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In this research study, the split tensile strength of the steel fibers-reinforced boroaluminosilicate geopolymers was evaluated. The design of experiments was carried out using the Taguchi method. The slag used in this work was obtained from the Rockwool furnace slag. A mixture of anhydrous borax (as an alternative to the silicate composition) and NaOH was used as the alkaline activator. The effect of the amount of flat-end steel fibers (1, 3, 5, and 7 wt. %) on the strength of the material was assessed. Four effective factors, including the curing time of the boroaluminosilicate geopolymer, weight percentage of the fibers, weight ratio of the anhydrous borax to NaOH solution, and weight ratio of the alkaline activator (NaOH + anhydrous borax) to the slag, were designed each at four levels. In total, 16 experiments were performed based on the L9 array. Based on the ANOVA analysis results, the optimum parameters were the curing time of 14 days, 7 wt. % of steel fiber, the weight ratio of the alkaline activator to the slag of 0.65, and the weight ratio of anhydrous borax to NaOH solution of 0.5; and the highest split tensile strength was found to be 10.08 ± 0.86 MPa. Also, the specimen prepared using the optimum parameters (with no fiber addition) demonstrated a split tensile strength of 8.10 ± 0.95 MPa. In addition, the Taguchi experimental design method was found to be an appropriate technique to study the strength of the boroaluminosilicate geopolymers reinforced with the steel fibers.

The current inquiry aimed at using core-shell Fe3O4@Humic acid/montmorillonite nanocomposites for removing methyl orange dye from an aqueous solution. The samples were characterized by FT-IR, TEM, SEM, XRD, BJH, and BET analytical methods. The efficiency removal has been utilized for 300 min reaction time using the response surface methodology by a design of five-factor-three-level central composite. The adsorption kinetics followed the pseudo-second-order rate kinetic model, showing an acceptable correlation (R2 > 0.99). Langmuir, Freundlich, Temkin, Dubinin–RadushKevich, and Harkins–Jura isotherms were utilized for the analysis of the equilibrium data. Also, we have estimated standard Gibbs free energy (∆G°), standard enthalpy (∆H°), standard entropy (∆S°), and the activation energy (Ea). The findings of this investigation suggest that the absorption of methyl orange on the adsorbent pursues the Frondelich isothermal formulation. The ∆G° values obtained showed physical absorption in this adsorption process. ∆H° showed that the dye adsorption mechanism was endothermic, and ∆S° indicated an increase in irregularity and the probability of contact between methyl orange molecules and the adsorbent surface in the dye adsorption process. Positive Ea values pointed out the nature of the endothermic absorption process. S* value was minimal and close to zero, which established the process of physical absorption.

In the current study, zinc–aluminum (Galfan) and zinc (galvanized) coatings were coated on steel sheets using the hot-dip technique. The effect of process parameters on the microstructure, corrosion behavior, hardness, and formability of the coatings was assessed. The results demonstrated that both the corrosion area and corrosion rate of the galvanized coatings were reduced by increasing the immersion time. In contrast, the process temperature did not affect the corrosion behavior. Furthermore, by prolonging the dipping time, the hardness of the coatings decreased. The Galfan coatings showed higher formability and the superiority of mechanical and corrosion properties of Galfan coatings over conventional galvanized coatings was indicated.

Material degradation is accompanied by the changes in surface structure, morphology, and composition. These changes can be recorded by a variety of image acquisition devices that export digital images in grayscale or true color to a detector. Information regarding corrosion type and extent can be extracted with image processing methods. This paper provides a comprehensive review of material degradation assessed by digital image processing. Digital image processing systems used to assess material degradation are briefly reviewed, and the algorithms developed to process metallic materials degradation images are described. Physical and electrochemical methods that can be used to support digital image processing results are summarized, and future work that will augment the present methods of evaluating material degradation are discussed.

