Wet Corrosion Research Articles

Enhancement in Corrosion Resistance of Low-Carbon Steel via Surface Modification

This research investigated the corrosion resistance of surface layers on low-carbon steel exposed to a chloride environment at room temperature. This study systematically evaluated the effects of varying pack compositions, coating temperatures, and application durations on the characteristics of the deposited coatings. The potentiodynamic polarization corrosion test was employed to assess the wet corrosion behavior of the specimens. Elemental compositions and microstructural features were analyzed using energy-dispersive X-ray spectroscopy (EDX) in conjunction with scanning electron microscopy (SEM), providing insights into phase distribution. The chromizing, titanizing, and chromotitanizing treatments were conducted at temperatures of 900 °C, 1000 °C, and 1100 °C, respectively, with varying coating times. X-ray diffraction analysis revealed a complex arrangement of elements and compounds within the coatings, including Cr, Ti, Cr1.9Ti, FeTi, Al2O3, Cr2O3, TiO2, Cr1.36Fe0.52, and (Ti0.86)3.58. The study found that as the deposition duration increased, the coating thickness increased, comprising a thin inner layer and a substantially thicker outer layer. This layered structure resulted from the outward diffusion of Fe atoms and the inward diffusion of Cr and Ti atoms. Electrochemical analysis in a 3.5% NaCl aqueous solution indicated a marked enhancement in the corrosion resistance of the coated specimens compared to their uncoated counterparts. The potentiodynamic polarization tests confirmed that the protective coatings significantly reduced the corrosion rate, with performance influenced by both the temperature and duration of the deposition process. These findings highlighted the potential of tailored coating techniques to improve the durability and performance of low-carbon steel in corrosive environments.

(Invited) Unveiling Fundamental Reaction Mechanisms at the Electrochemical Interface by Ab Initio Simulations

Direct experimental exploration of atomistic mechanisms governing electrocatalysis or wet corrosion at the solid-liquid interface is notoriously difficult. While fully parameter-free ab initio calculations have the potential to accurately elucidate such mechanisms, they encounter substantial conceptual challenges. Recent methodological breakthroughs, including the advent of efficient computational electrodes and the development of effective thermopotentiostats, overcame many of these limitations thus providing new research opportunities. This presentation outlines the fundamental concepts underlying these innovative methodologies and demonstrates their application in performing fully explicit calculations of structure and chemical reactions at electrified solid-water interfaces. The power of this approach in discovering new mechanisms will be demonstrated for fundamental electrochemical reactions such as metal dissolution and the hydrogen evolution reaction (HER). The identified mechanisms challenge existing understandings and empfasize the active involvement of water molecules in electrochemical reactions, challenging the perception that they are passive bystanders.

Wet corrosion of incinerators under chloride deposits: Insights from experimental study on stainless steels and nickel-based alloy weldments

The deliquescence of the corrosion species produced by nuclear waste incineration, in particular ZnCl2, makes wet corrosion possible even in dehumidified atmosphere complicating the corrosion risk management of the equipment. A specific cyclic corrosion test was used to assess the compatibility of corrosion resistance alloys to such conditions. Thereby, AISI 316 L welds resisted somehow to pitting but experienced severe stress corrosion cracking, while UR66™ showed only pitting in the heat affected zone. Hastelloy® C22 exhibited better performance, with localized corrosion only in the fusion zone, that was greatly influenced by the composition of the filler materials and welding techniques.

Application of MgO/ZrO2 coating on 309 stainless steel to increase resistance to corrosion at high temperatures and oxidation by an electrochemical method

