Surface hardness improvement of plasma-sprayed AISI 316L stainless steel coating by low-temperature plasma carburizing

Low-temperature carburizing below 773 K of austenite stainless steel can produce expanded austenite, known as S-phase, where surface hardness is improved while corrosion resistance is retained. Plasma-sprayed austenitic AISI 316L stainless steel coatings were carburized at low temperatures to enhance wear resistance. Because the sprayed AISI 316L coatings include oxide layers synthesized in the air during the plasma spraying process, the oxide layers may restrict carbon diffusion. We found that the carbon content of the sprayed AISI 316L coatings by low-temperature carburizing was less than that of the AISI 316L steel plates; however, there was little difference in the thickness of the carburized layers. The Vickers hardness of the carburized AISI 316L spray coating was above 1000 HV and the amount of specific wear by dry sliding wear was improved by two orders of magnitude. We conclude that low-temperature plasma carburizing enabling the sprayed coatings to enhance the wear resistance to the level of carburized AISI 316L stainless steel plates. As for corrosion resistance in a 3.5 mass% NaCl solution, the carburized AISI 316L spray coating was slightly inferior to the as-sprayed AISI 316L coating.     

Novel hydroxyapatite/tantalum surface coating for metallic dental implant

The aim of this study was to design and produce a novel surface composite coating on metallic substrate in order to improve the biocompatibility of metallic dental implant and the bone osteointegration simultaneously.Stainless steel 316L (SS) was used as a metallic substrate and a novel double-layer hydroxyapatite/tantalum (HA/Ta) coating was prepared on it. Tantalum coating was made using physical vapor deposition process and HA coating was produced using plasma-spraying technique on it. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized to investigate the coating characterization. Electrochemical polarization tests were performed in two types of physiological solutions at 37 ± 1 °C in order to determine the corrosion behavior of the coated and uncoated specimens as indication of biocompatibility.The results indicated that the decrease in corrosion current density was significant for HA/Ta coated specimens and was much lower than the value obtained for uncoated 316L SS. The novel double-layer HA/Ta composite coating could improve the corrosion resistance and thus the biocompatibility of 316L SS dental implant.     

Fabrication of nanoporous Sr incorporated TiO2 coating on 316L SS: Evaluation of bioactivity and corrosion protection

In this paper, nanoporous TiO₂ and Sr-incorporated TiO₂ coated 316L SS were prepared by sol–gel methodology. The effect of Sr incorporation into TiO₂ coating on bioactivity and corrosion resistance was investigated. Attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy, X-ray diffraction analysis (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) results obtained after in vitro bioactivity test confirm the excellent growth of crystalline hydroxyapatite (HAp) over nanoporous Sr-incorporated TiO₂ coated 316L SS which may be attributed to the slow and steady release of Sr ions from the coatings. The electrochemical evaluation of the coatings confirms that Sr-incorporated TiO₂ coating offer excellent protection to 316L SS by acting as a barrier layer. The results showed that the incorporation of Sr enhanced both bioactivity and corrosion resistance of 316L SS. Hence Sr-incorporated TiO₂ coated 316L SS is a promising material for orthopaedic implant applications.     

Tribology of laser modified surface of stainless steel in physiological solution

The laser surface treatment of stainless steel (SS) 316L, an important alloy for biomedical applications, was used to improve its corrosion and wear-corrosion resistance in bio-environment. Microstructural and X-ray diffraction (XRD) pattern analysis showed presence of an austenitic phase in both untreated and laser-treated SS316L. Laser melting produced homogenized and refined microstructure on the surface with higher hardness (143–171 HV) compared to untreated SS316L (131 HV). Increase in intensity of γ (200) peaks in XRD pattern for laser-treated (>800 W) SS316L indicated possible crystallographic orientation along γ (200) plane. Passive currents were reduced to <2.8 μA/cm² and pitting potentials was increased to >+344 mV for samples laser surface treated at greater than 1200 W. The volume-loss and wear-rate of laser-treated SS316L were significantly reduced compared to untreated sample. Abrasive wear was the main wear mechanism for both untreated and laser surface treated SS316L. Wear particles/debris were found to be cold welded on the surface of SS316L and showed brittle cracking with further wear-straining.     

