Bare 316L Research Articles

Chemical and Mechanical Characterization of Thermal-Multilayered Al2O3 Atomic Layer Depositions on AISI 316L Stainless Steel

In this work, three different nanometric, multilayered Al2O3 coatings, obtained by alternating two different deposition temperatures, have been applied on AISI 316L stainless steel by atomic layer depositions. The coating morphology has been investigated using atomic force microscopy (AFM) and scanning electron microscopy. Thickness analysis has been performed using AFM and glow discharge optical emission spectrometry (GDOES). In-depth compositional profiles have been performed using GDOES. The corrosion protection has been investigated using polarization curves in aggressive NaCl electrolyte. All variations of the coatings appeared to be adherent to the substrate with thickness in the range of the nominal values. Compositional analysis confirmed the presence of the Al2O3 layers. Vickers indentations used to evaluate coating adhesion showed that all coatings have a good adhesion to the substrate and in particular the amorphous/crystalline 20-nm-thick coating showed almost no sign of coating delamination. All samples show a higher corrosion resistance when compared with bare AISI 316L.

Enhancement of endothelialisation of coronary stents by laser surface engineering

Coronary stents have been widely used in the treatment of coronary heart disease. However, complications have hampered the long-term success of the device. Bare-metal stents (BMS) have a high rate of restenosis and poor endothelialisation. The drug-eluting stents (DES), although dramatically reduce restenosis, significantly prevent endothelialisation leading to late thrombosis and behave the same way as BMS after drug releasing. Rapid adhesion and growth of endothelial cells on the stent surface is a key process for early vascular healing after coronary stenting which contributes to the reduction of major complications. Surface properties manipulate cell growth and directly determine the success and life-span of the implants. However, the ideal surface properties of coronary stents are not yet fully understood. The objective of this research is to understand how surface micro/nano textures and associated material chemistry changes generated by a laser beam affect the behavior of endothelial cells on bare metal 316L stents. A high power laser beam was applied to modifying the surface properties of 316L coronary stent material and the commercial coronary stents, followed by examination of the adhesion and proliferation of human coronary endothelial cells that were growing on the surfaces. Surface properties were examined by scanning electron microscopy, contact angle measurement, and X-ray photoelectron spectroscopy. A novel surface with combined micro/nano features was created on stent material 316L and coronary stent with a specific surface chemistry. This surface gives rise to a threefold increase in the adhesion and eightfold increase in the proliferation of endothelial cells. Interestingly, such effects were only observed when the surface texture was produced in the nitrogen atmosphere suggesting the importance of the surface chemistry, including the dramatic increase of chromium nitride, for the interaction of endothelial cells with the material surface. This novel surface is also super-hydrophilic with close to zero water/cell culture fluid contact angles and low cytotoxicity. A novel surface created by laser surface-engineering with a combination of defined surface texture and surface chemistry was found beneficial for the improvement of coronary stent endothelialisation. The technology presented here could work with both DES and BMS with added benefit for the improvement of the biocompatibility of current coronary stents.

Improving endothelialization on 316L stainless steel through wettability controllable coating by sol–gel technology

Rapid endothelialization by surface coverage is considered as a way to increase blood compatibility of the vascular stent and reduce smooth muscle cell (SMC) mediated restenosis. Coatings on 316L stainless steels with different wettabilities and similar topographies were obtained through sol–gel process by regulating the proportions of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES). Adhesion and proliferation of vascular endothelial cells (EC) and SMC on these substrates have been evaluated by cell numbers, cell morphology, and expression of cytoskeletal protein. Results showed that EC and SMC responded differently to the coated surfaces. Enhanced endothelialization of bare 316L was found at the moderately hydrophilic coating (contact angle 45.3°) which exhibited effective inhibition of SMC and negligible influence on EC. These results are expected to lay foundation for the solution of the vascular restenosis which was mainly derived from the hyperplasia of SMC.