Abstract 309 stainless steel is one of the steels that have the highest resistance to corrosion and thermal oxidation compared to other steel grades, but it should not be used at temperatures higher than 980°C if there are temperature fluctuations. Additionally, 309 stainless steel is not designed for use in wet environments and has the least corrosion resistance. This study aims to cover 309 stainless steel with MgO/ZrO2 particles using a two-step electroplating deposition method and then sintering to increase its resistance to wet corrosion and oxidation in temperature fluctuations. The intermediate ZrO2 coating makes the outer MgO layer about two times thicker and reduces the corrosion current density. The morphology of the coatings was determined using scanning electron microscopy and X-ray diffraction, and oxidation resistance was determined using cyclic oxidation tests and the wet corrosion test of the corrosion solution. 3.5% NaCl was used. The results showed that the coated samples, due to the use of TiO2 middle layer and MgO protective layer in the electrochemical method, have a 2-fold increase in wet corrosion and an increase in hardness of about 77%, as well as an increase in oxidation resistance of 1.8% compared to the sample without coating. Also, the reason for using the electrochemical deposition method is for better surface smoothness and less porosity of the coating as well as its use on all metals compared to thermal spray methods.

Comparative study of alternating dry and wet corrosion behavior of Q345qDNH steel and Q420qENH steel in industrial atmospheric media containing PM2.5

AbstractThe corrosion behavior of Q345qDNH steel and Q420qENH steel under the industrial atmosphere containing PM2.5, as well as the effect of PM2.5 on the rust layer were studied by dry–wet alternating accelerated corrosion experiment. The results show that the corrosion rate of Q345qDNH is always less than that of Q420qENH, the Cr content of rust layer is higher than that of Q420qENH steel. After 30 days of corrosion, compared with Q420qENH steel, the self‐corrosion potential of Q345qDNH is larger, the self‐corrosion current density is smaller, and the rust resistance is 1.49 times of Q420qENH steel, the Iα‐FeOOH/Iγ‐FeOOH ratio is 1.29 times of Q420qENH, indicating that the protection of the rust layer of Q345qDNH is better than that of Q420qENH. This is due to the effect of microstructure factors in the early stage of corrosion and alloying elements in the late stage of corrosion. PM2.5 with SiO2 as the main component is easy to deposit at cracks and holes, which becomes the nucleation substrate for corrosion products, promotes the nonuniform nucleation of corrosion products, making the rust layer develop unevenly, leading to an increase in holes in the outer rust layer.

Synthesis, characterization, and studies of the interfacial and anticorrosion properties of a ternary cationic ionic liquid on carbon steel in a molar concentration of hydrochloric acid: Experimental and computational insights

Corrosion in acidic environments is a serious industrial challenge that must be addressed and cationic ionic liquid play a critical role in tackling the wet corrosion menace for the metal industry. For this purpose, a novel ternary cationic ionic liquid namely N1-(3-(11-(octadecyldimethylammonio)undecanamido)propyl)-N1,N1,N2,N2,N2-pentamethylethane-1,2-diaminium tribromide (Mono-18–11-di-N) is synthesized and elucidated for anticorrosion activity on St37–2 grade steel in a molar concentration of hydrochloric acid medium. The structural elucidation of Mono-18–11-di-N was achieved by FT-IR, 1H NMR, and 13C NMR methods while the electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), dynamic-EIS, density functional theory (DFT) calculations, and Monte Carlo (MC) simulation techniques were adopted in the anticorrosion evaluation. The Critical Micelle Concentration (CMC) of Mono-18–11-di-N is 0.000491 M and at CMC, the surface tension is 21.86 dyn cm−1 inferring good surface activity properties. Mono-18–11-di-N is effective against the wet corrosion of St37–2 steel. It can, at 20 mg/L decrease the corrosion rate of the metal from 0.57 mm/y to 0.11 mm/y and enhance the polarization resistance from 363 Ω cm2 to 1908 Ω cm2. A corrosion rate of 0.03 mm/y and an inhibition efficiency of 93% is achievable after 24 h of immersion at 25 °C. Additionally, surface morphological examination using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), optical profilometer (OP), and atomic force microscope (AFM) methods prove the adsorption of Mono-18–11-di-N molecules on the substrate surface. Moreover, DFT and MC simulations revealed that Mono-18–11-di-N relies on lone pairs of electrons in bromide anion, oxygen, and nitrogen atoms to adsorb parallel to the St37–2 surface and protect it against corrosion.

