Anodic Polarization Tests Research Articles

Effect of target composition on the microstructural, mechanical, and corrosion properties of TiAlN thin films deposited by high-power impulse magnetron sputtering

Ti1−xAlxN thin films were deposited using reactive high-power impulse magnetron sputtering on silicon Si (100), tungsten carbide (WC-Co), and SUS304 substrates using three metallurgical TixAly alloy targets with Al/(Al + Ti) atomic ratios of 0.19, 0.36, and 0.57. A fixed duty cycle of 1% and a N2/Ar ratio of 15.8% was used. The current–voltage characteristics of the TixAly alloy targets were first investigated. Then, the microstructural evolution and the mechanical and corrosion properties of the as-deposited Ti1−xAlxN thin films were analysed by scanning electron microscopy, grazing incident X-ray diffractometry, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and anodic potentiodynamic polarisation tests. The power density of 1.86 kW/cm2 achieved with the square-like power output wave obtained in the constant current mode was higher than the 1.37 kW/cm2 power density obtained with the triangular-like power output wave. The deposition rates of the Ti1−xAlxN thin films increased from 13.4 to 28.6 nm/min with an increasing alloy target Al/(Al + Ti) atomic ratio due to the higher sputter yield of Al than Ti. The Al/(Al + Ti) atomic ratio of the alloy target determines the structure, which changed from a highly preferred TiN (111) orientation (Al/(Al + Ti) ratio = 0.19) to a nanocomposite structure (Al/(Al + Ti) ratio = 0.57). The nanoindentation results indicated that the highest hardness and elastic modulus values of the Ti1−xAlxN thin films were 33.3 GPa and 405.9 GPa, respectively, obtained using the Al/(Al + Ti) = 0.19 alloy target. In addition, the friction coefficients of the Ti1−xAlxN thin films were between 0.68 and 0.77. However, the potentiostatic polarisation measurements showed that the amorphous TiAlN films exhibited the highest corrosion resistance in 3.5% NaCl solution, as the corrosion resistance of the Ti1−xAlxN coatings increased as the Al/(Al + Ti) atomic ratio increased.

Capacitance characteristics of carbon-based electrochemical capacitors exposed to heteropolytungstic acid electrolyte

A Keggin-type heteropolytungstic acid, H3PW12O40, is evaluated as new high ionic conductivity aqueous electrolyte of potential interest for electrochemical capacitors, with enhanced safety and low environmental concern. For the performance evaluation, two types of electrode materials have been selected, i.e. mesoporous multi-walled carbon nanotubes and microporous activated carbons. To address the influence of changes in the porous structure and surface properties on capacitors performance, the materials have been subjected to additional oxidation treatment under liquid or gas phase conditions. The electrochemical parameters of two-electrode cells were evaluated from a series of voltammetric, galvanostatic, constant power, and AC impedance measurements and compared with those obtained for conventional H2SO4 electrolyte. It has been shown that due to the size of the heteropolytungstate anion (exceeding 1 nm), the selection of carbon electrode materials in terms of appropriate porous structure and wettability is a key factor in avoiding capacitance limitations. As a result, the specific capacitance, energy density as well as the rate capability of H3PW12O40 supported capacitors may approach the performance of conventional H2SO4-based systems. Furthermore, the potentiodynamic anodic polarization tests and post-mortem scanning electron microscopy analysis confirmed a higher corrosion resistance of 316 L type steel in the presence of H3PW12O40 solution, in comparison to the conventional H2SO4 electrolyte. It enables stable capacitor performance upon utilization of low cost non-noble current collectors which was evaluated during galvanostatic cycling (13 000 cycles) and accelerated ageing by potentiostatic floating during 120 h.

Microstructural Changes During Plastic Deformation and Corrosion Properties of Biomedical Co-20Cr-15W-10Ni Alloy Heat-Treated at 873 K

