Uncoated Stainless Steel Research Articles

Sporicidal efficacy of thermal-sprayed copper alloy coating.

Approximately 200 000 Canadians acquire healthcare-associated bacterial infections each year and several-fold more acquire food-borne bacterial illnesses. Bacterial spores are particularly problematic because they can survive on surfaces for several months. Owing to its sporicidal activity, copper alloy sheet metal is sometimes used in hospital settings, but its widespread use is limited by cost and incompatibility with complex furniture and instrument designs and topographies. A potential alternative is the use of thermal spray technology to coat surfaces with copper alloys. We compared the sporicidal activity of thermally sprayed copper alloy on stainless steel with that of copper alloy sheet metal against Bacillus subtilis spores. Spores remained intact for at least 1 week on uncoated stainless steel, whereas spore fragmentation was initiated within 2 h of exposure to either copper surface. Less than 15% of spores were viable 2 h after exposure to either copper surface, as compared with stainless steel. By day 7, only degraded spores and petal-like nanoflowers were present on the copper surfaces. Nanoflowers, which are laminar arrangements of thin crystal sheets composed of carbon - copper phosphate, appeared to be derived from the degraded spores. Altogether, these results indicate that a thermal-sprayed copper alloy coating on stainless steel provides sporicidal activity similar to that afforded by copper alloy sheet metal.

Characterization of mechanical properties and electrochemical behaviour in a Hank´s solution of 316L/Cr1- xAlxN system

Cr1-xAlxN hard coatings were successfully deposited by R.F. reactive magnetron co-sputtering in an Ar/N2 gas mixture using chromium and aluminium targets on 316L stainless steel substrates. Crystallographic orientations associated to the Cr1-xAlxN FCC based in the conjugate complex of CrN and w-AlN phases, with ao=4.18Å lattice parameter for the ternary Cr1-xAlxN compound were identified by X-Ray diffraction. The thickness and roughness of the deposited coatings are 1.00±0.05nm and 2.65±0.6nm, respectively. The mechanical properties were determined by nanoindentation leading to a hardness of 27.8±2.6GPa and elastic modulus of 346GPa. The corrosion resistance of the coated 316L/Cr1-xAlxN system under simulated body fluid (SBF, Hank’s solution) was determined via electrochemical impedance spectroscopy. A reduction in the corrosion rate of 99% in relation to uncoated 316L stainless steel substrate was found by Tafel. Thus, these coatings seem to be excellent candidates to be used in biomedical applications.

Combined Slurry and Cavitation Erosion Resistance of Hvof Thermal Spray Coated Stainless Steel

The combined slurry and cavitation erosion resistance of thermal spray coatings were studied and compared to that of an uncoated martensitic stainless steel (SS 410). The thermal sprayed 70Ni30Cr coatings were obtained by High velocity oxy fuel (HVOF) process. The specimens were characterized for its hardness, bending and peel-off tests. The resistance to synergy effect of slurry and cavitation erosion of the thermal sprayed coatings was measured in a slurry pot tester with prismatic bluff bodies known as Cavitation Inducers. The results showed that the slurry erosion resistance of SS 410 can be improved by HVOF coating. It is observed that the HVOF coated specimens showed better erosion resistance than the uncoated specimen, subjected to erosion test under similar conditions. The observation has showed mixed (brittle and ductile) mode of erosion mechanism in HVOF coated specimen.

Platinum-free, graphene based anodes and air cathodes for single chamber microbial fuel cells.

Microbial fuel cells (MFCs) exploit the ability of microorganisms to generate electrical power during metabolism of substrates. However, the low efficiency of extracellular electron transfer from cells to the anode and the use of expensive rare metals as catalysts, such as platinum, limit their application and scalability. In this study we investigate the use of pristine graphene based electrodes at both the anode and the cathode of a MFC for efficient electrical energy production from the metabolically versatile bacterium Rhodopseudomonas palustris CGA009. We achieve a volumetric peak power output (PV) of up to 3.51 ± 0.50 W m-3 using graphene based aerogel anodes with a surface area of 8.2 m2 g-1. We demonstrate that enhanced MFC output arises from the interplay of the improved surface area, enhanced conductivity, and catalytic surface groups of the graphene based electrode. In addition, we show a 500-fold increase in PV to 1.3 ± 0.23 W m-3 when using a graphene coated stainless steel (SS) air cathode, compared to an uncoated SS cathode, demonstrating the feasibility of a platinum-free, graphene catalysed MFCs. Finally, we show a direct application for microwatt-consuming electronics by connecting several of these coin sized devices in series to power a digital clock.

