Pit Depth Research Articles

Plasticity in extended phenotypes: how the antlion Myrmeleon crudelis adjusts the pit traps depending on biotic and abiotic conditions

Abstract The physical structures built by animals are considered extended phenotypes that reflect how organisms make decisions and deal with changes in their biotic and abiotic environment. We summarize the results of several studies on Myrmeleon crudelis, a neuropteran larva that digs pit-traps in the soil to capture small arthropods (mostly ants) in the tropical dry forests of Costa Rica. Specifically, we showed how this species responds to varying biotic and abiotic conditions with changes in the design and/or location of its pit traps. Several experiments and field comparisons indicate that: 1) antlions adjust the pit design according to the abundance and type of prey. When prey is scarce, antlions increased trap diameter, an architectural adjustment that enhances the probability of prey encounter. Antlions that experienced high prey abundance, but the prey easily escaped, then increased pit depth, an adjustment that increases the chance of prey retention; 2) soil compaction strongly reduced pit-trap size and abundance; 3) antlions preferred soils with high proportion of fine-particle size to build pits. In fine-grained soil, pit-traps are larger and more efficient to capture prey than traps in coarse-grained soils; and 4) pit-traps may also be affected through indirect effects of soil structure and vegetation cover. Areas with fine-soil presented less plant cover, and plant cover could be beneficial for antlions because it acts as a shelter against direct sunlight and rainfall, or it may represent a cost because it is a source of leaflitter falling in the pits. The works summarized here how trap-building predators can exhibit considerable flexibility in trap construction in response to various biotic and abiotic factors, emphasizing how the study of extended phenotypes can be a useful approach to better understand the flexibility of foraging behaviors.

Experimental and numerical investigation on the corrosion effects on the bonding behavior between CFRP and steel

This paper intends to investigate the corrosion effects on the bonding behavior between CFRP and steel. The corrosion parameters such as the pit density Pd, the average pit depth Dave and width Wave were acquired by using an immersion simulation algorithm. By conducting the shear tests of the CFRP/steel single lap specimens, the bonding parameters such as the ultimate load Fu, the shear strength τmax and the fracture energy G were obtained and their relationships with corrosion parameters were established. In addition, finite element models considering the corrosion topography were proposed to simulate the bonding behavior. Results showed that the Fu and the G increased first and then stabilized as the Pd increased, and increased slightly then decreased as the Dave and the Wave increased, indicating that the corroded surfaces distributed with a large number of pits of appropriate sizes may maximize the bonding strength and the fracture energy; the τmax increased with the Pd, and decreased as the Dave and the Wave increased, indicating that a larger pit number and a smaller pit sizes would lead to a higher shear strength; the Fu and the interfacial shear stress distribution in finite element analysis were similar to the experimental results.

Electron transfer mediator PCN secreted by aerobic marine Pseudomonas aeruginosa accelerates microbiologically influenced corrosion of TC4 titanium alloy

Titanium alloys possess excellent corrosion resistance in marine environments, thus the possibility of their corrosion caused by marine microorganisms is neglected. In this work, microbiologically influenced corrosion (MIC) of TC4 titanium alloy caused by marine Pseudomonas aeruginosa was investigated through electrochemical and surface characterizations during a 14-day immersion test. Results revealed that the unstable surface caused by P. aeruginosa resulted in exposure of Ti2O3 and severe pitting corrosion with maximum pit depth of 5.7 μm after 14 days of incubation. Phenazine-1-carboxylate (PCN), secreted by P. aeruginosa, promoted extracellular electron transfer (EET) and accelerated corrosion. Deletion of the phzH gene, which codes for the enzyme that catalyzes PCN production, from the P. aeruginosa genome, resulted in significantly decreased rates of corrosion. These results demonstrate that TC4 titanium alloy is not immune to marine MIC, and EET contributes to the corrosion of TC4 titanium alloy caused by P. aeruginosa.