Microstructural changes were observed during the plastic deformation of ASTM F90 Co-20Cr-15W-10Ni (mass pct) alloy heat-treated at 873 K (600 °C) for 14.4 ks, and analyzed by electron backscatter diffraction and in situ X-ray diffraction techniques. The obtained results revealed that the area fraction of the e-phase (fe) in the as-received alloy was higher than that in the heat-treated alloy in the low-to-middle strain region (≤ 50 pct), whereas the fe of the heat-treated alloy was higher than that of the as-received alloy at the fracture point. During plastic deformation, the e-phase was preferentially formed at the twin boundaries of the heat-treated alloy rather than at the grain boundaries. According to the transmission electron microscopy observations, the thin e-phase layer formed due to the alloy heat treatment acted as the origin of deformation twinning, which decreased the stress concentration at the grain boundaries. The results of anodic polarization testing showed that neither the heat treatment at 873 K (600 °C) nor plastic deformation affected the alloy corrosion properties. To the best of our knowledge, this is the first study proving that the formation of a thin e-phase layer during the low-temperature heat treatment of the studied alloy represents an effective method for the enhancement of the alloy ductility without sacrificing its strength and corrosion properties.

Corrosion resistance and cytocompatibility of Ti-20Zr-10Nb-4Ta alloy surface modified by a focused fiber laser

The corrosion resistance and cytocompatibility of Ti-20Zr-10Nb-4Ta (TZNT) alloy modified by surface laser treatment were investigated. The scanning electron microscopy (SEM) measurements indicated that laser treatment on TZNT alloy generated groove morphologies with the width of ~40 μm and the depth of ~10 μm on the surface. The water contact angles along the groove direction decreased by 51% compared with that of the untreated alloy. The laser treatment promoted the oxidation of metallic Ti, Zr and Nb and produced more stable oxides on surface. The corrosion potential increased by 50% and corrosion current density decreased by 72% compared with that of the untreated alloy in the anodic polarization test for the alloy in Hank’s solution at 37°C. This indicated the improvement of the corrosion resistance by laser treatment. The cytotoxicity testing results showed that the laser-treated TZNT alloy performed similar MC3T3-E1 cell viability compared with the untreated alloy. The cells displayed oriented growth along the groove direction due to the increased hydrophilicity. This novel material may be a new candidate in orthopedics and dentistry implantations fields.

CP-Ti 및 Ti-6Al-4V 합금의 전기화학적 특성에 미치는 제조공정의 영향

Ti and its alloys show the excellent corrosion resistance to chloride environments, but they show less corrosion resistance in HCl, H2SO4, NaOH, H3PO4, and especially HF environments at high temperature and concentration. In this study, we used the commercially pure titanium and Ti-6Al-4V alloy, and evaluated the effect of the manufacturing process on the electrochemical properties. We used commercial products of rolled and forged materials, and made additive manufactured materials by DMT (Directed Metal Tooling) method. We annealed each specimen at 760℃ for one hour and then air cooled. We performed anodic polarization test, AC impedance measurement, and Mott-Schottky plot to evaluate the electrochemical properties. Despite of the difference of its microstructure of CP-Ti and Ti-6Al-4V alloys by the manufacturing process, the anodic polarization behavior was similar in 20% sulfuric acid. However, the addition of 0.1% hydrofluoric acid degraded the electrochemical properties. Among three kinds of the manufacturing process, the electrochemical properties of additive manufactured CP-Ti, and Ti-6Al-4V alloys were the lowest. It is noted that the test materials showed a Warburg impedance in HF acid environments.

Síntesis, caracterización y evaluación de la resistencia a la corrosión de recubrimientos híbridos Sol-Gel base TEOS/MPS sobre la aleación AA2050-T8

El presente trabajo tuvo como objetivo sintetizar, caracterizar y evaluar la resistencia a la corrosión de recubrimientos híbridos sol-gel base TEOS/MPS, sintetizados sobre la aleación AA2050-T8 (Al-Cu-Li) bajo diferentes condiciones experimentales de polimerización, tales como solvente y tiempo de envejecimiento, así como diferentes relaciones molares de los precursores inorgánico tetraetoxisilano (TEOS) e híbrido 3-metacriloxipropiltrimetoxisilano (MPS). Se monitoreó la evolución de los soles durante el proceso de envejecimiento mediante espectroscopía infrarroja (FT-IR) y ensayos reológicos. Los recubrimientos se obtuvieron mediante dip-coating y fueron caracterizados a través de microscopía electrónica de barrido (MEB-EDX). La evaluación de la resistencia a la corrosión se realizó mediante ensayos de polarización anódica potenciodinámica, en solución aireada 0,1 M de NaCl. Los resultados obtenidos revelaron que, de los tres solventes evaluados, el etanol es el que permite mejor estabilización del precursor híbrido y favorece el proceso de polimerización de los grupos metacrilato del precursor MPS. Por otra parte, la variación de la relación molar TEOS:MPS conlleva a la obtención de recubrimientos más homogéneos y continuos al incrementar la relación del precursor inorgánico. Finalmente, todos los recubrimientos sintetizados mejoraron la resistencia a la corrosión de la aleación AA2050-T8, en especial los sintetizados bajo la relación TEOS:MPS 80:20.

