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Gas tungsten arc welding (GTAW) is commonly used for joining pipelines; however, it often leads to discoloration in the heat-affected zone (HAZ). In this study, 316L pipes were welded with different concentrations of oxygen present in the argon purge gas during welding. The objective of this study was to investigate the effect of oxygen concentration in the protective gas on the pitting corrosion resistance of welded pipes. The experimental results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas resulted in an increase in pitting corrosion resistance until a critical value, beyond which the resistance decreased. The results showed that the thickness of the oxide layer formed in the HAZ depends on the concentration of oxygen in the protective gas. Increasing the oxygen concentration in the protective gas increased the pitting corrosion resistance until a critical value, beyond which the resistance decreased due to the formation of iron oxide. This study provides valuable insights for improving the corrosion resistance of welded pipes in the oil and gas industry. [ABSTRACT FROM AUTHOR]

In this paper, Zr(Hf)xCN coatings were deposited onto 316L stainless steel (316L SS) substrates at 400 °C using the radio-frequency (R.F.) magnetron sputtering technique with Hf-Zr-C composite target materials. The influence of Hf element content on microstructure, mechanical properties, and corrosion resistance and platelet interaction with the surface of Zr(Hf)xCN coatings were then investigated. The results indicate that the microstructure, mechanical properties, and corrosion resistance of coatings depend on their chemical composition. Corrosion resistance and platelet interaction with the surface could be improved by adding Hf to the Zr2CN. By optimizing the Hf-Zr-C ratio, Zr(Hf)xCN coatings with excellent corrosion resistance were obtained. The ZrHfCN-3 coating with a Hf element content of 7.33% possesses excellent mechanical properties and good corrosion resistance. The result of the platelet interaction with the surface confirms that Zr(Hf)xCN coatings have better platelet interaction with the surface than 316L SS. [ABSTRACT FROM AUTHOR]

Impact of sintering temperature and aging time was investigated on purity and phase of hydroxyapatite powders synthesized through sol–gel process. Phase, composition, and morphology of the prepared hydroxyapatite powders were characterized using X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR), and scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS). Plausible mechanism respective to the formation of HAP from the precursors Ca(NO3)2·4H2O and triethyl phosphite (TEP) by sol–gel process was determined from 31P NMR analysis. Further, the development of hydroxyapatite coatings on 316L SS metallic surfaces was done by varying the spin coating parameters such as spin speed, spin time, and sintering atmosphere, and their corrosion resistance behavior in SBF solution was evaluated by electrochemical impedance spectroscopy (EIS) and TAFEL polarization analysis. From the results, we inferred that the HAP coatings deposited on 316L SS surfaces at 3000 rpm/min under nitrogen atmosphere sintering have shown improved corrosion resistivity. The effect of aging time, sintering atmosphere, and spin speed was evaluated in terms of corrosion resistance behavior. [ABSTRACT FROM AUTHOR]

Graphene oxide incorporated hydroxyapatite hybrid films were coated on 316L stainless steel substrate with the aid of electrochemical studies at the voltage of −1.5 V for 30 min using three electrode arrangements. Purity and crystallinity of the formed HAP/GO composite coatings were examined using X-ray diffraction and Fourier transform infrared spectroscopic studies. Phase of the hydroxyapatite was not affected with incorporation of graphene oxide into its matrix. Well-ordered and compact coating morphology was observed for the electrochemically deposited HAP/GO on 316L substrate using the scanning electron microscopy. High-resolution transmission electron microscopic studies reveal the tight bonding and growth of HAP particles on to the sidewalls of GO sheets. Electrochemical studies for the HAP/GO composite coating against the physiological solution showed improved corrosion efficiency. Addition of GO into HAP enhances the apatite precipitation and bone-bonding ability. These results concluded that the electrochemical deposition of bioceramic coatings on implant may be treated as an effective method for orthopedic repair and replacements. [ABSTRACT FROM AUTHOR]

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

Polymer coatings are increasingly used in varied fields and applications from simple coatings of barrier to intricated nanotechnology based composite. In the present study, polyvinylidene fluoride(PVDF)/Hydroxyapatite (HA )coatings were produced by spin coating technique over 316L SS. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were used to observe the coated 316L SS substrates surface morphology. The corrosion protection efficiency of pure polyvinylidene fluoride and polyvinylidene fluoride/HA nanocomposite coatings on 316L SS was inspected using potentiodynamic polarization along with the ions release techniques in Hank’s solution. A superior biocompatibility and an improved protection performance against corrosion were obtained for the 316L SS samples with nanocomposite coatings compared with the pure polyvinylidene fluoride coatings and pristine 316L SS counterparts. The 316L SS samples coated by PVDF/HA nanocomposite showed enhanced corrosion protection within Hank’s solution. The corrosion of 316L SS samples within Hank’s solution increased from 92.99% to 99.99% when using 3wt% HA due to increasing the PVDF inhibition efficiency. Good agreements in the electrochemical corrosion parameters were obtained from using ions release and potentiodynamic polarization tests.

