Pitting Corrosion Resistance Research Articles

Corrosion Resistance of Low-Temperature and Conventional Plasma-Nitrided 410S Ferritic-Martensitic Stainless Steels

Abstract Low-temperature plasma nitriding (LTPN) of 410S ferritic-martensitic stainless steel was carried out in a 75 % N2 – 25 % H2 gas mixture, at 400°C, for 20 h. Conventional plasma nitriding (CPN) was also carried out in the same atmosphere but at 530°C. The corrosion resistance was assessed by potentiodynamic polarization (PP) testing in 3.5-wt. % NaCl. Measuring of the mass loss was carried out after immersion of the specimens in a 3 % FeCl3 solution during 88 h. To define the sensitivity to intergranular corrosion, the degree of sensitization (DOS) was measured using the double-loop electrochemical PP technique (DL-EPR). DL-EPR results indicated that the potentiodynamic-polarization measurements showed that pitting corrosion resistance of the nitrided samples was enhanced, whereas the weight loss experiments showed that LTPN samples presented a corrosion resistance equal to the untreated samples. The DOS results displayed that the untreated samples were less resistant to intergranular corrosion correlated with the LTPN specimens. On the contrary, the CPN specimens exhibited typical behavior of general corrosion.

Effects of Microstructure and Material Composition on the Formation Kinetics of Passive Film and Pitting Behavior of Super 13Cr Stainless Steel

The effects of the microstructure and material composition on the formation kinetics of passive film and pitting behavior of super 13Cr stainless steel (S13Cr SS) were investigated and compared with those of 2Cr13 stainless steel (2Cr13 SS). The results indicated that the passive film formed on S13Cr SS surface quickly reached a stable state, which was attributed to two reasons. The small grain size coupled with the high dislocations density increased the number of nucleation sites for passive film formation, and the high material composition enhanced the Cr and Mo compound contents in the passive film. The passive film on S13Cr SS was more compact and thicker than that on 2Cr13 SS. The pit depth on S13Cr SS was relatively shallow after potentiodynamic polarization. Therefore, the protective properties of the passive film on S13Cr SS increased, and the pitting corrosion resistance of S13Cr SS was enhanced.

Influence of Aging Heat Treatment on Pitting Corrosion Resistance of Martensitic Stainless Steel

In this research is to study the influence of the aging heat treatment on the pitting corrosion resistance of martensitic stainless steel (MSS), where a number of specimens from martensitic stainless steel were subjected to solution treatment at 1100 oC for one hour followed by water quenching then aging in the temperatures range (500-750) oC for different holding times (1,5,10,15&20) hr. Accelerated chemical corrosion test and immersion chemical corrosion test were performed on samples after heat treatment. The results of the research showed that the pitting corrosion resistance is significantly affected by the aging temperature. Where found that the aging samples at a temperature of 500 °C have the highest rate of corrosion which may be due to an increase in the ratio of the Delta type ferrite (δ-ferrite) and very soft precipitates from other phases of heterogeneous form in the basic martensitic phase; which leads to increased corrosion rate, whereas aging samples in the temperature range (550–650) °C have the smaller rate of corrosion values, this is due to the high volumetric ratio of remaining austenite. The aging samples at temperatures above 650 °C show an average corrosion rate. It was also found that the type of pits resulting from both the chemical corrosion tests and their shape were not related to the ferrite type and the carbides present in the microstructure

Pitting Corrosion of Biomedical Titanium and Titanium Alloys: A Brief Review

Thanks to their excellent corrosion resistance, superior mechanical properties and good biocompatibility, titanium (Ti) and Ti alloys are extensively applied in biomedical fields. Pitting corrosion is a critical consideration for the reliability of Ti and Ti alloys used in the human body. Therefore, this article focuses on the pitting corrosion of Ti and Ti alloys, which introduces the growth stages of pitting corrosion and its main influencing factors. Three stages, i.e. (1) breakdown of passive film, (2) metastable pitting, and (3) propagation of pitting, are roughly divided to introduce the pitting corrosion. As reviewed, corrosive environment, applied potential, temperature and alloy compositions are the main factors affecting the pitting corrosion of Ti and Ti alloys. Moreover, the pitting corrosion of different types Ti alloys are also reviewed to correlate the types of Ti alloys and the main factors of pitting corrosion. Roughly speaking, β-type Ti alloys have the best pitting corrosion resistance among the three types of Ti alloys.

