Surface Of 316L Stainless Steel Research Articles

A mechanism for the enhanced attachment and proliferation of fibroblasts on anodized 316L stainless steel with nano‐pit arrays

In this study, 316L stainless steel with tunable nanometer pit sizes (0, 25, 50, and 60 nm) were fabricated by an anodization procedure in an ethylene glycol electrolyte solution containing 5 vol % perchloric acid. The surface morphology and elemental composition of the 316L stainless steel were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The nano-pit arrays on all of the 316L stainless steel samples were in a regular arrangement. The surface properties of the 316L stainless steel nano-pit surface showed improved wettability properties as compared with the untreated 316L stainless steel, as demonstrated by the lower contact angles which dropped from 83.0° to 28.6 to 45.4°. The anodized 316L stainless steel surfaces with 50 nm and 60 nm diameter pits were also more rough at the nanoscale. According to MTT assays, compared with unanodized (that is, nano-smooth) surfaces, the 50 and 60 nm diameter nano-pit surfaces dramatically enhanced initial human dermal fibroblast attachment and growth for up to 3 days in culture. Mechanistically, this study also provided the first evidence of greater select protein adsorption (specifically, vitronectin and fibronectin which have been shown to enhance fibroblast adhesion) on the anodized 316L stainless steel compared with unanodized stainless steel. Such nano-pit surfaces can be designed to support fibroblast growth and, thus, improve the use of 316L stainless steel for various implant applications (such as for enhanced skin healing for amputee devices and for percutaneous implants).

Thermal stability of a nanostructured layer on the surface of 316L stainless steel

Abstract

Performance of Plasma Sprayed Al2O3 Coating in Bio-Simulated Environment

Alumina coatings deposited on the surface of stainless steel 316L by the method of plasma spraying are studied. Tests for wear and corrosion are preformed in Ringer’s solution simulating a human body environment. The structure, microhardness, wear resistance and corrosion resistance of the steel are determined with and without a coating. Deposition of a coating onto the stainless steel is shown to be an effective means for protecting implants from corrosion and wear.

Proliferation and Adhesion of L929 Fibroblasts on Surface with Different Microtopography

ABSTRACTThree types of 316L stainless steel surface with different topography were prepared by a Fine Particle Peening (FPP) treatment using titania, silica and alumina shot particles and analyzed the cell proliferation and cell-scaffold interaction. FPP-treated surface with titania and silica particles had micro asperities at low frequency. On the other hand, the alumina treated surface had micro asperities at high frequency. L929 fibroblasts were seeded on these specimens and then the number of cells was counted after 72 hours of culturing. The FPP-treated surfaces showed good cell proliferation comparing to polished surface. This indicates that micro asperities formed on the surface encourage cell adhesion. Cell adhesion behavior was evaluated by a scanning electron microscope (SEM) and a fluorescence microscope. Dense filopodia were observed when cells cultured on the FPP-treated surface. This means that FPP treatment enhances cell adhesion and proliferation. The number of cells observed on the FPP-treated surface depended on the shape of asperities formed by FPP treatment; the highest cell counts were obtained on alumina treated surface. This is because cell migration was not inhibited by the shape of alumina treated surface asperities.

Photoactivated titania-based nanomaterials for potential application as cardiovascular stent coatings

Intravascular stenting of atherosclerotic coronary arteries is a life-saving, widely used procedure in interventional cardiology. Adverse clinical outcomes such as restenosis highlight the importance of meeting the excellent biocompatibility by cardiovascular implants. Many attempts have been made to improve the safety profile of implant surface. We for the first time developed the photoactive intravascular titania-based nanomaterials for the application as cardiovascular stent coating. Photoactive biomaterial deposited on the cardiovascular stent surface demonstrated promising features, making it an excellent substrate for endothelial cells growth and proliferation. The biocompatibility of these coatings has been compared with 316L stainless steel surfaces typically used in commercial coronary stents production. The results of the study proved that the innovative titania-based coatings have better biocompatibility characteristics than the 316L stainless steel and in regard of its antithrombotic potential provided protection against restenosis. Furthermore, the titania coating supported endothelial cells attachment and proliferation, and induced prolonged plasma recalcification time in comparison with stainless steel surface. Innovative photoactive titania coating can be an important factor to prevent the process of the restenosis in the place of implantation.

