Corrosive Media Research Articles

Progress of material degradation: metals and polymers in deep-sea environments

Abstract Given the critical need for ocean exploration, improving the durability of materials in the deep-sea has become a paramount concern. The harshness of deep-sea, such as high pressure, variable seawater flow rates, and corrosive media, lead to premature aging and failure. This work examines the utilization of metals and polymer coatings in deep-sea applications, detailing the characteristics of the deep-sea and its influence on these materials. In particular, chloride ions in seawater pose significant hazards to metal corrosion, which is the main reason for metal failure. Then, the degradation process and the latest research advances of various materials in the deep-sea environment are summarized, and the failure mechanism of the metal/coating system in the deep-sea is analyzed. It was found that the failure of polymer coatings can be divided into three processes, and adding an appropriate amount of fillers to the coating (such as adding 0.2 % graphene to water-based polyurethane) can extend the service life of the coating. Finally, the development trend of the company in the future is predicted. It has guiding and reference significance for the study of the failure behavior of metals and polymers in the deep-sea environment.

Surface-Grinding-Induced Recrystallization and Metal Flow Causes Corrosion-Assisted Penetrating Attack of High-Mn–Low-CR Casting Steel in Humid Environments

This study examined the surface-grinding-induced microstructural modifications and corrosion attacks in a penetrating form of a high-Mn–low-Cr casting steel slab under humid environments. Various experimental and analytical findings from field-emission scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and electrochemical analyses revealed that the abrasive grinding process led to the formation of a surface deformed region, comprising a recrystallized fine grain layer and multiple streamlines. Corrosion initially occurs preferentially along the boundary areas where Cr(Mn)23C6 particles are precipitated. Moreover, the corrosion products (Fe-based oxy/hydroxides) with a high volumetric expansion ratio detach readily from the surface deformed regions, facilitating the easy penetration of corrosive media. In contrast to conventional low-alloyed steels, which exhibit uniform corrosion behavior, corrosion-assisted penetrating attacks on ground high-Mn–low-Cr casting steel slabs occur more severely and frequently during the summer/dry season (i.e., relative humidity levels around 60% to 80%, rather than 100%) when a thin water film can form on the steel surface. Based on the result, effective technical strategies in terms of metallurgical and environmental aspects to mitigate the risk of corrosion-assisted penetrating attack of high-Mn–low-Cr casting steel were discussed.

Hollow conductive polypyrrole microtubes as microwave absorbents with good seawater corrosion resistance

Conductive polymers materials with hollow micro/nanostructure due to their special electrical properties and corrosion resistance have potential applications in microwave absorption, especially in marine environment. Herein, one-dimensional hollow conductive polypyrrole microtubes (H-PPyM) were prepared by in-situ polymerization of pyrrole monomer with methyl orange (MO) as soft template and FeCl3 as oxidant based on structural regulation strategy. The morphology and conductivity of H-PPyM can be easily controlled by adjusting the content proportion of MO. The results indicated that the surface morphology of polypyrrole changed from random granular to microtubular and the conductivity also gradually rose with the content increase of MO. When the content proportion of MO was 0.25 g, the obtained H-PPyM-0.25 composites possed notable microwave absorption capacity, simultaneously achieving ultrabroad effective absorption bandwidth (EAB, 6.7 GHz) and strong reflection loss value (RL, -33.6 dB) at a thickness of 2.6 mm with the filling content of only 10 wt.%, respectively. Furthermore, the corresponding H-PPyM-0.25 products soaked in corrosive medium (3.5 wt% NaCl solution) for one month still displayed stable tubular hollow structure and excellent microwave absorption performance with RLmin of -43.8 dB and EAB of 6.2 GHz. The research results can not only help to understand the relationship among the morphology and microwave absorption of PPy, but also open a new avenue for preparing excellent seawater corrosion resistant microwave absorption materials.