Comparative studies on microstructure evolution and corrosion resistance of 304 and a newly developed high Mn and N austenitic stainless steel welded joints

Welding has a negative effect on the corrosion resistance of both 304 and newly developed steel (QN1803). Microstructure observation and element distribution analysis found that, due to the existence of nitrogen loss and the retardation of manganese on phase transition, the fusion zone (FZ) of the QN1803 has more δ-ferrite residual than that of 304, causing more serious element segregation. Therefore, QN1803 FZ has lower pitting corrosion resistance than base metal. In terms of intergranular corrosion, nitrogen promotes the formation of precipitates, so the weight loss rate of QN1803 weldments is higher than that of 304 weldments in immersion tests.

Pitting resistance of 316 stainless steel after laser shock peening: Determinants of microstructural and mechanical modifications

• Grain refinement was avoided through modified LPwC. • Compressive residual stress after LSP reduces the metastable pitting rate. • Microdefects induced by LSP dominate the growth of metastable pits. • Adjacent metastable pits combine easily to transform into a stable pit after LSP. Laser shock peening (LSP) was performed on a 316 stainless steel for microstructural and mechanical modifications. To identify the dominant factor controlling pitting corrosion resistance, a single LSP impact was performed and various characterization techniques, such as scanning electron microscopy, X-ray diffraction, transmission electron microscopy, electron backscattered diffraction, microhardness and residual stress analysis were conducted. The results show that a considerable increase in the microdefects, microhardness, and compressive residual stress occurred at a depth of ∼200 μm from the surface, while no evident grain refinement was observed. The compressive residual stress reduced the metastable pitting nucleation rate. However, microdefects after LSP treatment resulted in larger metastable pits, which are more likely to combine to transform into a stable one. It is summarised that the substantial microdefects can deteriorate the superiority of compressive residual stress induced by LSP in the pitting resistance of 316 stainless steel.

Effects of nitrogen element on microstructure and pitting corrosion resistance of duplex stainless steel welded joints

The microstructure, element distribution and pitting corrosion resistance of Gas Tungsten arc welding (GTAW) duplex stainless steel welded joints under 100% argon (Ar) and 98% Ar + 2% nitrogen (N2) shielding gas were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrochemical corrosion methods. These results show that the addition of N2 to the shielding gas promotes the formation of austenite (γ) phase in the weld joint. Also, the austenite phase distribution is dendritic and the ferrite (δ) and austenite phases in the heat-affected zone are no longer banded structures. Moreover, the austenite phase in the welded joint is enriched in nickel (Ni) and nitrogen (N) elements, while the ferrite phase is enriched in chromium (Cr) and molybdenum (Mo) elements. The pitting corrosion index (PREN) of the austenite/ferrite (δ/α) phase boundary is lower than that of δ and γ phases, which leads to their preferential corrosion. The appearance of chromium nitride (Cr2N) decreases the corrosion resistance of the weld seam and the heat affected zone. N2 in the 98% Ar + 2% N2 shielding gas can restrain Cr2N precipitation, increase the pitting corrosion index of secondary austenite structure (γ 2), and improve the pitting corrosion resistance of welded joints.

Microstructure evolution and corrosion mechanism of laser cladded Zr-Cu-Ni-Al in-situ metallic glass matrix composite coatings

