Investigating the efficacy of Curcuma longa against Desulfovibrio desulfuricans influenced corrosion in low-carbon steel

The effectiveness of Curcuma longa extract in the control of low-carbon steel corrosion caused by sulfate-reducing bacteria (SRB) in Baar’s medium was investigated. The SRB taken for the study was Desulfovibrio desulfuricans. Specimens in contact with the medium containing SRB exhibited a corrosion rate more than 10 times that of the specimens in contact with the medium without SRB. The weight loss studies showed that the addition of 50 ppm C. longa extracts to the medium containing SRB resulted in an average inhibition efficiency of 91.2% for a four week immersion period. The inhibitor extract altered the reaction rates of both cathodic and anodic reactions which were confirmed from the potentiodynamic polarization (PP) studies. Electrochemical impedance spectroscopy (EIS) studies showed a reduction in the number of sessile bacteria upon inhibitor addition which was confirmed by the microscopy. Severe pitting was observed in the morphological analysis of the specimen in the absence of inhibitor treatment. Apart from adsorption onto the specimen surface to minimize the biocorrosion, the inhibitor extract also served as an anti-film forming and antibacterial agent.

Effect of carbon nanotubes on microstructure and corrosion resistance of PEO ceramic coating of magnesium alloy

Plasma electrolytic oxidation (PEO) ceramic coating modified by carbon nanotubes (CNTs) was prepared on Mg–Gd–Y alloy. The microstructure, hydrophobicity and corrosion resistance of the coating were investigated by SEM, contact angle meter and electrochemical test system. Carbon nanotubes (CNTs) are staggered in the ceramic coating and partially filled with plasma discharge micropores. To some extent, CNTs can promote the plasma discharge and improve the film formation rate. With the increase of the content of CNTs, the content of carbon nanotubes in the ceramic coating increases. CNTs can effectively improve the hydrophobicity of ceramic coating. With the increase of the content of CNTs, the corrosion potential E coor and polarization resistance R p increase, the corrosion current i coor decreases and the AC impedance |Z| increases, which leads to the decrease of corrosion rate.

A review on the corrosion resistance of electroless Ni-P based composite coatings and electrochemical corrosion testing methods

This paper aims to review the impact of different factors influencing the corrosion resistance of electroless Ni-P based coatings. Emphasis has been given onto the impact of phosphorus content, incorporation of alloying elements, addition of particles and heat treatment which have been discussed in detail and critically reviewed. The effect of corrosive media and coating process parameters on corrosion resistance are studied concisely. Furthermore, the role of the incorporation of various elements and particles’ contents on the corrosion resistance of electroless Ni-P coating are studied systematically. This paper also presents an overview of the latest electrochemical corrosion measuring techniques. The following approaches deserve special attention in the analysis: localized electrochemical impedance spectroscopy (LEIS), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET), scanning droplet cell (SDC), scanning electrochemical microscopy (SECM), scanning Kelvin probe (SKP) and novel contactless technique (NCT).

Corrosion characteristics of plasma spray, arc spray, high velocity oxygen fuel, and diamond jet coated 30MnB5 boron alloyed steel in 3.5 wt.% NaCl solution

30MnB5 boron alloyed steel surface is coated using different coating techniques, namely 60(Ni-15Cr-4.4Si-3.5Fe-3.2B 0.7C)-40(WC 12Co) metallic powder plasma spray, Fe-28Cr-5C-1Mn alloy wire arc spray, WC-10Co-4Cr (thick) powder high velocity oxy-fuel (HVOF), and WC-10Co-4Cr (fine) diamond jet HVOF. The microstructure of the crude steel sample consists of ferrite and pearlite matrices and iron carbide structures. The intermediate binders are well bonded to the substrate for all coated surfaces. The arc spray coated surface shows the formation of lamellae. The cross-section of HVOF and diamond jet HVOF coated surfaces indicates the formation of WC, W2C Cr, and W parent matrix carbide structures. The corrosion characteristic of the coated steel has been investigated in 3.5 wt.% NaCl solution using electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDAX) techniques. The results reveal that the steel corroded in the medium despite the coatings. However, the extent of corrosion varies. HVOF coated sample demonstrated the highest corrosion resistance while arc spray coated sample exhibited the least. EDAX mapping reveals that the elements in the coatings corroded in the order of their standard electrode potential (SEP). Higher corrosion resistance of HVOF coated sample is linked to the low SEP of tungsten.

