Cyclic Potentiodynamic Polarization Research Articles

Corrosion and Microhardness Behavior Improvement of 316L Stainless Steel via Fiber Laser Surface Treatment

This study investigated how fibre laser surface treatment affects stainless steel 316L’s microhardness and corrosion resistance. The laser parameters utilized in this investigation were four different readings of laser power applied at a constant frequency and scanning speed to stainless steel 316L specimens. A digital micro-Vickers hardness tester was used to measure the microhardness of the samples before and after laser treatment. The TAFEL cyclic potentiodynamic polarization technique was employed to study corrosion behaviour. The microstructure of the base metal and the effect of laser power were investigated using optical microscopy. The phases before and after laser treatment were identified through X-ray diffraction, and the cross section of the heat-affected zones and the molten pool’s depth were examined using a scanning electron microscope. Results revealed that laser treatment affected microstructural transitional phase alterations. Compared with the average microhardness of the base metal, the microhardness of the laser-treated specimens improved to 78.23% as the laser power increased. The increase in microhardness considerably enhanced corrosion resistance to 36.13% relative to that of the base metal.

Effects of electropolishing and plasma ion nitriding on UNS S31603 corrosion in ship scrubber water

Marine scrubbers use seawater as washing water and are damaged by sulfur oxides and chlorides during desulfurization. Therefore, surface treatments to enhance corrosion and pitting resistance of scrubber materials must be investigated. This investigation conducts cyclic potentiodynamic polarization experiments to analyze the effects of electropolishing and plasma ion nitiriding of UNS S31603 in washing water. The corrosion current density (0.186 μA cm-2) of electropolishing is significantly lower than mechanical polishing (1.125 μA cm-2), but plasma ion nitriding is higher (18.995 μA cm-2). Electropolishing forms a uniform and dense passivation film, increasing corrosion resistance, whereas plasma ion nitriding reduces corrosion resistance due to CrN formation. All specimens present local corrosion. Electropolishing reduces the maximum damage depth by 110.13 μm and increases pitting potential by 0.32 V compared to mechanical polishing. Plasma ion nitriding reduces maximum damage depth by 46.59 μm due to suppression of local acidification during hydrolysis.

Corrosion and stress corrosion cracking resistances of the 17-4 precipitation hardened martensitic stainless steel additively manufactured using binder jet printing

The corrosion and stress corrosion cracking (SCC) properties of an additively manufactured (AM) 17-4 PH martensitic stainless steel that was produced using the binder jet printing (BJP) technique are compared with those of the conventionally manufactured (CM) steel, to critically examine the influence of porosity and subtle microstructural variations, introduced due to sintering and hot isostatic pressing (HIP), on them. Microstructures of the BJP and HIP specimens contain porosity, δ-ferrite, and MnS inclusions, while the CM ones do not contain either, but have NbC inclusions. All the corrosion properties of the BJP alloy, investigated using the immersion, cyclic potentiodynamic polarization, and galvanostatic (GL) tests, are inferior (compared to those of the CM alloy) due to the porosity in it, while the NbC inclusions present in the CM alloy adversely affected its corrosion characteristics. Surprisingly, the CM 17-4 PH specimens subjected to the SCC tests failed, while those of the BJP specimens did not (despite the relatively large porosity in it). Detailed analyses (including the X-ray computed tomography) show that crack bridging induced by the δ-ferrite phase, which has superior corrosion resistance compared to the martensite, is the reason for the BJP alloy's SCC resistance. HIP, which reduces both the porosity and δ-ferrite content, resulted in enhanced corrosion and SCC resistances that are even superior to those of the CM 17-4 PH. These results demonstrate, emphatically, that the subtle microstructural variations in the AM alloys can have profound effects on their properties, especially those related to structural integrity and reliability.