Spinodal decomposition in AISI 316L stainless steel via high-speed laser remelting

A 1.5kW CO2 pulsed laser was used to melt the surface of AISI 316L stainless steel with a view to enhancing the surface properties for engineering applications. A 90μm laser beam spot size focused onto the surface was used to provide high irradiances (up to 23.56MW/cm2) with low residence times (as low as 50μs) in order to induce rapid surface melting and solidification. Variations in microstructure at different points within the laser treated region were investigated. From this processing refined lamellar and nodular microstructures were produced. These sets of unique microstructures were produced within the remelted region when the highest energy densities were selected in conjunction with the lowest residence times. The transformation from the typical austenitic structure to much finer unique lamellar and nodular structures was attributed to the high thermal gradients achieved using these selected laser processing parameters. These structures resulted in unique characteristics including elimination of cracks and a reduction of inclusions within the treated region. Grain structure reorientation between the bulk alloy and laser-treated region occurred due to the induced thermal gradients. This present article reports on microstructure forms resulting from the high-speed laser surface remelting and corresponding underlying kinetics.

Nitric Acid Reduction on 316L Stainless Steel under Conditions Representative of Reprocessing

Steels comprise the largest class of metal-based materials encountered on nuclear sites. An understanding of how process steels interact with HNO3 in spent fuel treatment plant environments is required to enable informed decisions to be made about the design and effective application of different steel types within nuclear environments. Stainless steels readily passivate in nitric acid. However, increasing the oxidising power of the media can lead to passive film dissolution, resulting in rapid transpassive corrosion. The corrosion of steels in nitric acid is further complicated by the autocatalytic reduction of HNO3 to aqueous HNO2 which attacks the steel surface. This paper describes the effect of this behaviour on process steels in stagnant and/or flowing conditions using electrochemical and microgravimetric based methods. We describe linear sweep voltammetry studies performed on a 316L stainless steel rotating disk electrodes in varying concentrations of nitric acid and rotation speeds and provide a qualitative interpretation of the results and what these imply about the mechanism of HNO3 reduction. These findings will be used in follow on studies to determine the kinetic parameters of the nitric acid reduction reaction at the surface of 316L stainless steel.

Nanocomposite-carbon coated at low-temperature: A new coating material for metallic bipolar plates of polymer electrolyte membrane fuel cells

A nanocomposite-carbon layer is coated onto the surface of 316L stainless steel (SS316) using a beam of accelerated C60 ions at low temperature. The coating is composed of textured graphite nanocrystals ranging in size from 1 to 2 nm, with the graphene plane normal to the coating plane; the nanocrystals are separated by amorphous carbon. This orientation of the graphene layer provides low film resistivity in the direction of the substrate normal. Corrosion resistance tests performed in aggressive anodic and cathodic environments of a polymer electrolyte membrane fuel cell (PEMFC) show that the nanocomposite-carbon coated SS316L exhibits better anticorrosion properties than does bare SS316L. The interfacial contact resistance (ICR) of the nanocomposite-carbon coated SS316L is 12 mΩ cm2, which is similar to that of graphite at a compaction force of 150 N cm−2 and lower than a target of ∼20 mΩ cm2. A low value of ICR is maintained even after corrosion tests in aggressive anodic and cathodic environments. The fabricated nanocomposite-carbon coated SS316L exhibits excellent corrosion resistance and low interfacial contact resistance under simulated PEMFC bipolar plate conditions.

Enhanced corrosion resistance of strontium hydroxyapatite coating on electron beam treated surgical grade stainless steel

The surface of 316L stainless steel (316L SS) is irradiated by high energy low current DC electron beam (HELCDEB) with energy of 500keV and beam current of 1.5mA followed by the electrodeposition of strontium hydroxyapatite (Sr-HAp) to enhance its corrosion resistance in physiological fluid. The coatings were characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and High resolution scanning electron microscopy (HRSEM). The Sr-HAp coating on HELCDEB treated 316L SS exhibits micro-flower structure. Electrochemical results show that the Sr-HAp coating on HELCDEB treated 316L SS possesses maximum corrosion resistance in Ringer's solution.

Al2O3 reinforced Fe–Al composite coatings prepared by double glow discharge technique

Alumina (Al2O3) particles reinforced iron aluminide coatings (Fe–Al coatings) were prepared on the surface of 316L stainless steel at only 580°C by a novel approach, namely double glow discharge technique. The chemical composition and morphology of the coatings were characterised by means of glancing angle (1°) X-ray diffractometry, X-ray photoelectron spectroscopy and scanning electron microscopy (SEM) respectively. The hardness, wear and corrosion behaviours of the aluminide coatings were also evaluated. The results indicated that the aluminide coatings exhibited a good wear and corrosion resistance since Al2O3 particles were well distributed in the coatings. The friction coefficient of the composite coatings increased first and then decreased with the increment of Al2O3 particles, meanwhile the corrosion potential and microhardness tended to increase. Finally, the wear mechanisms of the coatings were discussed.