Degradation behavior of a polymer electrolyte membrane fuel cell employing metallic bipolar plates under reverse current condition

To examine durability of metallic bipolar plates (BPs) under reverse current conditions, the degradation of PEMFC employing graphite, bare 316L, and CrN-coated 316L BPs is investigated via a 1.4V pulse cycling test. After 20 cycles, the average voltage decay rate at 160mAcm−2 is 6.8, 16.8, and 12.0mVcycle−1 for the single cell using graphite, bare 316L, and CrN-coated 316L BPs, respectively. SEM, EPMA, and TEM analyses of the cathodes that experienced an extraordinary high voltage of 1.4V show that carbon corrosion and Pt migration/agglomeration occur similarly for the single cells, irrespective of the bipolar plate material. In contrast, in the membrane tested with bare 316L and CrN-coated 316L, Fe and Cr are detected; the amounts of Fe and Cr in the membrane are higher for bare 316L than for CrN-coated 316L. The membrane contamination results in a decrease in the ionic conductivity of the membranes, which mainly contributes to the faster performance decay of the single cells employing bare 316L and CrN-coated 316L bipolar plates. Thus, if automotive PEMFCs using metallic BPs are exposed to reverse current conditions upon start/stop cycles, metal contamination of the membrane could accelerate the performance decay in addition to the cathode degradation, such as carbon corrosion and Pt migration/agglomeration.

Electrochemical Properties of NiO-YSZ Thin Films on 316 Stainless Steel Bipolar Plates Under a Simulated PEMFC Environment

E-mail: hojang@korea.ac.krReceived November 16, 2011, Accepted December 30, 2011The corrosion resistance of 316L stainless steel coated w ith NiO-YSZ (Ni adde d yttria stabili zed zirconia) wasexamined in a proton exchange membrane fuel cell (PEMFC) environment. The NiO-YSZ coating was carriedout using a sol-gel dip coating method, and the corrosion resistance and interfacial contact resistance (ICR)were determined by the composition and morphology of the NiO-YSZ film. The corrosion resistance increasedwith increasing Ni content in the NiO-YSZ film, but rapid corrosion was observed when the YSZ filmcontained more than 15 wt % Ni due to surface cracks. The polarization resistance was improved by severalorders of magnitude when 316L stainless steel was coated with a 15 wt % NiO-YSZ film compared to bare316L. The ICR of the NiO-YSZ film was decreased to that of bare 316L when the YSZ film contained 25 wt %NiO, suggesting the possible application of NiO-YSZ coated stainless steel for a bipolar plate. Key Words : Ni, YSZ, Sol-gel, Metallic bipolar plate, PEMFCIntroductionThe bipolar plate used in proton exchange membrane fuelcells (PEMFCs) is a multifunctional component because itelectrically connects the cells in series, separates the gases inthe adjacent cells, and accommodates the gas flow channels.Therefore, bipolar plates need to be electrically conducting,mechanically strong, and resistant to corrosion.

An electrochemical method for functionalization of a 316L stainless steel surface being used as a stent in coronary surgery: irreversible immobilization of fibronectin for the enhancement of endothelial cell attachment

An electrochemistry-based method for the formation of functionalized alkanethiol layers on a 316L stainless steel surface was developed. The method was efficient in forming a very stable, irreversibly-attached COOH-terminated (mercaptoundecanoic acid) surface layer. This layer was used as a 'linker' to immobilize the extracellular matrix protein fibronectin to the 316L stainless steel surface. Fibronectin was irreversibly attached to the surface and, unlike physisorbed fibronectin, resisted detachment more in aggressive 0.1 M NaOH under sonication. The fibronectin-modified 316L stainless steel surface was more biocompatible towards attachment of endothelial cells than a bare (unmodified) 316L stainless steel surface, yielding a 25% improvement in cell density.

