Electrochemical Corrosion Characteristics Research Articles

Wire Arc Deposition Additive Manufacturing and Experimental Study of 316L Stainless Steel by CMT + P Process

The cold metal transfer plus pulse (CMT + P) process was performed to produce a 316L vertical wall through the single-channel multi-layer deposition method. The microstructure of different regions on deposited samples was observed by an optical microscope and a scanning electron microscope (SEM). The phase composition of the as-deposited wall was checked by X-ray diffraction, and the element distribution in the structure was analyzed by an energy-dispersive spectrometer. The tensile strength and microhardness of samples were tested, and the fracture morphology was observed by an SEM. Finally, the electrochemical corrosion characteristics of the as-deposited wall in different regions along the building direction were tested. Results from the experiments indicated that the microstructure of metallography showed a layer band. The metallurgical bounding between layers was carried out by dendrite remelting and epitaxial growth. Along the building direction, the alloy of different regions solidified in an ferritic-austenitic (FA) manner, and due to having undergone different heat histories, their SEM microstructures were significantly distinct. The ultimate tensile strength (UTS) and yield strength (YS) of the vertical specimens were higher than those of the horizontal specimens, displaying obvious anisotropy. Due to a large amount of precipitation of precipitated phases in terms of intermetallic compounds in the middle and upper regions, the tensile strength and microhardness along the building direction showed a trend of first decreasing and then increasing. In the bottom region, a small amount of ferrite precipitated in the austenite matrix, while in the middle of the as-deposited wall, the amount of ferrite gradually increased and was distributed in the austenite matrix as a network. However, due to the heat accumulation effect, the ferrite dissolved into austenite in large quantities and the austenite showed an obvious increase in size in the top region. A stable passivation film was caused by a relatively low dislocation density and grain boundary number, and the middle region of the arc as-deposited wall had the best corrosion resistance. The large consumption of chromium (Cr) atoms and material stripping in the top region resulted in the integrity of the passivation film in this region being the weakest, resulting in the lowest corrosion resistance.

Effects of Sputtering Current on Electrochemical Corrosion Characteristics of Nanoscale Chromium Films Deposited by Direct Current Magnetron Sputtering.

Chromium coatings are often used for surface treatment of metals and alloys. In this study, nanoscale chromium coatings were deposited on 316L stainless steel by direct current magnetron sputtering. The effects of sputtering currents on electrochemical corrosion behavior of nanochromium coatings were investigated in 0.5 M H²SO⁴ + 2 ppm F- solution by electrochemical methods at room temperature. Results showed that the corrosion rates for nano-chromium coatings deposited at 0.25 A, 0.35 A, and 0.4 A were lower than bare steel by more than two orders of magnitude. The chromium coatings deposited at 0.25 A were inclined to degrade in the electrolyte after long-term immersion in the electrolyte, due to lesser coverage of passivity film on chromium coating. Moreover, the chromium coatings deposited at 0.3 A and 0.4 A exhibited excellent corrosion resistance due to formation of a continuous, compact and protective passive film.

Electrochemical and Exfoliation Corrosion Behavior of Reversion-Treated High-Strength Aluminum Alloy

The present study aims to understand the microstructural modification affecting the electrochemical and exfoliation corrosion (EXCO) characteristics of aluminum alloy 7010. The alloy was aged for two different tempers, namely peak aging (T6) and retrogression and re-aging (RRA). The standard electrochemical polarization tests and EXCO tests were performed on the treated alloys. The microstructure of the alloy observed under a scanning transmission electron microscope revealed the presence of continuous grain boundary precipitates in T6 alloy. These precipitates were formed discontinuously after RRA treatment. The RRA alloy microstructure resulted in a shift toward positive potential. The exfoliation corrosion depth was reduced to 60–70 μm after RRA treatment, which was measured to be about 250 μm in T6 condition. The resistance toward the exfoliation corrosion was found to be influenced by the enriched Cu content of precipitates on grain boundary after reversion treatment. The results confirm that the RRA-tempered alloy improves both electrochemical corrosion and EXCO resistance.