Creep rupture of smoothed and notched DD6 single crystal superalloy specimens subjected to high-temperature hot corrosion

This work studies the creep rupture behaviors of both smoothed and V-notched DD6 Ni-based single crystal superalloy specimens under both air and corrosion conditions, within a stress range of 300 to 700 MPa at 950 °C. The corrosive medium used consisted of a mixed salt containing 95 wt% Na2SO4 and 5 wt% NaCl. Experimental results revealed that notched specimens exhibited a creep rupture life extended by 6–16 times compared to smoothed specimens, with the extension becoming more pronounced as the stress concentration increased. High-temperature hot corrosion (HTHC) shortened the creep rupture time by up to 75 %. A significant HTHC-creep interactive effect was found through comparative creep experiments in air and corrosion conditions. The HTHC affected the fracture modes of the specimens, with factors such as the amount of salt infiltration into the superalloy, the corrosion duration, and specimen configurations playing critical roles. Microstructural analysis revealed that, compared with γ′ precipitates, γ matrix phase was more prone to creep damage and was more susceptible to corrosion.

Impressive reinforcement on the anti-corrosion ability of the commercial fluorocarbon paint via an amino groups modified graphene

The interaction with the matrix and the dispersion within the matrix hinder the realization of graphene's potential as an anti-corrosive filler. Herein, a -NH2 modified graphene-based filler (PS-PVP@NH2-rGO) was designed to simultaneously address these issues in the fluorocarbon resin (FEVE) coating. Reinforing FEVE coating with PS-PVP@NH2-rGO, the wear rate and the lowest-frequency impedance modulus after a 7-day immersion were found to be 0.35 times and 177.3 times those of FEVE coating respectively. Ultraviolet-Visible spectra confirmed the excellent dispersibility of PS-PVP@NH2-rGO. The designed differential scanning calorimeter experiment demonstrated the close interaction between PS-PVP@NH2-rGO and the FEVE matrix. Due to this close interaction, PS-PVP@NH2-rGO exhibited a high degree of dispersion within the FEVE matrix rather than self-aggregation, then concentrated the stress outside, absorbed energy produced during the friction process, and enhanced the coating's wear resistance. A complicated “labyrinth” was also created by the fillers. With chemical interactions, the fillers and the surrounding FEVE matrix formed an integrated whole, making the “obstacles” created by the fillers more significant. Consequently, the strong barrier effect resulted in superior anti-corrosion performances of PS-PVP@NH2-rGO/FEVE coating. Introducing -NH2 groups in was proven to effectively complete the coating, improve coating's quality and barrier effect, and finally prevent corrosive media. This study aims to provide design ideas and theoretical supports for high-performance heavy-duty anti-corrosive coatings.

Poly aryletherketone chemically modified multi-walled carbon nanotubes/poly etheretherketone electromagnetic interference shielding foam suitable for high temperature and strong corrosive media

Poly aryletherketone chemically modified multi-walled carbon nanotubes/poly etheretherketone (PAEK-m-CNTs/PEEK) electromagnetic interference (EMI) shielding foams were fabricated using supercritical carbon dioxide (Sc-CO2) foaming technique saturated near-melting point (Tm). The percolation thresholds for conductivity and EMI shielding of PAEK-m-CNTs/PEEK foams were both significantly reduced by the presence of the porous structure, reaching to 0.0457 vol% and 0.123 vol%, respectively. These reductions were observed to be 87.72% and 75.20% of those of PAEK-m-CNTs/PEEK composites. This could be attributed to the heterogeneous nucleation of PAEK-m-CNTs, which are uniformly dispersed in PEEK, in addition to the Sc-CO2 foaming technique saturated near Tm. By comparison, it could be observed that the specific total electromagnetic shield effectiveness (SSETotal) of PAEK-m-CNTs/PEEK foam with a filler content of 0.440 vol% was 687.9% higher than that of PAEK-m-CNTs/PEEK composite with a filler content of 0.496 vol%. Moreover, the introduction of the porous structure transformed the electromagnetic shielding material from reflective to absorptive. In addition, PAEK-m-CNTs/PEEK foams demonstrated the capacity to maintain stable performance even in high temperatures of up to 315 °C and in the presence of strong corrosive media.

