Bare Alloy Research Articles

Effect of niobium oxide thin film on the long-term immersion corrosion of the 2198-T851 aluminium alloy

This work aims to study the effect of niobium oxide coating on the long-term immersion corrosion of the 2198-T851 aluminium alloy. The niobium oxide thin film was successful obtained on freshly plates of 2198-T851 alloy by reactive sputtering technique. Scanning vibrating electrode tests, electrochemical impedance spectroscopy and immersion tests measurements were used to reveal the insights of global and localised corrosion behaviour of the functionalised material in different concentrations of sodium chloride solution. The electrochemical impedance spectroscopy spectra showed that the coating significantly influenced on the corrosion resistance of the 2198-T851 alloy, since the functionalised alloy immersed in 0.6 mol L−1 NaCl solution during 720 h (30 days) displays the same result as the bare material for 3 h of immersion. The scanning vibrating electrode tests demonstrated the coated material was free of local corrosive attack by the electrolyte in the first 10 h of immersion, whilst the bare alloy exhibited active anodic and cathodic sites over the surface with increasing current density values for longer immersion times. The deposited coating was able to increase the corrosion resistance of the 2198-T851 aluminium alloy used as fuselage skin material by the aeronautical industry as verified by the immersion tests. Finally, experimental results confirm the extraordinary properties of niobium oxide as-deposited coating.

In situ fabrication of flower-like ZnO on aluminum alloy surface with superhydrophobicity

A hierarchical structure ZnO is fabricated on aluminum alloy substrate by hydrothermal method at low temperature of 90 °C, following treated by the solution of PDMS to achieve superhydrophobicity. We investigate the effect of PDMS concentrations on surface hydrophobicity. Results are shown that the optimum superhydrophobic surface (Al-ZnO-PDMS8) possesses a water contact angle as high as 161.1° and a low water sliding angle of 3.3°. The chemical compositions and surface morphologies are investigated using FTIR, XPS, EDS, FESEM, and AFM. The delayed-icing time of 7 μL water droplets on Al-ZnO-PDMS8 at − 15 °C is 5.46 times longer than that of the bare aluminum alloy surfaces. Furthermore, the influence of temperature and droplet volume on delayed-icing time is measured and analyzed. Also, the superhydrophobic surface displays excellent anti-frost performance with decreased icing weight and area. Meanwhile, the superhydrophobic surface shows good self-cleaning performance by different types of daily water-based pollutions. The behavior of impacting water droplet is researched by using highspeed photography, indicating that pollutants were difficult to adhere to the surfaces, which could be easily cleaned up by rolling water droplets. These investigations are believed that there is an extent promotion to practical applications of superhydrophobic surface, especially in the fields of anti-icing and self-cleaning.

Antibacterial Ca/P-coatings formed on Mg alloy using plasma electrolytic oxidation and antibiotic impregnation

Antibacterial coatings were formed on Mg alloy by plasma electrolytic oxidation (PEO) with subsequent antibiotic impregnation. Morphological features and composition of formed layers were studied by SEM and EDS. Corrosion current density of formed coatings substantially decreased compared to bare alloy. Incorporation of Vancomycin did not lead to a decrease in the electrochemical properties. The antibacterial activity of the coatings against S. aureus and methicillin-resistant S. aureus was investigated in vitro model. It was established that for antibacterial coatings the number of colony-forming units significantly decreased compared to both base PEO-coating and bare alloy.

Control of ZM5 alloy ignition via PEO/aluminum phosphate composite coating

A composite coating consisting of the plasma electrolytic oxidation (PEO) and aluminum phosphate layer was fabricated to improve the ignition resistance of ZM5 alloy. The influences of PEO coating and PEO/aluminum phosphate composite coating on the ignition resistance of ZM5 alloy were investigated by torch ignition and non-isothermal oxidation test. The ZM5 alloy with PEO/aluminum phosphate composite coating possesses the best ignition resistance and does not ignite when exposes to flame for 20 min, about 16 min longer than that of ZM5 alloy with PEO coating, and about 18 min longer than that of bare ZM5 alloy. The ignition protection was achieved through synergetic combination increased oxidation resistance, high strengthening and thermal expansion coefficient match of the composite coating. The incombustible ceramic component and metallurgical bond to the substrate endow the PEO coating with a self-extinguishing property. In addition, three characteristic stages (protective oxidation, non-protective oxidation and burning) of ZM5 alloy and its coating were identified based on the non-linear mass gain behaviors at different temperatures. The ZM5 alloy with PEO/aluminum phosphate composite coating had higher non-protective oxidation initial temperature (605 °C) than 437 °C of the bare ZM5 alloy. Meanwhile, the non-protective oxidation energy of the ZM5 alloy coated with PEO/aluminum phosphate composite coating was remarkably improved from 61 kJ/mol to 136 kJ/mol.