Corrosion behaviors of carbon steel induced by life activities of Phaeodactylum tricornutum in a marine environment

AbstractMicrobiologically influenced corrosion induced by bacteria has been studied for many years. Corrosion is known to be sensitive to the presence of microalgae, such as Phaeodactylum tricornutum. However, the life activity of P. tricornutum that influences the general and localized corrosion of carbon steel is not fully understood. The current study uses a combination of immersion tests and electrochemical experiments with a detailed surface characterization to reveal the naturally formed corrosion products with/without the presence of P. tricornutum. The results show that samples suffer from pitting corrosion and the averaged pit depths are approximately 15 μm under a light–dark cycle condition or a 24‐h constant light condition. Meanwhile, the corrosion products are mainly comprised of γ‐FeOOH and Fe3O4 in a constant light condition. However, γ‐FeOOH, Fe3O4, and FeCO3 are found in a light–dark cycle. This study proposes the fundamental mechanisms of the effect of P. tricornutum life activities on the corrosion performance of Q235 carbon steel, to fulfill the knowledge gaps of the presence of microalgae inducing the general and pitting corrosion of carbon steel.

Investigation on Ultrasonic Cavitation Erosion Behaviors of Al and Al-5Ti Alloys in the Distilled Water

Al and Al-5Ti alloys were manufactured by an ultrasonic casting method with a new device, and their ultrasonic cavitation erosion behaviors of Al and Al-5Ti alloys in the distilled water were clarified. The damage mechanism was analyzed by macro photograph, scanning electronic micrograph and three-dimensional morphology, and the results demonstrate that Al-5Ti alloys have better cavitation erosion resistance than Al in terms of the mass loss and the surface damage. The deformation mechanism of Al and Al-5Ti alloys under cavitation erosion is mainly dislocation slip, and the Al3Ti phase enhances the cavitation erosion resistance of Al-5Ti alloys. In addition, the maximum depth of cavitation pits in the Al-5Ti sample is less than that in the Al sample for 31.3%.

Research on corrosion performance of 6061 aluminum alloy in salt spray environment

AbstractSalt spray corrosion test was carried out on 6061 aluminum alloy, and quasi‐static tensile test at room temperature was carried out on the sample with universal testing machine. The effect of salt spray corrosion on the mechanical properties of 6061 aluminum alloy was studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electrochemistry. The corrosion rate of 6061 aluminum alloy was quantitatively characterized by different corrosion parameters. It was found that local corrosion of 6061 aluminum alloy occurred in salt spray environment, mainly pitting corrosion and intergranular corrosion. With the increase of corrosion time, the polarization resistance of 6061 aluminum alloy decreases, and the corrosion rate significantly increases. The average corrosion rate and the maximum corrosion rate of 6061 aluminum alloy were characterized by corrosion weight loss and corrosion pit depth. And they can be transformed into each other. The mechanical properties of 6061 aluminum alloy were mainly affected by the depth of corrosion pit. With the increase of corrosion time, the tensile strength and fracture strain decreased, resulting in poor plasticity of the sample. At the same time, the change of elongation of 6061 aluminum alloy can be accurately predicted by the depth of corrosion pit.

Исследование стойкости к высокотемпературной газовой и солевой коррозии жаропрочного интерметаллидного титанового сплава ВТИ-4