Using of Extracted Tannin from the Bark of Gray Avicennia Marina (Avicennia Marina) and Cordia Myxa (Cordia Myxa) Trees as Corrosion Green Inhibitors for Carbon Steel Alloy in Acidic Media.

This study evaluated the corrosion inhibiting properties of natural tannins extracted from gray Avicennia marina bark and Cordia myxa bark for carbon steel alloys. Such alloys are widely used in shipbuilding construction where corrosion poses challenges. Tannin extracts were tested as green inhibitors across varying concentrations in 0.5 M hydrochloric acid solution, a corrosive medium. Trials were conducted at different temperature parameters to determine the inhibition efficiencies. The amount of hydrogen gas released over time was quantified to compare corrosion rates in the absence and presence of tannin inhibitors. The Langmuir and Freundlich isotherm models for adsorption were also studied, as well as the kinetic and thermodynamic functions, where the change in free energy and activation energy were calculated. The results of the study showed a promising possibility to use the compounds under study as corrosion inhibitors for carbon steel with high efficiency up to more than 83% at a temperature of 25 degrees Celsius. The results showed an increase in the free energy change (ΔGcorro) values for the corrosion reaction in the presence of the inhibitors under study compared to corrosion in the absence of inhibitors, The free energy change (ΔGcorro) values at 25 degrees Celsius were (184.4538, 184.9246, 111.9616) kJ.mol-1 in the presence of the Avicennia marina inhibitor, Cordia myxa inhibitor and blank) consecutively. As a result, the speed of the corrosion reaction will decrease in the presence of inhibitors.

Formation mechanisms of product film on high corrosion resistant EW75 Mg alloy: The effect of corrosive media

Compact and uniform product films with the similar microstructure as magnesium substrate are formed on EW75 alloy in both NaCl and Na2SO4 solution, and the film growth rate in Na2SO4 was even faster than that in the higher corrosive NaCl. This special phenomenon was investigated by electrochemical measurements, transmission electron microscopy (TEM) observation and X-ray diffraction (XRD) analysis, experimental design of corrosive media with different conductivity and concentration was used, and the corrosion process of Mg matrix and Mg-RE precipitates was explored, respectively. The results show that compared with Cl-, SO42- exhibits the stronger binding trend with Mg2+/RE3+, resulting in the faster charge transfer of the anodic metal in SO42- containing solution. And the higher dissolution rate of Mg substrate in Na2SO4 solution promotes the formation of the product film.

Investigating the Tribocorrosion Behaviour of NiTiNOL60 Alloy in Engineering and Biomedical Applications—An Overview

This review covers the literature that is currently accessible, as well as emerging research into the performance of NiTi-based alloys exposed to corrosive environments in both engineering and medical applications. It provides an overview of the state-of-the-art research in the study of tribocorrosion of Ni-rich NiTi alloy by highlighting significant discoveries, research approaches, and future research directions following the limited reviews on tribocorrosion in the past decade. The practical impacts, as well as the economic implications of tribological applications on daily life, coupled with the increasing failures of metals and biomaterials, make it imperative to investigate tribocorrosion and update the subject area on the recent focus. Tribocorrosion is commonly observed on the surface of different metals, including NiTi alloys, such as NiTiNOL60 (60 wt.% Ni and 40 wt.% Ti), which possess unique properties applicable across various engineering and biomedical fields. In its application, the material experiences wear due to the depassivation of tribofilms caused by relative motion (sliding, fretting, or impact) in aggressive environments, including corrosive mediums, high temperatures, and pressures. This study elucidates the synergistic interactions between mechanical wear, corrosion, and their associated tribocorrosion mechanisms in corrosive media.

