Corrosion Pits Research Articles

Microstructure, corrosion behavior, and fatigue resistance of laser powder bed fusion-produced precipitation-hardening martensitic M789 stainless steel

Additive manufacturing has facilitated the fabrication of stainless steel components with intricate designs, providing exceptional strength and corrosion resistance. This advancement, however, poses challenges in accurately predicting fatigue resistance under high-cycle loading, especially when surface features resulting from the printing process and corrosion are overlooked. This study investigates the microstructure of laser powder bed fused Böhler M789 AMPO stainless steel aiming to elucidate its relationship with corrosion resistance and fatigue properties.Through a comprehensive examination of the microstructural features using El-Haddad’s model and extreme value extrapolations, this research reveals the predominant influence of surface roughness, resulting from the printing process, on the fatigue strength of net-shaped specimens. For a stress ratio of 0.1, the estimated fatigue strength ranges between 69 MPa and 162 MPa. Upon mechanically polishing the surface to eliminate the surface roughness effects, the significance of other features is highlighted. Particularly, the effect of corrosion pits, shallow pores and oxides, and internal discontinuities follow in importance.Moreover, this study evaluates the impact of the as-received-oxide layer on corrosion resistance. Upon removal of this layer via surface etching or polishing, an improvement in the stability of the re-formed passive layer was observed. This enhancement is evident in the expanded potential range between the pitting and corrosion potentials, increasing from 0.2 V for the net-shaped surface to 1.05 V for the polished one.This work emphasizes the significance of characterizing microstructural characteristics to predict both fatigue and corrosion resistances. It also highlights potential research areas in additively-manufactured stainless steels.

Investigation of the size effect of mica sheets on the anticorrosion behavior of UV‐cured coatings

AbstractIn this article, four different grades of mica sheets were used to investigate the influence of the size of mica sheet on the UV‐curing process and the anticorrosion performance of UV‐cured coatings. The dispersion of mica sheets in coating matrix was explored by viscosity and morphology measurements. The curing behavior of the composite coatings was studied by gel content and double bond conversion rate. The dispersing behavior of the mica sheets with different grades was investigated by SEM image and rheology measurement. And the anticorrosive performance of the UV‐cured composite coatings was studied by electrochemical measurements and neutral salt spray tests. It was found that the curing degree of the UV‐cured coating was not affected with incorporation of mica sheet as well as its size. Mica sheets with medium size (10 μm) could be more efficiently dispersed in UV‐cured coating than other grades, which helps to form a denser filler pathway and suppresses the diffusion of corrosive agents into the coating matrix, leading to the lowest water adsorption and best anticorrosion performance. After 45 days of immersion in NaCl solution, the impedance modulus of the UV‐cured composite coating with 10 μm mica sheets did not decrease and still maintained at the initial impedance value. After 1500 h's salt spray test, the corresponding coating remained intact without bubbling, peeling, corrosion, and other defects, whereas the coating with other grades of mica sheets all exhibited corrosion pits and blisters, demonstrating that the size of mica sheet played an important role in enhancing the anticorrosion performance of UV‐cured coatings.

Design of a smart protective coating with molybdate-loaded halloysite nanotubes towards corrosion protection in reinforced concrete

Using protective coatings is widely acknowledged as an effective strategy for preventing the corrosion of reinforcing steel and improving the durability of reinforced concrete structures. Nevertheless, a common challenge faced by the traditional coatings lies in the significantly reduced corrosion resistance due to its damage and cracking during the service life. Accordingly, a smart protective coating with active anti-corrosion performance was successfully designed and synthesised in this study, including a PA-polyvinyl alcohol (PVA) pretreatment layer and the molybdate-loaded etched halloysite nanotube (EHNT@MO). The PA-PVA grafting solution could fix EHNT@MO on the steel surface due to its strong chelating ability, resulting in an increased thickness of the pretreatment layer (∼5 μm) and exceptional barrier properties. Moreover, the release of molybdate from EHNT enables the smart protective coating to actively repair corrosion pits, thereby exhibiting excellent anti-corrosion performance. As a newly developed smart protective coating, it is expected to confer multifunctional properties to reinforcing steel in cementitious materials when subjected to aggressive environments.