Corrosive-wear behavior of LSP/MAO treated magnesium alloys in physiological environment with three pH values

A laser shock peening (LSP) layer, a micro-arc oxidation (MAO) coating, and an LSP/MAO composite coating were fabricated on the surface of AZ80 magnesium alloy by laser shock and micro-arc oxidation process. The ball-disc grinding method was used to perform wear test on the three treated specimens in simulated body fluids (SBF) with pH values of 4, 7.4 and 9. The morphology and element content of worn surface were investigated by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results indicated that the wear rates of the three treated specimens in three pH environment in numerical order were pH 4 > pH 7.4 > pH 9, respectively. The wear rates of the three treated specimens in the same pH environment were arranged in the order of MAO > LSP > LSP/MAO, respectively. The main wear mechanisms of the LSP specimen in pH 4 environment were fatigue wear and corrosion wear, while it were corrosion wear and adhesive wear in pH 7.4 and pH 9 environments. Abrasive wear, fatigue wear and corrosion wear were the main wear mechanisms of the MAO specimen in pH 4 environment, while abrasive wear, adhesive wear and corrosion wear were the main wear mechanisms of that in pH 7.4 and pH 9 environments. The corrosion wear resistance of the LSP/MAO specimen in SBF solution with three pH values was improved due to the synergism of LSP fine crystal layer and MAO coating.

Water-droplet erosion behavior of high-velocity oxygen-fuel-sprayed coatings for steam turbine blades

The water-droplet erosion of low-pressure steam turbine blades under wet steam environments can alter the vibration characteristics of the blade, and lead to its premature failure. Using high-velocity oxygen-fuel (HVOF) sprayed water-droplet erosion resistant coating is beneficial in preventing the erosion failure, while the erosion behavior of such coatings is still not revealed so far. Here, we examined the water-droplet erosion resistance of Cr3C2–25NiCr and WC–10Co–4Cr HVOF sprayed coatings using a pulsed water jet device with different impingement angles. Combined with microscopic characterization, indentation, and adhesion tests, we found that: (1) both of the coatings exhibited a similar three-stage erosion behavior, from the formation of discrete erosion surface cavities and continuous grooves to the broadening and deepening of the groove, (2) the erosion rate accelerates with the increasing impingement angle of the water jet; besides, the impingement angle had a nonlinear effect on the cumulative mass loss, and 30° sample exhibited the smallest mass loss per unit area (3) an improvement in the interfacial adhesion strength, fracture toughness, and hardness of the coating enhanced the water-droplet erosion resistance. These results provide guidance pertaining to the engineering application of water erosion protective coatings on steam turbine blades.

The corrosion behavior and cracking susceptibility of the disbonded coating in the X80 steel pipeline by theoretical simulations and experimental measurements

The corrosion behavior and cracking susceptibility of the disbonded coating in the X80 steel pipeline were investigated by different methods. The oxygen content in the trapped solution decreased rapidly with the formation of an airtight disbonded area. The airtight system affected the electrode reaction process, resulting in the inhibition of corrosion in the center of the disbonded area and the more refined surface finish of the sample. The bottom of the disbonded area underwent a relatively intense and accelerated corrosion reaction controlled by the diffusion process. The cracking susceptibility of the X80 steel firstly decreased and then increased in the pointing direction.

The role of anticorrosive polymer coatings for the protection of metallic surface

Research on corrosion-resistant polymer coatings has attracted scientists in both academia and industry to prevent corrosion-related damage in modern industrial equipment and to extend the working life of industrial metallic surfaces. To achieve realistic applications, diverse methodologies have been designed to magnify the anticorrosion efficiency of these coatings. The current review describes the conventional and advanced methods utilized for the synthesis of corrosion-resistant polymer coatings. The main intent of this review article is to provide an overview of the design and preparation of anticorrosive polymer coatings with important examples. The promising anticorrosion applications of self-healing polymer coatings for metallic materials and alloys are highlighted. The advantage of a superhydrophobic surface to prevent the corrosion of the materials is discussed. A brief discussion over the anticorrosion mechanism of conducting polymer coatings is also provided. Finally, the current challenges and future perspectives to prolong the anticorrosion performance of these coatings are also addressed.