316L SS Surface Research Articles

Electro-discharge deposition of zinc powder on 316L stainless steel: Synthesis, deposition rate, and characterization

This study investigated the potential of powder-mixed electrical discharge machining (PM-EDM) to deposit metallic powder, specifically zinc powder, on 316L stainless steel (316L SS). This study aimed to evaluate the effect of zinc (Zn) deposition on 316L SS for oil and gas application. Minitab 19 software was employed to design the experiments using screening DOE option and to analyse and model the results through screening response optimiser from Minitab 19 software. Surface morphology, microstructure and coating thickness were examined through field-emission scanning electron microscopy (FESEM) and scanning electron microscope (SEM). The results suggested an improvement in the coating thickness with an increase in powder concentration and discharge current. An average coating thickness of 91.47 μm was achieved in samples fabricated at 20 g/L powder concentration. X-ray diffraction analysis revealed the formation of hard carbides, such as Cr3C2 and TiC, on the PM-EDMed 316L SS surface. Further characterisation through energy-dispersive X-ray spectroscopy confirmed the deposition of both the tool electrode and Zn powder particles. The adhesion test confirmed that all specimens failed under 100% adhesive failure. The hydrophobicity analysis confirmed that the coated surfaces are hydrophobic. Significant improvement has been established for microhardness, wear resistance and corrosion performance. Screening results revealed that discharge current, pulse-on time, and powder concentration were the most significant parameters. The average predicted errors of 2.055%, 6.782%, and 2.396% for material deposition rate, tool wear rate, and surface roughness were achieved, respectively. These affirmed the excellent reproducibility of the model developed. This study presents a methodology for the formation of carbide- and oxide-based coatings specifically for oil and gas applications (flanges and connectors).

Investigation and In Vitro Studies of a ZrO2/g‐C3N4 Composite Coated on 316L Stainless Steel for Biomedical Applications

ABSTRACTThe advancement of smart coatings for bioimplants has yielded a combination of biocompatibility and corrosion resistance. 316L stainless steel (316LSS) is a commonly used commercial implant, but it has limitations in biocompatibility and durability, which hinders the widespread utilization of 316LSS alloys. In this study, the 316LSS alloy is coated with a mixture of zirconium dioxide (ZrO2), prepared using the sol–gel method, and graphitic carbon nitride (g‐C3N4), synthesized by thermal polymerization. XRD and Raman analyses confirmed the crystal structure and purity of the synthesized samples. The corrosion resistance property was assessed using OCP, POL, and PEIS. The findings demonstrate that the ZrO2/g‐C3N4‐coated 316LSS shows significantly enhanced corrosion resistance and biocompatibility in a simulated body fluid. The in vitro bioactivity test reveals that the ZrO2/g‐C3N4 coating leads to the formation of an apatite layer over the surface of 316LSS. The elemental composition of the HAP deposition was confirmed by Raman analysis. The results suggested that the ZrO2/g‐C3N4–coated 316LSS substrate is a promising material for use in biomedical applications.

Development and electrochemical investigations of enhanced corrosion-resistant Polyvinylcarbazole-TiO2 hybrid nanocomposite coatings on 316L SS for marine applications

The present study focuses on evaluating the corrosion resistance of 316L stainless steel substrates with Polyvinylcarbazole (PVK)/TiO2 hybrid nanocomposite coatings (HNC). Using the chronoamperometry approach, the HNC were electrochemically synthesized on 316L stainless steel substrates, incorporating various weight (%) 1 %, 2 %, 3 % of TiO2 nanoparticles into the PVK matrix. The findings of the surface morphology investigation verified that the 316L SS had a dense and smooth PVK/TiO2 coating. A low surface roughness and high contact value of the PVK/TiO2 coatings are also responsible for the decrease in corrosion rate of the 316L SS. The corrosion protection efficiency of the PVK/TiO2 HNC were investigated through open circuit potential (OCP) measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis in 3.5 wt% NaCl solution. The corrosion rate obtained from the polarization studies of the HNC coatings as follows PVKT-2 < PVKT-3 < PVKT-1 < PVK < 316L SS. Results revealed that an optimal loading of 2 wt% TiO2 nanoparticles significantly enhanced the corrosion resistance of the coating. The enhanced electrochemical impedance response for PVK/TiO2 coatings was verified by EIS experiments. The study demonstrates that the incorporation of TiO2 nanoparticles into the PVK matrix effectively creates a barrier layer at the coating-metal interface, inhibiting the entry of aggressive ions. Microhardness studies revealed the increase in hardness value of the PVK and PVK/TiO2 coatings indicated the protective nature of the coating and provided high mechanical strength to 316L SS. The tape adhesion tests carried out on the coated specimens also indicated a good adhesion of the PVK/TiO2 on the 316L SS surface.