Microcapsule-type multifunctional microwave absorbing material with self-warning and corrosion resistance performances

The corrosion and damage from the environment directly reduce the lifespan of metal-based absorbing materials, severely limiting their widespread application. Designing a novel system to promptly alert against corrosion, subsequently offer corrosion inhibition after the alert to create a window for artificial repair of the materials, this would be a completely new approach. Herein, a “microcapsule-type” multifunctional absorbing material (CIP-M) is obtained. CIP-M is composed of self-warning and anticorrosive core material, Fe3+ responsive inner shell, and microwave absorbing CIP particles outer shell. The multifunctional CIP-M in coating (CIP-M-EP) exhibits a significant fluorescence self-warning effect under 254 nm light in the early stages of corrosion. Meaningfully, thanks to the 3D CIP core–shell structure, the maximum reflection loss of CIP-M-EP is up to −35.96 dB, much higher than other coatings. Meantime, once corrosion occurs, the corrosion resistance properties of CIP-M greatly inhibit further the attack by the corrosion medium. CIP-M-EP coating maintains higher impedance modulus at 0.01 Hz and microwave absorbing performances during the first 45 days of corrosion, providing sufficient time for artificial repair of the coating. More interestingly, CIP-M also endows materials with good flexibility, anti-counterfeiting, and information encryption functions. These effective extend the application fields of CIP-M.

Corrosion behaviors of electromagnetic wave absorbing coatings with varying absorber content under combined UV and salt spray exposure

Despite extensive research on the impact of environmental weathering on the degradation of electromagnetic wave absorbing (EWA) coatings, the influence of material composition on their service stability remains underexplored. In this study, we prepared EWA coatings with epoxy resin as the matrix and flaky carbonyl iron (FCI) as the absorber, at concentrations of 50 wt%, 60 wt%, and 70 wt%. These coatings underwent a 192-h combined UV irradiation-salt spray accelerated aging test to examine the effects of varying absorber concentrations on their corrosion behavior and mechanisms. Surface morphology, chemical structure evolution, and corrosion diffusion were analyzed using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDX). Corrosion behaviors and their impact on wave absorption performance were further investigated using electrochemical impedance spectroscopy (EIS) and electromagnetic simulations. Our results show that increasing FCI content accelerates the corrosion rate of the composite coating. This acceleration is attributed to the reduced protective effect of the epoxy matrix at higher FCI concentrations and the defects caused by FCI corrosion, which facilitate the penetration of corrosive media. This study elucidates the influence of varying absorber concentrations on the weather resistance of the coatings and their microscopic mechanisms, providing valuable insights for optimizing the service stability of EWA coatings.

Synthesis and evaluation of tribo-mechanical and corrosion properties of electroless Ni-P coating on AZ91D Mg alloy with stannate conversion underlayer

The work reports on synthesis and comprehensive evaluation of different properties of a bilayer protective coating on Mg alloy of AZ91D grade. Initially the alloy substrates were treated in stannate bath for 15, 30, 45, 60, 75 and 90 min for synthesizing an MgSnO3.3H2O layer. Electroless Ni-P was then deposited for 30 and 60 min, on the stannate layer synthesized for 60 min. A time-dependent cyclic growth behaviour was observed for stannate layers, characterized by formation and dissolution of MgSnO3.3H2O globules. The stannate coatings displayed polycrystalline structure. Hardness and scratch resistance were strongly influenced by uniformity of the coatings. While the uncoated alloy exhibited hardness of only 93 HV0.05, a remarkable improvement in hardness to 484 HV0.05 was obtained after 60 min of stannate treatment. High critical load of adhesion (Lc3) of 29 N was also obtained for the same. The stannate layers exhibited coefficient of friction (CoF) of 0.4–0.6 as compared to 0.7–0.8 for bare alloy. The wear loss also notably reduced. In tribo-test, hard and well-adherent coating restricted surface deformation under action of normal load. This in-turn, reduced mechanical engaging at interface, leading to low CoF and wear loss. The dense stannate coating also reduced corrosion rate by 19 times by hindering penetration of corrosive medium. Electroless deposition for 30 min on stannate conversion layer yielded only sporadic growth of Ni-P, which improved to a dense, uniform layer after 60 min of deposition. The Ni-P top coating aided the stannate underlayer in furthering the tribo-mechanical and corrosion characteristics.

