Reduced Corrosion Resistance Research Articles

Electrochemical corrosion and high temperature hot corrosion behavior of NbTaTiV and CrNbTaTiV high entropy alloy

NbTaTiV and CrNbTaTiV were fabricated by arc melting and effect of Cr element on electrochemical and high temperature hot corrosion behavior were compared. Electrochemical corrosion investigations revealed that Laves phase at grain boundaries of CrNbTaTiV would underwent galvanic corrosion, resulting in a marginal reduction in corrosion resistance. The results of high temperature hot corrosion showed that within Na2SO4 + 25 wt% NaCl molten salt environment, the oxide film formed by Cr element effectively improved the surface stability, reduced the formation of unprotected loose corrosion products and the generation of low melting point chlorides with strong volatility, which improved the resistance of molten salt corrosion.

Evaluating the Influence of Hydrophobic Nano-Silica on Cement Mixtures for Corrosion-Resistant Concrete in Green Building and Sustainable Urban Development

The use of hydrophobic nano-silica particles in concrete for improved corrosion resistance and durability has been explored in recent years, and its potential impact on sustainable urban development and green building practices has been studied. The impact of substituting hydrophobic nano-silica particles for 2% of the cement weight in high-strength concrete mixes was investigated in this research. The study focuses on evaluating the physical-mechanical properties, including compressive strength, tensile strength, modulus of elasticity, and Poisson’s ratio. Additionally, the influence of these mixes on corrosion resistance is examined. The concrete designs feature a high strength of 42 MPa, and the hydrophilic nano-silica particles undergo functionalization processes to obtain hydrophobic properties. Contact angle measurements and water absorption tests confirm the hydrophobicity of the material. Physical, electrochemical, and electrical tests were conducted to determine the corrosion resistance contribution of the nano-silica particles when substituted at 2% of the cement weight. The research findings reveal that concrete containing nano-silica particles demonstrates improved physical-mechanical properties compared to other mixes. Incorporating nano-silica enhances concrete by accelerating hydration, increasing early-age strength, and providing hydrophobicity, resulting in improved physical-mechanical properties over other mixes. However, it was observed that the addition of hydrophobic and non-hydrophobic nano-silica tends to reduce corrosion resistance compared to concrete without these particles, despite exhibiting greater compactness. This suggests a direct influence of nano-silica on the corrosion phenomenon.

Corrosion behavior of 7050 and 7075 aluminum alloys processed by reactive additive manufacturing

In this work, high-strength 7075 and 7050 aluminum alloys were processed by the laser powder bed fusion (LPBF) technique. Titanium and boron carbide particles were added to base 7050 and 7075 alloy feedstocks. These reacted in the melt to form inoculants in situ, resulting in a crack-free, refined, and textureless microstructure. X-ray diffraction, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectroscopy (EDS) techniques were used to characterize the process-induced microstructure of the alloys. Reactive Additive manufactured (RAM) alloys showed precipitation of various sub-micron to nanoscale phases such as Zn-Cu, Cu-Fe, Mg-Cu, Mg-Zn, and pure Zn. The corrosion response of RAM alloys was analyzed and compared with respective wrought alloys by various electrochemical measurements such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and atomic spectroelectrochemistry (ASEC) techniques. A reduction in corrosion resistance was observed in RAM alloys as compared to wrought counterparts due to thepresence of unreacted Ti and B4C particles and a higher cathodic activation attributed to the underlying microstructure. Time evolution surface imaging and post-corrosion microstructures were analyzed to support the understanding of underlying corrosion mechanisms.

Investigation of aqueous slurry erosion-corrosion behaviour of Tantalum in different pH solutions

Erosion-corrosion behaviour of pure Tantalum (Ta) was investigated using corrosive slurry solutions (pH 4, 7, and 10) containing 7 wt% SiC as erodent particles. Tests were carried out using an impinging jet erosion-corrosion apparatus with a jet velocity of 5 ms−1 and at two impact angles (30° and 90°). Under particle bombardment conditions, a marked reduction in corrosion resistance offered by Ta was observed amid a significant cathodic shift in the ECorr values for all pH values investigated. Results showed that interaction between erosion and corrosion was higher under 30° impact leading to a higher rate of material removal. On the contrary, negative synergism was observed for experimental conditions of normal impact for pH 7 and pH 10. Scanning electron microscopy studies revealed typical ductile erosion mechanisms of material removal which consisted of dominating micro-cutting for 30° and plastic deformation resulting in lip formation for normal impact angle. These appeared to be assisted by dissolution of weakened areas and passive layer removal as corrosion mechanisms. Potentiostatic erosion-corrosion experiments were utilised for calculation of synergistic and antagonistic effects and have been presented in the paper.