DFT and electrochemical studies of new superplasticizers on the corrosion inhibition of 316L stainless steel in neutral medium: A comparative study

In this study, new corrosion inhibitors such as polycarboxylate ether (PCE), sulfonated naphthalene formaldehyde (SNF), modified lignosulphonate (MLS), and sulfonated melamine formaldehyde (SMF) are utilized for 316L stainless steel in a 3.5% NaCl medium. ATR-IR and UV–Vis spectroscopy were used to study the superplasticizers' structural characterization. Based on the ATR-IR and UV–Vis results, all of the spectrum information for PCE, SNF, MLS, and SMF are closely matched to the findings of the significant superplasticizers described in the literature. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) measurements and the weight loss method were used to investigate the corrosion inhibition efficacy of new superplasticizers on 316L stainless steel in a 3.5% NaCl solution. According to the EIS, PDP, and weight loss results, SMF has the highest inhibitory efficiency of all the inhibitors examined. These could be attributed to the presence of additional heteroatoms (N, O, and S) in the SMF than in the other three inhibitors. The inhibition efficiencies were in the order of SMF > MLS > SNF > PCE, with the maximum inhibition efficiency of 88.8% for the SMF inhibitor at 0.00012 mol L−1 concentration. The adsorption of all inhibitors, including PCE, SNF, MLS, and SMF, is well-fitted and follows the Langmuir isotherm model. SEM and EDX analyses were used to study the corrosion mechanism of the adsorbed inhibitor molecules PCE, SNF, MLS, and SMF and their elemental composition on the metal surface. The SEM and EDX result reveals that the SMF inhibitor is substantially adsorbed onto the 316L SS surface as a protective layer. Quantum chemical calculations were utilized to give further evidence of the mechanism of inhibition action of all corrosion inhibitors such as PCE, SNF, MLS, and SMF. All the DFT studies demonstrate that sulfonated melamine formaldehyde (SMF) has outstanding inhibitory capabilities on 316L stainless steel in a 3.5% NaCl solution at room temperature out of the four proficient superplasticizers studied.

Temperature dependence of surface microstructure of 316 L stainless steel exposed to low-energy hydrogen ion irradiation

The austenitic 316 L stainless steel (316LSS) is an important metal for nuclear installations due to its high strength, good plastic toughness and excellent corrosion resistance, and is commonly used as the plasma-facing and structural material. In this study, 316LSS samples are irradiated with low-energy hydrogen ions (35 eV) at the temperature of 400–1300 K to investigate the surface microstructure evolution. The experimental results show that the surface of 316LSS samples remains relatively smooth at 400 K and 600 K after irradiation. Significant surface roughening including spherical protrusions is formed on the surface at 800 K and 1100 K, and step-like streaks are observed at 1300 K. However, no drastic change in the surface morphology is observed in the separate annealing experiments at 800–1300 K. It has been shown that hydrogen ion irradiation mainly causes the surface microstructure evolution of 316LSS samples. After hydrogen plasma exposure, a large number of adatoms are first formed on the surface of 316LSS because of bubble growth. The adatoms then preferentially reach the defects by diffusion at certain temperatures, and aggregate into spherical protrusions with low surface energy. The qualitative simulation results show that the irradiation temperature affects the diffusion and aggregation of adatoms on the surface, and the radius of the spherical protrusions gradually increases due to the decrease of the surface binding energy and the increase of the irradiation fluence.

A Novel Method for the Fabrication of Antibacterial Stainless Steel with Uniform Silver Dispersions by Silver Nanoparticle/Polyethyleneimine Composites.