Assessment of fatigue and electrochemical corrosion characteristics of dissimilar materials weld between alloy 617 and 12 Cr steel

In the current work, welding between dissimilar material (Nickel 617 and 12 Cr steel) was carried out by two types of techniques i.e. welds with and without buttering. Buttering welding was carried out on 12 Cr steel side to enhance the metallurgical compatibility of the weld. To evaluate the integrity of dissimilar weld between alloy 617 and 12 Cr steel, fatigue strength, fatigue crack growth in corrosion environment and in air was investigated. Potentio-dynamic polarization test was performed to assess the electrochemical corrosion susceptibility of these welds at different temperatures. The results showed that fatigue limits for buttering welded specimens were relatively higher than those without buttering welding in both the environments (air and corrosive medium), and the fatigue strength significantly decreased in corrosive environment. The electrochemical corrosion susceptibility increased with increase in temperature for both type of welds. Fatigue crack growth rate of dissimilar material welded specimen without buttering welding was slightly higher than that of buttering welded specimen. Buttering weld enhanced the corrosion characteristics and fatigue strength of weld between alloy 617 and 12 Cr.

Development mechanism of local corrosion pit in X80 pipeline steel under flow conditions

In this paper, local corrosion pits were stimulated by arc defect pits (ADP) of different sizes. The corrosion of specimens was tested in high-speed flow CO2-saturated NACE solution. Electrochemical corrosion characteristics were monitored online. The characteristics of corrosion scale were then investigated by SEM and Raman spectroscopy. The results showed deepening and expansion of corrosion pits will occur at the same time under flow conditions for shallow pits. The development of corrosion pits at certain depth led to formation of complete corrosion scale, which inhibited further corrosion. As corrosion pits deepened, expansion process decreased and deepening rates accelerated. In-depth analysis suggested that corrosion rates were mainly affected by mass transfer rate and integrity of formed corrosion scale.

Effect of Corrosion Characteristics on Long-Term Aging of Austenitic 304 Steel

The objective of this study is to investigate the effect of long-term aging on electrochemical corrosion characteristics of austenitic AISI 304 steel. AISI 304 steel was subjected to aging treatment for an extended period at 700 °C up to a maximum of 10,000 h. The variation in the microstructure of aged specimens was observed with an optical microscope (OM) and a scanning electron microscope (SEM). The electrochemical polarization test was conducted to obtain the corrosion current density (Icorr) and corrosion potential (Ecorr). The metastable intermetallic M23C6 carbides generated in the vicinity of γ/γ grain boundaries and coarsened with aging time. The δ-ferrite island decomposed into σ-phase and M23C6 carbide with an aging time increase. As the aging time increased, the current density increased, but the corrosion potential of the austenitized specimen exhibited a minimum value of 0.04 μA/cm2. The highest pitting resistance exhibited at the austenitized specimen due to the absence of carbides. Consequently, the corrosion resistance of austenitic AISI 304 steel decreases with long-term aging time. The microstructural analyses well support this result.

Microstructure and Corrosion Resistance to H2S in the Welded Joints of X80 Pipeline Steel

The microstructure and corrosion resistance in H2S environments for various zones of X80 pipeline steel submerged arc welded joints were studied. The main microstructures in the base metal (BM), welded metal (WM), coarse-grained heat-affected zone (CGHAZ), and fine-grained heat-affected zone (FGHAZ) were mainly polygonal ferrite and granular bainite; acicular ferrite with fine grains; granular bainite, ferrite, and martensite/austenite constituents, respectively. The corrosion behavior differences resulted from the microstructure gradients. The results of the micro-morphologies of the corrosion product films and the electrochemical corrosion characteristics in H2S environments, including open circuit potential and electrochemical impedance spectroscopy, showed that the order of corrosion resistance was FGHAZ > BM > WM > CGHAZ.

Effect of Heat Treatments on the Mechanical and Electrochemical Corrosion Behavior of 38CrSi and AISI 4140 Steels

The aim of this investigation was to compare the microstructural, mechanical and electrochemical corrosion characteristics of 38CrSi steel with widely used AISI 4140 steel under various heat treatment processes to widen its field of applications. Experimental steels 38CrSi and AISI 4140 were subjected to austenitizing at 900 °C for 30 min followed by annealing, quenching in oil and quenching followed by tempering at 400 °C for 120 min. Microstructure of 38CrSi and AISI 4140 steels was characterized by light optical and scanning electron microscopy. Tensile, Charpy impact toughness and Rockwell hardness testing techniques were used to evaluate the mechanical properties. Electrochemical corrosion behavior was evaluated by a Tafel scan in tape water. Results show that microstructure of both steels comprised of ferrite and pearlite after annealing, packets and blocks of lath martensite with retained austenite after quenching and tempered lath martensite with retained austenite after quenching, and tempering with varying grain size distribution and volume fractions of different phases. Hardness and tensile properties of both steels varied in quite identical manner, while impact toughness of both steels varied in inverse manner. 38CrSi steel was found to be brittle, while AISI 4140 steel exhibited excellent properties under all heat treatment processes. In 38CrSi, the corrosion rate decreases as compared to the as-received sample from 0.515 to 0.486 mpy in quenching and tempering heat treatment, while in AISI 4140 steel the corrosion rate decreases during quenching from 0.620 to 0.472 mpy.