On electrochemical corrosion of mechano-activated and thermally processed AlxCryNiz 2D decagonal quasicrystalline structures and crystalline approximants

This article represents a pioneering study centered on the corrosion kinetics of untreated and thermally processed mechano-synthesized AlxCryNiz two-dimensional decagonal quasicrystalline structure and crystalline approximants. It sheds light on the distinguished corrosion behavior of untreated and heat-treated mechano-synthesized Al72Cr15Ni13 and Al86Cr12Ni2 alloys, including a wide diversity of miscellaneous intermetallic phases. A comprehensive characterization was performed to analyze crystallographic structure and thermal characteristics of AlxCryNiz powder particles. Electrochemical evaluations of the mechano-synthesized Al72Cr15Ni13 and Al86Cr12Ni2 specimens and their heat-treated counterparts were conducted under cyclic potentiodynamic polarization tests with 0.1 mol/L Na2SO4 (pH=2) and 3.5% NaCl (pH=8.5) electrolytes at room temperature, respectively. Al72Cr15Ni13 two-dimensional decagonal quasicrystalline phase was attained following 6 h mechano-synthesis and subsequent annealing treatment at 1035°C. There is no evidence of quasicrystal formation in the Al86Cr12Ni2 alloy system after 6 h mechano-synthesis and successive thermal processing at 445 and 570°C. In this study, we conducted the first investigation into electrochemical performance of both Al72Cr15Ni13 and Al86Cr12Ni2 intermetallics. Both Al72Cr15Ni13 and Al86Cr12Ni2 alloys develop a protective passive film in 0.1 mol/L Na2SO4 electrolyte. It was determined that 6 h mechano-synthesized Al72Cr15Ni13 sample, subjected to annealing at 1035°C, stands out in the Al-Cr-Ni alloy systems for applications necessitating exceptional corrosion resistance, passivation behavior, and minimal susceptibility to pitting corrosion when compared to other tested counterparts. This alloy is characterized by a corrosion current density of 3.73 µA/cm2 and a corrosion potential of -0.16 V(vs. Ag/AgCl), revealing a remarkably stable passive film up to a current density of 0.02 A/cm2 and a potential of 2.41 V(vs. Ag/AgCl) within 0.1 mol/L Na2SO4 medium. Likewise, it exhibited a drastically diminished corrosion current density of 11.65 µA/cm2 and a reduced corrosion potential of -0.27 V(vs. Ag/AgCl) within 3.5% NaCl electrolyte, attributed to the formation of two-dimensional decagonal quasicrystalline phase and hexagonal δ-Al3Ni2 crystalline approximant at 1035°C. It also encompassed a re-passivation current density and potential of 50.35 µA/cm2 and -0.04 V(vs. Ag/AgCl), respectively, within the latter solution. Its corrosion mechanism may be ascribed to a two-step surface precipitation process: initially, Al dissolves into a hydroxide, succeeded by the formation and precipitation of Al oxides, such as NaAlO2 and Al2O3∙xH2O.

Impact of cooling methods on the corrosion behavior of AA6063 aluminum alloy in a chloride solution

Abstract In this work, the AA6063 Al alloy was processed by cooling at four different conditions. The impact of the type of cooling method on the corrosion behavior of the produced alloys after 1 and 24 h in 3.5% NaCl solutions was carried out. Various electrochemical measurements, such as cyclic potentiodynamic polarization (CPP), chronoamperometric, and electrochemical impedance spectroscopy (EIS) measurements, were employed. The CPP data revealed that the intensity of corrosion of the alloys is highly influenced by the cooling method. The change in the chronoamperometric current at −650 mV (Ag/AgCl) over time indicates the possibility of pitting corrosion, particularly after 24 h, where the recorded currents showed a continuous increase over time. The scanning electron microscopy images taken for the surfaces of the alloys after corrosion confirmed that the lowest deterioration occurring on the surface was for the AA6063 alloy that was quenched in water. The EIS plots also demonstrated that AA6063 alloy exhibits different corrosion resistances when different cooling methods are applied. All measurements indicated that the corrosion resistance increases in the following order: the quenched alloy in water > the air-cooled alloy > the furnace-cooled alloy > the as-received alloy. The exposure for 24 h decreases the corrosion damage of all alloys via the formation and thickening of a top layer of corrosion products on its surface over time.