Porous thermosensitive coating with water-locking ability for enhanced osteogenic and antibacterial abilities.

Preferable antibacterial property and osteogenesis are the permanent pursuit for metallic implants. However, it is difficult to satisfy both the properties. In fact, implants may be contaminated with bacteria during storage and surgery, leading to inflammation. Therefore, the antibacterial property of biomaterial surfaces is required not only in the human environment but also at room temperature. In this study, porous structures loaded with a thermosensitive poly (N-isopropylacrylamide) (PNIPAM) hydrogel on a nitinol (NiTi) substrate were constructed. When the temperature is 25 ​°C, almost all bacteria cannot adhere to the sample surface due to the abundant hydration layer of the PNIPAM hydrogel. Meanwhile, when the temperature is 37 ​°C, the structure of the PNIPAM hydrogel collapses and the hydration layer disappears due to the temperature change. However, the porous structures lock water in the pores, which results in a high-hydration-rate sample surface. This surface has few bacterial adhesion sites; nevertheless, the adhesion of larger cells to the surface is not impeded by the porous structure. In addition, the PNIPAM hydrogel is soft and biocompatible, so the sample can have better cell adhesion and proliferation than a bare NiTi alloy. Based on these results, it can be concluded that the porous NiTi sample loaded with the thermosensitive PNIPAM hydrogel has the antibacterial property before implantation and the dual function of inhibiting bacterial adhesion and promoting cell adhesion and proliferation after implantation, which shows promising applications in the biomedical field such as orthopedic implantation.

Manganese – iron coated flexible graphite sheet having wide potential window for energy storage devices

Due to their high-power density, manganese-based electrodes have been studied for energy storage systems. However, they are not stable over high potential windows limiting their use as supercapacitor electrode materials. Manganese was electrodeposited with iron to increase the potential window because manganese-based electrodes are electroactive in the positive region (in Na2SO4 electrolyte) whereas iron-based electrodes are electroactive in the negative region. Graphite was coated potentiostatically with Mn-Fe alloys in a deep eutectic solvent (DES) ionic liquid, Ethaline. The effect of deposition potential on surface morphology, chemical structure, and electrochemical behavior was investigated. XRD, Raman, FTIR, CV and SEM were utilized to characterize bare graphite and alloy deposited graphite. The areal capacitance of the alloy-coated graphite electrode was determined to be 1.66 F cm−2 at 5 mV s−1. The potential window of the alloy-based coating electrodeposited from Ethaline DES was 2.0 V (from −1.0 to +1.0 V). The Mn-Fe-coated graphite electrode material reacts with the neutral electrolyte via a combination of surface-controlled and diffusion-controlled mechanisms. The production of Mn-Fe-coated graphite electrodes from ionic liquid (Ethaline) media allowed for flexible, easy-to-prepare, and cheap electrodes with wide potential windows for supercapacitor applications.

Influence of ZrO2/SiO2 nanomaterial incorporation on the properties of PEO layers on Mg-Mn-Ce alloy

The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing mechanical mixture of zirconia and silica nanoparticles in concentrations of 2, 4 and 6 g/l have been investigated. It has been established by SEM, EDS, and XPS that ZrO 2 /SiO 2 nanoparticles successfully were incorporated into the coatings. Micro-Raman spectroscopy showed the presence of ZrO 2 in tetragonal and monoclinic forms in the PEO-coating composition as well as Mg 2 SiO 4 in tetrahedral configuration uniformly distributed in the outer part of coatings. Obtained coatings significantly reduce corrosion current density in comparison with bare Mg alloy and base PEO-layer (from 2.4 × 10 –7 A/cm 2 for base PEO layer to 0.7 × 10 –7 A/cm 2 for coatings with nanoparticles). It has been found that the presence of solid nanoparticles in the composition of coating has a positive effect on their hardness (this parameter was increased from 2.1 ± 0.3 GPa to 3.1 ± 0.4 GPa) and wearproof (the wear was reduced from (4.3 ± 0.4)×10 –5 mm 3 /( N × m ) to (3.5 ± 0.2)×10 –5 mm 3 /( N × m )).