Only a few studies have so far focused on the addition of silver to SS316L alloys by conventional sintering methods. Unfortunately, the metallurgical process of silver-containing antimicrobial SS is greatly limited due to the extremely low solubility of silver in iron and its tendency to precipitate at the grain boundaries, resulting in an inhomogeneous distribution of the antimicrobial phase and loss of antimicrobial properties. In this work, we present a novel approach to fabricate antibacterial stainless steel 316L by functional polyethyleneimine-glutaraldehyde copolymer (PEI-co-GA/Ag catalyst) composites. PEI is a highly branched cationic polymer, which makes it exhibit very good adhesion on the surface of the substrate. Unlike the effect of the conventional silver mirror reaction, the introduction of functional polymers can effectively improve the adhesion and distribution of Ag particles on the surface of 316LSS. It can be seen from the SEM images that a large number of silver particles are retained and well dispersed in 316LSS after sintering. PEI-co-GA/Ag 316LSS exhibits excellent antimicrobial properties and does not release free silver ions to affect the surrounding environment. Furthermore, the probable mechanism for the influence of the functional composites on the enhancement of adhesion is also proposed. The formation of a large number of hydrogen bonds and van der Waals forces, as well as the negative zeta potential of the 316LSS surface, can effectively enable the formation of a tight attraction between the Cu layer and the surface of 316LSS. These results meet our expectations of designing passive antimicrobial properties on the contact surface of medical devices.

A comparison study of crevice corrosion on typical stainless steels under biofouling and artificial configurations

In this work, the crevice corrosion behavior and biofouling coverage of 316L stainless steel (316L SS), 2205 duplex stainless steel (2205 DSS), and 2507 super duplex stainless steel (2507 SDSS) in natural seawater were investigated through long-term field exposure tests. The results revealed that both artificial crevice corrosion and biofouling-induced crevice corrosion occurred on the surface of three stainless steels. The corrosion rate was ranked as 316L SS » 2205 DSS＞2507 SDSS. The deepest area of the artificial corrosion pit was at the edge of the crevice, which was related to the IR drop and acidification of the localized solution. The highest biofouling coverage and the most severe biofouling-induced corrosion occurred on the surface of 316L SS. The attachment of large organisms to the metal surface formed a fouling barrier layer, further blocking the flow of material over the crevices, and the artificial crevice corrosion was accelerated. The initiation of barnacle-induced corrosion was due to the formation of a crevice between the barnacle and the substrate, resulting in the entry of seawater. The acidification of the solution caused by catalytic-occluded cells was responsible for the continuous development of barnacle-induced corrosion, which was similar to the propagation of the artificial crevice corrosion.

Corrosion behaviour characterisation of 316L stainless steel and Inconel 625 in supercritical water containing hydrochloric acid and high oxygen

ABSTRACT Corrosion was currently the most crucial factor hindering the commercial development of supercritical water oxidation (SCWO) technology. Stainless steel represented by 316L and Ni-based alloy represented by Inconel 625 were performed and compared with corrosion resistance in supercritical environment with high concentrations of oxygen and chlorides. The results shown that the duplex layer was formed on two samples. The surface of 316L SS was mainly composed of loose magnetite and haematite, resulted in pitting corrosion, microcracks, and the exfoliation of oxide. The inner layer were separately a small amount of Cr2O3 oxide and FeCr2O4 spinel, which were caused by the lower content of chromium. Compared with 316L SS, the oxide film structure of Inconel 625 was composed of the outer layer of spinel and the inner layer of Cr-rich oxide. Some nodular oxides were formed, and it can be explained by the volatilisation process of chromium.