Laser cladding provides a widely applicable method for the preparation of metallic glass matrix composite (MGMC) coatings, where the mechanical property and the corrosion resistance can be tailored by the in-suit precipitated crystalline phases. Thus, the investigation on the microstructure evolution and corrosion mechanism of MGMC coating to achieve superior performance is of great importance. In the presented work, Zr50.7Cu28Ni9Al12.3 MGMC coatings, which are constituted by Zr&Cu enriched dendrites and Ni&Al enriched metallic glass (MG) matrix, were prepared by laser cladding. The effect of the laser power on the microstructure and the corrosion property of the MGMC coatings was investigated. It has been found that the MG content increases and the size of the dendrites decreases with decreasing laser power. Increasing MG content in the coating can decrease the self-etching current density due to the rapid surface oxidation, and decrease the open-circuit-potential due to the higher chemical activity of MG. Besides that, a probable corrosion mechanism of the Zr-Cu-Ni-Al MGMC coating in the NaCl solution was proposed. The segregation of Cu could be the main inducement for pitting. The increasing MG phase content can suppress the segregation of Cu and therefore increase the pitting corrosion resistance of the coating.

Improvement of Wear, Pitting Corrosion Resistance and Repassivation Ability of Mg-Based Alloys Using High Pressure Cold Sprayed (HPCS) Commercially Pure-Titanium Coatings

In this study, a compact cold sprayed (CS) Ti coating was deposited on Mg alloy using a high pressure cold spray (HPCS) system. The wear and corrosion behavior of the CS Ti coating was compared with that of CS Al coating and bare Mg alloy. The Ti coating yielded lower wear rate compared to Al coating and Mg alloy. Electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization (CPP) tests revealed that CS Ti coating can substantially reduce corrosion rate of AZ31B in chloride containing solutions compared to CS Al coating. Interestingly, Ti-coated Mg alloy demonstrated negative hysteresis loop, depicting repassivation of pits, in contrast to AZ31B and Al-coated AZ31B with positive hysteresis loops where corrosion potential (Ecorr) > repassivation potential (Erp); indicating irreversible growth of pits. AZ31B and Al-coated AZ31B were most susceptible to pitting corrosion, while Ti-coated Mg alloy indicated noticeable resistance to pitting in 3.5 wt % NaCl solution. In comparison to Al coating, Ti coating considerably separated the AZ31BMg alloy surface from the corrosive electrolyte during long term immersion test for 11 days.

Friction surfacing of AISI 904L super austenitic stainless steel coatings: Microstructure and properties

Microstructure, texture, pitting corrosion resistance and hardness of surfaces and cross-sections of the friction-surfaced (FSed) super austenitic stainless steel 904L coatings fabricated at various spindle speeds were investigated. The microstructure of the coatings was governed by both dynamic recovery (DRV) and continuous dynamic recrystallization (cDRX) owing to the high stacking fault energy (SFE) of 904L. The grain orientations in DRV were in A 2 ⁎ shear texture component, while the rotated cube textures were related to the cDRXed grains. Immersion tests of the FSed coatings in 3.07 mol/L Cl − solution showed that the corrosion pits were slightly preferred to generate at the {111} DRVed grains on the coating surfaces, since these grains were likely to have a higher elastic strain during FS. Compared with AISI 304, the pitting potential of the FSed coatings in 3.5 wt% NaCl solution was significantly shifted to nobler direction and also insensitive to spindle speed owing to the high SFE of 904L. However, the passive films of the FSed coatings were thinner and more difficult to reform, as evidenced by slightly larger average pit diameters and lower protection potentials owing to the high residual stress caused by FS. • Microstructures of FSed 904L coatings were governed by DRV in A 2 ⁎ shear component and cDRX in rotated cube textures. • Increment of spindle speed tended to enhance cDRX but suppress DRV at the same time. • The FSed coatings could maintain excellent pitting corrosion resistance of as-received 904L. • Due to high SFE of 904L, elastic strain in {111} grains was reduced. • Crystallographic effect on pitting cororsion resistance of the coatings was weakened. • Increase in misorientation density induced by cDRX led to hardness improvement and ductility reduction for the coatings

Corrosion Characteristics of TiNbMoMnFe High Entropy Thin Film Deposited on AISI316L for Biomedical Applications

