Pitting Corrosion Resistance Research Articles

The effect of heat treatment on microstructure, microhardness, and pitting corrosion of Ti6Al4V produced by electron beam melting additive manufacturing process

There has been limited studies on corrosion behaviour of post-processed electron beam melted (EBM) Ti6Al4V, given that the factors affecting corrosion resistance of AM Ti6Al4V remain unclear. This paper proposes using heat treatment method to improve the pitting corrosion resistance of EBM Ti6Al4V. Different treatment profiles alter the microstructure of EBM Ti6Al4V. A clear trend is observed between microhardness and α lath width. As-printed EBM Ti6Al4V exhibits an inferior pitting potential, while heat treatment provided a significant improvement in the corrosion resistance. This study finds that the β phase fraction is a better indicator than the α lath width for pitting corrosion resistance. Solution air-cooled and ageing heat-treated EBM Ti6Al4V exhibits good mechanical and corrosion properties, and even performs better than commercial cast Ti6Al4V.

Effect of Repeated Repair Welding on the Mechanical Properties and Pitting Corrosion Resistance of Super Duplex Stainless Steel

The study investigated the effect of repeated repair welding on the mechanical properties and pitting corrosion resistance of 25% Cr super duplex stainless steels (UNS S32750). The test coupons were prepared by gas tungsten arc welding (GTAW) with ER2594 filler metal and repaired 3-times at the same weld locations, where the remaining previous welds were 2-3 mm in depth. The number of repairs provided various reheating to the original welds (as-welded condition) and to the previously repaired welds. The effect of repair welding reheating on the microstructure, ferrite content, hardness, impact toughness and pitting corrosion was investigated. The pitting corrosion occurred in the root region of the first repair weld (R1). Secondary phases such as austenite (γ2) and sigma (σ) were observed in the reheated regions with a consumption of ferrite content, where impact toughness and pitting corrosion resistance were significantly reduced. The vicinity of the pitting corrosion region was analyzed, and showed that sigma (σ) was precipitated in the secondary austenite (γ2) and at the boundary between ferrite and austenite. The fraction of the sigma phase was determined by electron back scatter diffraction (EBSD) to be 0.3% in the vicinity of the pitting corrosion region. This study also discusses the applicability of 3-times repair welding in the offshore industry.

Understanding the nature of passivation film formed during corrosion of Fe39Mn20Co20Cr15Si5Al1 high entropy alloy in 3.5 wt% NaCl solution

In metallic materials, the nature of passivation film plays an important role in governing corrosion behavior. The present work focuses on a detailed analysis of the passivation film characteristics of a transformation induced plasticity Fe39Mn20Co20Cr15Si5Al1 (at%) high entropy alloy (HEA) in 3.5 wt% NaCl solution at room temperature. The characteristics of the passivation film were assessed using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The microstructural analysis of the alloy achieved using electron backscattered diffraction revealed that it consisted of two different phases: γ phase (face-centred cubic crystal) and ε (hexagonal closed pack), with the area fraction of ε phase being 96.5%. The electrochemical experiments showed that the HEA maintained excellent uniform corrosion resistance but low pitting corrosion resistance. The scanning electron microscopy revealed deep pits covered with perforated layers, and the average pit size and pit depth was determined to be 202.8 µm and 168 µm, respectively. The EIS revealed a bilayer type of passivation film formations at different voltages. For the passivation film grown at −0.1 V, the upper layer film thickness was 2.08 nm and the inner layer film thickness was 3.14 nm. For the passivation film grown at −0.05 V, the upper and inner film thicknesses were 1.78 nm and 3.10 nm. The passivation film resistance was found to be one order of magnitude higher for the passivation films grown at −0.1 V and −0.05 V than that for the naturally grown passivation film. The XPS of the sample that corroded during the potentiodynamic polarization test revealed that the passive layer contained Fe, Mn, Co, Cr, Si, and O elements as metal oxides and hydroxides with Mn and Cr based chemical species present as dominant species. Their oxidation states were estimated to be present as Fe2+, Fe3+, Mn3+, Co2+, Cr3+, Si4+, O2-, and OH1- along with their corresponding metallic states. According to the proposed corrosion mechanism, a bilayer type of passivation film forms on the alloy. The film’s upper layer is rich in Mn and Cr and the inner layer is devoid of Mn and Cr. The detection of two particles in the same pit with two different chemical compositions seems to corroborate the formation of a bilayer passivation film and its chemical compositions.