Inorganic Acid Resistance Performances of Magnesium Phosphate Cement: A Two-Year Observation.

Magnesium phosphate cement (MPC), a cementitious material that hardens through an acid-base reaction, is theoretically expected to exhibit strong acid resistance. However, studies on the durability of MPC in acidic environments remain limited. This study aims to systematically evaluate the acid resistance of MPC in common inorganic acid solutions across various pH levels. By measuring changes in compressive strength, mass loss, apparent changes, pH changes, and the microstructure evolution of MPC under acidic conditions, the mechanisms and influencing factors of its acid resistance are revealed. The results indicate that at pH levels of 1.0 and 2.0, MPC's resistance to H2SO4 and HCl erosion is markedly superior compared to its performance against H3PO4, as evidenced by compressive strength retention, mass loss, and visible erosion. At pH levels above 2.0, MPC demonstrates robust resistance to all tested corrosive media, with compressive strength retention ranging from 68.9% to 86.9%, irrespective of the acid source. Although new corrosion products form in these acidic environments, the adverse effects of NH4/P loss from struvite, along with the redissolution of corrosion products due to their higher solubility, increase porosity and subsequently reduce the mechanical strength. Nevertheless, considering that strength retention is significantly higher than that of other cement-based materials reported in the literature, MPC still exhibits good acid resistance and is suitable for environments requiring enhanced resistance to acid corrosion.

Phenylurea-based corrosion inhibitor with ultra-high protection efficiency under acidic conditions

The pickling process often poses significant environmental challenges, particularly due to the addition of surface-active organic compounds to acidic solutions to inhibit corrosion on stainless steel surfaces. To minimize the generation of waste solutions and prevent excessive corrosion of stainless steel, the development of high-efficiency corrosion inhibitors for pickling solutions is of substantial practical and industrial importance. In this study, organic corrosion inhibitors prepared from aniline, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine with 1,4-phenylene diisocyanate were investigated. The structure of the resulting inhibitor films was characterized using FTIR, EDS, Mapping, and SEM, revealing good homogeneity and density, which effectively form protective layers on metal surfaces. The inhibitors exhibited excellent corrosion inhibition performance, with the protection efficiency of aniline-based inhibitors reaching 98.6 % at a concentration of 200 ppm in a 1 M HCl solution, significantly reducing the dissolution of Q235 stainless steel (Q235SS). Additionally, the relationship between inhibitor performance and molecular structure was analyzed using DFT calculations. The results demonstrate that phenylurea-based corrosion inhibitors with large π-conjugated planar structures and amine-based polar functional groups provide superior corrosion protection in HCl corrosive media.

Green corrosion inhibitors for nickel in acidic media utilizing novel imine ligand and its Zn (II) metal chelate supported by DFT calculation