Corrosion behaviour of single and double layer hydroxyapatite coatings on 316L stainless steel by plasma spray

AISI316L stainless steel is extensively used in orthopedic and dental applications. However, this alloy exhibits low integration behaviour when it comes in contact with surrounding bone tissue and implant healing duration can be as much as few months. The aim of this study is the fabrication of biocompatible hydroxyapatite (HA) coatings on stainless steel substrate in order to accelerate the process of osseointegration of implants. The biocompatible single layer of Titania (TiO2), Hydroxyapatite and bi-layer TiO2/HA coatings were deposited by atmospheric plasma spray on 316L stainless steel. Coated and uncoated stainless steel specimens were incubated in simulated body fluids and 0.9% NaCl solutions for 1h and 7 days. In vitro electrochemical-corrosion evaluation of coated and uncoated stainless steel specimens have been investigated by Tafel extrapolation and linear polarization methods. Results indicates that corrosion resistance of single layer HA coated stainless steel specimens are superior to single layer TiO2 and bi-layer HA/TiO2 coated stainless steel specimens.

Wear protection potential of TiN coatings for 304 stainless steels used in rotating parts during olive oil extraction

Abstract The aim of this study is to determine the damage mechanisms affecting 304L Stainless Steel (SS) parts used in olive oil production, and to evaluate the performance of TiN coatings in improving their resistance to these effects. Tribological behavior of 304L SS parts was investigated through pin on disc tests against olive seed counter bodies, both in uncoated state and after TiN coating via cathodic arc physical vapor deposition. Further assessment of tribological behavior was carried out through the means of an in house centrifugal testing setup, designed to simulate the environment encountered during the de­seeding step of oil production, and cavitation erosion tests with an ultrasonic probe. The results of pin on disc tests showed considerable wear damage of uncoated SS while TiN coated samples exhibit excellent wear resistance, with no visible damage to the coatings. Further results obtained from centrifugal tests indicated a damage mechanism related to impact from olive seed particles. Plastic deformation of the SS substrate surface was observed via SEM, both for uncoated and TiN coated samples, leading to fracturing of the TiN coatings and their subsequent removal in the latter. This observation is supported by the results of cavitation erosion tests, in which similar damage can be observed on TiN coated SS samples. The same test carried out on TiN coated high speed steel samples which have a higher substrate hardness than SS showed better resistance to fracture of the coating.

Tribology and wear resistance of the stainless steel. The sol–gel coating impact on the friction and damage

The sol–gel coating method is considered to be simple, easy to adopt, requires low processing temperature and leads to high degree of purity oxide coatings. Moreover, the fabrication of metal oxide thin films by sol–gel technic is cost effective, reproducible and applicable to large substrates without any shape restriction. This work focuses on optimizing conditions for depositing alumina coatings by sol–gel method on stainless steel substrates with a low annealing temperature, in order not to degrade the metal substrate. Moreover, to obtain coatings of several micron thick, the sol–gel was adapted by adding ceramic powder or by successive layers deposition which reduces the stresses occurring in the coatings during the heat treatment. The various as-obtained layers are characterized in terms of morphological features, microstructure, hardness and the tribological behavior and wear resistance.The results showed that the deposited alumina coating at low temperature crystallized in δ-Al2O3. Adding to that, the increase of the temperature favors the presence of α-Al2O3 structure. Moreover, the measurements demonstrate that the mechanical properties of sol–gel deposited alumina coatings in terms of hardness, wear resistance are improved in comparison with uncoated stainless steel or the classic nitrited steel.

Tailored surface energy of stainless steel plate coupons to reduce the adhesion of aluminium silicate deposit

Fouling in heat exchangers not only reduces heat transfer performance significantly, but also causes considerable pressure drop, resulting in higher pumping requirements. It would be much more desirable if surfaces which are inherently less prone towards fouling could be developed. In this paper, autocatalytic Nickel–Phosphorus–Polytetrafluoroethylene (Ni–P–PTFE) composite coatings and modified diamond-like carbon (DLC) coatings were applied to the coupons of the 316L stainless steel plates. The effects of surface energies of the coatings on the adhesion of aluminium silicate fouling were investigated and the best surface energy for which the fouling adhesion is lowest was obtained. The experimental results show that the coating with the most favourable surface energy reduced the adhesion of aluminium silicate deposit by 97%, compared with uncoated stainless steel plate coupons. The anti-fouling mechanism of the coatings was explained with the extended Deryagin, Landau, Verwey and Overbeek (DLVO) theory.