Cast High-Strength Wear- and Corrosion-Resistant Austenitic Nitrogen Steel for Fittings Used in Shipbuilding

The paper presents the results of studies of a new cast high-strength austenitic corrosion-resistant steel, which can be successfully used in shipbuilding for the manufacture of fittings. The authors included data on the structural-phase state of steel, the results of evaluating the mechanical properties, wear and corrosion resistance of the metal of castings in the cast and heat-treated state. The mechanical properties of steel are considered in detail in a wide temperature range. The impact strength was considered at low temperatures and static strength at 20 to 350 ° C. It is shown that steel has higher mechanical and corrosive properties in a wide temperature range than those of traditional stainless steels. The corrosion resistance of steel is considered. This is intergranular and pitting corrosion; the main types of corrosion are peculiar for shipbuilding. It has been shown that cast steel is superior to traditional corrosion-resistant steels in pitting corrosion resistance estimated by the pitting coefficient PREN and the critical temperature of pitting. The new cast steel has the same wear resistance as Hadfield steel.

High-Temperature Heat-Treatment at 1673 K: Improvement of Pitting Corrosion Resistance at Inclusions of Type 304 Stainless Steel under Applied Stress

MnS inclusions in Type 304 stainless steel were mainly transformed into oxide/oxysulfide inclusions by heat-treatment at 1673 K. In 0.1 M MgCl2 under both the no-stress and stress conditions, the pitting potential of the steel heat-treated at 1673 K was higher than the steel heat-treated at 1373 K. The pitting potential of the stainless steel heat-treated at 1673 K did not decrease due to applied stress. For the steel heat-treated at 1673 K, the dissolution current of oxide/oxysulfide inclusions was lower than that at MnS inclusions. The results show no significant decrease in the pitting potential of the steel heat-treated at 1673 K even under applied stress.

Plasma processing of Fe-P/rGO powder for making robust wear resistance and anticorrosion coating over mild steel

Phosphating is a widely used metal pre-treatment process due to its ability to improvise pitting corrosion resistance, wear-resistance, and adherence properties. In the present investigation, we report the manufacturing of spray grade powder of Fe-P metal ingot by mechanical hammering, milling and sieving process. The Fe-P powder and its blending with reduced graphene oxide (rGO) (2 and 4 vol%) were successfully coated over mild steel by the thermal plasma spray method for the first time. Successful retention of rGO was observed even after thermal plasma spraying of Fe-P/rGO (2 vol% and 4 vol%), which was challenging and yet to be reported. The morphological investigation of the top-coat layer and cross-section was analysed using a field emission scanning electron microscope (FESEM). The presence of G, D and 2D bands at 1580 cm−1, 1350 cm−1, and 2700 cm−1, respectively in the Raman spectra were the straightforward demonstration of the retention of rGO. Hardness and air-jet erosion tests were performed to evaluate mechanical properties in view of exploring commercial applications of such coatings. We found that Fe-P-rGO composite coatings exhibited improved hardness, erosion, and corrosion resistance properties with increasing reduced graphene oxide content.