In this research study, the effect of zirconia nanoparticles on the biological properties of the hydroxyapatite (HA) scaffolds was evaluated. The zirconia nanoparticles with various weight percentages of 5, 10, and 20 were mixed with hydroxyapatite powder using a ball-milling process. Then, they were cold pressed and heat-treated at 1150 °C. Scanning electron microscope and x-ray diffraction analysis were used to evaluate the morphology and phase analysis of the samples, respectively. The results of the microstructure and phase analysis revealed that some zirconia nanoparticles reacted with the HA during the sintering process, which besides the formation of the tertiary calcium phosphate and calcium zirconium phases, it resulted in creating some microporosities in the scaffold. The biological behavior of the samples was investigated by osteoblast-like cells. The results of the biological assessment demonstrated that the presence of the zirconia nanoparticles in the HA scaffold improved the biological behavior (cell attachment and cell proliferation). The HA specimen composed with 10 wt.% zirconia nanoparticles showed the highest bioactivity. In addition, the compressive strength of the HA sample composed of 10 wt.% zirconia nanoparticles was improved by 30%.

Purpose This paper aims to quantify atmospheric corrosion by image analyses. The corrosion extent, form and distribution of corrosion product on Q235B and T91 steels exposed to a Zhoushan marine atmosphere over one year are characterized by image analysis. Design/methodology/approach Image analysis of corrosion images were achieved using the gray value, wavelet analysis and fuzzy Kolmogorov–Sinai (K–S) entropy. Findings As corrosion becomes extensive, the gray value of corrosion images decreases, and the energy value of nine subimages after wavelength decomposition decreases. Fuzzy K–S entropy increases as localized corrosion propagates but decreases as uniform corrosion spreads. Originality/value The methods proposed in this work open a new way for fast corrosion evaluation of metallic materials exposed to atmospheric conditions.

Atmospheric corrosion is the most common cause of the deterioration of metallic materials. Effective monitoring of atmospheric corrosion provides scientific basis for understanding its underlying mechanisms. Atmospheric corrosion in metallic materials can be detected and quantified with an electrochemical noise (EN) technique that includes an electrode system of probes/sensors and a test equipment system. Different electrode systems are compared, and approaches to data processing and to the solution of potential problems are reviewed.

The electrochemical reactivity of a defect in organic coating was investigated by electrochemical noise (EN) and scanning electrochemical microscopy (SECM). Time dependent EN spectra and SECM image on a metal with defective organic coating was measured, and corresponding EN frequency domain spectra and probe approach curves (PACs) were used to obtain electrochemical reactivity information within the coating defects. All time domain and frequency domain analyses, and SECM measurements were successful indicators of corrosion intensity within the defect. The amplitude of electrochemical current noise (ECN) and the low-frequency plateau of the power spectral density (PSD) WL increased significantly with corrosion intensity.

This work aims to develop field corrosion detection method for identifying the defect levels in organic coatings by using electrochemical noise (EN) measured at Singe Cell (SC) mode. An electrochemical sensor was used for defects identification, the results indicate that, as the defect levels rise, the amplitudes of the electrochemical current noise (ECN) increase. Further data analysis based on power spectral density (PSD), and discrete wavelet analysis confirmed that white noise level WL, and wavelet energy distribution can successfully discriminate the levels of protectivity of the organic coating.

Composite sleeve repairs have been used in the pipeline industry for the last 25+ years. Fiberglass sleeves (e.g., Clock Spring®) were initially introduced in the market and are still being used as a proven pipeline repair method. For the last 15+ years, new composite materials have been introduced in the industry to provide a wider variety of repair options depending on the type of imperfections being repaired. Regulations in the U.S.A. and Canada share some requirements regarding design, installation, testing, and assessment of composite sleeve repairs. The U.S. Department of Transportation (DOT) through the Pipeline and Hazardous Materials Safety Administration (PHMSA) recommends the use of repair methods consistent with industry standards. The 2019 version of the Canadian CSA Z662 Oil and Gas Pipeline Standard includes requirements for testing and qualification according to the American Society of Mechanical Engineers (ASME) regulation PCC-2 or ISO/TS 24817, and requirements for conducting an engineering assessment to determine the subsequent maximum stress on the pipe sleeve. This paper compares the regulatory requirements for pipeline composite sleeve repairs in the U.S.A. and Canada; it describes some of the options for composite sleeve repair, and reviews engineering assessments of methodologies for composite sleeve repair.