The corrosion behavior of graphene reinforced titanium matrix composites in 3.5 wt% NaCl solution

Graphene is widely preferred as a reinforcement element to enhance mostly mechanical properties of titanium matrix composites due to its unique properties. However, the number of detailed studies is quite limited in the literature on the corrosion properties of graphene reinforced titanium composites. Therefore, the effects of graphene amount on the corrosion properties of titanium composites were evaluated in this study. Pure titanium and graphene‑titanium composites for various amount of graphene (0.15, 0.30 and 0.45 wt%) were produced by powder metallurgy. The electrochemical impedance spectroscopy was used to analyze the corrosion properties of the samples in 3.5 wt% NaCl solution. From the results, TiGr15 sample was observed as maximum corrosion resistance with 6.6939 × 10+5 (Ω·cm2). The cyclic potentiodynamic polarization method results showed that TiGr15 sample (0.0007 mA/cm2) has the lowest corrosion flow rate. Moreover, the SEM-EDX images of the corroded samples showed that the highest cohesion of constituent particles and the least amount of corrosion, particle separation were observed at Ti-0.15 wt% graphene.

On the microstructure, corrosion behavior and surface films of the multi-principal element alloy CrNiTiV

A multi-principal element alloy consisting of equi-atomic concentrations of Cr, Ni, Ti, and V, was produced by arc melting. The CrNiTiV alloy was characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and scanning transmission electron spectroscopy (STEM), revealing a complex microstructure containing five phases. The corrosion performance of the alloy was evaluated with cyclic potentiodynamic polarization tests, indicating a low corrosion current density, a high breakdown potential and high repassivation potential. X-ray photoelectron spectroscopy and STEM were carried out after constant immersion in 0.6 M NaCl solution, revealing the passive (surface) film for each of the five phases. The Cr and V dominant phase consisted of an oxidized Cr/V-rich surface film, while the remaining four Ti-containing phases were predominantly TiO2-rich surface films. Ni enrichment and Ti deficiency were observed at the metal/oxide interface in certain Ti-containing phases.

Evaluation of Passive Films on 17-7PH and 410 Stainless Steel Exposed to NaCl Solution.

This work covers the formation of a passive state for two different alloys used in the aeronautical industry. The aim of this study is to investigate the effectiveness of passivation treatments on 17-7PH and 410 SS (stainless steel) samples, specifically when performed with citric and nitric acid solutions at 49 °C using an immersion time of 90 min and subsequent exposure in 3.5 wt.% NaCl solution. Employing the cyclic potentiodynamic polarization (CPP) technique, the corrosion properties of the passivated material were evaluated according to the ASTM G65-11 standard. A microstructural analysis was performed using scanning electron microscopy (SEM). The passivated layer was characterized via X-ray photoelectron spectroscopy. In the results, the CPP curves showed positive hysteresis, indicating pitting localized corrosion, and 17-7PH steel passivated at 49 °C for 90 min in citric acid exhibited lower corrosion rate values equivalent to ×10-3 mm/year.

Effect of Temperature on Passive Film Characteristics of LPBF (Laser Powder-Bed Fusion) Processing on UNS-S31603.

The effect of temperature on the localized corrosion resistance and passive film characteristics of laser powder-bed fusion (LPBF) 316L (UNS S31603) was studied in a buffered 3.5 wt% NaCl solution at 25, 50, and 75 °C. DC techniques such as cyclic potentiodynamic polarization showed lower passive current densities, high breakdown potentials, and a higher resistance to initial breakdown compared with wrought 316L samples at all temperatures. However, LPBF 316L was more susceptible to metastable pitting at potentials before film breakdown and higher damage accumulation post film breakdown. AC techniques, such as Mott-Schottky analysis and electrochemical impedance spectroscopy, showed that the formed passive film was more robust on the LPBF 316L samples at all temperatures, accounting for the higher initial resistance to pitting. However, with increasing temperatures, the film formed had an increasing concentration of defect density. Passive compositions at the various test temperatures studied using X-ray photoelectron spectroscopy (XPS) showed that the LPBF samples showed higher amounts of Cr and Fe oxides and hydroxides compared with the wrought samples, which made the passive films on the LPBF samples more compact and protective. Investigation of the pits formed on the LPBF showed the preferential regions of attack were the melt-pool boundaries and cell interiors due to their being depleted of Cr and Mo when compared with the boundaries and matrix.