Effect of thermally induced B2 phase on the corrosion behavior of an Al0.3CoCrFeNi high entropy alloy

The corrosion resistance of Al-Co-Cr-Fe-Ni high entropy alloys (HEAs) is probably affected by B2 phases. In this paper, the effect of B2 phases on the corrosion behavior of Al0.3CoCrFeNi HEAs in 3.5 wt% NaCl solution is clarified in this paper by purposely controlling the formation of B2 phases using annealing treatment. The microstructure characterization reveals that the content of (Al, Ni)-rich and Cr-poor B2 phases increases and the electrochemical measurements show that the pitting corrosion resistance is deteriorated as the annealing temperature decreases. Accordingly, the B2 phase is confirmed to be detrimental to the corrosion resistance of Al0.3CoCrFeNi HEAs. It can be attributed to the preferential dissolution of B2 phases causing easier pit initiation, which is evidenced by the corrosion morphology observation and scanning Kelvin probe force microscopy measurements, and to the slower repassivation rate leading to easier pit propagation, as demonstrated by the quantitative analysis of potentiostatic polarization curves.

Enhancement of electrical conductivity and corrosion resistance by gold-nickel coating of additively manufactured AlSi10Mg alloy

Gold-nickel coatings (Au–Ni) were applied by electrodeposition (ED) and electroless deposition (ELD) on additively manufactured (AM) AlSi10Mg alloy to improve the electrical conductivity and electrochemical behavior. Characterization of the Au–Ni coatings was performed by a scanning electron microscope equipped with energy dispersive X-ray spectroscopy (EDS) and x-ray diffraction to study the tiny features. The surface indentation hardness of the coated alloy was evaluated to study the coating strength. The electrochemical behavior of the as-built part and its counterpart, Au–Ni coated surfaces, were evaluated by conducting potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution.The results revealed that the Au–Ni coatings with layers thickness of ∼2 and 10 μm, respectively, could overcome the surface critical defects, i.e., pores and flaws. The surface hardness of the coated AM alloy has significantly increased six times due to the hard Ni layer. The electrochemical measurements showed a significant decrease in the anodic dissolution rate and increase in pitting corrosion resistance for the Au–Ni coated surfaces compared to the bare AM AlSi10Mg alloy with the as-built and polished surface condition in chloride solution. This was attributed to the stability of the Au–Ni coatings against the anodic overpotential. Moreover, it was observed that the Au–Ni coatings reduce the electrical resistance of the studied AM alloy by 40%. Consequently, the surface electrical conductivity property of the AM AlSi10Mg alloy was enhanced by both Au–Ni coating procedures.

Improvement of Pitting-Corrosion Resistance of Ultrafine-Grained 7475 Al Alloy by Aging.

The effect of aging on the resistance to pitting corrosion of ultrafine-grained 7475 aluminium (Al) alloy processed by hydrostatic extrusion (HE) is studied. Differences in the microstructure were investigated using secondary electron (SEM) and transmission electron microscopy (TEM). Corrosion tests were performed in 0.1 M NaCl, and characterization of corroded surface was performed. The results of this work show that the pitting susceptibility of ultra-fine grained 7475Al is related to the distribution of MgZn2 precipitates. After HE, the formation of An ultrafine-grained microstructure at the grain boundaries of ultrafine grains is observed, while subsequent aging results in the formation of MgZn2 precipitates in the grain interior. Grain refinement increases susceptibility to localized attack, while the subsequent aging improves the overall corrosion resistance and limits the propagation of corrosion attack.

Corrosion of austenitic stainless steels and nickel-based alloys in concentrated phosphoric acid at elevated temperatures

The corrosion sensitivity of several austenitic stainless steels (316L, 316Ti, Sanicro28, Sanicro35) and nickel-based alloys (Hastelloy G30 and Hastelloy G35) was determined at elevated temperatures in food grade phosphoric acid (FGPA). The materials were submerged in a harsh environment of >85 wt% FGPA at temperatures ranging from 80 to 160°C. The main aim was to understand the corrosion phenomena occurring in such environment and define the temperature range for which corrosion is within acceptable limits for these materials. Moreover, the role of a material's chemical composition on the corrosion resistance in phosphoric acid was experimentally elucidated. The corrosion sensitivity was determined by weight loss measurements, scanning electron microscopy and energy dispersive X-ray spectroscopy. The high concentrations of alloying elements in the selected metals allow them to form a protective passive surface film, which inhibits further oxidation. Depending on the stability of the passive film, materials will be corrosion resistant up to higher temperatures. Alloys with an increased molybdenum content showed a higher general and pitting corrosion resistance up to 140°C. Moreover, copper alloying resulted in an improved corrosion resistance at higher temperatures.