The Effect of Thermal Treatment Modes on the Structure and Corrosion Resistance of Plasma Coatings Made of Alloys Based on Nickel and Iron

The structural state and corrosion resistance of the plasma coatings based on iron (FBKh6-2 alloy) and nickel (RW 12496 alloy from Castolin Co.) in aqueous solutions of sodium hydroxide and nitric acid upon varied thermal treatment modes have been investigated. Structural and electrochemical characteristics of these coatings have been compared to those of their analogs in the as-cast state that underwent respective thermal pretreatment. The morphological heterogeneity of the coatings’ surface has been demonstrated to determine the formation of their corrosion-electrochemical characteristics. The specific character of the corrosion process evolution responsible for significant degradation of the coatings’ corrosion resistance as compared to the cast alloys has been described. It has been established that the effect of morphological defects of the coatings’ surface (cavities, microcracks, roughness, open pores, etc.) on the corrosion process evolution can be substantially reduced and, in some cases, completely excluded through impregnation by the hydrophobizing fluid Anakrol-2501 with high penetrating ability. Corrosion tests of the coatings have been performed. It has been demonstrated that impregnation results in a significant reduction of the corrosion rate that becomes compatible to that of the annealed cast samples.

SOME PROPERTIES OF BIOMEDICAL Ti6Al4V ALLOY IN DIFFERENT SOLUTIONS

The aim of the present investigation is to study the effect of different simulated solutions onwear behavior, chemical properties and ion release of Ti-6Al-4V alloy which used in humanbody. For this purpose three solutions have been used (Hank's solution, 0.9NaCl andartificial saliva). The corrosion properties of Ti-6Al-4V implant alloy were examined at37ºC by using electrochemical techniques, such as the potentiodynamic method and opencircuit potential (OCP). The electrochemical corrosion characteristics of Ti-6Al-4V implantalloys in three biological solutions were measured in terms of the corrosion potential (Ecorr)and the corrosion current density (icorr ).Wear behavior was investigated by using pin-ondisctribometers at human temperature under different loads (10,15,20)N. The wear testconsisted of measuring the weight loss of samples. The metal ion release of base andalloying element by immersed specimens into various solutions for 7 days (168 hours) at37ºC. The result found that the Ti6Al4V implant alloy in three biological solutions exhibiteda characteristic of a good behavior. The superior corrosion resistance these alloy whichcurrent density measured in (nA/cm2). The weight loss of samples by wear test increase withincrease load and time. After applied heat treatment, about 40% enhancement in the wearbehavior of alloy. The quantity of Al element metal release of implant alloy with variationfluids which increase with decrease the value of pH and little amount of vanadium elementin hank's solution.

Salt spray corrosion and electrochemical corrosion characteristics of CAIP and LTPN fabricated AlCrN/NL composite coating

An AlCrN/nitrided layer (NL) composite coating was fabricated on H13 hot work mould steel using a cathodic arc ion plating (CAIP) and low temperature plasma nitriding (LTPN). The surface and cross–section morphologies, chemical composition and phases of obtained coating were characterized using a scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and x-ray diffractometer (XRD), respectively. The salt spray corrosion (SSC) and electrochemical corrosion properties of AlCrN/NL coating in 3.5 wt% NaCl solution were analyzed using a salt spray corrosion chamber and electrochemical workstation. The results show that the AlCrN/NL composite coating consists of AlN, Cr1.75V0.25N2, AlCrFe2 and SiC phases, the formation of ceramic phases increases its corrosion resistance. The aggressive Cl– is adhered on the corrosion products after the SSC test, the corrosive micro–cells and pitting corrosion are formed due to the differences of structure and relative potentials. The corrosion current densities of AlCrN/NL coating, NL and substrate are 3.255 × 10–6, 9.848 × 10–6, and 1.522 × 10−5 A · cm–2, respectively, indicating that the corrosion resistance of AlCrN/NL coating is higher than that of NL and substrate. The polarization resistance of 11 798 Ω · cm2 on the AlCrN/NL coating is 1.68 and 3.67 times higher than that of NL and substrate, respectively, which shows that the AlCrN/NL coating increases the corrosion resistance of substrate.