International audience; Electrochemical noise (EN) can be used in situ to investigate corrosion processes and to detect and monitor the corrosion of metallic materials. EN data are largely influenced by the measurement mode, the surface area of the working electrodes, the electrolyte resistance, and the symmetry of the electrode system. Herein, the advantages and limitations of electrochemical kinetics, equivalent circuit, and shot noise methods for quantifying corrosion rates with EN are discussed.; Le bruit électrochimique (EN) peut être utilisé in situ pour étudier les processus de corrosion et pour détecter et surveiller la corrosion des matériaux métalliques. Les données EN sont largement influencées par le mode de mesure, la surface des électrodes de travail, la résistance électrolytique et la symétrie du système d'électrodes. Ici, les avantages et les limites de la cinétique électrochimique, du circuit équivalent et des méthodes de bruit de grenaille pour quantifier les taux de corrosion avec EN sont discutés.

In this study, ZK60 alloy matrix composites reinforced by 10 wt% boron carbide (B4C) and various 0–1 wt% multi-walled carbon nanotubes (MWCNTs), and 0.5 wt% MWCNTs and different 5–20 wt% B4C contents were prepared via stir casting method. The wear behavior of the samples was assessed using the pin-on-disk configuration at room temperature under loads of 40 and 80 N, and the sliding speed of 0.5 m/s. The worn surface and tribo-layer generated were investigated using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses. The results demonstrated that at low loading the friction coefficients of samples containing MWCNTs were lower compared to those of the samples with different B4C contents. The wear rates were decreased by increasing the MWCNTs content up to 0.5 wt%, while they were increased by increasing the B4C content to higher levels. The worn surfaces of the samples showed that at 40 N, the abrasion and plastic deformation mechanisms were dominant, while delamination and oxidation wear were dominant at 80 N. All in all, the sample containing 10% B4C and 0.5% MWCNTs showed the highest wear resistance.

The growth rate of pits formed on Alloy 800 in chloride solutions containing various thiosulphate concentrations was assessed by potentiostatic polarisation, in situ corrosion image observation, an...

In this work, the corrosion degradation of tinplate in contact with salty water is investigated by scanning electrochemical microscopy (SECM) electrochemical impedance spectroscopy (EIS). Experimental results indicate tin maintains at passive state during the exposure; however, pores and defects existed in tin coating leads to an exposure of carbon steel substrate to the electrolyte, in which localized corrosion tends to occur within the pore. A phenomenological model is proposed to interpret corrosion mechanism of tinplate in contact with salty food based on the proposed electrochemical equivalent circuit.

A hash service environment containing H2S and CO2 in oil industry usually causes corrosion of carbon steel. In this study, the chromized coatings with different deposited time were prepared on the surface of carbon steel by the method of pack cementation to enhance its corrosion resistance. Then the microstructure, hardness, corrosion resistance as well as the semiconductor behavior of coatings in the simulated solution with saturated H2S and CO2 were investigated. The results show that the content of Cr in coating was increased by prolonging deposited time, and both chromium carbides and chromium nitrides were formed. Furthermore, coatings display higher polarization resistance, Rp, than that of the substrate, indicating a higher resistance to charge transfer on coating surface. The corrosion rates of coatings with different deposited time were significantly lower than that of substrate. Chemical analysis showed the formation of heavy sulfides on the surface of substrates after corrosion, while the least corrosion products were detected on the surface of coating with deposited time of 12 h. Mott-Schottky results indicated that coating of 12 h displayed less defects than the other two coatings with deposited time of 4 h and 8 h, which will be beneficial to improve corrosion resistance. The investigation showed that chromized coatings exhibited high corrosion resistance and owned a potential application in oil industry for corrosion prevention.

Corrosion behavior of alloy 316L stainless steel capsule was studied by exposure to the supercritical water (SCW) at 500 °C and 25 MPa for 20,000 h. The microstructural observations have been conducted on the cross section of the exposed surfaces to the SCW to perceive the internal oxidation of the grains and/or grain boundaries. Transmission electron microscopy (TEM) observations as well as elemental analyses such as energy dispersive spectroscopy (EDS) and Electron energy loss spectroscopy (EELS) were used to study the internal oxidation and micro-crack initiation on the surface. Elemental analyses indicated that long-term exposure to the SCW resulted in formation of scales identified as Fe 3 O 4 (outer layer), Fe-Cr spinel/(Fe,Ni)Cr 2 O 4 /(Mn,Cr) 2 O 3 /SiO 2 (inner layer) on the substrate, and Ni-enrichment (chrome depleted region) in the alloy 316L. Micro-crack initiation was observed ahead of the oxidized grain boundaries in which elemental enrichments happened ahead of the crack tip. The relevance of the observed oxidation phenomena on the crack susceptibility of Alloy 316L was discussed. Finally, prolonging the exposure time up to 20,000 h has shown that the alloy 316L might be susceptible to micro-crack initiation in the supercritical water.