Corrosion studies of various salt solutions on metals and alloys

Corrosion studies of various salt solutions on metals and alloys

Intergranular Corrosion in X39CrMo17-1 – A Review

Abstract The aim of this contribution is to review cases of repeated snap ring failures in large gas turbine engine service due to intergranular attack, or intergranular corrosion, IGC, and to shed some light on metallurgical aspects of the wet corrosion resistance of the subject high-alloy martensitic stainless chromium steel X39CrMo17-1, DIN 1.4122. It is important to note that only snap rings, a.k.a. retaining rings for bores or Seeger rings, were affected by those failures, namely fractures resulting from intergranular attack (IGA, Kornzerfall). It was determined that the metallurgical root cause of failure was sensitization, resulting from secondary chromium carbide precipitation at grain boundaries (GB), and the ensuing chromium depletion in narrow bands adjacent to the GB, which rendered the matrix there sensitive to selective corrosion (the chromium content in these narrow seams, measuring only a few 10 nm in width, drops below the corrosion resistance threshold of ca. 10.5 %). Snap rings, as the name suggests, require a certain “snappiness” to serve their purpose. It is because of this requirement that all snap rings that experienced failures in the field were heat treated per DIN EN 10088-2, providing for a low tempering temperature of max. 250 °C, leading to a relatively high hardness of ca. 580 HV 10, providing said “snappiness”. It turned out that the microstructure resulting from this heat treatment (H/T) is sensitized, rendering the material sensitive to IGA. To the knowledge of the authors, no other components made of this martensitic stainless chromium steel are given this H/T, but rather a high-temperature tempering of 650 °C–750 °C per DIN EN 10088-3, producing a lower hardness in the order of ca. 300 HV 10 and largely a lack of “snappiness”, the latter being not required by those non-snap ring applications. Metallurgically, it became clear that high-temperature tempering per DIN EN 10088-3 eliminates sensitization by “backfill” diffusion of chromium from the non-depleted matrix into formerly depleted regions next to GB. It was therefore decided in the authors’ organization to eliminate X39CrMo17-1 per DIN EN 10088-2 as a possible material selection. The metallurgical investigations described in this contribution corroborate and support this decision.

Electrochemical and Microstructural Characterization of Cr-Coated NdFeB in Neutral Wet Environment

Naturally, NdFeB–based permanent magnets exhibit high chemical instability, especially, in wet environments. This makes them highly susceptible to corrosion, which leads to severe structural collapse. Applying thin surface coatings can improve the resistance to wet corrosion. In this work, 0.5 µm of chromium (Cr) film was sputtered on a sintered NdFeB–based magnet and the resistance to corrosion and microstructural damage was investigated in 3.5% NaCl solution with respect to an uncoated magnet. This was achieved by complementing potentiodynamic polarization and electrochemical impedance spectroscopy with scanning electron microscopy (SEM). The Cr coating caused a positive displacement of corrosion potential and lowered the rate of anodic dissolution. It also favored higher charge transfer resistance at the magnet–solution interface, and delivers a protection efficiency of ~ 60 %. Furthermore, grain boundary attack and deterioration were also significantly reduced by the Cr coating.

Research on AlN thin film microstructure processing technology based on ultra-thin cantilever beam structure

Aiming at the problem of poor solution selection ratio when the AlN film and porous silicon sacrificial layer are released in the ultra-thin cantilever structure and at the problem of large surface roughness after AlN graphing, the wet corrosion process parameters were optimized, and the influence of different corrosive fluids and corrosion times on the surface roughness of AlN and the influence on the etching rate of AlN were studied, and different process parameters were selected for experiments. According to the experimental results, a suitable microstructure processing method was selected to effectively reduce the surface roughness of AlN and improve the integrity of the AlN film and the reliability and yield of the cantilever structure when the sacrificial layer is released. The microstructure fabrication of AlN films in ultra-thin cantilever structures enables the fabrication of ultra-micro-force sensors, accelerometers, acoustic sensors, and other devices.