Anti-inflammatory Effect of (-)-Epigallocatechin-3-O-gallate on Human Umbilical Vein Endothelial Cells Grown on 316L Stainless Steel via STAT3/NF-κB Signaling

Stainless steel (316L SS) is commonly used to build coronary artery stents for the treatment of occluded arteries. However, tissues in contact with the stent may develop inflammation that can lead to restenosis. The natural substances derived from normal diet provide a pool of candidates that have potential to treat cardiovascular diseases. (-)-Epigallocatechin-3- O-gallate (EGCG), a polyphenolic flavonoid present in green tea, has antioxidant, antithrombogenic, and anti-inflammatory effects, and may reduce the risk of cardiovascular diseases. This study aimed to investigate whether EGCG has an anti-inflammatory effect on human umbilical vein endothelial cells (HUVECs) attached to the surface of 316L SS. We evaluated cell proliferation using the dimethyl thiazolyl tetrazolium bromide method in HUVECs after treatment with EGCG. Enzyme-linked immunosorbent assay (ELISA) assessed the level of inflammatory cytokines, including interleukin 6 (IL-6) and tumor necrosis factor (TNF) in HUVECs. We further investigated the regulatory mechanisms of the signal transducer and activator of transcription 3 (STAT3)/NF-κB signaling pathway in HUVECs by Western-blot analysis. We found that HUVECs cultured on 316L SS had increased cell proliferation and inflammation, and these can be inhibited by treatment with EGCG. EGCG reduced the secretion of IL-6 and TNF and decreased the expression of STAT3 and NF-κB in HUVECs cultured on 316L SS. Consequently, our study demonstrated that EGCG treatment ameliorates the proliferation of HUVEC when cultured with 316L SS, potentially by modulating the inflammation responses via the STAT3/NF-κB signaling pathways.

High wear resistance and better pitting corrosion resistance of AISI 316L stainless steel by a self-protective oxy-nitrocarburizing paste

Simultaneous oxidation and nitrocarburizing of AISI 316 SS at 580 °C for 5, 10, 15, and 20 min were studied using self-protecting pastes of sodium cyanate and sodium carbonate. The analytical techniques of XRD and SEM/EDS allowed the characterization of surface modifications. The corrosion resistance was evaluated in a synthetic seawater solution using the cyclic potentiodynamic polarization technique. The cross-section hardness and wear resistance were assessed by Vickers indentation and pin-on-disc, respectively. This thermochemical process formed an oxidized compound layer above a solid nitrogen solution in austenite. The compound layer was composed of intermixed crystals of Fe3O4, ε-Fe3N, and expanded austenite. With increasing relative proportions of the first two phases and decreasing relative proportions of the third phase with increasing treatment time. The balance between the expanded austenite and the chemical composition of the compound layer improved the hardness, the wear-resistant, and the pitting corrosion resistance of the AISI 316L SS surface simultaneously. Oxy-nitrocarburizing at 580 °C for 10 min allowed the best-localized corrosion resistance. However, the sample oxy-nitrocarburized for 20 min reached a more stable passive zone with the highest wear resistance. Self-protective pastes based on sodium cyanates and carbonates allowed the oxy-nitrocarburizing process to consume less salt than the traditional molten salts.

Corrosion resistant and conductive TiN/TiAlN multilayer coating on 316L SS: a promising metallic bipolar plate for proton exchange membrane fuel cell

The single layers of TiN, TiAlN and TiN/TiAlN multilayer coatings were deposited on 316L SS bipolar plate by physical vapor deposition technique. The X-ray diffraction studies revealed that the formed coatings exhibited single-phase cubic structure. The low surface roughness and high contact angles of the TiAlN and TiN/TiAlN coatings governed the better water management in the fuel cell. Nyquist and Bode-impedance studies of TiN/TiAlN coating ensured higher electrochemical impedance behavior. The polarization results revealed that the current densities (icorr) of TiN/TiAlN coating were below 1 µA/cm2 in the PEMFC environments, which satisfied the U.S. Department of Energy’s 2020 target. The contact resistance of the TiN/TiAlN-coated 316L SS was the lowest and fulfilled the requirements of bipolar plate (≤ 10 mΩ cm2) in PEMFC environment. Surface morphology results revealed that the surface of 316L SS is well protected by multilayer TiN/TiAlN coating. Inductive coupled plasma-optical emission spectroscopy results are in good agreement with electrochemical studies revealing the TiN/TiAlN coating significantly reduced the metal ions dissolution.