Sputter-grown hierarchical nitride (TiN & h-BN) coatings on BN nanoplates reinforced Al7079 alloy with improved corrosion resistance

A boron nitride nanoplates (BNNPs) reinforced aluminium alloy (Al7079) based ex-situ metal matrix (MM) nano-composite was successfully developed via mechanical stir casting process. This MM nano-composite shows better wetting and anti-corrosion properties in comparision of bare Al7079 alloy. To further enhance the aforementioned properties, two dissimilar hard coatings (TiN & h-BN) with hierarchal rough surfaces were employed on the BNNPs functionalized MM composite surface via a single-step PVD technique, which provide a tough barrier with non-wetting surface to prevent the base material from corrosion attack. The addition of these layers led to a significant change in physical, chemical, mechanical and anti-corrosion properties. The results also revealed the hydrophobicity of developed coatings with optical contact angle meter of TiNNCs and h-BNNPs surfaces ~102.1° and 141.6°, respectively. The collective results obtained from electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests revealed the one order higher corrosion resistance of h-BN coated sample than TiN coated sample under saline media (3.5 wt%). This coating may be a promising candidate in various applications, where the protection of materials against corrosion is necessary. • Development of BN nanoplates reinforced aluminum alloy (Al-7079) metal matrix by mechanical stir casting. • The MM nano-composite shows better wetting and anti-corrosion properties as compare to base Al7079 alloy. • TiNNCs and h-BNNPs were employed on the BNNPs-Al7079 composite surface via a single-step PVD technique. • Better hydrophobicity and high corrosion resistance shown by BNNPs coated sample compared to TiNNCs coated sample.

A heterogeneous TiO2/SrTiO3 coating on titanium alloy with excellent photocatalytic antibacterial, osteogenesis and tribocorrosion properties

In order to meet the clinical demand for titanium implants, the heterogeneous structure of TiO2/SrTiO3 coating was in situ fabricated on the surface of Ti6Al4V alloy by a facile way. The well-designed Ti6Al4V/TiO2/SrTiO3 composite exhibits a strong photocatalytic antibacterial efficiency against Escherichia coli (E. coli). The suitable energy band structure, improved light absorption and enhanced carrier separation of TiO2/SrTiO3 heterojunction facilitate the generation of bactericidal reactive oxygen species (ROS) under the illumination of UV light. The biocompatible SrTiO3 component effectively favors the adhesion, proliferation and osteogenic differentiation of human bone mesenchymal stromal cells (hBMSCs) in vitro. It is worth noting that the dense oxide coating provides a reliable barrier against tribocorrosion for the titanium alloy substrate, and the wear volume loss of the Ti6Al4V/TiO2/SrTiO3 reduces to 1/8 of that of the bare Ti6Al4V alloy in simulated body fluid. In this work, a multifunctional coating system was proposed to provide inspiration for the development of novel artificial bone implant materials.

Concrete-filled and bare 6082-T6 aluminium alloy tubes under in-plane bending: Experiments, finite element analysis and design recommendations

The application of aluminium alloys in structural engineering is growing owing to their high strength-to-weight ratio, aesthetic appearance and excellent resistance to corrosion. However, the low modulus of elasticity of aluminium poses adverse effects on the flexural response of structural members made of aluminium alloys. In case of tubular members, the performance can be improved with the addition of concrete infill. Research on the flexural response of concrete-filled aluminium alloy tubes is still minimal. This study presents experimental and numerical investigations on the behaviour of concrete-filled and bare 6082-T6 aluminium alloy tubular members under in-plane bending. In total 20 beams, including 10 concrete-filled aluminium alloy tubular (CFAT) and 10 bare aluminium alloy tubular (BAT) specimens, were tested. The specimens comprised of square and rectangular hollow sections and were filled with 25 MPa nominal cylinder compressive strength concrete. The experimental results are reported in terms of failure mode, flexural strength, flexural stiffness, ductility and bending moment versus mid-span deflection curve. Compared to the BAT specimens, the counterpart CFAT specimens have shown remarkably improved flexural strength, stiffness and ductility due to the concrete infill and the improvement is more pronounced for the specimens with thinner sections. Finite element models of BAT and CFAT beams were developed by taking into account the nonlinearities in geometry and material and validated against the experimental data. A parametric study considering a broad range of cross-sections and different concrete grades was conducted based on the validated models. The FE results have shown that the flexural strength of the BAT and CFAT members increases with the increase of cross-sectional aspect ratio, wall thickness and concrete grade. The results obtained from experiments and numerical analysis for BAT members were used to assess the flexural capacity predictions and the applicability of the slenderness limits provided in the European standards. It was demonstrated that the slenderness limits provided by Eurocode 9 are conservative for Class A aluminium sections. Hence, revised Class 1, Class 2 and Class 3 limits are proposed which appear to be better applicable to Class A aluminium alloys. In the absence of design specifications for CFAT flexural members, the design rules for concrete-filled steel tubular flexural members provided by Eurocode 4 were adopted and the material properties of steel were replaced with those of aluminium alloy. It was shown that the proposed design methodology is suitable for the design of CFAT flexural members. Moreover, a slenderness limit for compact sections of CFAT flexural members is proposed based on Eurocode 4 framework.