A comprehensive study on the effect of rock corrosion and CO2 on oil-water interfacial tension during CO2 injection in heavy oil reservoirs

This study is focused on addressing issues related to the interaction mechanism between reservoir rocks and fluids during CO2 injection in heavy oil reservoirs. The results indicate that the carbonated water formed after high-pressure CO2 injection is causing corrosion in the core structure. Furthermore, the average corrosion rate increases from 0.358% as pressure increases from 8 MPa to 16 MPa to 0.742%. The core slices exhibit corrosion pits and cracks on their surface, as well as surface particles flaking and dissolving. The dynamic IFT between decyl trimethyl ammonium bromide solution and crude oil exhibited slower stabilization and less change without CO2 injection. However, with increasing pressure post CO2 injection, the dynamic IFT decreased at a more rapid rate. Furthermore, positive correlation between equilibrium IFT and temperature was observed with low-pressure CO2. In contrast, the surfactant played a more dominant role in reducing IFT with high-pressure CO2. The findings of this study can help for better understanding of the mechanism of microscopic action on reservoir rock and oil-water interface after CO2 injection, and offer theoretical basis and reference for CO2 injection in heavy oil reservoirs to enhance the recovery rate.

Evaluation of the efficiency of coconut dust extract as a corrosion inhibitor for steel reinforcement in concrete by mass spectrometry

Ethanol extraction was employed to isolate a range of compounds from waste products derived from coconut fiber production (coconut dust) in Ben Tre, Vietnam. Phytochemical screening confirmed the presence of flavonoids, tannins, polyphenols, saponins, alkaloids, flobatannins, and anthraquinones among the extracted substances. FT-IR spectroscopy analysis supported the identification of oxygen and nitrogen atoms within functional groups (e.g., O–H, N–H, C–O) and aromatic rings, characteristic of typical corrosion inhibitors. Mass spectrometry investigations indicated that when St3 steel was exposed to an alkaline solution lacking chlorides, a passive film composed of FeOOH formed on the surface. However, upon the addition of NaCl at a concentration of 1.00 mol/dm3, FeCl, FeCl2Cl–, and FeCl3Cl– compounds were detected across the analyzed surface, while peaks corresponding to FeOO– were absent. Remarkably, areas with the highest concentration of particles corresponded to regions exhibiting visible corrosion damage under magnification. The addition of 2.00 g/dm3 of coconut dust extract to the chloride solution prevents the formation of Fe and Cl compounds on the steel surface. Consequently, only peaks characteristic of FeOO– and organic fragments containing oxygen atoms from the extract were observed. Based on these results, it can be assumed that coconut dust extract has the potential to inhibit local (pitting) corrosion of low-carbon steel (St3) when exposed to aqueous alkaline solutions simulating concrete pore liquid containing chlorides. The addition of 2.00 g/dm3 of the extract has been shown to prevent pitting formation at a chloride concentration of 1.00 mol/dm3. Conversely, in the absence of the extract, visible local corrosion damage was observed upon magnification. These findings provide a basis for further exploration of the protective properties of coconut dust extract as an environment-friendly corrosion inhibitor for mild steel in concrete environments containing chlorides.

Influence of Sulfate and Iron Reducing Bacteria on Carbon Steel Corrosion in Marine Environments

The current study highlights the corrosion consequences observed in API 5L X65 carbon steel when exposed to a marine-like environment containing carbon dioxide (CO2), in the presence of sulfate- reducing bacteria consortium (C-SRB), iron-reducing bacteria consortium (C-IRB), and a combination of both (C-SRB+C-IRB). The corrosion behaviour was assessed through the utilisation of weight loss and surface analysis techniques. The biofilms and corrosion products were characterised using field emission scanning electron microscopy (FESEM) and infinite focus microscope (IFM), respectively. The results obtained from the weight loss technique provided confirmation that in the absence of bacteria, uniform corrosion was the prevailing mechanism in the medium. The uniform corrosion rate was found to be 0.95 mm/year, which was higher than the pit penetration rate of 0.28 mm/year. The combined actions of the C-SRB+C-IRB consortium result in a synergistic impact, leading to a significantly higher rate of pit penetration compared to the individual activities of SRB. Specifically, the pit penetration rate value of 2.13 mm/year is observed, which is notably higher than the uniform corrosion rate of 0.59 mm/year. The utilisation of surface analysis techniques has shown evidence of the existence of sulfur on carbon steel samples that were subjected to exposure from the C-SRB+C-IRB consortium in a CO2 environment. This sulphur presence is believed to potentially play a role in the development of the iron sulphide (FeS) layer. FeS presence is a contributing factor to the occurrence of pit corrosion due to the SRB metabolite activities. The activities of these metabolites readily dissolve in the medium, hence altering the chemical interface properties of both the metal and the biofilm. For specimens exposed to C-SRB only, the results obtained were almost identical to exposure to the C- SRB+C-IRB consortium. However, the corrosion rate value measured for the C-SRB+C-IRB consortium was higher due to the synergistic effect of the two bacteria. In conclusion, the presence of C-SRB alone and the consortium of C-SRB+C-IRB in a CO2 environment induces the formation of pitting corrosion. The findings of this study are presumed to contribute a deep understanding of the microbiology-influenced corrosion (MIC) mechanism in CO2 environments troubling the oil and gas industry. With a better understanding of MIC, new and improved corrosion prevention strategies can be put into action.