Corrosion, ion release and Mott–Schottky probe of chromium oxide coatings in saline solution with potential for orthopaedic implant applications

We report our investigation on chromium oxide thin film coatings that show a negligible ion release during electrochemical corrosion testing in saline solution. The chemical constituents of the films prepared by reactive magnetron sputtering were identified to be predominantly Cr2O3 based on Raman spectroscopy anti-symmetric stretching vibration modes for CrIII–O and other peaks and an FTIR spectroscopy Eu vibrational mode at 409 cm−1. X-ray photoelectron spectroscopy, multiplet fitting for 2P3/2 and 2P1/2 states also confirmed the predominantly Cr2O3 stoichiometry in the films. The prepared chromium oxide coatings showed superior pitting corrosion resistance compared to the native chromium oxide films on bare uncoated stainless steel when tested under open circuit potential, potentiodynamic polarisation and cyclic voltammetry in saline solution. The chromium ion released into solution during the corrosion testing of stainless steel substrates coated with chromium oxide coatings was found to be negligibly small based on atomic absorption spectroscopy measurements. Our Mott–Schottky analysis investigation showed that the negligibly small ion release from the chromium oxide coated steel substrates is most likely due to a much lower defect density on the surface of the deposited coatings compared to the native oxide layer on the uncoated steel substrates. This opens up the opportunity for using chromium oxide surface coatings in hip, knee and other orthopaedic implants where possible metal ion release in vivo still poses a great challenge.

Characterization and tribocorrosion behavior of sputtered NiTi coatings

Abstract In this study, NiTi coatings were deposited onto AISI 316L stainless steel substrates by closed field unbalanced magnetron sputtering. The microstructure and properties of the coatings were characterized by means of X-ray diffraction, scanning electron microscopy, and nano-indentation. The tribocorrosion resistance and corrosion behavior of the stainless steel substrates and NiTi coatings were investigated in Hanks' solution. The experimental results indicated the NiTi coatings show higher corrosion polarization resistance and a more stable corrosion potential in the Hanks' solution than the uncoated stainless steel substrate. The NiTi coatings also exhibited excellent wear resistance and chemical stability in sliding tests with an Si3N4 ball in the Hanks' solution. The tested samples showed different wear mechanisms in the sliding tests. Compared to the SS substrates, the NiTi coatings were more compatible with the Si3N4 ball.

Frictional behavior between silicon and steel coated with graphene oxide in dry sliding and water lubrication conditions

With growing concern over environmental problems, green technologies associated with reducing pollution have been rapidly progressing to attain a sustainable future. Among numerous green technologies currently under development, water lubrication technology that can replace the use of conventional oil lubricants can be a promising technology that may lead to huge benefits with respect to environmental and economic issues. In this work, good-lubricating performance was achieved by using reduced graphene oxide (rGO) coating on AISI 440C stainless steel (SS) ball that was slid against a silicon (Si) specimen under water lubrication condition. Compared to the sliding tests performed in dry condition, the friction coefficient of the rGO coated SS ball slid against the Si specimen under water lubrication condition could be reduced by 12 times. Also, it was shown that friction coefficient of the uncoated SS ball slid against the Si specimen in water and dry conditions were relatively higher than that of the sliding test conducted with the rGO coated SS ball in water lubrication. The experimental results demonstrated that the rGO coating on SS can effectively lower the friction in water lubrication conditions. This work are expected to aid in the development of environmental-friendly lubrication technology for mechanical components.

Boosting the Detection Potential of Liquid Chromatography-Electron Ionization Mass Spectrometry Using a Ceramic Coated Ion Source.

Detection of target and non-target substances and their characterization in complex samples is a challenging task. Here we demonstrate that coating the electron ionization (EI) ion source of an LC-MS system with a sol-gel ceramic film can drastically improve the detection of high-molecular weight and high-boiling analytes. A new ion source coated with a ceramic material was developed and tested with a mixture of polycyclic aromatic hydrocarbons (PAH) with an increasing number of rings. Comparison of the results obtained with those for an uncoated stainless steel (SS) ion source shows a dramatic improvement in the MS signals, with a nearly 40-fold increase of the signal-to-noise ratio. We also demonstrate the ability of the new system to produce excellent chromatographic profiles for hard-to-detect hormones.

Surface modifications of stainless steel to minimise contamination in mass spectrometers

The effect of electrochemically grown and vapour deposited coatings on the build-up of contamination on stainless steel surfaces in the electrospray ionisation source of a mass spectrometer is investigated, together with their influence on the robustness of the instrument response. Quantification of the contamination build-up on flat samples, using white light interferometry, allowed the identification of the most beneficial treatments. Coating with electrochemically-grown anodic oxide and cathodic oxide films and amorphous carbon films doped with silicon or nitrogen resulted in reduced contamination compared with the uncoated stainless steel surface, and provided improved robustness of the instrument response.