L and ZnL complex act as corrosion inhibitors were synthesized and their structural elucidation were characterized via various spectroscopic and physicochemical tools. Correlation of experimental data with DFT calculation affords that ZnL complex is octahedral. L and ZnL compounds were used as essential components and environmentally benign inhibitors to reduce the rate at which Nickel as metal and its alloys corroded. In the investigative research, 0.5 M H2SO4 was used as the corroding medium. Electrochemical impedance spectroscopy and the Tafel plot were used to analyse the electrochemical performances of L, its complex with Zn, and the inhibitory effect in the acid under test. Processes of Ni corroding in an acidic solution have been examined in relation to additive existence and deficiency. The obtained data demonstrate that while the inhibitory effect increases as the dose of the additives is increased, density of corrosion current Icorr. gradually decreases. It is noted that inhibition efficiency decreases with increasing temperature especially at high temperature (55 °C) in the case of presence of 1 × 10−3 M of L as an additive (η = 70.4 %). Although, in the case of utilizing ZnL complex as an additive, it in noted that inhibition efficiency η% is nearly the same and slightly changed with raising temperature. In the case of existence high dose of ZnL, η% slightly increases with temperature indicating chemisorption process of the additive on Ni surface in the acidic medium. When the additives are present in the solution, both the cathodic and anodic reaction processes are impacted. Furthermore, the presence of the ligand or its complex reduces the amount of NiO that forms on the electrode’s exterior sides. This finding implies that the adsorption mechanism of ZnL additive species follows Langmuir model and that kind of ligand and its complex adsorption on its outside are chemical in nature. These results have also been confirmed by electrochemical impedance spectroscopy. The ligand and its complex were included as additives, which significantly improved nickel’s corrosion resistance, according to the results. Studies on the effects of temperature have been done with different additive doses and Tafel plot method. High activation energy value of (−79.3 kJ. mol−1) was achieved when using 1 × 10−4 M of the L as well as (−82.8kJ. mol−1) in the presence of 1 × 10−3 M of ZnL in 0.5 M H2SO4. The standard enthalpy change ΔH0ads. for Ni in the acidic medium taking many dosages of L and ZnL were −31.16 and –32.72 kJ/mol, respectively. In light of this result, the adsorption process was chemisorption and the adsorption method was exothermic. Positive ΔS0ads values are correlated with an increase in solvent energy and a rise in the water desorption entropy. Employing scanning electron microscopy, the outward side morphology of the corroded samples was examined. Through a scanning electron microscope, the framework and texture of the films of oxide that are generated on Ni after potentiodynamic polarisation at different doses of ZnL additive are apparent.

Assessment of Oil Paints for Corrosion Protection of Reinforcing Steel Bars in Concrete

Corrosion becomes a threat to reinforced concrete structural integrity during the service life of the structural member. This situation has become a global concern because of the economic and safety implications. Hence, many corrosion inhibition techniques including coating with materials (organic and inorganic) were used to prevent its devastating effects. The present study used three oil paint brands (mat, red-oxide and gloss Leyland oil paints in Ghana) to variedly coat reinforcing steel bars to ascertain their corrosion protection capacity in concrete. There were zero, one, two and three paint coats of average film thickness, 72 µm, 129 µm and 220 µm respectively explored. An Electrochemical process involved simulated concrete pore solution made of 10% sodium chloride (NaCl) in distilled water with three electrode systems to represent a corrosion medium was used to determine corrosion protection capacity of the paints. The results indicate over 90% corrosion resistance of the paints used. Comparing the corrosion rates of the coated and uncoated reinforcing steel bars, while it would take a one coat steel bar 342.5 years and 237 years respectively for spraying and manual brushing modes to reduce in diameter by 0.616mm, it would take only one year for an uncoated steel bar to reduce by this same 0.616mm. The protection capacity proved better with increasing coats on all corrosion variables for the selected paints used. The implication is that the selected oil paint brands are capable of protecting reinforcing steel bars in concrete against corrosion and therefore recommended for application to reduce maintenance cost. Statistically, no significant difference existed between coating mode, number of coatings, paint type and steel type on the corrosion variables for the coated steel bars. However, a further study about the durability of the coating in the concrete during its service time is recommended.

EVALUATION OF PHYSICAL AND MECHANICAL PROPERTIES OF THERMOPLASTIC COATING BASED ON POLYOLEFINS

The article presents an analysis of the results of physical and mechanical tests of thermoplastic coating samples after exposure to corrosive solutions. To obtain a thermoplastic coating, powder polymer paint of two original compositions was used. According to the results of the experiments conducted to study the change in the strength of the thermoplastic coating material based on polyolefins after its exposure to corrosive solutions, it is received that the decrease in the tensile strength is no more than 5 %. This is quite a good result, and is a background for their use on the metal surface of oil and gas equipment operating in corrosive mediums.