Corrosion protection of CrN/TiN multi-coating for bipolar plate of polymer electrolyte membrane fuel cell

The electrochemical corrosion cells will be generated from the possible pinholes of the promising CrN and TiN coatings in a PEMFC environment. To prevent the elution of possible pinholes, CrN/TiN multi-coatings on SS have been considered. This study examined the electrochemical behavior of three CrN/TiN coatings on 316L stainless steel deposited at different CrN/TiN thickness ratios by rf-magnetron sputtering as potential bipolar plate materials. Potentiodynamic tests of CrN/TiN-coated 316L stainless steel carried out in a 1 M H₂SO₄ + 2 ppm HF solution at 70 °C revealed a significantly lower corrosion current density than that of uncoated 316L SS, as well as a decrease in the corrosion current density with decreasing inner-layer CrN thickness. Electrochemical impedance spectroscopy also showed that the CrN/TiN-coated 316L SS sample had higher charge transfer resistance than the uncoated 316L SS sample, which increased with decreasing inner-layer CrN thickness. This was attributed to the crystalline-refined CrN/TiN(200).     

Analysis of material degradation for uncoated and NiCoCrAlY cold spray coated Superfer 800H in the secondary chamber of medical waste incinerator

NiCoCrAlY coating was deposited on Superfer 800H superalloy with cold spray process to reduce the degradation rate of substrate superalloy in actual medical waste incineration environment. Erosion–corrosion performance of uncoated and cold sprayed superalloy was evaluated in the secondary chamber of medical waste incinerator. The degradation rate of the specimens was assessed by measuring the thickness loss of the specimen after cyclic exposure for 1000 h in medical waste incineration environment. Average degradation rate for uncoated and cold sprayed superalloy was found to be 157.95 mpy and 36.56 mpy respectively. The better performance of cold spray coated specimen might be attributed to the formation of protective Al₂O₃ scale at the top of surface and dense structure of the deposit coating.     

Effects of chloride ions on electrochemical reaction of 316 stainless steel in mixtures of molten nitrate salts

Effects of chloride ion on decomposition of ternary nitrate and corrosion behaviors of 316 stainless steel (316 SS) were studied by electrochemical corrosion tests in molten salt. Chemical composition and morphology of the corrosion products were analyzed using x-ray diffraction and scanning electron microscopy equipped with energy disperse spectroscopy. Composition analysis for molten salt combined with morphology analyses of corrosion layer showed that presence of chlorine ions slowed down decomposition of ternary nitrate and increased corrosion rate of stainless steel markedly. The polarization curve obtained indicated that the corrosion current density increased from 3.02 mA ⋅ cm⁻² to 8.76 mA ⋅ cm⁻² with the addition of 10 % NaCl. Electrochemical impedance spectroscopy indicated a decrease in charge-transfer resistance of the double layer between 316 SS and ternary Nitrate containing 10 % NaCl, resulting in a decreased corrosion resistance of 316 SS.     

In-vitro bioactivity,biocorrosion and antibacterial activity of silicon integrated hydroxyapatite/chitosan composite coating on 316 L stainless steel implants

A simple and effective ultrasonication method was applied for the preparation of 0, 0.4, 0.8, 1.0 and 1.6 wt% silicon substituted hydroxyapatite (HAp) (SH). The Ca/P ratio of the synthesised SH nanoparticles were in the range of 1.58–1.70. Morphological changes were noticed in HAp with respect to the amount of Si from 0 to 1.6 wt%. The morphology of the particles changed from spherical shape to rod-like morphology with respect to the amount of Si which was confirmed using transmission electron microscopy. X-ray diffraction studies confirm the formation of phase pure SH nanoparticles without any secondary phase. Chitosan (CTS) blended SH nanocomposites coating on surgical grade 316 L stainless steel (316 L SS) implant was made by spin coating technique. The surface of the coated implant was characterised using scanning electron microscopy which confirms the uniform coating without cracks and pores. The increased corrosion resistance of the 1.6 wt% of SH/CTS-coated SS implant in the simulated body fluid (SBF) indicates the long-term biostability of SH composite-coated ceramics in vitro than the 0 wt% SH/CTS. The testing of SH/CTS nanocomposites with gram-positive and gram-negative bacterial strains confirms that the antibacterial ability improves with the higher substitution of Si. In addition, formation of bone-like apatite layer on the SH/CTS-coated implant in SBF was studied through SEM analysis and it confirms the ability to increase the HAp formation on the surface of 1.0 wt% SH/CTS-coated 316 L SS implant.     