Polymer coatings are increasingly used in varied fields and applications from simple coatings of barrier to intricated nanotechnology based composite. In the present study, polyvinylidene fluoride(PVDF)/Hydroxyapatite (HA)coatings were produced by spin coating technique over 316L SS. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were used to observe the coated 316L SS substrates surface morphology. The corrosion protection efficiency of pure polyvinylidene fluoride and polyvinylidene fluoride/HA nanocomposite coatings on 316L SS was inspected using potentiodynamic polarization along with the ions release techniques in Hank's solution. A superior biocompatibility and an improved protection performance against corrosion were obtained for the 316L SS samples with nanocomposite coatings compared with the pure polyvinylidene fluoride coatings and pristine 316L SS counterparts. The 316L SS samples coated by PVDF/HA nanocomposite showed enhanced corrosion protection within Hank's solution. The corrosion of 316L SS samples within Hank's solution increased from 92.99% to 99.99% when using 3wt% HA due to increasing the PVDF inhibition efficiency. Good agreements in the electrochemical corrosion parameters were obtained from using ions release and potentiodynamic polarization tests. [ABSTRACT FROM AUTHOR]

Ceramic oxide coatings are widely used in biomedical applications due to their ability to bond with bone and soft tissues. In the present study, we focus on improving the biocompatibility and corrosion resistance with self-healing properties of 316L SS by coating with cerium (Ce) incorporated niobium oxide (Nb 2 O 5) bioceramics synthesized by sol-gel technique. The effect of Ce concentrations in Nb 2 O 5 on the surface properties of 316L SS and its self-healing process during electrochemical corrosion in simulated body fluid (SBF) were deeply analyzed. The surface functional groups, morphology, chemical composition and phase transitions present in the coatings were analyzed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), high resolution scanning electron microscopy (HRSEM) with elemental dispersive X-ray (EDX) and X-ray diffraction (XRD) studies respectively. Chemical states of Ce and Nb in the Ce incorporated niobium oxide coating were identified by X-ray photoelectron spectroscopic (XPS) studies. Results show that Ce is present as both Ce3+ and Ce4+ oxidation states in CeO 2 form whereas Ce3+ is the main species and Nb is present as Nb5+ oxidation state exists in Nb 2 O 5 form. Ce incorporated Nb 2 O 5 coatings improved the surface roughness (R a) and hydrophilic nature of 316L SS, studied through atomic force microscopy (AFM) and water contact angle measurements. Electrochemical studies were performed for the specimens immediate and after 7 days immersions in SBF solution to evaluate the corrosion resistance with self-healing behavior. Results show that increased corrosion resistance with reduction in current density (i corr) and corrosion potential (E corr) and breakdown potential (E break) shifts towards more positive potentials from potentiodynamic polarization studies whereas increased impedance values and good capacitance behavior in the low frequency regions were measured from electrochemical impedance spectroscopic (EIS) studies for the Ce incorporated Nb 2 O 5 coated 316L SS specimens. Cell culture studies were performed on specimens using osteoblast MG 63 cells, among those Ce incorporated Nb 2 O 5 coatings were showed enhanced biocompatibility for 316L SS with improved cell adhesion, significant cell spreading, proliferation and differentiation of cells. Schematic representation of the self-healing behavior of Ce incorporated Nb 2 O 5. Unlabelled Image • Successful fabrication of functional Ce incorporated Nb 2 O 5 coating over 316L SS to best fit for implant applications. • Surface morphology and properties of 316L SS were greatly enhanced by Ce incorporated Nb 2 O 5 coatings. • Enhanced corrosion resistance with self-healing behavior by Ce incorporated Nb 2 O 5 coating over 316L SS. • The Ce incorporated Nb 2 O 5 coated 316L SS exhibited more biological activity in promoting MG 63 osteoblast cells. [ABSTRACT FROM AUTHOR]

Brass alloys are used in many applications. However, improving their surface properties would help to increase their service life. For that, this study proposed to deposit using high velocity oxygen fuel (HVOF), nickel-chromium-boron-silicon (NiCrBSi) alloy, and 316L stainless steel (SS) coatings on brass substrates and investigate the mechanical properties and corrosion resistance of the coatings. The surface–interface morphologies, phases, and porosity of the coatings were analyzed using a scanning electron microscope and 3D profilometer. The adhesive strength and microhardness of the NiCrBSi and 316L SS coatings were also studied. Corrosion investigations were carried out using the salt fog test in an acetic acid salt spray atmosphere according to the NF EN ISO 9227 standard. This work showed that the 316L SS coatings presented a lower microhardness and higher adhesion strength than the NiCrBSi coatings despite their lower corrosion resistance. This could be explained by the microstructure of the coatings, the 316L SS coatings exhibiting more defects such as pores, un-melted particles, and oxides. [ABSTRACT FROM AUTHOR]