Microstructure and its Effect on Pitting Corrosion Resistance of a New Fe-Cr-Mn-Al Duplex Stainless Steel

Microstructure and its Effect on Pitting Corrosion Resistance of a New Fe-Cr-Mn-Al Duplex Stainless Steel

A study on the physicochemical properties of surface modified Ti13Nb13Zr alloy for skeletal implants

As it is widely stated in the literature, biofilms are responsible for most chronic infections, which have grown exponentially over the past three decades. The use of so-called alloys, as a new generation of materials, enables us to find the golden mean in the arena widely known as implantology. The use of the surface layer, using the chosen Atomic Layer Deposition method, is to be the basis for minimizing the risk of an organism reactions. Therefore, the primary objective of this study was to observe the impact of physicochemical properties of the surface layers (bactericidal) on the processes that occur on the implants surface made of titanium biomaterials used in bone structures. The study also attempted to evaluate the physicochemical properties of the ZnO coatings, deposited on the substrate of one of the new generation Ti13Nb13Zr alloys, using the ALD method. Included in the assessment of the physicochemical properties of the surface layers formed in this manner, we perform pitting corrosion resistance tests, scratch tests, tribological tests and surface wettability tests. Based on the obtained data, the differing physicochemical properties of the alloy with ZnO coatings are found to be dependent on the applied surface modification. For the conducted tests, differences are determined for the tests on the corrosion resistance, surface wettability and the abrasion resistance for samples with and without the ZnO coating. In addition, tests show that the coating applied to the alloy, which is previously subjected to the sand-blasted process, is characterized by improved adhesion.

New insights into the hardening and pitting corrosion mechanisms of thermally aged duplex stainless steel at 475 °C: A comparative study between 2205 and 2101 steels

• Ferrite hardening is caused by α'-α phase separation. • In LDSS 2101, Cr nitrides impact pitting corrosion more than α'-evolution. • G-phase contributes to a decrease in pitting corrosion in long-term aging. • Spinodal decomposition is the main cause of the drop-in pitting corrosion of DSS 2205. In this study, the relationship between spinodal decomposition and the formation of Ni-rich clusters and G-phase in the ferrite on hardening and pitting corrosion of two thermally aged duplex stainless steels (DSSs) at 475 °C was investigated. Results indicate that, for 2205 DSS, pitting corrosion behavior is influenced by the presence and size of G-phase precipitates for longer aging times, but this contribution is masked by the advanced stage of spinodal decomposition in the ferritic structure. On the other hand, for 2101 DSS, the formation of Cr-richer nitrides impairs pitting corrosion resistance more than spinodal decomposition.

Role of nitrogen shielding environment on microstructure and corrosion behavior of 2205 duplex stainless-steel A-GTA welds

The present study aims to understand the role of the shielding environment viz., argon (Ar) and nitrogen (N2) on microstructure, general and pitting corrosion behavior of activated gas tungsten arc (A-GTA) welds of 2205 duplex stainless steel. A-GTA welds made with activated flux SiO2 along with 100% Ar and 95% Ar + 5 % N2 are compared with conventional gas tungsten arc (C-GTA) welds made with 100% Ar. All the metallographic specimens of C-GTA and A-GTA welds are recorded to observe the microstructural changes using an optical microscope connected with image analyser. The basic GillAC electro-chemical system is used to perform potentio-dynamic polarization studies for general and pitting corrosion behavior in a 1 M NaCl solution. From the present study, it is established that activated-GTA welds with SiO2 flux resulted in reduced weld width and enhanced depth of penetrationachieved in a single pass compared to C-GTA welds. The grain morphology of the weld zone (WZ) is observed to be a mixture of austenite and delta ferrite in all the weldments. Secondary austenite is found in the interior of the ferrite whereas at the interfaces of ferrite and primary austenite, various forms of primary austenite are noticed in the weld zone of A-GTA welds. From the corrosion studies, it is found that A-GTA welds made with 95% Ar + 5 % N2 show higher general and pitting corrosion resistance compared to C-GTA and A-GTA welds made with 100% Ar.Improved corrosion behavior may be due to the favourable microstructure and presence of nitrogen as shielding environment, which favors the formation of austenite in the ferrite matrix.