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 48 h, respectively.     

Corrosion performances in simulated body fluids and cytotoxicity evaluation of Fe-based bulk metallic glasses

The aim of this work is to investigate the corrosion resistance and biocompatibility of three kinds of Fe based bulk metallic glasses (BMGs), Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ (BMG1), (Fe₄₄Cr₅Co₅Mo₁₃Mn₁₁C₁₆B₆)₉₈Y₂ (BMG2), and Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂ (BMG3) by electrochemical measurements and indirect contact cytotoxicity assays, respectively. In comparison with 316 L SS biomedical steel, Fe based BMGs show better corrosion resistance in both simulated body fluids (Hank's solution and artificial saliva). The OCP curves show that the passive film on the Fe based BMG surfaces is quite stable, like 316 L SS. The corrosion current densities obtained from the anodic polarization curves from the lowest to highest are as follows: BMG3 < BMG1 < BMG2 < 316 L SS. The EIS analysis indicates that the Fe Based BMGs have larger polarization resistance value than that of 316 L SS except for BMG2 in artificial saliva. The pitting corrosion potentials of Fe based BMGs are much higher than that of the 316 L SS, resulting in very few ions releasing into the electrolytes while a significant amount of Ni and Fe ions release was found for 316 L SS under the same condition. The indirect cytotoxicity results suggest that all three Fe based BMG extracts have no cytotoxicity to L929 and NIH3T3 cells. All these results demonstrate that Fe based BMGs will open up a new path for the biomedical applications, especially in dental implantology.     

铁氧化菌作用下316L不锈钢点蚀电化学特性的研究

采用电化学测量、交流阻抗技术、扫描电镜观察和能谱分析等实验方法,研究了316L不锈钢在铁氧化菌(IOB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制,结果表明,在含有IOB溶液中的自腐蚀电位(Ecorr)、点蚀电位(Epit)和极化电阻(Rp)均随浸泡时间的增加呈现出降-升-降的变化趋势;在含有IOB溶液中的腐蚀速率均大于在无菌溶液中;IOB的生长代谢活动及其生物膜的完整性和致密性影响了316L不锈钢表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L不锈钢的点蚀.     

Sol-gel derived TiO2 coating on plasma nitrided 316L stainless steel

Titania film is coated on plasma nitrided 316L stainless steel by sol-gel method. Crystallization of titania as well as N loss and formation of Fe₂O₃ occurs during the annealing heat treatment. The titania film has short cracks within the grooves of plasma etched grain boundaries. With the increase of annealing temperature and duration, surface hardness of the samples is increased, but the toughness is decreased due to oxidization of the surface layer. The coating sample heat treated at 350 °C for 10 min and 450 °C for 10 min has better corrosion resistance than the nitrided stainless steel tested by the potentiodynamic polarization in 0.9% NaCl solution. Water contact angle of the titania film on the rough nitrided steel substrate decreases with UV irradiation treatment, reaching 17° after 3 h treatment.     

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

Layers of TiN/TiO_xN_y 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/TiO_xN_y 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/TiO_xN_y 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.     

Synthesis and characterisation of nanostructured hardystonite coating on stainless steel for biomedical application