High entropy alloys (HEAs) have received tremendous attention in different applications because of their excellent corrosion resistance and superior mechanical properties. In the present work, a novel TiNbMoMnFe high entropy alloy system was synthesized and deposited on AISI 316L by DC magnetron sputtering system. The microstructure of the resulting thin film was evaluated by grazing incidence X-ray diffraction and field emission electron microscope. It was found that the thin film microstructure is composed of a crystalline solid solution (grain size of 76 nm) and an amorphous phase. The electrochemical investigations in Ringer’s solution revealed that a thin film of 670 nm thick high entropy alloy has a low corrosion current density of 0.024 μA cm−2, approximately 30% lower than that of the uncoated 316L. Meanwhile, the HEA thin film showed the highest pitting corrosion resistance and stability of the passive film. The wettability examinations exhibited that the coated sample has a high contact angle of 90° in contrast to 60° for the uncoated ones. In summary, the TiNbMoMnFe high entropy alloy thin film shows great potential for use in biomaterial applications.

Microstructure and Pitting Corrosion Resistance of Quenched, Single Tempered and Double Tempered AISI 420 Martensitic Stainless Steel

Abstract The crystallographic aspects after air-quenching treatment and the pitting corrosion resistance after single tempering and double tempering treatments of AISI 420 martensitic stainless steel were studied using optical microscopy, Electron Backscatter Diffraction and potentiodynamic polarization tests. The results showed that the observed average orientation relationship (OR) was closer to the Greninger-Troiano (G-T) OR model with a minimum average deviation of 2.66°. The average OR of AISI 420 steel with respect to austenite matrix was φ1 = 3.6°, Φ = 46.0°, φ2 = 6.2° in the area mapped. Blocks showed variant pairs belonging to the same Bain group forming sub-blocks with misorientation 5.51° (V1/V4 pair), consequently, the AISI 420 martensitic stainless steel showed higher intervariant boundary density for the same Bain group and close-packed plane group. In the same air-quenching condition, the different sizes of prior austenite grain in the microstructure did not influence the variant selection. The air-quenching and single tempering treatments did not impair the pitting corrosion resistance and did not cause significant loss of hardness in relation to the air-quenched treatment. Therefore, the double tempering should be dispensed saving production costs.

Relationship between pitting corrosion resistance and Cr-depleted zone in duplex stainless steel weld metals

Relationship between pitting corrosion resistance and Cr-depleted zone in duplex stainless steel weld metals

Effects of Laser Glazed Surface on Pitting Corrosion of Nickel Alloy 718 in Acidic and Seawater Environments

Studies on the effects of laser glazed and unglazed sample surfaces on the pitting corrosion resistance of nickel alloy 718 have been carried out. Both sample surfaces of nickel alloy 718 were cut to different dimensions for pitting corrosion tests using potentiostatic polarization process. The alloy samples used for electrochemical testing were connected to a flexible wire joined by spot weld process. The alloy samples were coated with low viscous polymeric wax leaving the surface areas to be tested exposed to seawater and one mole concentration of hydrochloric acid environments. These samples which are working electrodes have electrical connection between reference electrode and counter electrode and the entire system were connected to computer with PSTrace software that stands as potentiostat. Pre and post morphological examination of the sample surfaces were done using confocal laser scanning microscopy and scanning electron microscopy respectively. The results of pitting corrosion tests showed that the glazed and unglazed alloy sample surfaces immersed in seawater environment suffered from pitting corrosion as a result of the presence of pit initiation sites developed during surface laser treatment and also the presence of some aggressive anions like Cl^-, SO₄^- etc in the environment which migrated into the pits due to electrostatic balance and escalated pitting corrosion; while the samples of both surfaces immersed in 1MHCl suffered more from general corrosion. Post pitting corrosion examinations revealed that corrosion oxide films formed on the sample surfaces in acidic and alkaline environments were not protective as they flaked and exposed the sample surfaces to more corrosion attack.

Effect of heat treatment on the microstructure and corrosion properties of cast duplex stainless steels

The effect of the quenching temperature on the pitting corrosion resistance of lean duplex stainless steel (DSS) were examined. Using thermodynamic modeling of phase formation processes in steel during solidification and subsequent cooling was shown that the equal amount of austenite and ferrite is achieved at 1210°С for examined composition. Experimental steel samples were quenched from 1100 and 1200°С. It was found that as the temperature rises, the pitting potential increases significantly due to the achievement of a favorable phase ratio. The results of this experimental study made it possible to develop a heat treatment that provides high corrosion properties of lean DSS.