Friction/Wear Properties of Ta-Doped TiO<sub>2</sub> Films on Surface of Nano-Grained 316L

Ta-doped TiO2 films were deposited on surface of nano-grained 316L stainless steel by RF magnetron sputtering technology at room temperature. The surface morphology and friction/ wear properties of TiO2 films with different Ta-doped content were investigated. The results showed that the proper amount of Ta-doped could refine TiO2 film particles. The 23% Ta-TiO2 film on the surface of SNG-316L possessed the lowest friction coefficient (0.147), the best wear-resisting performance and the best friction performance.

Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite

Laser-engineered net shaping (LENS™), a commercial additive manufacturing process, was used to modify the surfaces of 316L stainless steel with bioactive hydroxyapatite (HAP). The modified surfaces were characterized in terms of their microstructure, hardness and apatite forming ability. The results showed that with increase in laser energy input from 32J/mm2 to 59J/mm2 the thickness of the modified surface increased from 222±12μm to 355±6μm, while the average surface hardness decreased marginally from 403±18 HV0.3 to 372±8 HV0.3. Microstructural studies showed that the modified surface consisted of austenite dendrites with HAP and some reaction products primarily occurring in the inter-dendritic regions. Finally, the surface-modified 316L samples immersed in simulated body fluids showed significantly higher apatite precipitation compared to unmodified 316L samples.

Characterization of Al2O3 coatings oxidized from Al with different proportion of seed crystals at a lower temperature

Al layer with α-Al2O3 seed crystals was prepared on the surface of 316L stainless steel (SS) by a double cathodes discharge technique, in which the mixed targets of pure Al doped with different proportions of α-Al2O3 were used. Then, Al2O3 coatings were obtained after plasma oxidization at 580°C. The phase composition, microstructure and morphology of the coatings were studied respectively by means of glancing-angle (1°) X-ray diffractometry (GAXRD) and scanning electron microscopy (SEM). Furthermore, the bonding force and corrosion resistance of the coatings were measured. The results indicated that α-Al2O3 nucleated and grew surrounding the seed crystals as the Volmer–Weber Mode. The Al2O3 coating was compact, performing a good corrosion resistance and metallurgical bonding. The inducing effects of α-Al2O3 with different fractions were discussed. α-Al2O3 (5.5wt.%) was distributed in the Al layer when the target possessing 10% α-Al2O3 was used. After plasma oxidation, 65.54wt.% α-Al2O3 was obtained which was 10.34% more than that obtained by the oxidation of pure Al at the same condition. However, the inducing effects became weak with the further increment of content of α-Al2O3 seed crystals.

Synthesis and characterization of di(ethylene glycol) vinyl ether films deposited by atmospheric pressure corona discharge plasma

This study concerns plasma deposition by atmospheric-pressure corona discharge processing of di(ethylene glycol) vinyl ether (EO2V) as vaporized precursor. Plasma polymerized EO2V (pp-EO2V) thin films were coated using mixed Ar–O2 plasma as carrier gas onto plasma pre-treated surfaces of surgical-grade 316L stainless steel (SS 316L) coupons. The influence of plasma operating conditions on physical and chemical properties of pp-EO2V films was evaluated by contact angle measurements, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). It was found that surface hydrophilic properties of the deposited film could be controlled by varying plasma deposition time, the carrier gas mixture and the applied plasma voltage. Spectral analyses of FT-IR and XPS affirm compositional changes occurred on the synthesized surface due to plasma activation of new polar and hydrophilic functional groups. There was a good correlation between the FT-IR results and the contact angle measurements. AFM images were used to investigate surface roughness and morphological aspects of the film. Rough estimate of the coating thickness was also provided based on AFM measurements. Stability of the film was evaluated by AFM before and after soaking in phosphate buffer saline solution.

Effect of a nanostructured surface layer on the tensile properties of 316L stainless steel

Abstract

Relationships between microstructures and properties of buffer layer with Inconel 52M clad on AISI 316L stainless steel by GTAW processing

This study employed gas tungsten arc welding (GTAW) to clad an AISI 316L stainless steel surface with a buffer layer of KMS 309L stainless steel and three subsequent layers of Inconel 52M cladding. Our objective was to identify the optimal cladding parameters required to produce high-quality weldments and investigate the properties of the cladding layers. This study then used these cladding specimens to examine the effects of variation in the dilution rates of several elements on the microstructure and properties of the AISI 316L stainless steel. Our results demonstrate that repeated thermal cycles reduced the hardness of the cladding layer to less than that of the KMS 309L buffer layer and the AISI 316L stainless steel base. This was due to a decrease in overall hardness as the number of cladding layers was increased, resulting from microstructural changes in the AISI 316L stainless steel. Observations of microstructure revealed that increasing the number of cladding layers led to the formation of various solidification morphologies. The primary reason for these changes was an alteration in the composition of the stainless steel (dilution effect) produced by variations in thermal efficiency resulting from the overlapping of layers in the welded cladding. Hot cracking susceptibility tests demonstrate that AISI 316L stainless steel clad with a KMS 309L buffer layer significantly reduced susceptibility to hot cracking through the formation of δ-ferrite precipitates at the interface between the KMS 309L buffer layer and Inconel 52M. As a result, AISI 316L stainless steel clad with a KMS 309L buffer layer showed a significant reduction in susceptibility to hot cracking.