Additive manufacturing of multiscale NiFeMn multi-principal element alloys with tailored composition

Abstract Nanostructured multi-principal element alloys (MPEAs) have been explored as next-generation engineering materials due to unique mechanical and functional properties which have significant advantages over traditional dilute alloys. However, the practical applications of nanostructured MPEAs are still limited due to the lack of scalable processing approaches to prepare a large quantity of nanostructured MPEAs, as well as lack of an efficient pathway for high-throughput discovery of better functional nanostructured MPEAs within their vast compositional space. Here we tackle these challenges by presenting an integrated approach by combining direct-ink-writing-based additive manufacturing, solid-state sintering, and chemical dealloying to manufacture hierarchically porous MPEAs. The hierarchical structure is comprised of macro- and micro-scale pores introduced via extrusion printing and polymer decomposition during sintering, as well as nanoscale pores formed via chemical dealloying. The macro- and micro-scale pores allow efficient dealloying of a large mass of material as the diffusion length that the corroding medium must penetrate remains at the scale of the ligaments formed after sintering (∼10 μm), despite the large volume of the 3D-printed samples. In addition, this integrated approach enables versatile control of the alloy composition via precisely tuning the ratio of elemental powders in the starting ink, thus offering a pathway for high-throughput discovery of novel functional MPEAs. As a case study, multiscale macro/micro/nanoporous NiFeMn MPEAs with three different compositions were investigated as catalysts to reduce the overpotential of oxygen evolution reaction (OER), where NiFeMn-based electrocatalysts display composition-dependent performance such that the overpotential measured at a current of 0.5 A g−1 for OER increases in the order of Ni58Fe29Mn13 ⩽ Ni64Fe26Mn10 < Ni76Fe18Mn6. This introduced manufacturing process offers new opportunities for scalable fabrication and rapid screening of nanostructured multi-component complex alloys.

ENHANCING SURFACE CHARACTERISTICS OF AA2024-T3 AIRCRAFT ALLOY THROUGH SYNERGISTIC ANODIZATION AND CERIUM CONVERSION COATING. PART I: PERFORMANCE IN MODEL CORROSIVE MEDIUM

The present study is devoted to the monitoring of the performance of AA2024-T3 specimens, after the formation of Anodic Aluminum Oxide (AAO) layer and/or deposition of a Ceruim Conversion Coating (CeCC), obtained at 20°C and 50°C, respectively. Although both methods are well described in the literature, there is no sufficient information regarding the effect of their combination on their behaviour in corrosive media. The performance of the respective specimens was elucidated after 24 h of exposure to 3.5 % NaCl model corrosive medium (MCM) by means of Electrochemical Impedance Spectroscopy (EIS) and acquisition of Potentiodynamic Scanning (PDS) curves. Since the combined AAO/CeCC coating primers revealed superior barrier properties, the respective specimens weresubjected to long-term corrosion tests of up to 672 h of exposure to the MCM to evaluate their durability. The results revealed the synergistic effect of the combination of the surface treatment procedures on effective corrosion mitigation.

Research on the multi environmental corrosion characteristics and mechanism of B4C doped Fe–Cr–Ni composite coating produced by laser cladding

Different Fe–Cr–Ni composite coatings doped with B4C were produced on the surface of Cr12MoV steel by laser cladding. Special attention was paid to the effects of B4C content on the phase composition, microstructure, and corrosion resistance of the cladded layers. The results indicated that the Fe–Cr–Ni composite coating was primarily composed of α-(Fe, Cr) and γ-(Ni–Cr–Fe) solid-solution phases, as well as Fe2B, M7C3, Fe3Si and M23C6 phases. Once the B4C content increased to 10 wt%, the microstructure of the cladding layer became coarse and exhibited the prominent carbide agglomeration. The composite coatings with different B4C contents exhibited superior corrosion resistance compared to the pure substrate in both 3.5 wt% NaCl and 1 mol/L HCl solutions. Furthermore, as the B4C content increased, the corrosion resistance of the coating initially increased and then declined. In particular, the Fe–Cr–Ni composite coating with an 8 wt% B4C content experienced the pronounced passivation in the corrosive media and possessed the optimal corrosion resistance due to the synergistic effect of the passive film and carbide barrier layer.