Effect of TiB2 on properties and microstructures of Cu[sbnd]W electrical contact materials

The W skeletons were pressed by the cold isostatic pressing process, and CuW alloys with different TiB2 contents were prepared by the sintering and infiltration method. The effects of TiB2 addition on the microstructures, properties, vacuum breakdown performance, and arc motion characteristics of CuW alloys were investigated. The results show that the conductivity of CuW alloy decreases with the addition of TiB2, while the hardness increases. Compared with CuW alloy, this method improves the breakdown strength, reduces the chopping current and extends the arc life of CuW alloy. The anti-arc erosion performance of CuW alloy with the addition of TiB2 was enhanced. For CuW alloy containing TiB2, the electric breakdown occurs on the TiB2 phase at the edge of the W phase, the cathode spots are split, the arc is effectively scattered, and the ablation area after multiple breakdowns is larger, but the erosion pits are shallow and dispersed.

The role of corrosion pit topography on stress concentration

Smooth semi-ellipsoids are typically used to simulate the effect of corrosion pits on stress, however, this does not account for pit geometry. Three corrosion pits were identified on Nickel Aluminium Bronze samples. These were scanned and converted to finite element models. The linear elastic stress concentration factor (Kt) of the corrosion pit FE models was 1.32–1.65 times larger than for an equivalent smooth semi-ellipsoid. This suggests that detailed consideration of pit geometry is needed to calculate accurate values of Kt and the assumption of a semi-ellipsoidal pit may not be conservative for fatigue lifetime predictions of pitted components.

Computer Simulation of Pitting Corrosion in Galvanostatic Conditions

Pitting corrosion of stainless steels has been the subject of substantial research over many years. The overall mechanism can be separated into nucleation and propagation stages, and the development of a reliable predictive model requires a robust treatment for both these processes. Over the years, several purely stochastic models have been developed, including those by Shibata and Takeyama [1], Williams et al. [2], Baroux [3] and Wu et al. [4]. Alternatively, Macdonald and co-workers [e.g., 5] have focused on a deterministic approach, based on the point defect model of passivity breakdown. Newman, Laycock and co-workers developed a deterministic model for the propagation of individual corrosion pits [6-8], which was then combined with a stochastic model of pit nucleation to enable simulation of pitting potential measurements [9]. Li, Scully and Frankel later published a series of papers based on a similar approach [e.g., 10-11].The majority of the prior modelling work has focused on potential-controlled conditions, where the pitting outcomes are determined mainly by the pit propagation element; for example, a limiting lower bound distribution of the pitting potential can be calculated without any consideration of pit nucleation processes [9]. However, real corrosion does not occur under potential control; rather, there is a limited supply of cathodic current that must be shared between all simultaneously propagating pits [12,13]. This situation is closer to that of experiments under galvanostatic control [14]. Krouse et al [15] described simulations that included possible interactions between multiple simultaneously propagating pits under galvanostatic conditions, supporting earlier suggestions that pits compete for the available current, and that ‘champion pits’ will ultimately use all available resources (see, e.g., Figure 1).In more recent work [16], we have further developed the earlier propagation model [6-9] to include the interactions and possible mergers between two simultaneously propagating pits. Here we expand on the work of Krouse et al [15] to carry out simulations of galvanostatic experiments that now incorporate the possibility of mergers between propagating pits. References Shibata, T. Takeyama, Corrosion 33 (1997) 243.E. Williams, C. Westcott, M. Fleischmann, J. Electrochem. Soc. 132 (1985) 1796.Baroux, Corros. Sci. 28 (1988) 969.Wu, J.R. Scully, J.L. Hudson, A.S. Mikhailov, J. Electrochem. Soc. 144 (1997) 1614.Engelhardt, D.D. Macdonald, Corrosion 54 (1998) 469.Ernst, N.J. Laycock, M.H. Moayed, R.C. Newman, Corros. Sci. 39 (1997) 1133.J. Laycock, S.P. White, J.S. Noh, P.T. Wilson, R.C. Newman, J. Electrochem. Soc. 145 (1998) 1101.J. Laycock, S.P. White, J. Electrochem. Soc. 148 (2001) B264.J. Laycock, J.S. Noh, S.P. White and D.P. Krouse, Corros. Sci, 47, 3140 (2005).S. Frankel, T. Li, and J. R. Scully, Journal of the Electrochemical Society, 164, C180 (2017).Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165, C484 (2018).Y. Chen, F. Cui and R.G. Kelly, J. Electrochem. Soc., 155, C360-C368 (2008).Y. Chen and R.G. Kelly, J. Electrochem. Soc., 157, C69 (2010).I. Suleiman and R. C. Newman, Corros. Sci., 36, 1657 (1994).Krouse, P. McGavin and N. Laycock, in Proceedings of Corrosion & Prevention 2008, Paper # 97, ACA, Wellington, 16-19 November (2008).A Nguyen, R.C. Newman and N.J. Laycock, J. Electrochem. Soc., 169, 081503 (2022) Figure 1