Here, nanostructured hardystonite bioceramic (Ca₂ ZnSi₂ O₇) was synthesised from tetraethyl orthosilicate, zinc nitrate hexahydrate, and calcium nitrate tetrahydrate via sol–gel method, dried at 60–120°C, and finally calcinated at 1300°C. X‐ray diffraction (XRD) analysis confirmed the formation of hardystonite bioceramic. Afterwards, electrophoretic method was utilised to coat the hardystonite ceramic on 316L stainless steel (SS). Methanol solution was used as suspension solvent. The best deposition procedure was carried out by electrophoretic device in the voltage of 50 V for 5 min. XRD analysis was employed for phase characterisation and scanning electron microscopy was utilised for microstructural and morphological characterisations of the coatings. Chemical composition of the coating was evaluated by energy‐dispersive X‐ray spectroscopy. The hardystonite coating improved the corrosion resistance of the substrate, so the corrosion current density in the coated samples was less than the uncoated ones (nine times). In order to assess the bioactivity of the coating, simulated body fluid was used. The main results of the coated sample bioactivity demonstrated that the nanostructured hardystonite coating could amend the in vitro SS bioactivity. Therefore, SS coated with nanostructured hardystonite may be a promising candidate to be applied as bioactive hard tissue implants.Inspec keywords: bioceramics, stainless steel, X‐ray diffraction, corrosion protective coatings, X‐ray chemical analysis, sol‐gel processing, calcium compounds, current density, nanofabrication, zinc compounds, scanning electron microscopy, corrosion resistance, calcination, crystal microstructure, nanostructured materials, prosthetics, nanomedicine, electrophoretic coatings, electrophoretic coating techniquesOther keywords: X‐ray diffraction analysis, electrophoretic method, XRD analysis, phase characterisation, microstructural characterisations, morphological characterisations, energy‐dispersive X‐ray spectroscopy, coated sample bioactivity, nanostructured hardystonite coating, zinc nitrate hexahydrate, sol–gel method, 316L stainless steel, tetraethyl orthosilicate, calcium nitrate tetrahydrate, suspension solvent, deposition procedure, scanning electron microscopy, chemical composition, corrosion resistance, corrosion current density, bioactive hard tissue implants, temperature 1300.0 degC, voltage 50.0 V, time 5.0 min, temperature 60 degC to 120 degC, Ca₂ ZnSi₂ O₇      

Effect of Surface Treatment and Metallic Coating on Corrosion Behavior and Biocompatibility of Surgical 316L Stainless Steel Implant

Surface engineering technology is a suitable method for coatings on the metal surfaces or performing surface modification treatment,which can improve corrosion resistance and biocompatibility of metals.In this research,corrosion behavior of Nb coating on H 2 SO 4 and HNO 3 treated AISI stainless steel 316L (SS) was evaluated.Nb coating was carried out using physical vapor deposition process on the SS.Characterization techniques including scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) technique were used to investigate the microstructure and morphology of the coated and treated SS.Electrochemical potentiodynamic tests were performed in two types of physiological solutions and compared with the pristine SS specimens.Cyclic polarization tests were performed to evaluate resistivity against pitting.Experimental results indicate that Nb coating and surface treatment of the SS had a positive effect on improvement of corrosion behavior.The decrease in corrosion current densities was significant for coated and treated specimens.The corrosion current density was much lower than the values obtained for pristine specimens.     

A study of the erosion-corrosion behavior of nano-Cr2O3 particles reinforced Ni-based composite alloying layer in aqueous slurry environment

To investigate the role of nano-Cr₂O₃ particles on the erosion-corrosion behavior of composite alloying layer, a nano-Cr₂O₃ particles reinforced Ni-based composite alloying layer was fabricated onto AISI 316L stainless steel (SS) via a duplex surface treatment, consisting of Ni/nano-Cr₂O₃ predeposited by electric brush plating, and subsequent Ni-Cr-Mo-Cu multi-element surface alloying by a double glow process. The microstructure and composition of composite alloying layer were characterized by means of X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). The results indicated that the added nano-Cr₂O₃ particles were homogeneously distributed in the alloying layer and didn’t decompose or react with surrounding metal matrix under alloying temperature (1000 °C) condition. A series of electrochemical techniques, including potentiodynamic polarization, open circuit potential (OCP), current response and electrochemical impedance spectroscopy (EIS), was employed to evaluate the corrosion properties of nano-Cr₂O₃ particles reinforced composite alloying layer under various hydrodynamic conditions. Erosion-corrosion tests were conducted in 3.5% NaCl solution plus sand particles with varying concentration (50-150 g/L) at different rotation speeds (600-1100 rpm). To estimate the influence of the nature of different nano-particles on the erosion-corrosion property of composite alloying layer, nano-SiO₂ particles reinforced Ni-based composite alloying layer, single alloying layer and 316L SS was selected as the reference materials for all the corrosion and erosion-corrosion tests.     