High corrosion protective behavior of water-soluble conducting polyaniline–sulfonated naphthalene formaldehyde nanocomposites on 316L SS

In this paper, water-soluble conducting polyaniline–sulfonated naphthalene formaldehyde nanocomposites (PAni–SNF NCs) were successfully synthesized by a one-step in-situ polymerization method. The structural characterization of the synthesized PAni–SNF NCs was confirmed by Fourier transform-infrared spectroscopy (FT–IR), Ultraviolet-visible spectroscopy (UV–Vis), Proton nuclear magnetic resonance spectroscopy (1H NMR), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Dynamic light scattering (DLS), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Conductivity measurements, Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), and Cyclic voltammetry (CV). The corrosion protective behavior of 316L stainless steel (316L SS) in 1 M HCl was examined using electrochemical measurements and weight loss methods at various PAni–SNF NCs. The inhibition efficiency of PAni–SNF NCs was found to 97.9% and 99.3% in the case of PANS-3 and PANS-10 NCs at the optimum concentration of 50 ppm. The potentiodynamic polarization method demonstrated that PAni−SNF NCs acted as a mixed-type inhibitor in both studied NCs. Moreover, adsorption of PAni−SNF NCs inhibitor on the 316L SS surface followed the Langmuir isotherm model. The present report provides extremely significant findings in preparing and designing novel and sustainable corrosion inhibitors with high inhibition efficiency.

CORROSION INHIBITION OF CASEIN AS A NATURAL PROTEIN FOR 316L STAINLESS STEEL IN SIMULATED BODY FLUID

The importance of biomaterials is increased steadily with the augmentation of population and aging. In this research, casein, a protein present in milk, used to modify the 316L stainless steel (316L SS) alloy surface, used in medical application, against corrosion in the corrosive body fluid. Due to the presence of hetero-atoms in its moiety, casein has the ability to form a protective thin layer. Self-assembled monolayers (SAMs) technique is a common tool providing a well ordered thin film on the metallic surface. Casein was assumed to form SAMs on the 316L SS surface and the corrosion inhibition efficiency was examined electrochemically. The results proved the formation of SAMs and displayed that casein reduce the corrosion rate and serves as a mixed type inhibitor. The inhibition efficiency is increased by increasing the casein’s concentration and immersion time in the casein’s solution. A maximum inhibition efficiency obtained at 1000 ppm with immersion time equals 120 minutes. Further modification is undertaken to increase the inhibition efficiency.

Heparin/poly-l-lysine nanoplatform with growth factor delivery for surface modification of cardiovascular stents: The influence of vascular endothelial growth factor loading.

The rapid re-endothelialization of the vascular stent surface is desirable for preventing thrombosis or reducing restenosis. Many biological factors that promote the biological behavior of endothelial cells have been used for the surface modification of stents. Vascular endothelial growth factor (VEGF), which plays an important role in angiogenesis, induces strong vascular growth. In this study, we investigated different VEGF concentrations (50 to 500 ng/ml) to determine the optimum concentration for biocompatibility. First, VEGF-loaded heparin/poly-l-lysine (Hep-PLL) nanoparticles were created by electrostatic interactions. Then, the VEGF-loaded nanoparticles were immobilized on dopamine-coated 316 L stainless steel (SS) surfaces. The physical and chemical properties of the modified surface were characterized and the biocompatibility was evaluated in vitro. The results indicated that the VEGF-loaded nanoparticles were immobilized successfully on the 316LSS surface, as evidenced by the results of Alcian Blue staining and water contact angle (WCA) measurements. The low platelet adhesion and activation indicated that the modified surfaces had good blood compatibility. The modified surfaces showed a good inhibitory effect on smooth muscle cells, indicating that they inhibited tissue hyperplasia. In addition, the modified surfaces significantly promoted endothelial cell adhesion, proliferation, migration, and biological activity, especially VEGF concentration was 350 ng/ml (NPV350). The optical VEGF concentration of the surface modified Hep-PLL nanoparticles was 350 ng/ml. The proposed method shows promise for potential applications for cardiovascular devices.