Effects of inclusions on the resistance to pitting corrosion of S32205 duplex stainless steel

In order to elucidate the effects of inclusions on the resistance to pitting corrosion of S32205 duplex stainless steel, a potentiodynamic anodic polarization test, a weight loss test, a SEM‐EDS analysis, an in situ analysis and ICP analysis are carried out. The results show that the (Ba, Cr, Si, Ca) oxides and (Mn, Si, Cr, Al) oxides are corroded more easily than (Cr, Mn, Al, Ti) oxides, and the equivalent diameter of the former is greater than that of the latter. The pits of dissolved inclusions act as the initial locations of pitting corrosion in the chlorine ions corrosion environment, which accelerates the corrosion of matrix. The proportion of matrix corrosion is higher than inclusions corrosion in the weight loss.

Effects of Aging at 450°C on the Pitting Corrosion Resistance and Toughness of AISI 317L Steel Welded by GTAW and FSW

Austenitic stainless steels are high corrosion resistant alloys widely used in many industrial fields. Among this family of steels, AISI 317L stands out due to its higher localized corrosion resistance when compared to the traditional grades AISI 304L and AISI 316L. In some applications in oil refineries, the AISI 317L is being specified for services at moderately high temperatures. At the same time as it is sought to use new stainless steels, is also desirable to apply and develop emerging welding processes, replacing conventional ones, in order to achieve better behavior in service. In this respect, this work studied the effects of thermal aging on the toughness and resistance to pitting corrosion of AISI 317L steel weld metals produced by the Gas Tungsten Arc Welding (GTAW) and Friction Stir Welding (FSW) joining processes. After prolonged exposures at 450°C, for 200h, 300h and 400h, the microstructural characterization by scanning electron microscopy (SEM), toughness evaluation and anodic polarization tests in 3.5% NaCl solution were performed. The results showed that the increase of the exposure time in both weld metals caused a toughness decrease. The pitting potentials measured in the polarization tests also decreased with the aging at 450oC.

Effect of pulsed duty cycle control on tribological and corrosion properties of AISI-316 in cathodic cage plasma nitriding

Austenitic stainless steels are of prime importance in many industrial sectors because of their excellent corrosion resistance; however, their poor mechanical and tribological features lead to their reduced applicability. In this regard, low-temperature cathodic cage plasma nitriding (CCPN) can be used to improve surface properties of steels without scarifying the inherent corrosion resistance. In this study, AISI-316 samples are processed in CCPN reactor at a temperature of 400 °C, for the treatment time of 4 h, at a pressure of 150 Pa and variable pulsed duty cycle (15–75%). The microstructure and mechanical features are analyzed using x-ray diffraction, scanning electron microscopy, microhardness tester and ball-on-disc wear tester. The anodic polarization test in 3.5% NaCl is conducted to examine the corrosion properties. The results show that hardness is enhanced up to 1327 HV at low duty cycle, which is considerably higher than base material (278 HV). The wear rate is found to be reduced up to 90% over base material by processing at low duty cycle. The base material exhibits severe abrasive wear, and the nitrided sample has dominant adhesive wear. The corrosion rate is found to be reduced up to 95% over base material for the sample nitrided at low duty cycle. This study shows that wear and corrosion resistance in CCPN can be significantly boosted by reducing the pulsed duty cycle.