We investigated high-temperature gaseous and salt corrosion resistance of heat-resistant intermetallic titanium VTI-4 (ВТИ-4) alloy samples by conducting accelerated cyclic laboratory testing in air, in a NaCl environment, and in a mixture of Na2SO4 and NaCl. While testing the VTI-4 (ВТИ-4) alloy in air, we observed corrosion of a chemical nature and pseudo-parabolic specific mass variation kinetics. After cyclic testing in a NaCl environment at 700 °C the surface of the VTI-4 (ВТИ-4) alloy was covered by a film consisting of two layers: a mixture of Al2O3 and (Ti, Nb)O2 oxides, and a (Ti, Nb)O2 layer. In a NaCl + Na2SO4 environment at temperatures of 650 and 700 °C a liquid ion conductor film may manifest on the alloy surface alongside the oxides, while corrosion becomes predominantly electrochemical, of the pitting type. Globular orthorhombic phase particles initiate the pitting process. We detected that the pit depth in the alloy after testing in a Na2SO4 + NaCl environment at 650 and 700 °C is twice that obtained in NaCl at 700 °C. At the temperatures of 650 °C in Na2SO4 + NaCl and 700 °C in NaCl and Na2SO4 + NaCl environments the specific mass variation becomes negative, which is due to the oxide film peeling and shedding as temperatures change. The corrosion rate for the VTI-4 (ВТИ-4) alloy in the Na2SO4 + NaCl environment at 650 °C is lower than those for the nickel alloys VV751P (ВВ751П) and VZh175-ID (ВЖ175-ИД)

The Stability Analysis of a Cofferdam Using the Numerical Modelling

The foundation of the bridge pillars required the construction of cofferdams in the Danube River. The cofferdams protected the area of the excavation pit mainly against the effects of flowing water. The paper includes analysis of the cofferdam for the foundation of the main central pillar of the asymmetrical bridge. The cofferdam has the ground plan dimensions of 44 x 20 m. It’s constructed of the double-row sheet pile walls. The stability of the cofferdam was analysed using numerical modelling based on the finite element method using Plaxis geotechnical software. The level of backfilling inside the cofferdam, required for construction of the foundations, was 6 m above the bottom of the river. The depth of the excavation pit of the cofferdam was about 4 m below the river bottom. The numerical model included 15 construction phases, which corresponded to the procedure of the construction. The analysis were focused mainly on construction phases, such as, e.g., the total backfill of the cofferdam, the loading from the piling rig, creating the excavation pit inside the cofferdam and installation of struts, and the load from the maximum level of the Danube River. The analysis showed that there are two critical phases. The first critical phase represents the situation when the piling rig works near the edge of the cofferdam, and the Danube River is at a minimal level. The second critical phase occurs when the full excavation pit created, and the Danube River is at a maximum level.

Soil organic carbon distribution for 0–3 m soils at 1 km 2 scale of the frozen ground in the Third Pole Regions

Abstract. Soil organic carbon (SOC) is very important in the vulnerable ecological environment of the Third Pole; however, data regarding the spatial distribution of SOC are still scarce and uncertain. Based on multiple environmental variables and soil profile data from 458 pits (depth of 0–1 m) and 114 cores (depth of 0–3 m), this study uses a machine-learning approach to evaluate the SOC storage and spatial distribution at a depth interval of 0–3 m in the frozen ground area of the Third Pole region. Our results showed that SOC stocks (SOCS) exhibited a decreasing spatial pattern from the southeast towards the northwest. The estimated SOC storage in the upper 3 m of the soil profile was 46.18 Pg for an area of 3.27 × 106 km2, which included 21.69 Pg and 24.49 Pg for areas of permafrost and seasonally frozen ground, respectively. The mean SOCS under different vegetation types showed a decreasing pattern as follows: forest > shrub > cropland > grassland > desert. Among all soil orders, histosols and gleisoil had the largest SOCSs, while gypsisols and salt flats had the smallest SOCS. Our results provide information on the storage and patterns of SOCS at a 1 km2 scale for areas of frozen ground in the Third Pole region, thus providing a scientific basis for future studies pertaining to Earth system models. The dataset is open-access and available at https://doi.org/10.5281/zenodo.4293454 (Wang et al., 2020).