In the present study, Nb 2 O 5 (NZ0) composite coatings with various concentrations of zinc (NZ2, NZ4 & NZ6) are produced on 316L SS by sol-gel method with the aim of improving its antibacterial activity, bone formability and corrosion resistance properties. This work studied the surface characterization of NZ0, NZ2, NZ4 & NZ6 coated 316L SS by ATR-FTIR, XRD, HR-SEM with EDAX. The synthesized coatings were different in the morphological aspects, NZ0 shows mesoporous morphology whereas irregular cluster like morphology was observed for the zinc incorporated coatings. The chemical composition of the NZ0 and NZ4 composite coatings were studied by XPS and the results revealed that the zinc exist as ZnO and Nb as Nb 2 O 5 in the coatings. The increase in the concentration of zinc in Nb 2 O 5 increases the hydrophilic nature identified by water contact angle studies. The potentiodynamic polarization studies in simulated body fluid reveals the increase in polarization resistance with decrease in current density (i corr ) and electrochemical impedance spectroscopic studies with increase in charge transfer resistance (R ct ) and double layer capacitance (Q dl ) were observed for NZ4 coated 316L SS. The inhibition of Staphylococcus aureus and Escherichia coli bacteria were identified for NZ4 coated 316L SS by bacterial viability studies. The NZ4 coated 316L SS showed better Osseo-integration by spreading the MG 63 osteoblast cells. The study results imply that zinc incorporated Nb 2 O 5 (NZ4) composite coating exhibits antibacterial activity and also enhance the corrosion resistance and biocompatibility of the 316L SS. [ABSTRACT FROM AUTHOR]

Niobium oxide is known for its biocompatibility; however it lacks on bioactivity. Sodium is one of the essential elements required for the formation and maintenance of bone. In this present study, we focus on improving the bioactivity of niobium oxide by incorporating sodium ions and obtaining nanoporous morphology by adding polyethylene glycol. Sodium niobate was prepared using sol-gel method and dip coated on 316L SS. The coated sample was sintered at the optimised heating rate of 0.5 °C min −1 . The surface morphology, chemical composition, phase composition and porosity were analysed using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction analysis (XRD) and porosimetry. The BET analysis and AFM studies showed that the coating exhibited pores with the average diameter of 97 and 101 nm. The Vicker's microhardness test showed that sodium niobate coating exhibits three fold higher microhardness compared to 316L SS. In vitro studies show that the coating exhibited good bioactivity. Electrochemical studies confirmed that the coating offers better corrosion resistance to the substrate at pH 5.2 and pH 7.4. The hemolysis percentage of the coating was found to be 1.54% and anticoagulation studies showed that coagulation time of sodium niobate coating was similar to that of the plasma. Better adhesion, proliferation and differentiation of MG-63 cells with significant cell spreading were observed in the coating. [ABSTRACT FROM AUTHOR]

The usage of conducting polymers as coating materials for bipolar plates to prevent corrosion is the recent trend in Proton Exchange Membrane Fuel Cell (PEMFC) technology. Paraphenylenediamine ( p PD) monomer was electropolymerized to poly p -phenylenediamine (P p PD) over 316L SS. The characterization of P p PD, the conducting polymer coating, over 316L SS was done using attenuated total reflectance infra-red (ATR-IR) spectroscopy to confirm the formation of P p PD. The surface morphology and topography were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion protection performance of the coating was evaluated using open circuit potential (OCP) measurement, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in PEMFC environment. EIS studies revealed that the charge transfer resistance for the coated substrates has increased by one order of magnitude than the bare substrate. Potentiodynamic polarization studies have registered lower corrosion current density by one order magnitude for the 0.06 M p PD coated substrate than the bare substrate and the polarization resistance values for the coated substrates have increased by two and a half time than the bare substrate. These results showed that P p PD coated substrates exhibited enhanced corrosion resistance in PEMFC environment. [ABSTRACT FROM AUTHOR]