Anodic Behavior of Steel in Sulfate-Rich Simulated Grout Pore Solution

Recent observations of severe corrosion of post-tensioned tendons in Florida Bridges were associated with segregated grout containing high sulfate ion concentrations (Lau et al, 2013). Generally, the role of sulfates for steel initiation in alkaline environments have not been well elucidated. In 1970, Gouda identified steel corrosion initiation in saturated calcium hydroxide solutions (pH=12.1) with sulfate concentrations greater than 0.2%; however, steel depassivation was not observed in concrete samples with sodium sulfate concentrations as high as 8%. Dehwah et al. 2002 reported that sulfates did not affect the time to chloride-induced corrosion initiation, but the corrosion rate increased with sulfate content. Research by Carsana and Bertolini in 2011 indicated a strong influence of solution pH on the anodic behavior of steel in sulfate solutions. The objective of the work presented here was to identify the role of early presence of sulfate ions on steel corrosion development. The experiments consisted of anodic polarization tests to determine the anodic behavior of steel samples exposed to alkaine solutions with pH 12.6 or 13.3. Those solutions contained sodium sulfate in the range of 0 to 20,000 ppm. The steel samples were preconditioned for 1 day at either the OCP condition or -1VSCE. The intent to pre-condition the sample at OCP was to initially allow any possible passive film growth to occur. The intent to cathodically pre-condition the steel sample at -1VSCE was to maintain the steel at a low corrosion rate but remaining at active corrosion condition prior to polarization. It this way, it was thought any adverse role of sulfate ions to impede stable passive film formation could be identified. Anodic polarization measurements were made initially from -1 VSCE to +500 mVSCE, with a slow scan rate (0.05 mV/s). Experimental results concluded that anodic polarization tests of steel in pH 13 solution with up to admixed 20,000 ppm sodium sulfate did not indicate strong tendency of sulfates to disrupt passive film formation. However, anodic polarization tests in pH 12.6 and admixed >4,000 ppm sulfate solution indicated instability of passive film resulting in pitting corrosion. It was observed that pH and admixed sulfate concentration will affect the stability of the passive layer. In some cases, as shown in Figure 1, anodic current excursions were indicative of localized depassivation. Indeed, some samples showed indications of pit development. This can be in part explained by the mechanism presented by Gavele (1976) where repassivation of pits can occur in the presence of increased sulfate concentrations within pits but may subsequently diffuse out leading to activation/passivation events. This change of a critical passivation sulfate concentration may result in the observed quick shifts in anodic current. More prominently however, the polarization graphs show transition from passive to active corrosion behavior of steel in solution with the admixed presence of 12,000 to 20,000 ppm sodium sulfate with anodic Tafel slope on the order of ~100 mV/dec. Figure 1

Effects of Thermal Treatments on Compact and Nanotubular Anodic Films on Titanium

Introduction Anodization constitutes a surface modification route that allows the design of the structure, chemistry and electronic properties of the films formed by carefully selecting process variables. This versatility is used to modify the surface of permanent titanium implants to improve osseointegration rate. Post anodization heat treatments are often performed to improve the crystallinity of the surface films and this leads to increase of bioactivity. However, thermal treatments may alter not only the crystal structure of anodized oxide film, but also induce growth of thermal oxide or alter the structure of the anodic films. Since anodic films on titanium may be inhomogeneous and porous, the effect of air heat treatments on such complex structures was evaluated in this work. EXPERIMENTAL Flat specimens of commercially pure titanium Grade 2 were used. Anodising was performed in a two-electrode cell with Pt wire as counter electrode. Two acidic solutions were employed, i) TP: 1 mol L -1 H3PO4, ii) TPF: 1 mol.L -1 H3PO4 + 0.3 % HF; for potentiostatic anodization. Post anodization heat treatments at 553, 623, 673 and 723 K during 3 hours and cooling in furnace were conducted. The surface morphology of the specimens was observed by scanning electron microcopy. The crystalline phases were determined by Raman spectroscopy and graze angle X-ray diffraction. Anodic polarization curves and electrochemical impedance spectroscopy (EIS) tests were performed in borax solution. RESULTS AND DISCUSSION DRX and Raman spectroscopy were complementary used to analyse the crystallographic phases detected and its spatial distribution. Not crystalline phases were detected on mechanical polished titanium (T), anatase was detected in most sites on TP and TPF presents a partial crystalline presence, with sites with anatase, rutile and amorphous film. Changes in colour of heat treated samples are observed in all cases, indicating that a certain degree of change in the surface films has occurred. With Raman spectroscopy an increase in crystalline phase amount was detected in T, TP and TPF samples. The oxide film formed in phosphoric (TP) behaves as a barrier, increasing the corrosion potential, diminishing the current density and increasing the total impedance. On the contrary, anodic films growth in phosphoric and fluoride solution, presents in anodic polarization experiments a similar response than non-anodized samples, but EIS evidences a complex structure of TPF anodic films characterized with two or even three time constants. Thermal treatments in air have different effects on the modified surfaces. On polished titanium, the growth of a thermal oxide is evidenced both on anodic polarization curves and EIS. The thermal oxide layer behaves as a barrier to electronic transfer, acting in a similar way than anodic films. In TP films, the thermal treatments do not produce differences in current density during anodic polarization, while with EIS changes in the inner (compact) and outer (more porous) part of the film are evidenced. Finally, in TPF samples, thermal treatment results in deleterious effects on the barrier efficiency of the anodic layer. Porous TPF films behaves in similar way than polished titanium in anodic polarization tests, since the thermal treatment induce diminish in current densities. However, EIS results indicates a deleterious effect of the thermal treatment on the anodic layer, evidenced by a diminish in the total impedance in Bode plots, and the appearance of a capacitive film governing the EIS response. The electrochemical evidence suggests the rupture of the anodic film of TPF during thermal treatments, corroborating Raman and GDRX results and also SEM evidence. It may be concluded that careful analysis of changes in structure both on the surface and in the substrate inner layer may be due in order to evaluate the influence of thermal treatments on the in vivo or in vitro response of surface modified titanium as a permanent implant, since is clear in this report that not only crystallization of amorphous portion of the surface oxide, but also growth, re-ordering and even destruction of anodic films may be occurring.