Effects of Anodization‐Assisted Electrodeposition Conditions on the Fabrication of CuO‐Cu2O Coatings on Nanoporous Stainless Steel

Surface functionalization can be utilized as a useful tool to improve the antibacterial performances of medical devices. Furthermore, some antibacterial agents are coated or impregnated on the surface of 316LSS to prevent contamination of bacteria. Here, CuO‐Cu2O coatings were prepared on 316L nanoporous stainless steel (NPSS) by anodization‐assisted electrodeposition for applications in antibacterial materials. The present study investigated influences of HClO4 concentration, reaction temperature, and load voltage on the morphology, structure, and composition of the coatings. SEM images showed that appropriate nanopores with an average size of about 93 nm were formed on the stainless steel surface and then were successfully filled with CuO‐Cu2O. The nanopore size increased with increasing application of electrolyte concentration. Both the diameter and depth of the nanopores increased with increasing voltage. The EDX result indicated that Cu and O were embedded in as‐prepared CuO‐Cu2O/NPSS. XRD analysis showed that the CuO‐Cu2O/NPSS surface comprised CuO and Cu2O.

Electrochemical evaluation of synthesized s-triazine derivatives for improving 316L stainless steel for biomedical applications

316L stainless steel (316L SS) alloy has been broadly used for the fabrication of dental, orthopedic, and cardiovascular implants. As the surface of the stainless steel suffers from corrosion in the human body’s environment, a surface modification is required. Self-assembled monolayers (SAMs) perform a simple and efficient method for carrying out surface adaptation of the metallic biomaterials. In this study, synthesized s-triazine dicarboxylic acid derivative and four different s-triazine tetracarboxylic acid derivatives were considered to form SAMs on the 316L SS surface. The formed SAMs were electrochemically evaluated, as corrosion inhibitors for 316L SS in simulated body fluid (SBF) at 37 °C by means of potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results revealed that all the studied compounds exhibit good corrosion inhibition and function as mixed-type inhibitors with anodic predominance. The inhibition efficiencies were increased with increasing the concentrations of the solution of s-triazine derivatives, except in case of one compound. The maximum inhibition efficiency (≈ 90%) was obtained for the most efficient compound at 700 ppm. The inhibition was assumed to occur via adsorption on the metal surface. The hydrophobicity of the modified surface was tested by contact angle measurements. The thermodynamic calculations suggested that the adsorption of these compounds on the metal surface is a spontaneous process obeying Langmuir adsorption isotherm.

Assessment of characteristics and cytotoxic effects of 316L stainless steel coated with a new titanium oxide nano-structure coating method

In order to fabricate the TiO2 nano-structure coating on the Ti-free stainless steel with good adhesion, commercially obtained 316L stainless steel (316L SS) plates were chemically treated by KOH aqueous solution including TiH2 powder at 60ºC for 3 days in an oil bath shaker, and subsequently heated up to 550-800ºC under the air atmosphere. The crystal structure, color, adhesive strength and cytotoxic effects of coating were investigated. Fiber-like hydrogen titanate nano-structures were formed on the 316L SS surface and made a fine network. X-ray diffraction (XRD) patterns showed that hydrogen titanate phase converted to anatase and rutile after heat treatment above 550ºC. The heat treated sample at 800ºC for 1 h showed the highest adhesive strength and the lowest cytotoxicity. The alkali treatment method in this study is expected to be used on the other Ti-free metals with further research.

Investigation of wettability of Li on 316L SS surface and interfacial interactions for fusion device

Improved liquid Li wettability on a solid substrate surface is a necessary component for the research and development of blanket coolants, tritium breeders, and first wall materials for fusion device. A systemic investigation of Li wetting a 316 L SS surface, along with interfacial interactions has been successfully carried out. The results indicate that base vacuum pressure of the vessel, substrate temperature, and surface conditions of the substrate are the main factors that influence Li wetting property. It has been found that poor vacuum (>10−1Pa) along with high impurity content, especially water, can prevent Li wetting due to the formation of a layer of complex Li compounds, such as LiOH, Li3N and Li2CO3. Also, Li wetting can be gradually improved with an increase of substrate temperature, mainly due to a decrease in surface tension of Li droplets. Moreover, Li wetting can be further improved by effective surface conditioning. It has been demonstrated that baking was beneficial in order to release impurity gas by thermal desorption and thereby achieve high vacuum during Li wetting, which resulted in a reduction of > 50 °C in Li wetting temperature on the SS substrate. He-GDC and Li coating can further decrease Li wetting temperatures to the Li melting point (∼180 °C) by avoiding the formation of Li2O at the interfacial surface during Li wetting. This is achieved primarily because these conditioning techniques can effectively remove and isolate the SS surface oxide layer (Cr2O3), respectively, which was verified by the related testing of interfacial interactions between liquid Li and SS. Finally, surface textured structures with trenches ∼μm in size, are demonstrated to promote Li spreading along the groove direction, driven by capillary forces. These results provide the technical support for liquid Li applications in future fusion reactors.