Improving pitting corrosion resistance of AISI 316L weld overlays via Inconel 82 additions

This work was aimed at improving pitting corrosion resistance of AISI 316L weld overlays by adding layers of Inconel 82, a Ni-based superalloy using gas tungsten arc welding (GTAW) process. Weld specimens were subjected to a thermal aging treatment of 750˚C/24 to induce sensitization into the material. Potentiodynamic scan was performed on the weld samples using potentiostat and paracell arrangement, and testing was performed in accordance with ASTM standard G-5. Poteniodynamic anodic polarization (PAP) testing results show that, hybrid composition 316L welds exhibited higher pitting potential and hence better pitting corrosion performance than the conventional 316L welds, both in the as welded as well as sensitized conditions. Aging decreased the pitting resistance of both the welds which was indicated by their lower pitting potential values but the extent of loss of pitting resistance was relatively lesser in hybrid weld overlays. The present work has a significant potential of being recommended to the welding industry, especially the ones dealing into 316L fabrications, as it is established that addition of Inconel 82 layers is found to beneficial in improving the pitting corrosion resistance of 316L weld overlays.

High wear resistance and better pitting corrosion resistance of AISI 316L stainless steel by a self-protective oxy-nitrocarburizing paste

Simultaneous oxidation and nitrocarburizing of AISI 316 SS at 580 °C for 5, 10, 15, and 20 min were studied using self-protecting pastes of sodium cyanate and sodium carbonate. The analytical techniques of XRD and SEM/EDS allowed the characterization of surface modifications. The corrosion resistance was evaluated in a synthetic seawater solution using the cyclic potentiodynamic polarization technique. The cross-section hardness and wear resistance were assessed by Vickers indentation and pin-on-disc, respectively. This thermochemical process formed an oxidized compound layer above a solid nitrogen solution in austenite. The compound layer was composed of intermixed crystals of Fe3O4, ε-Fe3N, and expanded austenite. With increasing relative proportions of the first two phases and decreasing relative proportions of the third phase with increasing treatment time. The balance between the expanded austenite and the chemical composition of the compound layer improved the hardness, the wear-resistant, and the pitting corrosion resistance of the AISI 316L SS surface simultaneously. Oxy-nitrocarburizing at 580 °C for 10 min allowed the best-localized corrosion resistance. However, the sample oxy-nitrocarburized for 20 min reached a more stable passive zone with the highest wear resistance. Self-protective pastes based on sodium cyanates and carbonates allowed the oxy-nitrocarburizing process to consume less salt than the traditional molten salts.

Benefits of passive element Ti to the resistance of AlCrFeCoNi high-entropy alloy to corrosion and corrosive wear

Wear behaviors of 5-element AlCrFeCoNi and 6-element AlCrFeCoNiTi0.5 high entropy alloys (HEAs) against the Si3N4 ball respectively in 3.5 wt% NaCl and HCl (pH = 3) solutions were investigated. The role of the Ti addition in affecting microstructure, hardness, wear and corrosion of the HEA was analyzed. Results showed that the AlCrFeCoNiTi0.5 exhibited higher hardness, ascribed to the solid solution strengthening and precipitation strengthening. The wear loss of AlCrFeCoNiTi0.5 is markedly lower than that of AlCrFeCoNi under the dry condition against Si3N4 balls of 4 mm and 6 mm in diameter, respectively. The Ti addition also improved the corrosion resistance, especially the pitting corrosion resistance, of the HEA, evidenced by lowered Icorr and Ipit and elevated Rp and Rct. This was attributed to the contribution of Ti in the formation of a more protective passive film, which impeded the point defect transport and passive film breakdown. The surface potential measured by means of atomic force microscopy (AFM) shows a smaller difference between adjacent domains in AlCrFeCoNiTi0.5, which should only result in weak local galvanic coupling. Thus, the Ti addition helps suppress the pitting attack to the HEA. The solutions and size of counterpart ball have large influences on the performance of AlCrFeCoNiTi0.5 during corrosive wear. Efforts are made to clarify the mechanism for the beneficial role of Ti addition in affecting the performance of the HEA during the destructive processes.