Technology for increasing safety of operation of pit-run and motor roads and prevention of dusting of tailings dumps by treatment them by natural bischofite water solutions

The ore mined in open pits, the depth of which often exceeds 200 m, is taken out of them as a ruie by dump trucks having capacity of up to 300 t. Provision of safety of pit-run motor transport and uninterrupted open pit operation, particuiariy in wintertime is an important task. Pecuiiarities of pit-run motor roads running presented. Existing methods of preventing winter siipperiness at motor roads considered, their possibilities and drawbacks highlighted. A technology elaborated to prevent the winter slipperiness and dusting of pit-run motor roads by treatment them by natural bischofite (MgCl2•6H2O) water solutions (RPB). The RPB has a density of 1250 kg/m3, freezing temperature -35 °С and is attributed to the substance of 4th class of danger. Dependence of rocks mass freezing temperature on the content of water RPB in it determined. Testing results of industrial technology of prevention winter slipperiness and dusting of motor roads in the open pits of Krivbas, Ukraine presented. The technology includes preliminary preventive treatment of the roads by a water solution of natural bischofite. Recommendations on its concentration, necessary for roads surface treatment were given, depending on the air temperature at various open pit depth and time of treatment commencement after receiving weather forecast. It was recommended to treat the pit-run motor roads by reagent of water RPB on the surface at air temperature down to -3 °С at the depth of more than 100 m - lower -3 °С, at the depth of more than 200 m - lower -5 °С. Recommendations elaborated to prevent dusting of motor roads, dumps and tailings dumps of mining and concentration plants by application natural bischofite water solutions, which effectively fasten the dusting surfaces preventing blowing-off the dust from them.

Electrochemical Behavior of Salt Film and Its Role in Pit Growth

In a recently published series of papers for pitting corrosion,1-5 a new concept of maximum pit dissolution current density, i diss,max, was proposed to establish a unifying framework for pit growth stability. This framework provides an opportunity to revisit several key topics of this field and generates new insights to interpret the previous observations in a self-consistent way. In this work, the unifying framework is further expanded to establish a mathematical model describing the electrochemical behavior of salt film after it precipitates, i.e. the situation when i diss,max > i lim. It can be mathematically shown that the main function of a salt film during diffusion-controlled pit growth is to accommodate the extra potential of (E max - E sat) by regulating its thickness to adjust the actual potential at the pit surface to E sat, thus restricting the anodic dissolution current density at the diffusion-limited value.4 The salt film will respond to any changes of the applied potential, temperature, pit depth, and perforation radius of the pit cover. In addition, an analytical model is proposed for salt film growth based on ion transport, in which the film grows at the metal/film interface and dissolves at film/solution interface. Any disturbance causing a difference in growth and dissolution rates will trigger a self-regulating process that will, in turn, bring the pitting system back to steady state. Acknowledgments: This work was supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584.Reference G. S. Frankel, T. Li, and J. R. Scully, Journal of the Electrochemical Society, 164 (4), C180-C181 (2017).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (9), C484-C491 (2018).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (11), C762-C770 (2018).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (6), C115-C124 (2019).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (11), C3341-C3354 (2019).

Photoelectrochemical Stability of NiO Thin Film As a Protective Layer Formed on GaN-Based Photoanode for Water Splitting Reaction Under Light Irradiation for 300 h