Effect of Temperature on the Corrosion Behavior of a Al2Cr5Cu5Fe53Ni35 Multi-Principal Element Alloy (MPEA) in Simulated Soil Environments

The effect of varying temperatures (15, 35, and 45 °C) on the corrosion behavior of a new single-phase distorted face-centered cubic (fcc) Al2Cr5Cu5Fe53Ni35 multi-principal element alloy (MPEA) was studied in simulated soil environments (NS4 solution). X-ray diffraction and electron backscattered diffraction were used to confirm the presence of a single phase throughout the microstructure. Electrochemical tests such as electrochemical impedance spectroscopy and linear polarization resistance were performed to evaluate the interfacial behavior and corrosion rate at various test conditions. Additionally, cyclic potentiodynamic polarization (CPP) tests were also carried out at the selected temperatures to study the pitting behavior of the MPEA. Surface characterization techniques such as X-ray photoelectron spectroscopy and scanning electron microscopy were used to identify the nature of the passive film formed in such complex materials as well as study the pitting characteristics after CPP testing. A stable passive film was found to be present all tested temperatures with the absence of preferential sites for pitting due to homogenous element distribution.

Anodizing of AA2024 Aluminum–Copper Alloy in Citric-Sulfuric Acid Solution: Effect of Current Density on Corrosion Resistance

Al–Cu alloys are widely used as a structural material in the manufacture of commercial aircraft due to their high mechanical properties such as hardness, strength, low density, and tolerance to fatigue damage and corrosion. One of the main problems of these Al–Cu alloy systems is their low corrosion resistance. The purpose of this study is to analyze the influence of anodizing parameters on aluminum–copper alloy (AA 2024) using a bath of citric-sulfuric acid with different anodizing current densities on the thickness, microhardness, and corrosion resistance of the anodized layer. Hard anodizing is performed on AA 2024 Al–Cu alloy in mixtures of solutions composed of citric and sulfuric acid at different concentrations for 60 min and using current densities (i) of 0.03, 0.045, and 0.06 A/cm2. Scanning electron microscopy (SEM) was used to analyze the surface morphology and thickness of the anodized layer. The mechanical properties of the hard anodized material are evaluated using the Vickers hardness test. The electrochemical techniques use cyclic potentiodynamic polarization curves (CPPC) according to ASTM-G6 and electrochemical impedance spectroscopy (EIS) according to ASTM-G61 and ASTM-G106, respectively, in the electrolyte of NaCl at 3.5 wt. % as a simulation of the marine atmosphere. The results indicate that corrosion resistance anodizing in citric-sulfuric acid solutions with a current density of 0.06 A/cm2 is the best with a corrosion current density (jcorr) of 1.29 × 10−8 A/cm2. It is possible to produce hard anodizing with citric and sulfuric acid solutions that exhibit mechanical properties and corrosion resistance similar or superior to conventional sulfuric acid anodizing.