Effect of Varying Hot Extrusion Temperatures on the Properties of a Sinterless Turning Induced Deformation Processed Eco-Friendly Mg-Zn-Ca Alloy

In this work, Mg-4Zn-1Ca (wt. %) alloy was primarily processed by disintegrated melt deposition. The resulting ingots were further pre-processed by the turning induced deformation technique (TID), and the turnings were subsequently consolidated by the hot extrusion process and sinterless powder metallurgy. A range of extrusion temperatures (200, 250 and 300 °C) was tested to understand the effect of the extrusion temperature on tailoring the microstructure and properties of TID-processed Mg-4Zn-1Ca (wt. %) alloys. The results indicated that the combined effect of TID and extrusion temperature plays a significant role in grain refinement, specifically at 200 °C. Overall, the sample extruded at 300 °C showed the best microhardness and compressive yield strength values. The resistance to ignition and wet corrosion increased and decreased, respectively, when the extrusion temperature was increased. Variations of basal texture and fine grain strengthening due to variations of extrusion temperature led to different properties peaking at different extrusion temperatures. Microstructure-property relationships are therefore discussed, highlighting that different extrusion temperatures have characteristic effects in improving and lowering the properties. Many of the investigated properties of TID-processed alloys exceed that of commercial Mg alloys, suggesting the capability of the sinterless TID technique to develop as an economical industrial way of recycling and manufacturing magnesium-based materials.

Impact of Processing on the Creep Properties of High Performance Ferritic (HiperFer) Steels

High performance ferritic (HiperFer) stainless steels constitute a new class of low-cost, heat resistant, hardenable materials which combine high creep and fatigue strength with increased steam oxidation and wet corrosion resistance. The fundamental relationships regarding the alloy composition, microstructure, and resulting mechanical properties are largely known and already published, while relevant commercialization issues, such as the effect of processing on the microstructure, have not yet been addressed. The current paper outlines the impact of the forming parameters on the resulting microstructure and the achievable creep properties. Thermomechanical treatment is demonstrated as an effective method for increasing the creep strength for a given chemical composition. This may constitute a key enabler for cost savings in component production, e.g., for the simple machining of “drop-in” turbine blades or bolts from forged bar stock material.

Fluorinated Agents Effects on Orthodontic Alloys: A Descriptive In Vitro Study.

Fluoride-based mouthwashes and gels are preventive measures in countering demineralization and caries but, modifying environmental acidity, can reduce the wet corrosion resistance of orthodontic alloys. To evaluate chemical stability, in vitro experiments were conducted on stainless steel and nickel–titanium wires, weighed before and after immersion in household fluorinated mouthwashes and gels, measuring weight variations and elution of metal ions from acid corrosion phenomena. Elution samples were analyzed by inductively coupled plasma mass spectrometry, detecting residual ion concentration, while surface changes were analyzed under scanning electron microscopy. Results showed stainless steel wires do not undergo significant erosion when exposed to most fluorinated mouthwashes but, at prolonged exposure, alloys elute gradually greater amounts of metals and Ni–Ti wires become more sensitive to some mouthwashes. Ions’ elution varies considerably, especially for Ni–Ti wires, if exposed to household fluorinated gels, for which significant negative values were obtained. Changes, affecting wires’ outer layer, negatively act on shiny appearance and luster, reducing corrosion resistance. Although examined orthodontic wires showed good chemical stability and low toxicity, surface corrosion from exposure to fluorinated agents was observed. Home use must be accompanied by clinician prescription and, for household dental gels, must follow manufacturers’ recommendations, ensuring prophylactic action without damaging alloys surfaces.

A combinatorial study of the effect of Al and Cr additions on the mechanical, physical and corrosion properties of Fe

The effects of Al and Cr additions on the mechanical, physical and corrosion resistance of Fe were investigated in a combinatorial approach on a total of 42 alloys with compositions ranging from 0 to 10 wt% of Al together with 0–12 wt% of Cr (in increments of 2 wt%). All alloys were subjected to hardness, tensile, density, Young’s modulus and salt-spray testing, along with structural analysis using x-ray diffraction. Selected alloys were additionally analysed with scanning electron microscopy (microstructure) and x-ray photoelectron spectroscopy (corroded surface). Increasing Al additions linearly reduced both density and stiffness, and led to a sudden strengthening above 2 wt% and embrittlement above 8 wt%. Cr additions counteracted the effects of Al on the mechanical and physical properties, and about 4–8 wt% of Cr could be substituted by 8–10 wt% Al for similar protective effects against wet corrosion. A decrease in Cr and increase in Al concentration in the bulk material results in a similar trend within the passive layer, preserving a significant degree of passivity. Evaluation of the comprehensive data by desirability functions allowed to identify most relevant compositions as the basis for the design of lightweight corrosion resistant steels.