Comparison Between Stainless Steels and Nickel Alloys Through Pitting Corrosion Resistance Electrochemical Tests

Critical pitting temperature (CPT) is one of the most accepted criteria for alloy classification concerning pitting corrosion. The techniques used nowadays to determine CPT have different parameters for alloys of different material classes, preventing the comparison between stainless steels and nickel based alloys. This study aims to compare the corrosion resistance of nickel based alloys and stainless steels with high corrosion resistance through potentiostatic tests for CPT determination, using a 3M MgCl2 aqueous solution. CPT values were effectively determined for the stainless steels studied but the technique did not have the same efficiency for nickel based alloys due to the occurrence of crevice corrosion, even considering the higher PRE of nickel based alloys.

Microstructure and Pitting Corrosion Resistance of Titanizing Coating Prepared by Pack Cementation on 316L Stainless Steel

Microstructure and Pitting Corrosion Resistance of Titanizing Coating Prepared by Pack Cementation on 316L Stainless Steel

Micro-electrochemical Properties and Pitting Corrosion Resistance of Microstructures of Carbon Steels

Micro-electrochemical Properties and Pitting Corrosion Resistance of Microstructures of Carbon Steels

Interstitial nitrogen enhances corrosion resistance of an equiatomic CoCrNi medium-entropy alloy in sulfuric acid solution

The corrosion resistance of the equiatomic CoCrNi medium-entropy alloy (MEA) and its 0.5 atomic % nitrogen alloyed variant in 0.1 M H2SO4 solution was investigated and compared with that of the 316 L stainless steel as a reference material. All of the investigated materials showed single-phase face centered cubic (FCC) microstructures, and nitrogen was fully dissolved in the solid solution structure of the CoCrNi MEA. Both the nitrogen-free and nitrogen-doped MEAs showed significantly higher corrosion resistance (lower corrosion currents and rates) than the 316 L steel. Compared to the nitrogen-free CoCrNi, the interstitial nitrogen dissolved in solid solution causes a significant improvement in the pitting corrosion resistance of the CoCrNiN. Under the same testing condition, pitting corrosion was not observed in the CoCrNiN alloy, while the CoCrNi MEA and 316 L steel showed distinct pitting cavities. The better anti-corrosion performance of the CoCrNiN compared to that of the CoCrNi is correlated with a higher fraction of chromium oxide in the passive films.

Al0.3CrxFeCoNi high-entropy alloys with high corrosion resistance and good mechanical properties

The effects of the Cr content on microstructure, corrosion behavior, and mechanical properties of the Al0.3CrxFeCoNi high-entropy alloys (HEAs) were studied. The Al0.3CrxFeCoNi alloys with x = 0–1.0 exhibited the single face-centered-cubic (FCC) structure, and the alloys with x = 1.5–2.0 consisted of the FCC and disordered body-centered-cubic (BCC)/ordered BCC (B2) structure. In the 3.5 mass% NaCl solution, the Al0.3CrxFeCoNi alloys are spontaneously passivated, and the pitting resistance of the alloys was improved with increasing the Cr content in the alloys. It is notable that the Al0.3CrxFeCoNi (x = 1.5–2.0) alloys with Cr-rich FCC and BCC phases demonstrated excellent pitting-corrosion resistance and low corrosion rates of less than 10−3 mm/year due to the formation of the protective surface films enriched in Cr2O3. Moreover, the Al0.3CrxFeCoNi (x = 0–1.0) alloys with the FCC structure exhibited relatively-low tensile strength and large elongation. The further increase in the Cr content to x = 1.5–2.0 improved the strengths and hardness of the alloys due to the increase in BCC/B2 phases. The Al0.3CrxFeCoNi (x = 1.5–2.0) alloys with high corrosion resistance presented good mechanical properties, including tensile strengths of 640–1078 MPa and tensile elongations of 11–44%. It is also demonstrated that increasing the Cr content of Al–Cr–Fe–Co–Ni HEAs is an effective approach for tailoring corrosion-resistant HEAs.