Corrosion behaviour of single (Ti) and duplex (Ti–TiO2) coating on 304L stainless steel in nitric acid medium

Sputter deposited single titanium (Ti) layer, and duplex Ti–TiO₂ coating on austenitic type 304L stainless steel (SS) was prepared, and the corrosion performance was evaluated in nitric acid medium using surface morphological and electrochemical techniques. Morphological analysis using atomic force microscope of the duplex Ti–TiO₂ coated surface showed minimization of structural heterogeneities as compared to single Ti layer coating. The electrochemical corrosion results revealed that, titanium coated 304L SS showed moderate to marginal improvement in corrosion resistance in 1 M, and 8 M nitric acid, respectively. Duplex Ti–TiO₂ coated 304L SS specimens showed improved corrosion resistance as compared to Ti coating from dilute (1 M) to concentrated medium (8 M). The percentage of protection efficiency for base material increases significantly for duplex Ti–TiO₂ coating as compared to single Ti layer coating. The oxidizing ability of nitric acid on both the coatings as well as factors responsible for improvement in protection efficiency are discussed and highlighted in this paper.     

Localized corrosion behavior of 316L stainless steel in the presence of sulfate-reducing and iron-oxidizing bacteria

Localized corrosion behavior of 316L stainless steel was investigated in the presence of sulfate-reducing bacteria (SRB) and iron-oxidizing bacteria (IOB) isolated from cooling water system using polarization measurement, scanning electron microscopy (SEM) examinations and energy dispersive spectrum (EDS) analysis. The results show the corrosion potential (E_corr) and breakdown potential (E_b) of SS decreased in turn with the presence of IOB, SRB and SRB + IOB, indicating decreased relative resistance to localized corrosion. E_corr in the sterile medium remained virtually unchanged with exposure time, indicating that localized attack did not occur. However, micrometer-scale pitting was observed on the SS surface in the presence of bacteria. The presence of SRB demonstrated higher corrosion rates than IOB. The combination of SRB and IOB yielded the highest corrosion rate. The presence and metabolic activities of bacteria on SS surface produce environments that can alter rates of partial reactions in corrosion processes and shift corrosion mechanisms. The most severe microbiologically induced corrosion takes place in aquatic solution where physiological groups of aerobic and anaerobic microorganisms interact.     

Microstructure-mechanical and chemical behavior relationships in passive thin films

The passive films play an important role in corrosion and stress corrosion cracking of austenitic stainless steels. The current research investigates the relationship between alloy chemistry, microstructure, and mechanical behavior of passive films formed on 316, 304, and 904L stainless steels (SS). X-ray photoelectron spectroscopy and transmission electron microscopy were used to investigate the effect of alloy chemistry and microstructure constituents on the thin film fracture properties determined by nanoindentation tests. The analyses showed that fracture loads are directly related to the crystallography of the thin films. It was found that decreasing the ratio of iron to other metallic elements in the film led to an increase in the load required to fracture the film. It was also found that films grown on 304, 316, and 904L stainless steels were the cubic polymorph of Cr₂O₃, rather than the lower energy rhombohedral form. In the case of 904L SS the film formed as an epitaxial layer. In the other two cases it consisted of small crystalline islands in an amorphous matrix. A dichromate treatment of 316 SS decreased the iron content in the oxide film and increased the hardness. It also resulted in an epitaxial film.     

Effect of bias voltage on the electrochemical properties of TiN coating for polymer electrolyte membrane fuel cell

The electrochemical properties of TiN film coated on AISI 316 stainless steel (SS) by the magnetron sputtering physical vapor deposition (PVD) were studied for application as a bipolar plate. The crystal structure and surface morphology of the coatings were examined by x-ray diffractometry (XRD) and atomic force microscopy (AFM), respectively. The corrosion behaviors of the TiN films were investigated by electrochemical methods, including potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) under + 600 mV_SCE application. The electrochemical behavior of the TiN coatings was enhanced with increasing bias voltage due to lower corrosion current density and higher R_ct values during an immersion time of 168 h. This result was attributed to the formation of crystalline-refined TiN(200) at high bias voltage, which increased the coating compactness and the protective efficiency, and decreased passive current density.