In this study, alumina-silica composite coating was coated on an aluminum substrate by the plasma electrolytic oxidation technique at 30 °C and current density of 20 A dm−2 for 30, 60, and 90 min. Microstructure of the coatings was evaluated by an atomic force microscope and a scanning electron microscope. X-ray diffraction analysis was employed to evaluate the phase analysis of the coatings. In addition, corrosion behavior of the coated and uncoated samples was investigated by using potentiodynamic polarization and electrochemical impedance spectroscopy tests in a 3.5 wt.% NaCl solution at 25 °C. Results showed that, by increasing the coating time, the coating thickness and porosity size were increased. However, the number of porosities was decreased by increasing the coating time. Phase analysis results revealed that the coating was mainly composed of mullite, alumina, and silica. Moreover, the results of the corrosion tests indicated that the alumina-silica composite coating formed by the plasma electrolytic oxidation technique considerably improved the corrosion resistance. The sample coated for 60 min showed a better corrosion resistance in comparison with other samples coated for 30 and 90 min.

The early stage atmospheric corrosion of T91 and Q235B steels exposed to Tianjin’s urban atmosphere over 20 days was studied using two electrochemical probes via an electrochemical noise (EN) technique. To identify the corrosion process and the corrosion form of the two steels, EN data were analysed by statistics and wavelet transform. The results revealed that the wavelet energy of decomposed EN mainly located at high-frequency level for Q235B steel, whereas it mainly located at the low-frequency level for T91 steel. Analyses of surface images confirmed that Q235B steel underwent uniform corrosion whereas T91 steel suffered from localised corrosion. The obtained noise resistance correlated well with weight loss data.

The effect of boiling bubbles on the passivation degradation of Alloy 800 in thiosulphate-containing aqueous electrolyte was experimentally investigated using corrosion potential, anodic polarization, combined with Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS). The results showed that the boiling bubbles decreased the pitting potential by enhancing the mass transport. The specimen immersed in boiling electrolyte have a thicker anodic film and a greater amount of sulfur incorporation into the passive layer compared with the experiments at 99 °C. Moreover, a higher ratio of low valance sulfur species was detected on the specimen in boiling test electrolyte, indicating that the boiling bubbles reduced the corrosion resistance of Alloy 800.

We study oxidation and crack susceptibility of alloy 310S stainless steel upon exposure to supercritical water (SCW) at 500 °C and 25 MPa for 20000 h. Electron microscopy observations and elemental analyses are conducted on the static capsule sample to investigate morphological features of the oxidation, micro-crack initiation as well as chemical composition along the micro-crack surface oxides and corrosion products around the micro-crack tip area. The elemental and phase analyses indicate that long term exposure to the SCW resulted in the formation of scales identified as Fe3O4 (magnetite, outer layer), Fe-Cr spinel (FeCr2O4, inner layer), [Mn,Cr]2O3 + SiO2 (Cr-rich spinel and silicon dioxide, transition layer) on the substrate, and Ni-enrichment (chrome depleted region) in the alloy 310S. The presence of carbides along with chromium depletion region most probably result in grain boundary embrittlement around the micro-crack tip. Additionally, crack region is filled Cr-rich oxide, SiO2 and lower amount of carbides. We believe that the intergranular crack initiation occurred through grain boundary oxidation, leading to stress concentration. The oxidation mechanism and scales grown on the alloy 310S stainless steel exposed to SCW and micro-crack initiation as the results of long term exposure at high temperature SCW are discussed.