Suitability evaluation of plasma ion beam sputtered TiN/TiOxNy multilayers on steel for bio implants

Layers of TiN/TiOxNy were coated onto 316L stainless steel substrates by plasma ion sputtering technique. The layers were sputtered with the arc current of 2.5 A and with an acceleration voltage of 1000 V, for a sputtering time of 120 min. The XPS survey spectra on the surface of coatings showed the characteristic Ti2p, N1s and O1s peaks at the corresponding binding energies. X-ray diffraction and TEM-SAD analysis showed mixed oxynitride phase with TiO2 and TiN for TiN/TiOxNy multilayer coatings. Cross sectional HRTEM analysis indicated the columnar structure of the coatings. Nanohardness value of 29 GPa was observed for mulilayered coatings. The electrochemical impedance measurements showed that the TiN/TiOxNy coatings on 316L SS exhibited superior corrosion resistance compared to the single layers and the bare 316L SS substrate in simulated bodily fluid solution. Platelet adhesion experiments were done to examine the interaction between blood and the materials in-vitro.

Surface modification of 316L stainless steel with magnetron sputtered TiN/VN nanoscale multilayers for bio implant applications

Nanoscale multilayered TiN/VN coatings were developed by reactive dc magnetron sputtering on 316L stainless steel substrates. The coatings showed a polycrystalline cubic structure with (111) preferential growth. XPS analysis indicated the presence of peaks corresponding to Ti2p, V2p, N1s, O1s, and C1s. Raman spectra exhibited the characteristic peaks in the acoustic range of 160-320 cm(-1) and in the optic range between 480 and 695 cm(-1). Columnar structure of the coatings was observed from TEM analysis. The number of adherent platelets on the surface of the TiN/VN multilayer, VN, TiN single layer coating exhibit fewer aggregation and pseudopodium than on substrates. The wear resistance of the multilayer coatings increases obviously as a result of their high hardness. Tafel plots in simulated bodily fluid showed lower corrosion rate for the TiN/VN nanoscale multilayer coatings compared to single layer and bare 316L SS substrate.

Corrosion properties and cell performance of CrN/Cr-coated stainless steel 316L as a metal bipolar plate for a direct methanol fuel cell

CrN/Cr-coated stainless steel (STS) 316L is investigated as the material for a metal bipolar plate for a direct methanol fuel cell (DMFC) under actual operating circumstances. Protective coating layers of CrN/Cr are formed on STS 316L using an unbalanced magnetron (UBM) DC sputter via Cr target in an effort to improve the corrosion resistance and long-term stability of the STS 316L. In a corrosion resistance test, the CrN/Cr-coated STS 316L shows much better corrosion resistance than bare STS 316L in simulated electrolytic environments under anodic and cathodic potentials relevant to DMFCs. The interfacial contact resistance (ICR) between CrN/Cr-coated 316L and carbon paper decrease to 4 mΩ cm 2 at a compaction force of 150 N cm −2 compared to bare STS 316L (570 mΩ cm 2). The CrN/Cr-coated STS 316L cell has better cell performance compared to the bare STS 316L cell. Furthermore, the CrN/Cr-coated STS 316L cell exhibit low voltage losses of 38.2 μV h −1 under long-term operation of 760 h. These results show that the CrN/Cr-coated STS 316L, demonstrating its feasibility for use as a metal bipolar plate in a DMFC under actual operating circumstances.

Study of the corrosion resistance and in vitro biocompatibility of PVD TiCN-coated AISI 316 L austenitic stainless steel for orthopedic applications

The aim of the present work was to study the corrosion resistance in Hanks' solution and the in vitro biocompatibility of a TiCN-coated AISI 316L stainless steel. The electrochemical behavior was assessed using potentiodynamic polarization and electrochemical impedance spectroscopy. Cytotoxicity and genotoxicity tests were performed to evaluate the potential biocompatibility of the specimens. TiCN morphology was investigated using scanning electron microscopy (SEM). Bare 316L specimens were also evaluated for comparison. The results showed that the film morphology strongly influences the electrochemical behavior of the coated underlying metal. TiCN-coated specimens presented neither cytotoxicity nor genotoxicity.