Gallium nitride (GaN) is expected as a photoanode to generate oxygen and hydrogen through a water splitting reaction. This is because the band-gap energy of GaN is 3.4 eV (λ ≤ 365 nm) and the top of the valence band is lower than the oxidation potential of water and the bottom of the conduction band is higher than the reduction potential of protons. However, some holes generated in the light-absorbing layer of a GaN-based photoanode are used not in the water oxidation reaction but rather in the etching reaction due to self-oxidation of the photoanode. As a result, the solar-to-hydrogen conversion efficiency η STH decreases over time. To improve η STH and prevent degradation of the GaN-based photoanode surface, it has been reported that supporting NiO on a GaN-based photoanode surface by spin coating using a metal organic decomposition solution is effective. The NiO/GaN-based photoanode has been evaluated under intermittent light irradiation for over 100 h [1]. To prevent the etching reaction from progressing, we have proposed to use NiO thin film as a protective layer for the photoanode on a sapphire substrate [2-4]. When we used this NiO thin film/GaN-based photoanode, the photocurrent density was 76% of the initial value after 100 h of continuous light irradiation [3]. Since some etch pits were observed after this time, we speculate that the decrease in photocurrent is related to the occurrence of etch pits. A transmission electron microscope (TEM) observation indicated that the etch pits are caused by dislocations that grew from the GaN-based layer to the surface. In this study, we investigated the photoelectrochemical stability to light irradiation for several hundred hours when using a GaN-based layer that was more crystalline than those in the previous studies as a photoanode.Al0.1Ga0.9N (AlGaN)/n-GaN heterostructures were grown by metal organic chemical vapor deposition on n-GaN substrate. Ni thin film (thickness: 1 nm) was fabricated on the AlGaN surface by vacuum evaporation. The sample was then heat-treated at 563 K for 60 min in air to form NiO thin film (thickness: 2.5 nm). The NiO thin film/AlGaN/n-GaN and Pt wire were immersed in 1 mol/L NaOH as the photoanode and cathode, respectively. The photocurrent was measured with a potentio-galvanostat (Solartron Analytical, 1287A) under UV light irradiation at 2.2 mW/cm2 (λ ≤ 365 nm). A Xe lamp (Asahi Spectra, MAX-303 with SHX450 filter) was used as the light source. The irradiated sample area was 1 cm × 1 cm.The photocurrent density 1 min after irradiation was 0.195 mA/cm2. The photocurrent density decreased with irradiation time and was 0.126 mA/cm2 at 300 h. However, in this experiment, the light intensity decreased by 30% after 300 h because the Xe lamp deteriorated with operating time. In order to correct the light intensity effect on the photocurrent density, the light intensity was adjusted to the initial value and the photocurrent was measured after continuous operation. The resulting photocurrent density at 300 h was 0.174 mA/cm2, which was 89% of the initial value. The surface and sectional structure of the photoanode before and after 300 h of irradiation were observed with a scanning electron microscope in order to investigate the structural change caused by the etching reaction. Most of the surface of the photoanode maintained its initial structure, though some hexagonal etch pits were observed. The etch pits occupied 8% of the surface area. The elemental analysis for pit depth direction was performed with TEM and an energy dispersive X-ray spectrometer in order to conform the layer structure at area with no pits and bottom of pit. The no-pit areas consisted of NiO, AlGaN, and n-GaN layers, while the AlGaN layer was not observed at the bottom of the pit. Therefore, the NiO and AlGaN layers occupied 92% of the photanode surface area. From these results, we consider that the loss of the effective reaction area due to the increase in etch pit density is the reason for the decrease in the photocurrent.[1] K. Ohkawa et al., Jpn. J. Appl. Phys., 52, 08JH04 (2013).[2] Y. Ono et al., Book of , ICARP, p4-17 (2017).[3] Y. Ono et al., The 85th ECSJ Spring Meeting, 1Q21 (2018) in Japanese.[4] K. Kumakura et al., The 79th JSAP Autumn Meeting, 19p-PA4-22 (2018) in Japanese. Figure 1

A One Dimensional Crevice Experiment for Determining the Critical Factors Contributing to Crevice Corrosion Repassivation