This study concentrated on the investigation of oxide scale grown on alloys 304 and 304-oxide dispersion strengthened steel in supercritical water (650 °C/25 MPa) environment. The corrosion rate was evaluated by measuring the weight change of the samples and by cross-section examinations. Results showed that weight gains vs. supercritical exposure time follows a parabolic law for alloy 304-ODS contrary to alloy 304 which possibly follows a cubic rate law. The general weight gain after 550 h exposure to the SCW was 131.8 and 621.6 mg/dm2 for alloys 304-ODS and 304, respectively. Electron microscopy observations and elemental analyses as well as X-ray diffraction and time-of-flight secondary ion mass spectrometry results revealed that the oxide scales formed on 304-ODS alloy composed of three distinct layers including Fe3O4 (outer layer), FeCr2O4/(Fe,Cr)2O3 spinel structures (inner layer) and Cr2O3 (transition layer). However, alloy 304 had two layers including Fe3O4 (outer layer) and Fe-Cr spinel structures (inner layer). It is believed that the formation of Cr2O3 layer at the diffusion layer/metal interface becomes the rate-limiting step for oxide advancement, since this change in oxide structure also corresponds to a decrease in corrosion rate in the alloy 304-ODS compared to alloy 304. Based on the results and observations, the oxidation mechanisms are discussed.

In this study, the influence of solutionizing and aging treatments on the microstructure and mechanical properties of alloy 625 superalloy samples produced by powder bed binder jet printing was investigated. Vacuum melted argon atomized 625 superalloy powder was used to fabricate green parts. Samples vacuum sintered at 1280 °C for 4 h to optimize density to 99.6% were subjected to solution and aging treatments at 1150 °C for 2 h and 745 °C for 20 h and 60 h, respectively, in order to improve microstructure and mechanical properties. Elemental analysis, phase formation and microstructure of the sintered, solution treated and aged samples were investigated by using optical, scanning/transmission electron microscopy with electron dispersive spectroscopy, and X-ray diffraction. The results indicate that the aging treatment resulted in the formation of intermetallic phases such as Ni3Nb and Ni2(Cr,Mo) as well as carbides such as NbC, Cr23C6 in the microstructure. While the microhardness and tensile strength of the aged specimen increased due to these phases, the ductility value decreased. This study shows that alloy 625 produced by binder jet printing subjected to aging treatments has comparable properties to cast alloy 625. Keywords: Additive manufacturing, Inconel 625, Heat treatment, Tensile test, TEM, Precipitation

The oxide scale grown of static capsules made of alloy 310S stainless steel was investigated by exposure to the supercritical water at 500 °C 25 MPa for various exposure times up to 20,000 h. Characterization techniques such as X-ray diffraction, scanning/transmission electron microscopy, energy dispersive spectroscopy, and fast Fourier transformation were employed on the oxide scales. The elemental and phase analyses indicated that long term exposure to the SCW resulted in the formation of scales identified as Fe 3 O 4 (outer layer), Fe-Cr spinel (inner layer), Cr 2 O 3 (transition layer) on the substrate, and Ni-enrichment (chrome depleted region) in the alloy 310S. It was found that the layer thickness and weight gain vs. exposure time followed parabolic law. The oxidation mechanism and scales grown on the alloy 310S stainless steel exposed to SCW are discussed.

This study investigates the oxidation behavior of several stainless steels and nickel-based superalloys exposed to supercritical water at 800 °C for 12 h. Characterization of the resulting oxide layers were conducted using weight change measurements, X-ray diffraction, scanning/transmission electron microscopy, and energy dispersive spectroscopy. Although the exposure time is only 12 h, the thickness of the oxide layers formed was as high as 1 μm, comprising different spinel structures. The influence of alloying elements such as Al, Nb, Mo, Mn and Ti on the corrosion behavior is investigated and possible corrosion mechanisms for each candidate alloy are discussed.

Electrochemical noise (EN), as one of the most promising in situ electrochemical methods in corrosion and electrochemical science, has been developing rapidly in recent years with the advancements in instrumentation and signal processing methods. One advantage of EN is its application in long-term or early stage corrosion process monitoring because it instantly detects corrosion rate and corrosion forms. Investigators have applied various mathematical methods to extract characteristic parameters from EN. In this paper, identifying corrosion forms using parameters obtained from time domain, frequency domain and time–frequency domain is reviewed, and the correlation between parameters and corrosion forms is discussed. Finally, other in situ techniques are recommended to be employed synchronously with EN measurement in order to obtain reliable analyses.