Facile Synthesis of Potassium-Doped Titanium Oxide Nanostructure (KTiOxs)/AlO(OH) Composites for Enhanced Photocatalytic Performance

Generally, nanoparticles (NPs) are used as photocatalysts, which sometimes results in difficulties in the separation and recycling of photocatalysts from suspensions after their application in water and wastewater treatment, which hinders industrial applications of NPs that are too fine to be removed by gravitational settling. This can be solved by using support NPs to overcome these problems. -OH enrich AlO(OH), which is produced by a steam coating process, has been could be used as a possible support, because the -OH groups on the surface can interact with foreign molecules; thus, various composite functional materials can be prepared. Potassium doped titanium oxide NPs, which are produced by a wet corrosion process, namely KTiOxs, have been selected as photocatalysts, because KTiOxs have sufficient K+ ions, thereby expecting the chemical bonding with -OH group from AlO(OH). This study fabricated a novel photocataysis system made by combining KTiOxs as catalysts and AlO(OH) as the catalysts’ support, namely KTiOxs/AlO(OH) composites. The KTiOxs nanowires, obtained from 10 mol/L of a KOH solution treated with Ti and AlO(OH) at 280 °C for 24 h through a steam coating process, yielded the highest surface area and the highest photocatalytic performance.

Facile synthesis of dual-phase lithium titanate nanowires as anode materials for lithium-ion battery

A facile method to synthesize dual phase Li4Ti5O12-TiO2 nanowires and their performance as anode material for lithium-ion battery are investigated. Li4Ti5O12-TiO2 nanowires are obtained from titanium nanoparticles by applying the wet corrosion process for the nanostructure formation and subsequent ion exchange processes. Post-heat treatments are adopted to tune the mixed phase composition of the nanowires, which significantly influences the electrochemical performance. The dual phase nanowires-based anode materials with a TiO2: Li4Ti5O12 phase ratio of 7:3 exhibit the highest delithiation capacity of 180 mAh/g and 105 mAh/g at 0.5 C and 5 C, respectively. In addition, it shows a remarkable capacity retention of ~95% after 150 cycles at 5 C, which is a significant improvement compared to previous reports on Li4Ti5O12-TiO2 based anode materials synthesized at low temperatures. This dual phase anode material based on Li4Ti5O12-TiO2 nanowires combines two advantages: i) High aspect ratio nanostructures increase the surface area and shorten the diffusion path of lithium ions and ii) the dual phase accelerates ion/electron migration owing to abundant interfaces/grain boundaries. Consequently, the proposed synthesis route for Li4Ti5O12-TiO2 nanowires provides an effective and highly reproducible approach to fabricate dual phase Li4Ti5O12-TiO2 nanowires as anode materials for lithium ion batteries.

Improved polarization retention in LiNbO3 single-crystal memory cells with enhanced etching angles

Multifunctional LiNbO3 material plays an important role in domain wall microelectronics and nonlinear optoelectronics. However, the material is hard and relatively inert, and hence is quite difficultly etched. A new oblique method to etch LiNbO3 memory cells at the surface of X-cut bulk crystals was proposed in this study. The process includes mask fabrication, oblique etching, and wet corrosion cleaning. The etching angle highly approaches 83° to achieve better polarization retention than others with etching angles of 0° and 70°. Meantime, the measured domain switching hysteresis loops become more symmetrical along the voltage axis than others with the presence of a strong imprint field. The horizontal electric field simulation along the polar Z axis exhibits the enhanced nucleating fields of the domains located at two edges of each memory cell in contact to Pt electrodes under the same applied voltage. The depolarization field was better screened in the memory with a higher etching angle. The new oblique method can improve the performance of the ferroelectric domain wall memory significantly.