Enhanced Mechanical and Biological Performance of an Extremely Fine Nanograined 316L Stainless Steel Cell-Substrate Interface Fabricated by Ultrasonic Shot Peening.

An extremely fine nanograined (NG) rough surface with the average grain size of 10 nm was successfully fabricated on 316L stainless steel (316L SS), which is a commonly used bioimplant metallic materials, via a simple physical therapy, namely, ultrasonic shot peening (USP). This extremely fine NG rough surface was proposed as the cell-substrate interface to enhance the mechanical and biological performance of 316L SS in orthopedic applications. Nanoindentation and micropillar compression tests indicated the significant improvement of the nanohardness and yield strength of the developed NG-316L SS, respectively, and the "in vitro" studies demonstrated that the developed extremely fine NG-316L SS rough surface could significantly enhance the attachment of the human osteoblast cells (Saos-2) compared with the as-received coarse-grained 316L SS surface. The observed mechanical and biological enhancement of the extremely fine NG-316L SS surface can be attributed to the ultrahigh-density nanosized grain boundaries, which could obstruct dislocation movement when the materials undergo plastic deformation and promote protein adsorption by providing a continuum of probable binding sites with partial surface coverage when the material encounters biological environments. In addition, aggregated protein particles were clearly observed on the proposed extremely fine NG-316L SS surface when it was used for the substrate of the human osteoblast cells. The findings and the advanced surface engineering technology utilized in this paper could promote the currently proposed concept that using nanograined/ultrafine grained cell-substrate interface for mechanical and biological enhancement of bioimplant materials from the current practice level of "hundreds of nanometers" to that of "tens of nanometers" or possibly even "several nanometers".

Anodic Electrophoretic Deposition of Graphene Oxide on 316L Stainless Steel with pH-Dependent Microstructures

This paper describes anodic electrophoretic deposition of graphene oxide (GO) on 316L SS with pH-dependent microstructures. GO flakes were synthesized by modified Hummers’ method. Detailed studies on structural characteristics, thermal stability, and elemental composition of the GO flakes were carried out using advanced characterization techniques. Results showed successful oxidation and exfoliation forming GO flakes that are hydrophilic in nature. Acidic (pH 3.4) and basic (pH 11) aqueous GO suspensions were prepared, and the zeta potential as well as the average particle size distribution of the suspensions was ascertained. The GO suspensions were exhibiting zeta potential values of −32.9 and −36.8 mV and average particle size of 1–2 µm and 800–900 nm at acidic pH of 3.4 and alkaline pH of 11, respectively. Using anodic electrophoretic deposition (EPD) methods, GO was coated on 316L SS substrate from acidic and alkaline suspension and coatings were characterized. The increased value of ID/IG by Raman spectra analysis, partial restoration of C = C skeleton in the de-convoluted C 1s XPS spectra analysis, and the presence of C–C and C–H stretching bands in ATR-FTIR spectra were correlated with partial reduction of GO during the deposition on 316L SS surface. Though there was no difference in the chemical composition of the coatings formed from the acidic and alkaline pH suspension, atomic force microscopy and field emission scanning electron microscopy characterization showed difference in topography and morphology of the coatings. 316L SS substrates coated with GO in acidic pH showed higher RMS and average roughness and dense agglomerated wrinkled microstructure compared to substrates coated with alkaline pH suspension. Again GO coating from acidic pH suspension showed hydrophobicity. The present study showed that the microstructures of the GO coatings on 316L SS can be tuned by varying the pH of the GO suspension during EPD process.