Electrochemical characteristics and damage mechanism in scrubber washing water of UNS N08367 with plasma ion nitriding and electropolishing

In this investigation, electropolishing and plasma ion nitriding are applied to super austenitic stainless steel for the purpose of improving its corrosion and pitting resistance. Electrochemical experiments are conducted with washing water collected directly from the ship’s scrubber. After electropolishing, the surface roughness is improved by about 73.6% compared to mechanical polishing. After plasma ion nitriding, CrN (precipitate), Fe4N (compound), and γN (solid solution) are observed on the surface. The thickness of the layer formed on the surface is measured to be about 10 μm. A hysteresis loop is observed in the cyclic potentiodynamic polarization curves of mechanical polishing and electropolishing, and the areas are calculated as 23.33 mW cm−2 and 0.17 mW cm−2, respectively. The polarization curve of plasma ion nitriding presents perfect passivation characteristics. Accordingly, mechanical polishing and electropolishing reveal local corrosion, whereas plasma ion nitriding presents a tendency towards general corrosion. In the mechanical polishing, electropolishing, and plasma ion nitriding, the corrosion current densities are 0.665 μA cm−2, 0.093 μA cm−2, and 16.47 μA cm−2, respectively, and the maximum damage depth is observed to grow progressively smaller from plasma ion nitriding to electropolishing and then mechanical polishing.

Development of electrophoresed anti-corrosion coating for copper from functionalized multi layered graphene nano-sheets synthesized through anionic acidic electrochemical exfoliation

Following the discovery of graphene, a two-dimensional carbonaceous substance, numerous possibilities in materials science domain have evolved, one being its function as a corrosion inhibitor. This investigation undertakes the synthesis of functionalized multi-layered graphene nanosheets (FMLGNs) from pyrolytic graphite sheets through electrochemical exfoliation involving four distinct acid-based solutions (H2SO4, HCLO4, HNO3 and combination of the above three in 1:1:1 ratio). Post-exfoliation analysis of FMLGNs included X-ray diffraction (XRD) wherein 2θ values were reported at 26° confirming graphene's presence. Raman spectroscopy reiterated the same observation along with an increase in ID/IG ratio to ≈ 1 hinting at the presence of functional groups and defects. UV–visible spectroscopy indicating π-π* transitions, Fourier transform infrared spectroscopy (FTIR) showing CO stretching and X-ray photoelectron spectroscopy (XPS) with a C/O ratio = 3.12 gave an idea about the functionalization in FMLGNs. Average particle sizes of FMLGNs was in the range of 400–500 nm and zeta potential measurements showed stable dispersion behaviour (≈−40 mV). Utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), authors observed a layered (10–15 layers), overlapping shape of FMLGNs. Electrophoretic deposition (EPD) method was employed to coat FMLGNs onto copper substrates under various iterative conditions (number of layers and time of deposition) which produced depositions of ≈20–30 μm. SEM images displayed adequate coverage of graphene sheets on copper surfaces, backed by energy-dispersive x-ray spectroscopy (EDS). Crack propagation resistance (CPR) values of 34.03 N highlighted better adherence than other similar coatings. The coated copper samples were subjected to cyclic voltammetry (CV), potentio-dynamic polarization (PDP) and electrochemical impedance (EIS) tests in 3.5 wt% NaCl solution for analysing the inhibitory impacts of coatings. An inhibition efficiency of 85 % and charge transfer resistance of 5535 Ω.cm2 was observed, which highlighted better corrosion mitigation than reported literatures. The authors also identified that 1 layered coatings showed better reliability than two layered coatings.

Effect of Artificial Aging in the Microstructure and Corrosion Performance of Superduplex UNS S32750 Stainless Steel

Superduplex stainless steels have great mechanical and corrosion properties. However, its chemical composition makes it prone to intermetallic phase precipitation during thermal processing. Sigma (σ), chi (χ), and chromium nitrides (Cr2N) remove Cr and Mo from the matrix, reducing the corrosion and mechanical resistance. Understanding the effects of thermal processing on the secondary phase’s precipitation and depletion of the material’s performance is crucial to its applications. Thus, this work aims to analyze the behavior of the corrosion performance of the UNS S32750 after thermal treatment at 800°C, for 60, 180, 300, and 420 minutes, in comparison to the as-received material. Optical emission spectrometry, X-ray diffraction, and SEM with backscattered electrons (BSE) were used to evaluate the material. The corrosion performance was evaluated with the cyclic potentiodynamic polarization technique. The main results and conclusions obtained in the study were a decomposition of the ferrite phase into the χ and σ phases, with the formation of the χ phase being predominant in shorter times, while for longer aging times σ formed in greater quantities. It was also possible to verify a more aggressive corrosion trend for aged samples in the regions adjacent to the formation of the χ and σ phases. It was also possible to observe that the losses generated in corrosion resistance were greater for aging times longer than 60 minutes. The aging treatment significantly reduced the material’s corrosion resistance in conjunction with the formation of precipitates.