EFFECT OF HEAT TREATMENT ON CORROSION RESISTANCE OF Al-Ni-Mn EUTECTIC ALLOY IN 3.5% NaCl SOLUTION

In this study, the effects of solution heat treatment (SHT) on how the Al-Ni-Mn eutectic alloy reacts to corrosion were looked into. The composition of the Al-Ni-Mn eutectic alloy was chosen as Al–5.3%Ni–1.3%Mn (wt). In solution heat treatment, firstly, the samples were kept at 570oC and 600oC for 2 hours and quenched with water at room temperature. Then, artificial aging was carried out by keeping 0-2-4 and 8 hours at 180oC. The corrosion behavior of the alloy was investigated by immersion tests in a 3.5% NaCl solution and electrochemical methods such as Tafel polarization curves and Electrochemical Impedance Spectroscopy (EIS). According to the immersion test results, the heat treatment applied at 600oC took the alloy to the more noble side and further increased its corrosion resistance. The α-Al matrix phase in the Al-Ni-Mn alloy system preferentially dissolves in untreated and heat-treated samples, and SEM images reveal the presence of corrosion pits. The corrosion performance of the heat-treated sample at 570oC is the highest. Heat treatment reduced the corrosion current density, indicating a lower corrosion rate and higher corrosion resistance. Also, the open circuit potential of the Tafel polarization curves of heat-treated and unheat-treated samples at 570oC and 600oC was found to be -685 mV, -693 mV and -761 mV, respectively. Similarly, the corrosion resistance of heat-treated and untreated samples at 570oC and 600oC was found to be 58 kΩ, 433 kΩ and 408 kΩ, respectively.

Immersion and electrochemical corrosion properties and combined corrosion mechanism of TC4 alloy by keyhole TIG welding

In this study, the effect of heat input on the microstructure and its correlation with the immersion corrosion properties of TC4 welded joints by Keyhole tungsten inert gas (TIG) process was researched. The combined corrosion mechanism between immersion corrosion and electrochemical corrosion was established. The results showed that immersion corrosion formed a passivation film on the surface of the welded joint and formed a minimal number of pitting pits. After immersion, electrochemical corrosion testing was carried out. Due to the existence of the passivation film, the self-corrosion potential increased from-0.6 V ∼ −0.2 V–0.1 V–0.6 V, and the self-corrosion current density decreased and the fitting impedance of the film increased. These all showed that the corrosion resistance of the joint was enhanced after immersion. However, due to the combined effect of immersion corrosion and electrochemical corrosion, the potential difference between the surface passivation film and the internal metal was sufficiently large to induce pitting corrosion on the surface. After the breakdown of the passivation film, spot corrosion pits formed. Microcracks propagated along the primary β grain boundary and the α′ phase interface, and continuous corrosion for a long time may even lead to cracking failure of the welded joints. With the increase of heat input, the self-corrosion potential and the self-corrosion current density of immersion corrosion increased firstly and then decreased. The fitting film resistance value of the impedance decreased firstly and then increased. The aforementioned findings indicated that as the heat input increased, the corrosion properties of the joints firstly deteriorated and then improved.