From its inception more than 40+ years ago, the one-dimensional pencil electrode experiment (1-D pit) has allowed investigators to study factors on pitting corrosion such as ohmic drop, concentration of species as a function of pit depth and the stability of salt films.[1,2] In recent work, Srinivasan and Kelly have developed a 1-D transport model of repassivation for pencil electrodes made of SS 316L.[3] Unfortunately, for the phenomenon of crevice corrosion, the understanding of these critical factors (that no doubt control crevice propagation and repassivation) are far less understood. The primary reason for this has been the inability to simultaneously measure the location of the active crevice front (e.g. its depth) and the active area (which fixes the current density). These two parameters are easily measured in the 1-D pit experiment.Previously, we introduced a method for measuring both the depth of the active front in crevice corrosion and the active area.[4] The method, similar to that which Pickering introduced years ago,[5] records video of a propagating crevice in the optical microscope. The crevice (RCA) is formed by an alloy 625 washer covered by an acrylic washer that acts as a crevice former. The potential of the assembly is controlled potentiostatically using a traditional three electrode set up and the current is recorded as a function of time. A stereo microscope equipped with a digital camera is used to record images of the initiation and propagation of crevice corrosion. Image processing software is used to quantify the area of the active front. We calculate the actively corroding area, crevice current density and wall potential (Eapp-IR) all as a function of time.In this presentation, we will present the results from our crevice repassivation study on alloy 625. We use the THE method (ASTM G192) to analyze the transition to repassivation in the 625 RCA. Once initiated, the crevice was allowed to propagate for various times, equivalent to increasing charge passed. After a fixed time, the applied potential was decreased in a stepwise fashion. At a critical potential, forward movement of the active corrosion front towards the mouth (e.g. new damage area) stopped, though crevice propagation continued. Transport calculations reveal that this potential may be associated with salt film dissolution, consistent with the transition potential (ET / Esat) reported for one dimensional pitting experiments. The results are discussed in terms of traditional crevice corrosion models (such as Oldfield-Sutton[6] and IR*[5]) and more recent models for pit growth stability (Li Scully Frankel[7]). A mechanism for crevice growth and the transition to repassivation that is similar to that believed to controlled pit propagation and repassivation is proposed.AcknowledgmentsWork on this project was made possible by a grant from the US DoD TCC #1000000149, program directors Gregory A. Shoales, USAFA, and Daniel Dunmire, Corrosion Policy Oversight.References JW Tester, HS Isaacs, JES, 122, 1438, 1975.RC Newman, HS Isaacs, JES, 130, 1621, 1983.J Srinivasan, RG Kelly, JES, 163, C768, 2016.RS Lillard, S Mehrazi, DM Miller, JES, 16 7, 2020.5. K Cho, HW Pickering, JES, 138, L56, 1991.6. JW Oldfield, WH Sutton, Br. Corr. J., 13, 1978.7. T Li, JR Scully, GS Frankel, JES, 166, 2019.

(Invited) Atmospheric Corrosion of Magnesium Alloys: Influence of Aluminium Content

Magnesium has gained considerable interest as a structural material for automotive and aerospace applications due to its low density and high specific strength. The use of magnesium alloys in engineering applications is, however, mainly limited by their unsatisfactory surface properties and their poor corrosion resistance. In recent years, significant improvements have been made in achieving a better corrosion resistance particularly by reducing the contents of impurities such as Fe, Cu, and Ni. Intermetallic phases, a result of the casting process, play an important role in the corrosion process. The role of these intermetallic phases has been addressed in a number of papers [1–3]. The role of aluminum in the atmospheric corrosion of magnesium alloys has less addressed in the literature [4]. Esmaily et al have shown recently that the rate of corrosion of magnesium alloys decreased when increasing the Al content. However these experiments were performed on commercial magnesium alloys produced high pressure die casting under constant RH exposure at 90% RH.In our work the corrosion behavior of binary Mg-Al alloys as well as that of commercial magnesium alloys with different aluminum contents have studied both under cyclic corrosion exposure in the laboratory and in field exposures in France and in Vietnam. Analyses of corrosion products have also been conducted. Additional in-situ measurements have been performed in order to better understand the atmospheric corrosion mechanisms of Mg alloys.An important decrease in the maximum pit depth can be observed after different laboratory exposures when increasing the aluminum content in the material. Similar results have been obtained after 9 months exposure in Field. Hence, from these results it is obvious that an increase of the aluminum concentration in Mg-Al alloys decreased the corrosion rate of the alloy. This lead in lower mass loss and less deep corrosion attacks in the magnesium grains. The analyses of corrosion products formed after the cyclic corrosion tests and field exposures revealed the presence of Magnesium carbonate and MgCO3(OH)4,4H20, respectively. In both cases magnesium hydroxide (Mg(OH)2 was also found in the corrosion products. The results will be discussed in relation with the microstructure of the cast materials. O. Lunder, J.E. Lein, S.M. Hesjevik, T.K. Aune, K. Nisancioglu, Werkstoffe und Korrosion 45 (6) (1994) 331–340. O. Lunder, J.H. Nordlien, K. Nisangliou, Corrosion Reviews 15 (3–4) (1997) 439–469.G. Song, A. Atrens, M. Dargusch, Corrosion Science 41 (1999) 249–273.M. Esmailly, D.B. Blucher, J.E. Svensson, M. Halvarson and LG Johansson, Scripta Materiala, 115 (2016), 91-96