Chromium nitride/Cr coated 316L stainless steel as bipolar plate for proton exchange membrane fuel cell

Chromium nitride/Cr coating has been deposited on surface of 316L stainless steel to improve conductivity and corrosion resistance by physical vapor deposition (PVD) technology. Electrochemical behaviors of the chromium nitride/Cr coated 316L stainless steel are investigated in 0.05 M H 2SO 4 + 2 ppm F − simulating proton exchange membrane fuel cell (PEMFC) environments, and interfacial contact resistance (ICR) are measured before and after potentiostatic polarization at anodic and cathodic operation potentials for PEMFC. The chromium nitride/Cr coated 316L stainless steel exhibits improved corrosion resistance and better stability of passive film either in the simulated anodic or cathodic environment. In comparison to 316L stainless steel with air-formed oxide film, the ICR between the chromium nitride/Cr coated 316L stainless steel and carbon paper is about 30 mΩ cm 2 that is about one-third of bare 316L stainless steel at the compaction force of 150 N cm −2. Even stable passive films are formed in the simulated PEMFC environments after potentiostatic polarization, the ICR of the chromium nitride/Cr coated 316L stainless steel increases slightly in the range of measured compaction force. The excellent performance of the chromium nitride/Cr coated 316L stainless steel is attributed to inherent characters. The chromium nitride/Cr coated 316L stainless steel is a promising material using as bipolar plate for PEMFC.

Structure and Properties of TaC<sub>x</sub> Coating on Biomedical 316L Stainless Steel by RF Magnetron Sputtering

In this paper, the TaCx coating with thickness around 1.2 μm was prepared by radio frequency magnetron sputtering technique on the 316L stainless steel substrate to improve its hemocompatibility. The structure and morphology of the coating were characterized by XRD and SEM. The XRD results indicated that TaCx, as a new species, appeared on the surface of the 316L stainless steel substrate. SEM images showed that the surface morphology of the TaCx coating was uniform and dense. The mechanical characteristics of the coating were measured by nanoindentation, giving a nanohardness of 13 GPa and a Young’s modulus of 210 GPa. The adhesion strength of the TaCx coating to 316L stainless steel depended on the sputtering bias voltages and increased for a higher bias voltage. The hemocompatibility of the TaCx coating, as evaluated by platelet adhesion tests, was compared to that of the bare 316L stainless steel. The results indicated that the hemocompatibility of 316L stainless steel with TaCx coating was significantly improved as compared to the original one.

RRR of copper coating and low temperature electrical resistivity of material for TTF couplers

In the framework of the R&D program on the TTF III main RF coupler, IPN Orsay developed in close collaboration with LAL institute, a dedicated facility for the electrical characterization of different materials at low temperature. This apparatus was used for measuring the electrical resistivity versus temperature (4.2 K–300 K) of various samples produced in the industry. These tests were performed in order to compare the RRR of the samples, qualify and find the optimum parameters for the coating process. Seven flat samples were tested in a saturated liquid helium bath under ∼1013 mbar pressure: measurements were performed on bare 316L samples, nickel coated 316L samples, and copper coated 316L samples with a nickel under layer. We investigated, in particular, the effect of vacuum annealing at 400 °C on the RRR of the copper coating. Our experimental data are compared to previous measurements reported by other groups, and theoretical results (e.g., Gruneisen–Bloch equation) and a good agreement was found. Finally, the tested samples fulfil the TTF III coupler design parameters requirements in terms of heat loads to the refrigerator at 2 K, 4 K and 70 K.

05/02069 A non-interior point approach to optimum power flow solution

A niobium nitride diffusion layer (Nb–N layer) has been synthesized via the plasma surface diffusion alloying (PSDA) technique on the surface of AISI316L stainless steel (316L SS), which is used as bipolar plates of direct formic acid fuel cells (DFAFCs). The niobium nitride-modified AISI316L stainless steel (Nb–N 316L SS) has a compact and successive niobium nitride diffusion layer with a single cubic NbN phase. The corrosion resistance and surface conductivity of Nb–N 316L SS are systematically investigated in the simulated anodic environments of DFAFC (0.05 M H2SO4 + 2 ppm HF + x M formic acid (x = 2, 5, 10 and 15) at 50 °C). The potentiodynamic and potentiostatic polarization tests demonstrate that the corrosion resistance of 316L SS is distinctly ameliorated in the simulated DFAFC environments after the PSDA modification. The interfacial contact resistances (ICR) of Nb–N 316L SS are much smaller than those of bare 316L SS before and after potentiostatic polarization tests.