A comparative study on the corrosion behavior of Q235 steel in saturated acidic red and yellow soils

Purpose The purpose of this paper is to study the corrosion behavior of Q235 steel in saturated acidic red and yellow soils. Design/methodology/approach The corrosion behavior of Q235 steel in saturated red and yellow soils was compared by weight-loss, SEM/EDS, 3D ultra-depth microscopy and electrochemical measurements. Findings Rp of the steel gradually increases and icorr gradually decreases in both the red and yellow soils with time. The Rp of the steel in the red soil is lower, but its icorr is higher than that in the yellow soil. The uniform corrosion rate, diameter and density of the corrosion pit on the steel surface in the red soil are greater than those in the yellow soil. Lower pH, higher contents of corrosive anions and high-valence Fe oxides in the red soil are responsible for its higher corrosion rates and local corrosion susceptibility. Originality/value This paper investigates the difference in corrosion behavior of carbon steel in saturated acidic red and yellow soils, which can help to understand the mechanism of soil corrosion.

Effects of different magnitudes of static stress on the in vitro corrosion behavior of biodegradable zinc

Cardiovascular stents are subjected to complex mechanical stresses in service, and local stress concentrations due to irregular stent shapes may lead to premature failure. This work investigated the corrosion behavior of pure zinc under different tensile stresses and found that stress accelerates corrosion and promotes the expansion of corrosion pits. A numerical model of the relationship between corrosion rate, corrosion current density, and tensile stress was established, and an exponential function relationship was found. This work can provide theoretical references for the investigation of the corrosion behavior of zinc-based biodegradable materials under physiological stress and possible clinical applications.

Effect of ultrasonic shot peening and intermediate cerium salt conversion bath treatment controlling corrosion of Mg-Y-Zn-based alloy in salt water

Ultrasonic shot peening (USP) is often regarded as beneficial in mitigating corrosion of Mg alloys. However, increasing surface roughness induced by USP promotes localized corrosion pitting. Herein, we show that an intermediate phosphate bath treatment (CePT) before USP can minimize the surface roughness and ameliorate corrosion resistance of Mg-4.0Y-4.0Zn-0.5Zr-0.2Ca alloy (wt.%) in 0.1 M NaClsolution. In this regard, WZ44 alloy was subjected to Ce(NO3)3 + NaH2PO4bath treatment followed by USP for 30 s using AISI52100 steel balls and vice versa. The sub-surface features ofspecimens analyzed using XRD, FESEM, surface topography, and Vickers hardness reveal that CePT coating before USP increases microhardness (∼142–149 HV0.05 vs ∼ 125–135 HV0.05) and decreases surface roughness (Ra = 1.91–2.38 μm vs Ra = 2.58–2.76 μm). Potentiodynamic polarizationand electrochemical impedance spectroscopy demonstrate that corrosion current decreased (Icorr ∼ 9.81–13.69 µA/cm2 vs. ∼ 23.82–26.22 µA/cm2), coating (R1), and polarization resistance (R2) increased to ∼ 1704–1907 Ω.cm2,and ∼ 1834–1902 Ω.cm2, respectively,for specimens subjected to USP + CePT treatment together indicating superior corrosion resistance.Overall, an intermediate CePT before USP can effectively minimize corrosion pitting phenomena of WZ44 alloy in chlorinated solution by developing a ceramic coating interlocked with surface acting as a barrier between the metal/solution interface.

Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., “circular” shaped in the talc group, “fine-grained” shaped in the chlorite group, and “donut” shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

Effects of corrosion on the fatigue fracture behavior of 4140 steel for offshore wind turbine bolts

The fatigue life of bolt directly affects the safety of offshore wind turbine. In this work 4140 steel was subjected to salt spray corrosion simulating the coastal atmospheric environment. After rust removal, the surface morphologies of specimens were examined using an optical profiler. Corroded specimens were also assessed by fatigue testing and the resulting fracture surfaces were examined by scanning electron microscopy. Irregular pits appeared on corroded specimen surfaces. The relationship between fatigue life and surface roughness was obtained. The fatigue cracking of 4140 steel initiated at corrosion pits in conjunction with cleavage-type fatigue zones and plastic-type final fracture zones. Increase in surface roughness provided more crack sources, thus rapidly decreasing the fatigue life.