Acceleration of Fe Corrosion in Cement Paste and Mortar By Enhancing Oxygen Supply

Generally, in concrete, alkalinity of the environment is maintained and reinforcing steels exhibit superior corrosion resistance owing to passive film. Therefore, it is difficult to demonstrate Fe corrosion in concrete in the laboratory in a short time. A new method for acceleration of Fe corrosion is necessary. Recently, some researchers tried to accelerate the Fe corrosion in concrete. They accelerated Fe corrosion by anodic polarization and cyclic corrosion test. In this study, an accelerated corrosion test method with enhancing oxygen supply was developed to enhance oxygen reduction on Fe surface and Fe corrosion in concrete. The effect of amount of oxygen supply on Fe corrosion in cement paste and mortar will be discussed in our presentation. The sample was 99.5% Fe sheet with 7×7 mm2and 1 mm thickness. The Fe sample was embedded in cement paste or mortar with 5 mm cover thickness and cured for 28 days. In order to prompt breakdown of passive film on the Fe sample, 2.06 M NaCl solution was mixed to the cement paste and mortar. Fig. 1 shows the schematic image of Hyperbaric-oxygen accelerated corrosion test we developed. In the gas pressure chamber, Fe in cement and Fe in mortar were immersed in 2.06 M NaCl solution under the pressured oxygen of 0.5 or 2.0 MPa for 14 days. For comparison, corrosion of Fe in cement and Fe in mortar immersed in the NaCl solution under ambient air was also discussed. After finishing the immersion under pressured oxygen or ambient air, surface and cross section of Fe sample were observed using an optical microscope and SEM. In addition, composition of the rust on Fe sample was analyzed using Raman spectroscopy measurement. Corrosion of the Fe in cement and Fe in mortar was obviously accelerated under the pressured oxygen of 0.5 MPa, and the corrosion of Fe in mortar was further enhanced than that of Fe in cement. Composition of the rust formed under the pressured oxygen of 0.5 MPa was similar to those formed in the real environment. It is thus demonstrated that the enhancement of oxygen supply is beneficial and effective to validly accelerate Fe corrosion in concrete. Corrosion of the Fe in cement and Fe in mortar was suppressed under the pressured oxygen of 2.0 MPa compared to corrosion under the pressured oxygen of 0.5 MPa. It is considered that corrosion of Fe in cement and Fe in mortar is dominated by oxygen reduction reaction under the pressured oxygen of 0.5 MPa, while the excess oxygen makes passive films more protective and corrosion of Fe is suppressed under the pressured oxygen of 2.0 MPa. Figure 1

Effects of rare earths on nanocrystalline for nitrocarburised layer of stainless steel

ABSTRACTSolution-treated stainless steel was plasma-nitrocarburised at the precipitation-sensitive temperature with and without rare earth (RE) addition. The nitrocarburised layers were characterised by means of X-ray diffraction, transmission electron microscope, nanoindentation and anodic polarisation test. Experimental results show that the depth of plasma-nitrocarburised layer can be apparently increased from 60 to 75 μm after RE addition. More importantly, microstructure of stainless steel surface is refined into nano-sized grains after plasma nitrocarburising. At the depth of 20 μm, the hardness and the modulus of the nanocrystallised layer are as high as 13.6 and 218 GPa. After RE addition, the hardness and the modulus of the nanocrystallised layer increase to 17.5 and 255 GPa, respectively.

