluated by plate counting method under the irradiation of 808 nm-near infrared light, in vitro cytotoxicity tests (MTT) and live/dead cell staining. The results indicate that a chelation of the organic molecules led to the formation of a MAO/(β[email protected])-SA-Mg(OH)2 coating with excellent corrosion protection, multi- antibacterial ability and almost no toxicity to the cells. Especially, the coating provided photothermal performance through the light absorption of Cur, which was encapsulated by β-CD to improve its bioavailability. SA enhanced the binding force between the drug and the substrate. This novel coating designated the potential application on bioabsorbable magnesium alloys.

Enhancement of the corrosion resistance of mild steel with femtosecond laser- nanostructuring and CrCoNi medium entropy alloy coating

In this work, the corrosion resistance of mild steel surface nanostructured with a femtosecond laser and coated with high corrosion resistant CrCoNi (CCN) medium entropy alloy through magnetron sputtering is studied. Substantial improvement in corrosion protection was achieved by applying a combination of high-power femtosecond laser surface nano-structuring at ambient conditions and thin-film coating with (CCN) medium entropy alloy. XRD analysis revealed that femtosecond laser structuring increases the susceptibility of the surfaces to Fe2O3 nucleation through oxidation. The surface wettability measurements and electrochemical polarization tests revealed that the combined approach of femtosecond laser structuring and magnetron sputter coating is the best for desired high corrosion resistance. Through this novel method, the resulting corrosion resistance of mild steel was improved by more than one-fold. The results are explained considering the detailed microstructural analysis. The presented findings open new possibilities for corrosion prevention using a combination of new powerful technologies that yield to unprecedented corrosion-inhibition efficacy.

Corrosion behavior of bulk amorphous steels with low carbon content

The Fe-Cr-Mo-(Y, Ga)-C-B-Si alloy system was chosen to synthesize bulk amorphous steels by water-cooled copper mold casting, in form of discs with 10 mm diameter. The structure of the obtained samples was evaluated using X-ray diffraction and differential scanning calorimetry and the corrosion behavior was assessed by electrochemical polarization tests and electrochemical impedance spectroscopy in 0.5 M H2SO4 electrolyte, as well as immersion tests in 3.5 wt% NaCl solution. It was found a better corrosion performance of the elaborated alloys compared to a reference 316 L stainless steel, the corrosion rate being strongly influenced by the content of Cr, Ga, and Y.