Semiconductivity of passive films on steam generator (SG) tubing alloys, Alloys 690 and 800, in simulated crevice chemistries containing lead and sulphur was investigated using the Mott–Schottky analysis. The interaction of the above species with other ions on the properties of passive film and the correlation between the semiconductivity and the breakdown of passive film were discussed. Experimental results revealed that semiconductivity could be either n or p type semiconductor; both Pb and S can incorporate into the passive layer, depending on the solution pH and alloy compositions. For n type semiconductors formed on Alloy 800, they are easily broken down but more resistant to anodic dissolution; for p type passive films formed on Alloys 690 and 800, they are not easily broken down but more prone to anodic dissolution. It is concluded that the semiconductivity of passive film on SG tubing alloys was dependent on the alloy compositions, the solutions, temperature and film formation potentials.

A layered Mo doped Pr 0.5 Ba 0.5 MnO 3−δ (Mo-PBMO) double perovskite oxide was prepared by a modified sol–gel method and the properties of the fabricated material are characterized by various technologies. The results of X-ray diffraction (XRD), H 2 -temperature programmed reduction (H 2 -TPR), NH 3 -temperature programmed desorption (NH 3 -TPD), and thermogravimetric analysis (TGA) demonstrate that the treatment in reducing atmosphere at high temperature lead to a significant phase transformation of the material to a single cubic phase as well as with the Mo in multiple oxidized states. Such character leads to the production of large amount of oxygen deficiency with facilitated oxygen diffusion. The electrochemical performance tests of half-cell and single cell SOFCs exhibit the promoted effect of Mo on catalytic activity for the oxidation of H 2 and CH 4 , indicating that Mo-PBMO could serve as an anode material candidate for SOFCs.

An LY12 aluminum alloy was coated with a self-assembled dodecyl phosphate film by employing a novel surface-modification protocol based on the chemisorption of sodium monododecyl phosphate from aqueous solution. The effect of solution pH on the self-assembled film properties was documented, and the corrosion resistances of the self-assembled film in a Cl−-containing solution and in a marine atmosphere were evaluated by electrochemical impedance spectroscopy and corrosion morphology analysis. Unlike self-assembled film formed in acidic and alkaline conditions, dodecyl phosphate films formed in neutral solution exhibited a multilayer structure with greater thickness and superior corrosion resistance due to the strong chemisorption and electrostatic attraction that are fostered in neutral solutions.

To evaluate the residual life and safe operation of metallic materials, it is crucial to accurately identify the intensity and depth of corrosion pits. Scanning acoustic microscopy (SAM) using tomographic acoustic microimaging (TAMI) under C-mode was employed to determine corrosion pit morphology and depth on aluminum alloy 7050, and the reults were cross-checked by optical microscopy. Maximum and average pitting depths of 204 μm and 80 μm, respectively, were determined by multilayer scannning, and a pitted area of 30 ∼ 40 % was calculated using binary image processing.

A site deficient La 0.2 Sr 0.7 TiO 3−δ (LST A ) and a highly proton conductive electrolyte BaCe 0.7 Zr 0.1 Y 0.2 O 3−δ (BCZY) are synthesized by using solid state reaction method. The performance of the electrolyte-supported single cell, comprised of LST A + Cr 2 O 3 + Cu//BCZY//(La 0.60 Sr 0.40 ) 0.95 Co 0.20 Fe 0.80 O 3−δ (LSCF)+BCZY, is fabricated and investigated. LST A shows remarkably high electrical performance, with a conductivity as high as 27.78 Scm −1 at 1150 °C in a 10% H 2 /N 2 reducing atmosphere. As a main anode component, it shows good catalytic activity towards the oxidation of ethane, causing the power density to considerably increase from 158.4 mW cm −2 to 320.9 mW cm −2 and the ethane conversion to significantly rise from 12.6% to 30.9%, when the temperature increases from 650 °C to 750 °C. These changes agree well with the polarization resistance which dramatically decreases from 0.346 Ωcm 2 to 0.112 Ωcm 2 . EDX measurement shows that no element diffusion exists (chemical compatibility) between anode (LST A + Cr 2 O 3 +Cu) and electrolyte (BCZY). With these properties, the pure phase LST A is evaluated as a high electro-catalytic activity anode material for ethane proton conducting solid oxide fuel cell (PC-SOFC).