Effect of the catalyst concentration, the immersion time and the aging time on the morphology, composition and corrosion performance of TEOS-GPTMS sol-gel coatings deposited on the AZ31 magnesium alloy

The aim of the present work was to evaluate the effect of the catalyst (acetic acid) concentration, the immersion time and aging time during the synthesis and deposition of TEOS-GPTMS hybrid sol-gel coatings on the AZ31 magnesium alloy and to analyse how these synthesis parameters affect the morphology, composition and corrosion performance of the coating resultant. The hydrolysis and condensation reactions occurred within the sols were monitored by rheological test and Fourier Transform Infrared (FTIR) Spectroscopy. In order to evaluate the corrosive power of the sols synthesised and their interaction with the magnesium surface, both the catalyst concentration and the immersion time using during deposition were varied from 2.5 to 10vol%, and from 15 and 120s respectively. Additionally, the effect of the aging time on the composition, morphology and corrosion performance of the hybrid coatings was analysed by employing different aging times up to 15days. Characterisation of the coatings was carried out using Scanning Electron Microscopy (SEM), Attenuated Total Reflection Infrared Spectroscopy (ATR-IR), and contact angle measurements. On the other hand, corrosion resistance was evaluated by potentiodynamic anodic polarisation test in aerated 0.1M NaCl solution. The experimental results showed that by suitable control of synthesis parameters studied it was possible to mitigate surface corrosion processes on the AZ31 magnesium alloy during the sol deposition. This allowed obtaining continuous, homogeneous coatings without cracking. Further, their corrosion evaluation revealed a decreasing the corrosion current density by about one order of magnitude with regard to the parent alloy providing, simultaneously, a protection range up to 150mV.

Influence of Microstructure on the Corrosion Resistance of AISI 317L (UNS S31703)

The AISI 317L stainless steel is an austenitic grade with at least 3%Mo. Recently, this steel has replaced AISI 316L in many applications in chemical and petrochemical industries, due to its higher pitting corrosion resistance. The microstructure of the hot rolled and annealed material studied in this work consists of austenitic grains and 4.0% of delta ferrite (δ) with elongated islands morphology. This microstructure was modified by three processes: cold rolling with 87% of reduction, aging at 450oC for 400 h, and welding by gas tungsten arc welding (GTAW) process. The corrosion resistance was evaluated by anodic polarization tests (ASTM G-61) and critical pitting temperature tests (ASTM G-150). Cold rolling produced a microstructure consisting of elongated grains of austenite and martensite α', high dislocation density and the elongated islands of delta ferrite present in the annealed material. Welding produced a dendritic microstructure with 7.0% of delta ferrite and some σ precipitated in the ferrite. Finally, the aging at 450oC for 400 h provoked the decomposition of ferrite. The results show that these microstructural changes affected the pitting corrosion resistance, as detected by ASTM G-61 and ASTM G-150 tests.

Effect of acetic acid on corrosion behavior of AISI 201, 304 and 430 stainless steels

AbstractAustenitic stainless steels are often used to handle organic acids such as acetic acid (CH3COOH), which are extensively used in food contact applications and chemical industries for manufacturing medicines, nutrition and various chemical amalgams. In the present investigation an attempt has been made to compare the corrosion behavior of Cr–Ni (AISI type 304), Cr–Mn–Ni (type 201) and Cr (type 430) stainless steel for economical replacement of higher cost Cr–Ni grade. Immersion testing was performed at room temperature and boiling temperature in acetic acid. Atomic absorption spectroscopy was carried out to evaluate metal ion concentration in the immersion solution. The surface morphology of pit formation was characterized using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The effect of elemental leaching on electrical conductivity of the immersion solution was evaluated and correlated with pH measurements. A new mechanism has been proposed for the pit formation due to manganese sulfide inclusions. The replacement compatibility was further confirmed with anodic polarization testing and a successful replacement was established for room temperature applications.

Corrosion behavior of surface modifications on titanium dental implant. In situ bacteria monitoring by electrochemical techniques.