Effect of T6 heat treatment on the surface tribological and corrosion properties of AlSi10Mg samples produced by selective laser melting

In this paper, the effects of T6 heat treatment at different solution-treated temperatures (400 °C, 450 °C, 500 °C and 540 °C) on the microstructure, wear and corrosion properties of AlSi10Mg samples prepared by selective laser melting (SLM) were investigated. The 1 M HNO3 solution was used to investigate the corrosion behavior of SLM-prepared and T6 heat-treated samples. The results showed that the Si is rejected from supersaturated α-Al matrix to form Si particles during T6 heat treatment and, at the same time, the Si-rich cellular boundaries of SLM-prepared samples are transformed into Si particles. The Mg2Si particles are also formed after T6 heat-treatment. The size of Si/Mg2Si particles increases with increasing the solution-treated temperature. The wear and corrosion resistance of as-built samples are significantly lowered by T6 heat treatment and, they decrease with increasing the solution-treated temperature. The SLM-prepared sample exhibits a selective corrosion attack at the border of the melt pools, whereas the T6 heat-treated sample shows a pitting corrosion. The depth and size of pits increases with increasing the solution temperature. Moreover, the size of pits is nonuniform due to the uneven distributed size of Si particles.

Pitting Morphologies and Characteristics of Low-Alloy Steel With and Without Plastic Deformation in Industrial and Non-industrial Marine Splash Zones

Pitting morphologies of E690 low-alloy steel in industrial and non-industrial marine splash zones are statistically analyzed, including the influence of plastic deformation. Results show that in a marine splash zone, E690 low-alloy steel experiences severe uniform corrosion and pitting corrosion, and the corrosion is more severe in the high-temperature non-industrial environment. The relationship between the pitting area changes and the depth can be well fitted to the Boltzmann cumulative distribution function to investigate the corrosion factors. In non-industrial marine splash zone, high content of chloride ions makes the metal surface have a high roughness and anodic dissolution is then promoted. The pitting depth is strongly promoted by anodic dissolution. In the marine splash zone, plastic deformation aggravates the maximum pitting depth, especially in the initial stage and in SO2-pollutant environments, although this effect gradually decreases. Pitting on low plastic deformation area in U bend samples may influenced by receiving electrons, which inhibits the protective FeOOH generation.