Enhancement of electrical conductivity and corrosion resistance by gold-nickel coating of additively manufactured AlSi10Mg alloy

Gold-nickel coatings (Au–Ni) were applied by electrodeposition (ED) and electroless deposition (ELD) on additively manufactured (AM) AlSi10Mg alloy to improve the electrical conductivity and electrochemical behavior. Characterization of the Au–Ni coatings was performed by a scanning electron microscope equipped with energy dispersive X-ray spectroscopy (EDS) and x-ray diffraction to study the tiny features. The surface indentation hardness of the coated alloy was evaluated to study the coating strength. The electrochemical behavior of the as-built part and its counterpart, Au–Ni coated surfaces, were evaluated by conducting potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution.The results revealed that the Au–Ni coatings with layers thickness of ∼2 and 10 μm, respectively, could overcome the surface critical defects, i.e., pores and flaws. The surface hardness of the coated AM alloy has significantly increased six times due to the hard Ni layer. The electrochemical measurements showed a significant decrease in the anodic dissolution rate and increase in pitting corrosion resistance for the Au–Ni coated surfaces compared to the bare AM AlSi10Mg alloy with the as-built and polished surface condition in chloride solution. This was attributed to the stability of the Au–Ni coatings against the anodic overpotential. Moreover, it was observed that the Au–Ni coatings reduce the electrical resistance of the studied AM alloy by 40%. Consequently, the surface electrical conductivity property of the AM AlSi10Mg alloy was enhanced by both Au–Ni coating procedures.

Dual Synergistic Effects of MgO-GO Fillers on Degradation Behavior, Biocompatibility and Antibacterial Activities of Chitosan Coated Mg Alloy

The aim of this work was to establish and characterize chitosan/graphene oxide- magnesium oxide (CS/GO-MgO) nanocomposite coatings on biodegradable magnesium-zinc-cerium (Mg-Zn-Ce) alloy. In comparison to that of pure CS coatings, all composite coatings encapsulating GO-MgO had better adhesion strength to the Mg-Zn-Ce alloy substrate. The result depicted that the co-encapsulation of GO-MgO into the CS layer leads to diminish of contact angle value and hence escalates the hydrophilic characteristic of coated Mg alloy. The electrochemical test demonstrated that the CS/GO-MgO coatings significantly increased the corrosion resistance because of the synergistic effect of the GO and MgO inside the CS coating. The composite coating escalated cell viability and cell differentiation, according to cytocompatibility tests due to the presence of GO and MgO within the CS. The inclusion of GO-MgO in CS film, on the other hand, accelerates the formation of hydroxyapatite (HA) during 14 days immersion in SBF. Immersion results, including weight loss and hydrogen evolution tests, presented that CS/GO-MgO coating enables a considerably reduced degradation rate of Mg-Zn-Ce alloy when compared to the bare alloy. In terms of antibacterial-inhibition properties, the GO-MgO/CS coatings on Mg substrates showed antibacterial activity against Escherichia coli (E. coli), with a large inhibition area around the specimens, particularly for the coating containing a higher concentration of GO-MgO. Bacterial growth was not inhibited by the bare Mg alloy samples. The CS/GO-MgO composite coating is regarded as a great film to enhance the corrosion resistance, bioactivity, and antibacterial performance of Mg alloy implants.