Surface properties and anti-fouling assessment of coatings obtained from perfluoropolyethers and ceramic oxides nanopowders deposited on stainless steel

Multilayer coatings were obtained on stainless steel surfaces by combining a commercial α,ω-functionalized perfluoropolyether film with a film of ceramic oxide nanopowders, namely, TiO2 or ZrO2. Ceramic oxides were impregnated with siloxanes in order to improve their hydrophobic behavior and favor the adhesion on metal substrates. The coatings obtained had homogeneous morphology and thickness of about 25 μm. A possible application of low energy surface coatings is fouling mitigation. Thus, the chemical and mechanical stability of the multilayer coatings was assessed in liquid environments and compared to the one of simple perfluoropolyether coatings. Moreover, particulate fouling (due to CaSO4 deposition) was investigated on perfluoropolyethers coatings and multilayer coatings. Results demonstrated good resistance of the multi-layer coatings toward aggressive chemicals and water erosion. With respect to an uncoated stainless steel surface, the CaSO4 particles adhesion on the coated surfaces was estimated 70–90% lower, in the fouling conditions adopted.

Beam Tests of Beampipe Coatings for Electron Cloud Mitigation in Fermilab Main Injector

Electron cloud beam instabilities are an important consideration in virtually all high-energy particle accelerators and could pose a formidable challenge to forthcoming high-intensity accelerator upgrades. Dedicated tests have shown beampipe coatings dramatically reduce the density of electron cloud in particle accelerators. In this work, we evaluate the performance of titanium nitride, amorphous carbon, and diamond-like carbon as beampipe coatings for the mitigation of electron cloud in the Fermilab Main Injector. Altogether our tests represent 2700 ampere-hours of proton operation spanning five years. Three electron cloud detectors, retarding field analyzers, are installed in a straight section and allow a direct comparison between the electron flux in the coated and uncoated stainless steel beampipe. We characterize the electron flux as a function of intensity up to a maximum of 50 trillion protons per cycle. Each beampipe material conditions in response to electron bombardment from the electron cloud and we track the changes in these materials as a function of time and the number of absorbed electrons. Contamination from an unexpected vacuum leak revealed a potential vulnerability in the amorphous carbon beampipe coating. We measure the energy spectrum of electrons incident on the stainless steel, titanium nitride and amorphous carbon beampipes. We find the electron cloud signal is highly sensitive to stray magnetic fields and bunch-length over the Main Injector ramp cycle. We conduct a complete survey of the stray magnetic fields at the test station and compare the electron cloud signal to that in a field-free region.

TiN coated stainless steel bracket: Tribological, corrosion resistance, biocompatibility and mechanical performance

Multi-arc ion plating was used to deposit TiN films to modify the 316L stainless steel brackets for orthodontic applications. XRD, SEM, Raman spectroscopy, electrochemical analysis, cell proliferation and enzyme-linked immuno sorbent assay (ELISA) were applied to compare the surface characteristics of TiN coated and uncoated stainless steel brackets. It was found that TiN coating is smooth, hard, well-adherent, biocompatible with super low friction coefficient (<0.03) and pretty good corrosion resistance (pitting potential higher than 600mV) in artificial saliva. High hardness (about 14.62GPa) is favored for the low friction coefficient, and great corrosion resistance ascribe to inert nature of TiN reduces the release of toxic elements, which improved the biocompatibility of TiN film. Better comprehension performances make TiN coated stainless steel very suitable for orthodontic applications.

Electrophoretic Co-Deposition of Chitosan and Graphene Oxide Results in Antibacterial Coatings for Medical Applications

Chitosan – graphene oxide (GO) composite coatings intended for antibacterial applications were obtained by cathodic electrophoretic deposition (EPD) on stainless steel. The coatings were characterized using SEM, FTIR, contact angle and roughness measurements and by antibacterial studies againstE.coli. The coating was observed to consist of a polymer matrix with embedded, agglomerated graphene oxide sheets. A decrease in bacteria cell viability of at least 50 % was measured on the chitosan – GO surface in comparison to uncoated stainless steel.