Corrosion Behavior of 316L Stainless Steel and Alloy 625 in Supercritical Water Oxidation for Coking Wastewater Treatment

The corrosion behavior of 316L stainless steel and alloy 625 were deteced in superciritical water oxidation (SCWO) process for coking wastewater treatment. The operation conditions were 500 °C, 25 MPa, oxygen ratio of 3.5 and the reaction time of 150 h. Surface morphologies of metal samples, oxide structure and compositions across the oxide thickness of the metal samples after SCWO were analyzed using SEM and ESD, and the corrosion rates for both samples were obtained. Pitting corrosion was found on the surface of 316L stainless steel with a corrosion rate of 0.334 mm/a. While no remarkable corrosion was found on the surface of alloy 625, and the corrosion rate is 0.052 mm/a.

Synthesis and Characterization of Modified Nano-TiO2 Films for Corrosion Protection of Stainless Steel

A TiO2 film and a B-Fe-Ce-modified TiO2 film were prepared on the surface of 316L stainless steel (316L SS) substrates by a sol-gel and dip-coating method. The corrosion resistance of the films and their protective properties for the stainless steel were investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve measurements. The results showed that the TiO2 film and the B-Fe-Ce-modified TiO2 film were composed of anatase TiO2 nanoparticles with the diameters about 15 nm and 10 nm, respectively. The EIS results suggested that the B-Fe-Ce-TiO2 film could provide more effective corrosion protection for 316L SS in 0.5 M NaCl solution. The potentiodynamic anodic polarization curve of the B-Fe-Ce-TiO2/316L SS electrode in the above solution showed a larger stable passive region and a higher breakdown potential (Eb ) than that of the TiO2/316L SS.

The Study of Micro-grating and Micro-square-column on Frictional Resistance Reduction of 316L Stainless Steel Surface

To reduce the frictional resistance and degree of wear on the surface of 316L stainless steel, three kinds of grating structures and square-column structures in different densities were textured with by nanosecond-laser on the surface of 316L stainless steel. The frictional characteristics on the smooth and textured surfaces were examined by the UMT-2 friction and wear test machine; the grating structures, square-column structures and wear scratches were observed by TOYOTA microscope; the mechanisms concerning frictional changes of grating structure and square-column structure were then analyzed. Research results show that the changes of frictional resistances of grating structure and square-column structure are more stable than that on the smooth surface, which means the former can stabilize the frictional resistance. As the friction time extends, the frictional resistance of smooth surface increase sharply, while the frictional resistance of grating structure and square-column structure remain small and unchanged. Therefore, the denser the grating structure and square-column structure, the smaller the frictional resistance. The experiments give rise to the conclusion that the grating structure and square-column structure can capture stereoplasm particles and store lubricating oil, which can produce secondary lubrication effect and retain the continuity of oil film under oil-poor conditions. Denser grating structure and square-column structure is prone to generate better fluid dynamic pressure effect and improve the bearing capacity. In addition, grating structure is superior to the square-column structure in the reduction of frictional resistance.

Reducing Staphylococcus aureus biofilm formation on stainless steel 316L using functionalized self-assembled monolayers

Stainless steel 316L (SS316L) is a common material used in orthopedic implants. Bacterial colonization of the surface and subsequent biofilm development can lead to refractory infection of the implant. Since the greatest risk of infection occurs perioperatively, strategies that reduce bacterial adhesion during this time are important. As a strategy to limit bacterial adhesion and biofilm formation on SS316L, self-assembled monolayers (SAMs) were used to modify the SS316L surface. SAMs with long alkyl chains terminated with hydrophobic (−CH3) or hydrophilic (oligoethylene glycol) tail groups were used to form coatings and in an orthogonal approach, SAMs were used to immobilize gentamicin or vancomycin on SS316L for the first time to form an “active” antimicrobial coating to inhibit early biofilm development. Modified SS316L surfaces were characterized using surface infrared spectroscopy, contact angles, MALDI-TOF mass spectrometry and atomic force microscopy. The ability of SAM-modified SS316L to retard biofilm development by Staphylococcus aureus was functionally tested using confocal scanning laser microscopy with COMSTAT image analysis, scanning electron microscopy and colony forming unit analysis. Neither hydrophobic nor hydrophilic SAMs reduced biofilm development. However, gentamicin-linked and vancomycin-linked SAMs significantly reduced S. aureus biofilm formation for up to 24 and 48h, respectively.