The effects of surface modifications and bacteria on the corrosion behavior of titanium have been studied. Five surface modifications were analyzed: two acid etchings (op V, op N), acid etching + anodic oxidation (op NT), sandblasting + acid etching (SLA), and machined surfaces (mach). The corrosion behavior of the surface modifications was evaluated by following the standard ANSI/AAMI/ISO 10993-15:2000. Cyclic potentiodynamic and potentiostatic anodic polarization tests and ion release by ICP-OES after immersion for 7 days in 0.9% NaCl were carried out. Microbiologically induced corrosion (MIC) of low and high roughness (mach, op V) was assessed in situ by electrochemical techniques. Streptococcus mutans bacteria were resuspended in PBS at a concentration of 3 × 108 bacteria mL-1 and maintained at 37°C. MIC was measured through the open circuit potential, Eoc , and electrochemical impedance spectroscopy from 2 to 28 days. Potentiodynamic curves showed the typical passive behavior for all the surface modifications. The titanium ion release after immersion was below 3 ppb. In situ bacteria monitoring showed the decrease in Eoc from -0.065 (SD 0.067) Vvs. Ag/AgCl in mach and -0.115 (SD 0.084) Vvs. Ag/AgCl in op V, to -0.333 (SD 0.147) Vvs. Ag/AgCl in mach and -0.263 (SD 0.005) Vvs. Ag/AgCl in op V, after 2 and 28 days, respectively. A reduction of the oxide film resistance, especially in op V (54 MΩcm2 and 6 MΩcm2 , after 2 and 28 days, respectively) could be seen. Streptococcus mutans negatively affected the corrosion resistance of titanium. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 997-1009, 2018.

Independence of EPR and PAP tests performed on resistance spot welding joints

ABSTRACTIn the present paper, the possible relationships among the variables of the potentiodynamic anodic polarisation (PAP) test and the electrochemical potentiokinetic reactivation (EPR) test, both performed on resistance spot welding joints of AISI 304 stainless steel, are investigated. Results show that PAP variables are statistically independent from those of EPR, which implies independence between the pitting corrosion behaviour and the degree of sensitisation of the material. Parameters from PAP test are dependent among them, but this association is found noisy since the current density along the passive zone is not exactly constant. The parameters from the EPR test are confirmed as very related, presenting a linear relationship and a high coefficient of determination.

Effect of Solution Annealing on Microstructure Evolution and Pitting Corrosion Resistance of SAF2906 Super Duplex Stainless Steel

The effect of solution annealing on the microstructure evolution and pitting corrosion resistance of SAF2906 super duplex stainless steel has been investigated. The samples are solution treated from 850 to 1100 °C for 30 min and then water quenched to room temperature. The results show that static recrystallization preferentially occurs within the δ ferrite phase at 900 °C, and the static recrystallization of the ferrite and austenite phases is completed at 1050 °C. When samples aere exposed to higher temperatures, the grain of the ferrite and austenite does not seem to coarsen. Inappropriate annealing at temperatures below 1050 °C inevitably lead to many secondary phases, which are characterized by transmission electron microscopy to be Cr2N and the σ phase. With an increase in the solution temperature, the σ phase dissolved into the matrix before Cr2N, and as the temperature reached 1050 °C, no secondary phases can be observed by scanning electron microscopy. The pitting corrosion resistance of the samples after solution annealing is determined by anodic polarization tests. The electrochemical results show that the σ phase and Cr2N decreased the pitting corrosion resistance and that the σ phase had a more significant effect on the corrosion resistance compared with Cr2N.

The Influence of Crystallographic Texture and Niobium Stabilisation on the Corrosion Resistance of Ferritic Stainless Steel

The objective of this work is to investigate the influence of the crystallographic texture on the corrosion resistance of 16% Cr ferritic stainless steel. Samples of ASTM S43000 ferritic stainless steel, both niobium-stabilised and non-stabilised, were used. The samples were subjected to crystallographic characterisation (EBSD) and analysed using an inverse pole figure (IPF) and a crystalline orientation distribution function (CODF). The samples also underwent anodic potentiodynamic polarisation tests (deaeration by high-purity argon gas) in 3.56% NaCl and 1N H2SO4 solutions, and the surface was examined by SEM after the tests. The results showed a clear influence of the crystallographic texture on the corrosion resistance. The niobium decreases the amount of the preferred orientation and thus the influence of the texture on the corrosion resistance, although the corrosion resistance of the stainless steel is increased as niobium carbides are formed.