Experimental investigation and mathematical modelling of water vapour corrosion of Ti3SiC2 and Ti2AlC ceramics and their mechanical behaviour

Commercially available Ti3SiC2 and Ti2AlC ceramics were used in this study to investigate their wet corrosion and mechanical behaviour as they were under investigation for years for their applications in the field of nuclear as cladding materials and aerospace. The test coupons of dimension 3 × 4 × 40 mm3 and 3 × 4 × 20 mm3 were machined out from commercially available samples for the 3-pt bend test and wet corrosion test, respectively. The water vapour corrosion studies of these samples were carried out at 800 ℃, 1000 ℃, 1200 ℃ for 10, 20 and 100 h in gas flow condition containing 50 % steam + 50 % air. Phase analysis of the as-received Ti3SiC2 and Ti2AlC ceramics revealed the presence of other impurity phases such as TiC and TiSi2. The XRD patterns of the oxidised samples show the formation of rutile as the major phase in both materials. The oxidation layer formed on Ti3SiC2 sample was measured to be 280 μm after exposing the sample in steam for 100 h at 1200 °C. The water vapour corrosion studies reveal that Ti2AlC has high oxidation resistance compared with the Ti3SiC2 due to the formation of protective layers of TiO2 and Al2O3 which resulted in reduced weight gain and oxidation layer thickness. Three-point bend tests were conducted at room temperature for the samples after the water vapour corrosion test at 1000 °C/100 h. The TAC samples showed no degradation in the bending strength (244 MPa) whereas the TSC samples showed reduced strength of 320 MPa. The tensile strength of the samples was measured at room temperature and hydrothermal condition (250 °C and 250 bars pressure) and it was observed that Ti3SiC2 had high tensile strength (190 MPa) in hydrothermal conditions. The tensile strength results were validated using Finite element analysis (FEA) using ANSYS and the FEA results showed a negligible variance of 7 % compared with experimental method. Mathematical modelling based on one dimensional solution of diffusion equation combined with Deal-Grove model was employed to study and compare the oxidation thickness for the linear and parabolic models for the ceramics. The model was effective in validating the oxidation thickness of Ti3SiC2 showing that the experimental thickness was closer to that of mathematical model.

Ni-Mo-Si]:Nb Bulk Metallic Glasses: Microstructure, Mechanical and Corrosion Studies

We examine the effect of substituting Niobium (Nb), on the glass-forming abilities (GFA), mechanical and corrosion properties of bulk metallic glasses (BMGs). BMGs are synthesized using the general formula of (Ni75Mo15Si10)100−xNbx (x = 0, 5, 10 and 15 at.%, labeled as NMSNb0, NMSNb5, NMSNb10 and NMSNb15) that are synthesized using high energy mechanical ball milling technique. Thermal, mechanical, and corrosion properties were enhanced significantly with an increase in Niobium (Nb) content of 10 at.% (NMSNb10). Using XRD analysis, the analysis related to phase attribution and crystallizability is scrutinized. Alloying this BMG with Molybdenum (Mo) and Niobium (Nb) helped avoid embrittlement in the sulphuric acid environment, overcoming strain cracking problems caused during welding, preventing pitting, crevice corrosion, and wet corrosion. Applicability of the present BMG system is examined in light of the correlation between morphology, mechanical, and corrosion studies.

Aspects on Early-Stage Corrosion of Different Zinc Alloys: Wet scCO2-Induced Corrosion

The surface activity of different zinc alloys was evaluated in wet scCO2. The zinc coating surface chemistry governed the corrosion product formation. On zinc and Zn-Al coatings, the Al2O3 layer prevented growth of corrosion products. A Zn-Al-Mg coating showed high initial reactivity due to active Zn-Mg phases. An electrogalvanized coating was very active due to a high ratio of exposed, less dense planes. In a Zn-Fe coating, several Zn-Fe phases were susceptible to wet scCO2 at the same time, triggering the sacrificial effect of Zn. Wet scCO2 is a convenient medium to assess the early-stage corrosion of metal coatings.