The effect of high temperature aging on the corrosion resistance, mechanical property and antibacterial activity of Cu-2205 DSS

The effects of high temperature aging on the corrosion resistance, mechanical property and antibacterial activity of a copper–bearing 2205 duplex stainless steel (Cu-2205 DSS) were investigated. The results from scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and EDS analysis showed that after aging the proportion of γ phase in microstructure was increased and new σ phase and copper-rich precipitates were formed. The mechanical properties including hardness and tensile and yield strengths of the aged Cu-2205 DSS were significantly enhanced compared to the solution-treated Cu-2205 DSS as well as the 2205 DSS. Electrochemical measurements including electrochemical impedance spectroscopy, potentiodynamic polarization curves and potentiostatic polarization scan were performed to evaluate the corrosion behavior of the Cu-2205 DSS. It was found that aging increased the uniform corrosion resistance but had slightly adverse effect on the pitting corrosion resistance. Additionally, the antibacterial performance of aged Cu-2205 DSS was significantly improved compared to the solution treated Cu-2205 DSS, which was attributed to the more release of copper ions from the matrix that killed the bacteria cells and inhibited the biofilm formation on the surface. The above results suggest that Cu-2205 DSS after high temperature aging revealed good mechanical property, antibacterial performance, and corrosion resistance, which will further expand the application of duplex stainless steel in marine engineering fields.

Experimental study on passivation and corrosion performances of pre-rusted steel in simulated concrete pore solution

ABSTRACT The influences of the rust layer on the passivation and corrosion of Q235b carbon steel in simulated concrete pore solution were studied. The differences between the inner and outer rust layer were characterized. Results show that the pre-rusted samples could still reach passive state at high pH condition free of chloride ions. However, the quality of the passive film formed on the pre-rusted steel were dramatically lower than that formed on the fine polished steel. The pitting corrosion resistance of the pre-rusted steel was significantly higher than that of the fine polished steel in the chloride-containing pore solution. The pitting corrosion potential would be further promoted after the elimination of the outer rust layer. The reaction between the hydrogen ions and the rust layer could inhibit the pitting initiation. Furthermore, the consumption of the corrosive agents induced by the rust layer could further retard the area expansion of the pits.

Effect of filler metal combination and post weld heat treatment on pitting corrosion and impact toughness of GTA welded AISI 410 SS joints

The Experimental work was done to investigate the role of pitting corrosion resistance as well as impact toughness behavior of gas tungsten arc welded martensitic stainless steel (AISI 410SS) joints. In this study 6 mm thick cold rolled AISI 410 stainless steel plates were utilized as a base plate. The welding was accomplished by using three different filler materials (Inconel 625, AISI 316 SS, and AISI 410 SS). The effect of post weld heat treatment (PWHT) and different filler materials on the pitting corrosion resistance, impact strength, and metallurgical performance of the GTA welded plates was investigated. The analysis for pitting and impact was studied in two circumstances first in as-received situation and second in PWHT situation.The outcomes formulated from research work indicates that the filler material composition induces the significant variation in the impact toughness along with pitting corrosion resistance of the experimental specimens. The minimum mass loss (1.3818 mg) of Inconel 625 filler welded joint indicates that the maximum resistance of the tested samples against the pitting corrosion. Furthermore, the PWHT helps to enhance the pitting resistance. The maximum impact toughness (average CVN 121.5 J) shown by (WJ-2P) in PWHT condition. The experimental study indicates that the Inconel 625 filler material helps to improve the pitting resistance and impact toughness of the welded specimens in as-received along with PWHT condition.