Bending performance of connection-corroded welded hollow spherical joints

Indoor swimming pools are a typical aggressive environment in which long-span steel structures are prone to corrosion, especially in the connection position of joints. In order to evaluate the impact of the corrosion on the mechanical properties of joints, a corrosion test of Q235 steel in a swimming pool environment was carried out for 48 and 72 months respectively. The surface pitting distribution of the corrosion specimens was measured and statistically analyzed, and a probability distribution model of surface pit depth was established. Then, a finite element model of welded hollow spherical joint, which could simulate local corrosion and pit distribution, was established, and the parameter analysis of connection-corroded joints on bending performance was conducted. The results demonstrated that the hoop corrosion range and corrosion depth rate were the most sensitive parameters to the bending performance. Taking the number of hoop corrosion zones and corrosion depth rate as parameters, the bending bearing capacity degradation rates of connection-corroded joints based on a specific guarantee rate and different conditions were obtained. Finally, a convenient method for evaluating the joints' bending bearing capacity degradation rate was proposed, which could provide a reference for studying the mechanical properties of similar connection-corroded joints and evaluating the safety performance of grid structures.

DYNAMIC CONSTRUCTION CONTROL METHOD FOR A DEEP FOUNDATION PIT WITH SAND-PEBBLE GEOLOGY

Taking the water-rich sand and pebble geology deep foundation pit of Jinfu Station of Chengdu Metro Line 6 as the research object, combined with the ladder excavation method of slotting, utilizing finite difference software FLAC 3D as well as on-site monitoring result, the deformation law of the diaphragm wall during the dynamic excavation of the foundation pit is analysed, and the influence of the relative stiffness between the vertical and horizontal walls of the foundation pit on the lateral deformation of the retaining structure is discussed. The results show that while using the ladder excavation method of slotting, the maximum lateral displacement of the underground diaphragm walls decreases gradually with the excavation depth of the foundation pit, which occurs at the intersection of the middle point of the oblique excavation line and the step distance section of the transverse excavation. Additionally, the lateral displacement increases closer to the excavation section. The lateral displacement of the envelope enclosure mainly depends on the relative constraint stiffness of the vertical and horizontal underground diaphragm wall of the foundation pit. The use of the ladder layered excavation method of slotting can effectively reduce the lateral displacement of the underground diaphragm wall. The simulated result and on-site monitoring result are nearly the same. These results can provide a corresponding theory and engineering basis for the selection of excavation methods for the same type of sand and pebble stratum foundation pit.

Nonlinear trending of corrosion of high nickel alloys in extended marine and atmospheric exposures

AbstractThe relatively limited data for the corrosion and pitting of high nickel alloys are reviewed herein and time-dependent trends developed for exposures in marine and atmospheric environments. Data sets for average or ‘uniform’ corrosion losses that are sufficiently extensive show topological consistency with the bimodal functional model previously observed for steels and various copper-nickel and aluminum alloys. Trends for localized corrosion (pit or crevice depth) plateau after earlier rapid growth over several years. The present observations add support to the concept that there is a change in corrosion behavior with extended temporal exposure and that this is generally consistent for many alloys. They also reinforce that shorter-term observations of maximum corrosion or pit depth usually is unsuited for extrapolation to, and prediction of, longer-term corrosion as typically important for practical infrastructure applications.

Modeling unidirectional corrosion damage evolution in a SS 316 pencil-electrode experiment

A three-stage, unidirectional pit growth model is developed to simulate corrosion damage evolution in a pencil electrode experimental setup. Stage I models initial pit growth, in the absence of a salt film, under activation control and a constant current density. Stage I is terminated when the ionic metal concentration reaches its saturation limit. Stage II models stable pit growth under diffusion control where the metal ion flux is the same as the dissolution rate of the metal at the bottom of the pit. During Stage II, the applied bulk potential is decreased at a specified scan rate. When the bulk potential reaches the transition potential, Stage III begins. In this stage the pit growth is under activation control that is defined by a prescribed polarization curve. Stage III continues until the metal repassivates as the potential is decreased. The governing system of equations for each stage is solved analytically, where possible, or numerically to determine the potential drop and the concentrations of sodium, chloride, and metal ions within the pit. The pit depth as a function of time is determined from Faraday's Law in Stages I and III, and from a mass balance at the electrolyte/metal interface in Stage II. The cumulative pit depth is compared with experimental pit depths in the literature for stainless steel in chloride solution.