Performance of air plasma sprayed Cr3C2–25NiCr and NiCrMoNb coated X8CrNiMoVNb16–13 alloy subjected to high temperature corrosion environment

Thermal barrier coating plays a vital role in protecting materials’ surfaces from high-temperature environment conditions. This work compares the demeanour of uncoated and air plasma sprayed Cr3C2–25NiCr and NiCrMoNb coated X8CrNiMoVNb16–13 substrates subjected to air oxidation and molten salt (Na2SO4 + 60%V2O5) environment condition at 900 °C for 50 cycles. Coating characteristics have been analyzed through microstructure, thickness, porosity, hardness, and bond strength. SEM, EDS and XRD analysis were used to analyze corrosion’s product at the end of the 50th cycle. Coating microstructures showed a uniform laminar structure that is adherent and denser with a coating thickness of 150 ± 20 μm and porosity less than 3.5%. The Microhardness of both the coated substrates were higher than that of the bare substrate. Cr3C2–25NiCr and NiCrMoNb coating bond strength was 38.9 MPa and 42.5 MPa. Thermogravimetric analysis showed the parabolic rate law of oxidation for all the substrates in both environments. In the molten salt environment, all the substrates exhibited higher weight gain compared to the air oxidation environment. In both environmental conditions, the uncoated X8CrNiMoVNb16–13 alloy exhibited higher weight gain than the coated substrates. The formation of Cr2O3, NiO and spinel oxide NiCr2O4 offers good resistance to corrosion to all the substrates in both the environmental condition. However, the presence of Mo and Nb significantly accelerated the corrosion of the substrate, thereby increasing the weight of the NiCrMoNb substrate. It is observed that Cr3C2–25NiCr and NiCrMoNb coating over the X8CrNiMoVNb16–13 substrate significantly protected the substrate against the hot corrosion than the bare alloy exposed to similar environmental conditions.

A pH-responsive cerium-imidazole decorated ZIF-8 to achieve self-healing barrier property for epoxy coating on Al alloy by controlled release

Ce-based imidazole complex (Ce-IM/ZIF-8) nanoparticles (NPs) were fabricated by doping cerium ions (Ce3+ /Ce4+) in zeolite imidazolate framework-8 (ZIF-8) through a one-pot co-precipitation method. The stimuli-responsive release of Ce3+/Ce4+ species from the Ce-IM/ZIF-8 NPs under acidic conditions was confirmed by UV–Vis spectroscopy. Electrochemical impedance spectroscopy and scanning electron microscope were applied to evaluate the corrosion inhibition efficiency of Ce-IM/ZIF-8 NPs on bare aluminum alloy, and it demonstrates that the released Ce3+/Ce4+, Zn2+ ions and imidazole could absorb on the surface of Al alloy by chelating effect, forming a compact corrosion barrier on the Al substrate. Furthermore, the Ce-IM/ZIF-8 NPs were encapsulated into epoxy (EP) resin to obtain a composite coating, and it is found that when the NPs addition amount was 1 wt%, the EP-based composite coating exhibits excellent corrosion barrier and promising self-healing ability, with its impedance at 0.01 Hz maintaining 2.2 × 108 Ω·cm2 even after 6 cycles of aging tests (720 h), which could be ascribed to the synergistic inhibition of released Ce ions and imidazole molecules on Al substrate beneath the defective coating.

Microstructure characteristics and properties of NiCrMoFeCoAl HVOF coating for T22 boiler tube steel

This paper demonstrates the characterization of HVOF sprayed NiCrMoFeCoAl coating on SA213-T22 bare alloy to improve surface properties for corrosion applications. The microstructure of the sample was examined using a range of characterization methods including XRD and SEM/EDAX methods. The as-deposited coatings are characterized as relating to microstructure & mechanical properties. The porosity, microhardness, coating thicknesses, and density of coating have been also evaluated. It has been found that microhardness values have declined from coating to bare alloy.

Microstructure characteristics and properties of WC-CrC-Ni HVOF coating for boiler tube steel

In the present work, the characterization of HVOF sprayed WC-CrC-Ni coating on three bare alloys of MDN-310, SA213-T22, and Superfer 800H was investigated with the HVOF technique. The microstructure of the specimens were examined using a range of characterization techniques including XRD analysis, SEM, and EDS interfaced to SEM. The as-sprayed coatings are characterized with respect to microstructure and mechanical properties. The porosity, surface roughness, coating thicknesses, density, and bond strength of coatings have been also evaluated.