Effect of surface treatment by sandblasting on the quality and electrochemical corrosion properties of a C-1020 carbon steel used by an Algerian oil company

The purpose of the different operations under the term surface preparation is to get a clean surface able to be coated. It is essential to adapt this preparation in terms of the metallurgical nature of the substrate, cleanliness, its shape and roughness. Surface preparations especially the operations of sandblasting, polishing, or grinding prove of capital importance. It allows to modify the superficial properties of these materials, after these treatments the surface becomes very active. This paper evaluates the mechanical surface treatments effect by sandblasting (Sa 1.5 and Sa 2.5) on the electrochemical corrosion characteristics of C-1020 carbon steel in 3% NaCl solution electrolyte simulating aggressive sea atmosphere. Investigations are conducted using stationary (free potential "E-t, polarization curves "E-i", the Tafel rights and the Rp) and nonstationary electrochemical tools such as electrochemical impedance. The results obtained allowed us to highlight that sandblasted carbon steel degrades with immersion time because of the roughness of the surface. These results were confirmed by the plot of the electrochemical impedance diagrams, confirming that the process governing kinetics is under charge transfer control. Good protection against corrosion cannot be obtained only with a good surface preparation of the adapted steel.

The Influences of Chloride Anions on Corrosion Electrochemical Characteristics of 904L Stainless Steel in Blast Furnace Gas/Water system

The Influences of Chloride Anions on Corrosion Electrochemical Characteristics of 904L Stainless Steel in Blast Furnace Gas/Water system

Tribo-fatigue behaviors of steel wires under coupled tension-torsion in different environmental media

Tribo-fatigue behaviors of carbon structural steel wires under coupled tension-torsion in the tests with different tribo-fatigue parameters in different environmental media were investigated in the present study. The coefficient of friction was recorded by the self-made test rig. The wear depth profile was measured using three-dimensional white light interferometer. Morphologies of the wear scar and fracture of steel wire were observed employing the scanning electron microscope. The electrochemical analyzer was used to investigate electrochemical corrosion characteristics of steel wire. The crack propagation of steel wire was explored employing the X-ray computed tomography. The results show that coefficients of friction in different environmental media decreases by the order: air, alkaline and neutral electrolyte solutions, deionized water and acid electrolyte solution. The decrease order of maximum wear depth and increase order of fatigue life are as follows: air, acid, neutral and alkaline electrolyte solutions, and deionized water. Wear mechanisms include abrasive wear, adhesive wear, corrosion wear, fatigue wear in cases of different environmental media. The degree of electrochemical corrosion and maximum crack depth of fatigue wire are the largest in the acid electrolyte solution. The fracture is divided into zones of crack initiation, crack propagation and final fracture. Increases of tribo-fatigue parameters cause overall decreases in the coefficient of friction, degree of electrochemical corrosion and fatigue life, and increases in the maximum wear depth, crack propagation rate and surface damage.

Improvement of electrochemical corrosion characteristics of AZ61 magnesium alloy with unconventional fluoride conversion coatings

Fluoride conversion coating was applied on wrought AZ61 magnesium alloy by the immersion of alloy in Na[BF4] molten salt. Two different temperatures 430 °C and 450 °C, and different treatment times of 0.5; 2 and 8 h were used for the coating preparation. The surface morphology and the cross-sections of the coatings were investigated by scanning electron microscopy, focused ion beam cutting and energy-dispersive X-ray spectroscopy. The electrochemical corrosion characteristics of coated material varied with processing conditions. A significant improvement of electrochemical corrosion properties of the AZ61 magnesium alloy coated with fluoride conversion coatings was revealed by the potentiodynamic tests and electrochemical impedance spectroscopy.

Effect of SnO2/SiO2 nano particle dispersant on the performance characteristic of complex multi-doped composite coating produced through electrodeposition on oil and gas storage tap

Abstract The effect of SnO2/SiO2 nano particle dispersant on the performance characteristic of complex zinc multi-doped composite coating produced through electrodeposition is studied. The degradation behaviour in term of wear and chemical corrosion activities were considered as a major factor in service. The wear mass loss was carried out with the help of reciprocating tester. The electrochemical corrosion characteristics were investigated using linear polarization technique in 3.5% simulated sodium chloride media. The outcome of the analysis shows that the developed coating was seen to provide a sound anti wear characteristics in its multidoped state. The corrosion resistance properties were observed to be massive compared to the binary based sample. It is expected that this characteristic will impact on the performance life span of storage tap in oil and gas.