In this study, a Ni–P–WC nanocomposite coating was prepared by electroless deposition methods, modifying the typical Ni–P coating through the addition of WC nano-particles. The morphology, structure, microhardness and corrosion resistance of the Ni–P–WC coating and conventional Ni–P coating were analyzed by using the optical stereoscopic microscopy (OSM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), anodic polarization curve and electrochemical impedance spectroscopy (EIS). It was observed that WC nano-particles and Ni–P deposited homogeneously on the Ni–P matrix, electroless deposited composite coatings exhibit an amorphous structure of the nickel matrix in which crystalline tungsten carbide is incorporated. The microhardness of the coating increased due to the existence of the nano-particles, and it will be improved after heat treatment. According to the results of corrosion testing in the 3.5 wt.% sodium chloride solution, the electroless Ni–P–WC coatings showed significantly improved corrosion resistance due to its special structure, compared to a conventional Ni–P electroless coating, even after 40 days immersion, it also exhibited good corrosion resistance ability.

The electrochemical noise (EN) experiment and instrumentation aspects are briefly summarized, and the direct current (DC) removal methods before EN analysis are illustrated. The results show that poly-nominal trend removal, wavelet analysis and Empirical mode decomposition are effective for DC removal whereas average trend removal and linear trend removal are not suitable for DC removal.

In this paper, failure analysis was carried out based on the available documents, metallographic studies and corrosion behavior of the welded joint pipe sample made of AISI 1518 low carbon steel. Nondestructive evaluations including penetration test (PT) and radiographic test (RT) were performed on the as-received pipeline and results indicated the presence of micro- and macro-cracks. Optical microscopic images and scanning electron microscopy (SEM) micrographs revealed various microstructures in the base metal (BM), heat affected zone (HAZ) and weld metal (WM). The microstructural variations may result in galvanic feature and lead to failure and rupture of the weld joint during the service. Microhardness measurements showed that hardness value was about 260 HV in the WM, while it declined in the HAZ and BM. Qualitative chemical analyses such as X-ray diffraction pattern (XRD) and SEM equipped with energy dispersive spectroscopy (EDS) confirmed the presence of corrosive media during weld joint rupture. Additionally, SEM and optical investigations indicated that micro-cracks were formed in HAZ due to residual stress as a consequence of improper welding condition. Surface fracture studies showed that the crack initiation, crack growth and finally crack propagation took place in the WM/HAZ interface. Electrochemical studies were conducted on the BM, HAZ and WM to investigate corrosion behavior of the failed joint sample. Finally, a proper corrosion mechanism is proposed based on the failure analyses and electrochemical studies.

Lap joint friction stir welding (FSW) between dissimilar AZ31B and Al 6061 alloys sheets was conducted using various welding parameters including tool geometry, rotation and travel speeds. Tapered threaded pin and tapered pin tools were applied to fabricate FSW joints, using different rotation and travel speeds. Metallurgical investigations including X-ray diffraction pattern (XRD), optical microscopy images (OM), scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM–EDS) and electron probe microanalysis (EPMA) were used to characterize joints microstructures made with different welding parameters. Intermetallic phases were detected in the weld zone (WZ). Various microstructures were observed in the stir zone which can be attributed to using different travel and rotation speeds. Mechanical evaluation including lap shear fracture load test and microhardness measurements indicated that by simultaneously increasing the tool rotation and travel speeds, the joint tensile strength and ductility reached a maximum value. Microhardness studies and extracted results from stress–strain curves indicated that mechanical properties were affected by FSW process. Furthermore, phase analyses by XRD indicated the presence of intermetallic compounds in the weld zone. Finally, in the Al/Mg dissimilar weld, fractography studies showed that intermetallic compounds formation in the weld zone had an influence on the failure mode.

In situ scanning electrochemical microscopy (SECM) and scanning tunneling microscopy (STM) assisted scanning reference electrode technique (SRET) were applied for the first time to study the interaction of thiosulfate with Alloy 800 surfaces in aqueous chloride solutions. Electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) were also performed to understand the interaction mechanism. The results showed that the effect of 0.075 mol/L thiosulfate in 0.6 mol/L chloride solutions strongly depended on the potential. There was no aggressive effect at the corrosion potential where the passive layer was intact, but a combined effect was observed with the presence of chloride ions at high potential where the passive layer was broken down.