Мырыш электродын өндірістік айнымалы токпен натрий хлориді ерітіндісінде поляризациялау арқылы мырыш оксидін алу

The purpose of the work is to dissolve the zinc electrode during polarization with an alternating current with a frequency of 50 Hz and to obtain zinc oxide. It is shown that the pre-recorded anode-cathode cyclic potentiodynamic polarization curves allow to predict to a certain extent the processes occuriing on the zinc electrode during alternating current polarization. It has been established that when two zinc electrodes are polarized in sodium chloride with an alternating current with a frequency of 50 Hz, they do not dissolve, but when one electrode is replaced with a titanium one, zinc dissolves intensively with the production of zinc hydroxide. It is shown that the rate of zinc dissolution directly depends on the current density at the titanium electrode. When the values of the current density on the titanium electrode change in the range of 5-10 kA/m2, the zinc dissolution current efficiency exceeds 100%. Based on the results of the research, it was established that zinc (II) hydroxide is produced during electrolysis, and zinc oxide can be obtained by dehydration. The composition of the resulting compound was identified by X-ray phase and elemental analyses

Influence of laser power on mechanical properties and pitting corrosion behavior of additively manufactured 316L stainless steel by laser powder bed fusion (L-PBF)

316L stainless steel parts were additively manufactured via laser powder bed fusion under different laser powers. We investigated the influence of laser power on the microstructure and mechanical properties of the printed parts by conducting scanning electron microscopy, X-ray diffraction, microhardness and tensile tests. In addition, we performed electrochemical corrosion tests including cyclic potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution to study the influence of laser power on the corrosion behavior of as-printed parts. The results indicate that as-printed parts exhibit a preferential orientation of (220) direction, and increasing the laser power results in grain refinement of the samples, but excessive laser power can lead to a re-increase in the grain size of the samples. Excessively low laser power can result in the formation of lack of fusion pores, while excessively high power can lead to the formation of keyhole pores. These defects lead to a reduction in tensile performance. Significant differences in corrosion resistance are observed for the parts printed with different laser powers, and between the building direction and normal direction. Some defects, such as micropore, MnS inclusions and boundaries of melt pools, have an impact on the pitting corrosion resistance of printed parts. However, due to low content of MnS inclusions, the presence of pore defects remains the major factor in the pitting corrosion process. Laser powers in the range of 300–375 W can effectively reduce pore defects and improve the resistance of pitting corrosion. These findings emphasize the importance of optimizing the laser power to enhance the overall performance and pitting corrosion resistance of 316L stainless steel parts.

Electrochemical corrosion behaviour of UNS S32205 duplex stainless steel dependent on sigma phase precipitation

Abstract In this study, the microstructure and electrochemical corrosion behavior of the UNS S32205 alloy were investigated. Firstly, the phase diagram of the studied samples was determined by Thermo-Calc 2022 software, and the solution treatment temperature was designated. The studied samples were cooled by various cooling rates following the solution treatment at 1050 °C for 30 min. The samples were characterized by optical microscope, scanning electron microscope, and XRD analysis. Also, electrochemical corrosion behavior was investigated by potentiodynamic polarization, cyclic potentiodynamic polarization and electrochemical impedance spectroscopy analyses. Microstructural examinations revealed that decreasing cooling rate causes the precipitation of the sigma phase, and the ratio of the sigma phase was increased up to 29 % by the decreasing cooling rate. Furthermore, it was determined that precipitation of the sigma phase reduces the E pit values, and the sample with the highest amount of sigma exhibits the lowest corrosion resistance. On the other hand, presence of the sigma changed the electrochemical impedance spectroscopy behavior of the UNS S32205 and double-layered model fit the results.