The use of metal additive manufacturing (AM) has strongly increased in the industry during the last years. More specifically, selective laser melting (SLM) is one of the most used techniques due to its numerous advantages compared to conventional processing methods. The purpose of this study is to investigate the effects of process parameters on the microstructural and corrosion properties of the additively manufactured AISI 316L stainless steel. Porosity, surface roughness, hardness, and grain size were studied for specimens produced with energy densities ranging from 51.17 to 173.91 J/mm3 that resulted from different combinations of processing parameters. Using experimental results and applying the Taguchi model, 99.38 J/mm3 was determined as the optimal energy density needed to produce samples with almost no porosity. The following analysis of variance ANOVA confirmed the scanning speed as the most influential factor in reducing the porosity percentage, which had a 74.9% contribution, followed by the position along the building direction with 22.8%, and finally, the laser energy with 2.3%. The influence on corrosion resistance was obtained by performing cyclic potentiodynamic polarization tests (CPP) in a 3.5 wt % NaCl solution at room temperature for different energy densities and positions (Z axis). The corrosion properties of the AM samples were studied and compared to those obtained from the traditionally manufactured samples. The corrosion resistance of the samples worsened with the increase in the percentage of porosity. The process parameters have consequently been optimized and the database has been extended to improve the quality of the AM-produced parts in which microstructural heterogeneities were observed along the building direction. [ABSTRACT FROM AUTHOR]

• The incorporation of GO and f-MWCNTs on HAP exhibits more corrosion resistive in SBF. • The hardness of the coatings with GO and f-MWCNTs revealed enhanced strength. • Hydrophilicity of the coated implant surface allows the formation of apatite layer. • The attachment of HAP on chemically modified f-MWCNTs and GO are proved by HR-TEM. Bioceramic composite coatings were deposited on surgical grade 316L stainless steel substrate via in-situ electrolytic method by supplying the voltage of −1.5 V for 30 mins using three electrode arrangements. Formations of pure HAP/GO and HAP/f-MWCNTs composite films were developed and the structure of hydroxyapatite was retained even with incorporation of secondary materials into its matrix. Homogeneously dispersed dense coating was observed for the electrochemically derived HAP composite films on 316L SS. The attachment of GO and f-MWCNTs with hydroxyapatite particles were observed using high resolution transmission electron microscopic (HR-TEM). In-vitro corrosion studies of the fabricated bioceramic composite coatings showed better corrosion protection against the simulated body fluid. Apatite mineralization formed at faster rate for the prepared bioceramic composite films; further which it enhance their bone bonding ability. These results concluded that the electrochemical deposition of bioceramic coatings on implant may be treated as an effective method for orthopedic repair and replacements. [ABSTRACT FROM AUTHOR]

Coatings have attracted much attention because they improve the surface properties while retain favorable bulk properties. For the development of coatings in biomedical applications, the combination of the mechanical characteristics, tribological properties, corrosion behavior, and biocompatibility should be noticed. The present work addresses the mechanical and tribological characteristics and corrosion resistance of ZrO 2 coatings on 316L SS as a function of sputtering gas flow rate for biomedical applications. DC reactive magnetron sputtering technique was employed to deposit the coatings at different argon gas flow rates (5–20 sccm). X-ray diffraction method (XRD) and atomic force microscopy (AFM) were used to characterize the crystallographic structure and surface morphology. Mechanical and tribological properties of the coatings were evaluated by nanoindentation and scratch tests. The electrochemical behavior of the samples was also studied in Hank's solution at a physiological temperature (37 °C). The growth mechanism of the coatings was analyzed and subsequently, its effect on structure, morphology, and different properties was investigated. The results showed that the coatings deposited at lower sputtering gas flow rates (≤10 sccm) are more resistant to plastic deformation, wear, and corrosion in Hank's solution than those deposited at higher rates (>10 sccm) due to their dense structure as well as smooth and crack-free surface. • ZrO 2 coatings were used to improve the properties of 316L SS. • The coatings were deposited by DC reactive magnetron sputtering technique. • The growth mechanism of the coatings was analyzed as a function of sputtering gas. • The coatings deposited at lower flows were more resistant to plastic deformation. • The coatings deposited at lower flows were more resistant to wear and corrosion. [ABSTRACT FROM AUTHOR]

• Interactions of the Hastelloy N-316 L SS couple affect the corrosion of material. • Corrosion of 316 L SS is accelerated while that of Hastelloy N is impeded. • Interactions of the Hastelloy N-316 L SS couple lead to the mass transfer of Fe. • Mass transfer relies on whether dissolved element can be alloyed by Hastelloy N. • Interactions of the couple depend on galvanic corrosion and Fe mass transfer. The corrosion behavior of a Hastelloy N-316 L stainless steel couple in molten LiF-NaF-KF salt at 700 °C was investigated using electrochemistry, immersion tests, and microstructure analyses. Hastelloy N exhibits better corrosion resistance than 316 L SS. Galvanic coupling between two metals accelerates the corrosion of 316 L SS but impedes the corrosion of Hastelloy N. Fe dissolved from 316 L SS was alloyed with Ni in Hastelloy N to form a concentration cell of Fe, which accelerated the mass transfer of Fe from 316 L SS to Hastelloy N. The interactions of the Hastelloy N-316 L SS couple depend on galvanic corrosion and the Fe transfer. [ABSTRACT FROM AUTHOR]