Stress corrosion behavior of B+F dual-phase X80 pipeline steel in different soil environments

The stress corrosion behavior and immersion corrosion behavior of B+F dual-phase X80 pipeline steel in simulated near-neutral and alkaline soil solutions were studied by slow strain rate tensile (SSRT) test, immersion corrosion test and polarization test. The results show that the strength and ductility of the samples in alkaline soil solution are weaker than those in near-neutral soil solution, and the elongation loss (Iδ) and area shrinkage loss (Iψ) are 2.81 and 2.76 times of those in near-neutral soil solution. Bainite and ferrite (B+F) dual-phase X80 pipeline steel is more sensitive to stress corrosion in alkaline soil solution than in near-neutral soil solution. The protective properties of the passive film determine the corrosion dynamics, because the more complete and uniform the passive film formed, the better the corrosion resistance. In both soil solutions, the cracks are mainly transgranular. The results of polarization and immersion experiments are consistent. The linear corrosion rate in alkaline solution is higher than that in near-neutral solution in immersion test. The corrosion pit of the sample is concentrated in bainite area in near-neutral solution while weak part around inclusions is preferentially corroded and forms large corrosion holes in alkaline solution. Therefore B+F dual-phase X80 pipeline steel is easier to corrode in alkaline soil solution.

Effect and simulation of tensile stress on corrosion behavior of 7050 aluminum alloy in a simulated harsh marine environment

The corrosion behavior of the 7050 aluminum alloy was investigated in the presence of high concentrations of H+ and Cl- ions simulating the marine environment of high salinity and local acidification in tropical seas. The results highlight the significant influence of tensile stress on the corrosion rate of the aluminum alloy with higher stress levels resulting in faster corrosion. Under the influence of tensile stress, corrosion pits form on the alloy surface, and their depth increases with higher levels of applied stress. It is important to note that the presence of a corrosion defect leads to a pronounced stress concentration, resulting in a much faster rate of corrosion compared to other regions. However, when subjected to low tensile stress (≤174 MPa), the corrosion at the defect exhibits uniform characteristics similar to a uniform corrosion process. Moreover, the potential at the defect shifts positively with increasing stress level. Furthermore, stress has an effect on the diffusive behavior of the aluminum alloy, leading to a higher potential at the defect center compared to its surrounding region. Nevertheless, as the tensile stress is further increased, this behavior is disrupted and stress corrosion cracking becomes the dominant mode of corrosion.

Corrosion and passivation behavior of in-situ TiC reinforced Al0.1CrNbSi0.1TaTiV refractory high entropy alloy coatings via doping C

This work is aimed to explore ways to further improve corrosion properties of single-phase RHEA coating by introducing in-situ TiC phase. Results shown that C/Al0.1CrNbSi0.1TaTiV RHEA coatings exhibited better comprehensive resistance to pitting and general corrosion compared to most of reported HEAs and traditional alloys. The passive film was dominated by a muti-oxide crystalline structure with a thickness of ∼ 11.52 nm. The small-size and evenly distributed TiC phase with most thermodynamically stable could be obtained via doping C and retard the nearby pitting process, improving the pitting behavior and the dense of passive film in 1.0 wt% C coating.

Numerical and experimental failure analysis of wind turbine blade fastener

The objective of this study is to conduct a root cause failure analysis on wind turbine fasteners constructed from carbon steel Grade 10.9. The presence of corrosion pits at the thread root, as well as beach and ratchet marks on the fracture surface, suggests that the fastener failed due to a corrosion-fatigue mechanism. The microstructure of the failed fastener predominantly consisted of 98 % tempered martensite, with some bainite and a small amount of chromium carbides, which is characteristic of quenched and tempered low alloy steel. Magnetic particle testing revealed similar crack marks on other fasteners in similar locations, indicating the points of maximum stress in these fasteners. Furthermore, finite element analysis using Abaqus software demonstrated that for a corrosion pit to grow, it required a minimum pit length and depth of 0.5 mm and 0.6 mm, respectively.