Effect of V Content on Corrosion Behavior of Al-V Alloys Produced by Mechanical Alloying and Subsequent Spark Plasma Sintering

Al-V alloys produced via high-energy ball milling have been reported to show simultaneous improvement of corrosion resistance and mechanical properties compared to traditional Al alloys. In these alloys, V content plays a crucial role in increasing or decreasing the corrosion resistance. Therefore, the effect of V and microstructure on corrosion of high-energy ball milled and subsequently spark plasma sintered Al-xV alloys (x = 2, 5, 10 at%) has been studied. Cyclic potentiodynamic polarization tests and electrochemical impedance spectroscopic analysis revealed the increment of V content up to 5 at% enhanced the corrosion resistance of the alloy. However, highly heterogeneous microstructure in Al-10 at%V resulted in significant localized corrosion over the immersion time. The electrochemical impedance spectroscopy studies over 14 days of immersion revealed underlying corrosion mechanisms.

Penetration depth, phase balance and corrosion behaviour in activated TIG welding of UNS S32205

The aim of this research is to investigate the impact of a flux containing 80% TiO2 and 20% CeO2, under protective atmosphere (100% Ar, 98% Ar-2% N2, and 95% Ar + 5% N2) on penetration depth, phase equilibrium, and corrosion behaviour of autogenous A-TIG welds generated at constant current density. The reason for choosing cerium in the flux composition and nitrogen in the shielding gas is their effect on the phase balance of austenite and ferrite in this alloy. Metallography, ferritoscopy, and potentiometry were employed in the examination of the welds. The use of a two-component flux increased the penetration depth in TIG welding by up to 87%. Adding 2% and 5% nitrogen gas to the shielding gas in active TIG welding further increased the penetration depth to 117% and 130%, respectively. The results of ferritoscopic analysis reported the amount of austenite in the base metal and conventional TIG weld as 48% and 32%, respectively. However, the use of two-component flux increased the amount of austenite in the weld metal to 39%. Additionally, the addition of 2% and 5% nitrogen to the shielding gas in active TIG welding increased the amount of austenite in the weld metals to 60% and 76.6%, respectively. According to cyclic potentiodynamic polarization studies, active TIG welding with different nitrogen gas concentrations showed improved general and pitting corrosion properties in weld metals compared to conventional TIG welding. Consequently, weld metal resulting from active TIG welding with 2% nitrogen gas exhibited corrosion properties almost identical to that of the base metal.

A comparative study on the corrosion of pure titanium and titanium–12%zirconium alloy after different exposure periods of time in sodium chloride solution

In this work, the powder metallurgy technique was employed to manufacture pure titanium (Ti) and 88% titanium–12% zirconium (TiZr) alloy. The electrochemical corrosion investigations for pure Ti and the TiZr alloy were carried out after exposure for 30 min and 3 days in 3.5% NaCl solutions. The Nyquist and Bode plots obtained from the electrochemical impedance spectroscopy experiments revealed that the presence of Zr remarkably magnifies the corrosion resistance of Ti via increasing the impedance and degree of the phase angle, as well as the polarization and solution resistances. The potentiodynamic cyclic polarization measurements revealed that the presence of 12% Zr highly enhances the corrosion resistance of Ti. These polarization results showed that Zr addition reduces the corrosion of Ti via decreasing its corrosion rate. The intensity of the current when measured with increasing time of the experiment at −0.10 mV (Ag/AgCl) indicated that the addition of 12% Zr greatly decreases the absolute current, which indicates that alloying Zr within Ti reduces the severity of its corrosion in the chloride electrolyte. The morphology of the surfaces and the possible surface layer(s) for the corroded Ti and TiZr samples were analyzed using a scanning electron microscope and energy dispersive x rays. Results collectively depicted that the presence of Zr increases the corrosion resistance when alloyed with Ti.