In Vitro Corrosion Assessment of Additively Manufactured Porous NiTi Structures for Bone Fixation Applications

NiTi alloys possess distinct functional properties (i.e., shape memory effect and superelasticity) and biocompatibility, making them appealing for bone fixation applications. Additive manufacturing offers an alternative method for fabricating NiTi parts, which are known to be very difficult to machine using conventional manufacturing methods. However, poor surface quality, and the presence of impurities and defects, are some of the major concerns associated with NiTi structures manufactured using additive manufacturing. The aim of this study is to assess the in vitro corrosion properties of additively manufactured NiTi structures. NiTi samples (bulk and porous) were produced using selective laser melting (SLM), and their electrochemical corrosion characteristics and Ni ion release levels were measured and compared with conventionally fabricated NiTi parts. The additively manufactured NiTi structures were found to have electrochemical corrosion characteristics similar to those found for the conventionally fabricated NiTi alloy samples. The highest Ni ion release level was found in the case of 50% porous structures, which can be attributed to their significantly higher exposed surface area. However, the Ni ion release levels reported in this work for all the fabricated structures remain within the range of most of values for conventionally fabricated NiTi alloys reported in the literature. The results of this study suggest that the proposed SLM fabrication process does not result in a significant deterioration in the corrosion resistance of NiTi parts, making them suitable for bone fixation applications.

Slurry erosion-corrosion resistance and microbial corrosion electrochemical characteristics of HVOF sprayed WC-10Co-4Cr coating for offshore hydraulic machinery

The slurry erosion-corrosion and microbial corrosion electrochemical behavior of high-velocity oxygen-fuel (HVOF) sprayed WC-10Co-4Cr cermet coatings and the reference stainless steel 1Cr18Ni9Ti were both investigated. The slurry erosion-corrosion test was performed in a rotating disk rig facility with circulating system using distilled water and 3.5 wt% NaCl slurries. The microbial influenced corrosion behavior in the presence of SRB was evaluated by electrochemical measurement. The results showed that WC-10Co-4Cr coating exhibited higher slurry erosion-corrosion resistance compared to the stainless steel 1Cr18Ni9Ti in both distilled water and 3.5 wt% NaCl slurries. The evolution of the slurry erosion mechanism of the coatings with the augment of NaCl concentration was cracks and microchipping in distilled water slurry, and a combination of detachment of binder phase, microchipping and fragments in 3.5 wt% NaCl slurry. Potentiodynamic polarization and electrochemical impendence spectroscopy (EIS) results showed that the WC-10Co-4Cr coating had a comparable microbial influenced corrosion resistance in seawater with SRB as compared to the stainless steel 1Cr18Ni9Ti.

Electrochemical properties of welded S355J2 steel before and after surface treatment by manganese phosphating

S355J2 steel is used for many applications in different industries. However, this material is attacked by corrosion in chloride environment where the most vulnerable part of a construction is a welded joint. In order to improve general corrosion resistanceof steels phosphate coatings are widely used. This paper evaluates the effect of a manganese phosphate coating prepared on welded joint produced by submerged arc welding (SAW) method on the electrochemical corrosion characteristics. These corrosion characteristics were assessed by potentiodynamic polarization tests and electrochemical impedance spectroscopy measurements in 0.1M Na2SO4 (simulation of industrial atmosphere) solution

Electrochemical Corrosion Characteristics of High Strength Low Alloy Domex 700 Steel After Mechanical Surface Treatment in Chloride Environment

Abstract Nowadays a large number of mechanical surface treatments of constructions materials is used in industry, mainly focusing on steel surface treatment. The aim of this study was to evaluate the effects of mechanical surface pre-treatment (grinding and shot peening) on corrosion resistance of high strength low alloy Domex 700 steel. Suitable mechanical surface treatment can by used for surface homogenization (eg. grinding) or for improvement of mechanical, strength and fatigue properties (shot peening). 0,1M NaCl solution of ambient temperature was used as an environment for electrochemical tests. Evaluation of the mechanical surface treatment effect on corrosion resistance of Domex 700 steel surface was realized by electrochemical tests: potentiodynamic polarization tests (using Tafel analysis) and electrochemical impedance spectroscopy (using equivalent circuit). From the obtained results it is possible to conclude, that the process of mechanical surface treatment by shot peening at choosen conditions has negative effect on corrosion resistance of Domex 700 steel.