Biocompatibility and electrochemical evaluation of ZrO2 thin films deposited by reactive magnetron sputtering on MgZnCa alloy

• Sputtered ZrO 2 nanocoatings on a MgZnCa alloy provides corrosion protection. • The ZrO 2 coated Mg alloy reduced the H 2 by half during the first 5 h. • The ZrO 2 -coated Mg alloy presented cell viability close to 100%. • Biofilm formation was avoided in the ZrO 2 -coated alloy. Biodegradable magnesium alloys are promising candidates for temporary fracture fixation devices in orthopedics; nevertheless, its fast degradation rate at the initial stage after implantation remains as one of the main challenges to be resolved. ZrO 2 -based coatings to reduce the degradation rate of the Mg-implants are an attractive solution since they show high biocompatibility and stability. In this work, the degradation, cytotoxicity, and antibacterial performance of ZrO 2 thin films deposited by magnetron sputtering on a Mg-Zn-Ca alloy was evaluated. Short-term degradation of ZrO 2 -coated and uncoated samples was assessed considering electrochemical techniques and H 2 evolution (gas chromatography). Additionally, long term degradation was assessed by mass-loss measurements. The results showed that a 380 nm ZrO 2 coating reduces the degradation rate and H 2 evolution of the alloy during the initial 3 days after immersion but allows the degradation of the bare alloy for the long-term. The ZrO 2 coating does not compromise the biocompatibility of the alloy and permits better cell adhesion and proliferation of mesenchymal stem cells directly on its surface, in comparison to the bare alloy. Finally, the ZrO 2 coating prevents the adhesion and biofilm formation of S. aureus .

Enhancing the corrosion protection of Ti-6Al-4V alloy through reactive sputtering niobium oxide thin films

Here, a set of polycrystalline niobium oxide thin films were produced by using reactive sputtering technique on the Ti-6Al-4V alloy surfaces and characterized by OM, SEM/EDX, AFM, DRX/Rietveld refinement, and XPS techniques. CPDP and SVET tests were performed on the coated and uncoated material considering an aggressive medium (NaF and Hank's solution). The results demonstrated the technique used in the present survey was advantageous to produce thin films on the Ti-6Al-4V surfaces. XPS analysis demonstrated that the niobium oxide thin films were composed by Nb2O5/NbO2. Measured and Rietveld refined X-ray diffraction patterns for the Nb-oxide thin film demonstrated the presence of the Nb2O5, NbO2, and NbO crystalline phases. The thin film acts as a barrier layer, suggesting a better corrosion performance when compared to the bare alloy (Ecorr = −111 mVSCE vs −290 mVSCE). The CPDP results demonstrated the current density of the coated Ti-6Al-4V specimen, at the same potential, was lower when compared to the bare alloy. SVET results revealed the coated material displayed low values of current density (~100 μA/cm2 for 15 h of immersion time), whilst the bare material (in the range 700–2200 μA/cm2 for 1 h of immersion time), suggesting the niobium oxide thin films act as an effective protective barrier against corrosion process evolution over time.

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 the in vitro Degradation, Mechanical and Biological Properties of AZ91-3Ca Mg Alloy via Hydrothermal Calcium Phosphate Coatings

For many years, calcium phosphate coatings to tailor the degradation behavior of magnesium and magnesium-based alloys for orthopaedic applications have received lots of research attention. However, prolong degradation behavior, its effect on biological and mechanical properties as well as osteoblastic response to single-step hydrothermally deposited calcium phosphate coatings remain poorly documented. In this study, Alamar blue assay, cell attachment, live/dead assay, and qRT-PCR were done to study the biological response of the coatings. Furthermore, immersion testing in SBF for 28 days and compression testing of the degraded samples were carried out to examine the degradation behavior and its effect on mechanical properties. The results indicated that coatings have a significant influence on both the substrate performance and structural integrity of coated AZ91-3Ca alloy. Immersion test revealed that coating deposited at pH 7, 100°C (CP7100) improves the hydrogen evolution rate by 65% and the degradation rate by 60%. As the degradation performance of coated samples improves so does the mechanical strength. CP7100 samples successfully retained 90% of their compressive strength after 14 days of immersion while bare AZ91-3Ca alloy lost its mechanical integrity. Furthermore, biological studies show that cells are happily proliferating, differentiating, and adhering to the coating surfaces, which indicates, improved osteointegration and osteogenesis with no sign of alkaline poisoning. qRT-PCR results showed that calcium phosphate coatings enhanced the mRNA levels for RUNX2, Col1A, and ALP that may exhibit a speedy bone recovery. Thus, calcium phosphate coatings produced via a single-step hydrothermal method improve the degradation behavior, mechanical integrity and stimulate the differentiation of osteoblast lining. This leads toward faster bone regeneration, which shows a great potential of these coatings to be used on degradable implants as a bioactive protective layer.