A comparative study of the corrosion performance of titanium (Ti), titanium nitride (TiN), titanium dioxide (TiO2) and nitrogen-doped titanium oxides (N–TiO2), as coatings for biomedical applications

The performance of four titanium coatings, namely, Ti, TiN, TiO2, and N–TiO2 was assessed in terms of their surface properties and electrochemical corrosion in simulated body fluid in relation to their medical applications. Ti, TiN, TiO2, and N–TiO2 coatings were deposited onto stainless steel substrates by a plasma surface alloying technique. Morphology, composition, and structure were investigated by SEM, GDOES, and XRD. Corrosion resistance results indicated that Ti, TiN, TiO2, and N–TiO2 coatings could achieve higher corrosion polarization resistance and a more stable corrosion potential in the SBF environment than the uncoated stainless steel substrate SS316L. In comparison with the Ti, TiN, and TiO2 coatings, the N–TiO2 coating exhibited superior corrosion resistance. This resistance may be attributed to the multilayered structure of the coating (an outer oxidative layer and an inner diffusion zone of Ti and N), which can hinder the diffusion of reactive ions.

Effect of Surface Pretreatment on Galvanic Attack of Coated Al Alloy Panels

A test assembly consisting of a coated and scribed aluminum alloy 7075-T6 panel galvanically connected to uncoated through-hole noble fasteners has recently been utilized to quantify corrosion attack during corrosion testing in laboratory chambers. In this work, the corrosion morphology and extent of attack of Al alloy panels with five different surface pretreatments prior to painting and scribing were compared after exposure to ASTM B117 with galvanic connection to uncoated stainless steel fasteners. The nature of the attack for samples with different surface pretreatment samples was found to exhibit two different trends: they either penetrated deeply into the substrate at the scribes or spread out under coatings. The galvanic currents between the coated Al alloy panel and the bare 316 stainless steel fasteners were monitored during 21 days exposure in an ASTM B117 chamber. The current trends measured for different surface pretreatment panels were consistent with optical profilometry (OP) results. However, the galvanic current and OP techniques both underestimated the extent of corrosion attack because of local H2 evolution and undercut attack, respectively. The results from both techniques were modified to compensate for these deficiencies. Acceleration factors associated with the galvanic interaction for the different surface pretreatment panels were determined.

Novel Antibiotic-loaded Point-of-care Implant Coating Inhibits Biofilm.

Orthopaedic biomaterials are susceptible to biofilm formation. A novel lipid-based material has been developed that may be loaded with antibiotics and applied as an implant coating at point of care. However, this material has not been evaluated for antibiotic elution, biofilm inhibition, or in vivo efficacy. (1) Do antibiotic-loaded coatings inhibit biofilm formation? (2) Is the coating effective in preventing biofilm in vivo? Purified phosphatidylcholine was mixed with 25% amikacin or vancomycin or a combination of 12.5% of both. A 7-day elution study for coated titanium and stainless steel coupons was followed by turbidity and zone of inhibition assays against Staphylococcus aureus and Pseudomonas aeruginosa. Coupons were inoculated with bacteria and incubated 24 hours (N = 4 for each test group). Microscopic images of biofilm were obtained. After washing and vortexing, attached bacteria were counted. A mouse biofilm model was modified to include coated and uncoated stainless steel wires inserted into the lumens of catheters inoculated with a mixture of S aureus or P aeruginosa. Colony-forming unit counts (N = 10) and scanning electron microscopy imaging of implants were used to determine antimicrobial activity. Active antibiotics with colony inhibition effects were eluted for up to 6 days. Antibiotic-loaded coatings inhibited biofilm formation on in vitro coupons (log-fold reductions of 4.3 ± 0.4 in S aureus and 3.1 ± 0 for P aeruginosa in phosphatidylcholine-only coatings, 5.6 ± 0 for S aureus and 3.1 ± 0 for P aeruginosa for combination-loaded coatings, 5.5 ± 0.3 for S aureus in vancomycin-loaded coatings, and 3.1 ± 0 for P aeruginosa for amikacin-loaded coatings (p < 0.001 for all comparisons of antibiotic-loaded coatings against uncoated controls for both bacterial strains, p < 0.001 for comparison of antibiotic-loaded coatings against phosphatidylcholine only for S aureus, p = 0.54 for comparison of vancomycin versus combination coating in S aureus, P = 0.99 for comparison of antibiotic- and unloaded phosphatidylcholine coatings in P aeruginosa). Similarly, antibiotic-loaded coatings reduced attachment of bacteria to wires in vivo (log-fold reduction of 2.54 ± 0; p < 0.001 for S aureus and 0.83 ± 0.3; p = 0.112 for P aeruginosa). Coatings deliver active antibiotics locally to inhibit biofilm formation and bacterial growth in vivo. Future evaluations will include orthopaedic preclinical models to confirm therapeutic efficacy. Clinical applications of local drug delivery coating could reduce the rate of implant-associated infections.