Effect of Plastic Deformation and Acidic Solution on the Corrosion Behavior of Ti-6Al-4V ELI Titanium Alloy

This study investigated the tensile deformation of Ti-6Al-4V ELI titanium alloy and its effect on corrosion performance. The results showed that the structural morphology of the samples’ strain levels of 0%, 5%, and 10% had minimal changes under an optical microscope. Further investigation of grain orientation information was conducted using electron backscatter diffraction (EBSD), revealing that tensile deformation induced grain rotation, resulting in the diversity of originally preferred orientation grains and a decrease in texture strength. A small amount of {10–12}<−1011> extension twinning formed during the tensile deformation process. The electrochemical properties of Ti-6Al-4V ELI samples with different strain levels were evaluated in 3.5% NaCl solution with pH values of 7 and 1.5. The results indicated that both plastic deformation and acidic environments were detrimental to the passivation film on the titanium alloy surface, leading to reduced corrosion resistance.

Effects of Al and Co contents on the microstructure and properties of AlxCoCryFeNi high-entropy alloys

AlxCoCryFeNi high-entropy alloys (HEAs) were prepared by vacuum arc melting. The effects of Al and Cr contents on the microstructure, corrosion resistance and mechanical properties of the alloys were evaluated. Results showed that with an increase in Cr content, the phase of the alloys changed from FCC + B2 + BCC to FCC + B2 + BCC + FeCr when the Al content was 0.75 (X = 0.75). Coarse FCC dendrites decreased. The alloys exhibited two mixed BCC/B2 structures with different morphologies: (i) the granular B2 phase distributed in the BCC matrix and (ii) the maze-like spinodal decomposition structure. At X = 1.5, the FCC and FeCr disappeared, and the microstructure of the alloy transformed into a mixed structure with a nanoparticle-like BCC phase distributed in the B2 matrix. During compression testing, the fracture type was brittle fracture for all alloys, except for X0.75Y1, which exhibited excellent mechanical properties with a fracture strain of 40% due to partial plastic tearing. Both B2 and FeCr phases, which were rich in AlNi and Cr, respectively, showed reduced corrosion resistance. For the former, the loose structure of Al2O3 reduced the compactness of the passivated film; for the latter, the precipitation of the Cr-rich phase led to a Cr-poor region in the periphery. The Al0.75CoCrFeNi alloy exhibited the highest corrosion resistance, which was attributed to its reduced FeCr and B2 phases.

Microstructure evolution and corrosion behaviors of cold-rolled 304 stainless sheets of steel in 3.5% NaCl solution

Austenitic stainless steel (ASS) is widely used in engineering applications due to its good corrosion resistance and mechanical properties. Several studies have indicated that the deformation-induced transformation of martensite in ASS significantly affects its corrosion resistance. However, corrosion resistance behavior in chloride-rich environments is more complex, and different cold-working methods have distinct impacts on localized corrosion. This study investigated the structural and corrosion resistance changes induced by cold rolling in AISI 304 samples. The used samples were initially subjected to a cold-rolling process with a thickness reduction of up to 50%. The results demonstrate an increase in the deformation-induced martensitic transformation and micro-hardness as the level of cold deformation increases. However, higher levels of deformation lead to the fragmentation of the formed a’‑martensite lath structure into smaller laths, ultimately resulting in a predominantly refined and diffuse dislocation-cell-type structure. Potentiodynamic tests were conducted to analyze conventional electrochemical parameters, revealing a reduction in corrosion resistance with increasing cold deformation. This suggests that the formation, amount, and microstructure of a’‑martensite, under imposed strain conditions, induce changes in the studied electrochemical parameters. Additionally, the more deformed samples exhibited a higher current density during passive layer formation, and exhibited more intense metastable pits, suggesting decreased corrosion resistance with higher degrees of deformation.

Effect of machining operations on mechanical properties, surface integrity and corrosion resistance of tungsten heavy alloy

Tungsten heavy alloys (WHAs) are metal-metal matrix composites which are suitable candidates for defence and nuclear applications. In order to meet the geometric complexity and dimensional tolerance of products made with these WHAs, secondary machining operations are necessary. The effect of three set of machining operations (wire EDM, rough turning and finish turning) on mechanical properties, surface residual stress, surface and sub-surface hardness and corrosion resistance are explored in this work. Uniaxial tensile test specimens were prepared with two different sets of feed rate and depth of cut corresponding to rough and finish turning. For the specimens prepared with harsher conditions around 20% reduction in elongation was noticed though there were no significant changes in yield strength or ultimate tensile strength. Finish turning resulted in a surface residual stress in the order of 700 MPa, compressive in nature. Though compressive, the magnitudes of the surface residual stress were significantly reduced for the other two operations. Turning operations were found to work harden the surface while WEDM caused a reduction in surface hardness. Subsequent variations in the subsurface hardness were also observed reaching upto a depth in the range of 50–150 µm. Surfaces produced under different machining conditions were exposed to chloride solution to examine the impact of surface integrity on the corrosion behaviour and the correlation among the two are investigated. Rough turned surfaces and wire EDM surfaces have shown reduced corrosion resistance.

Precipitate evolution and its effect on corrosion properties of different weld joints for Al-Mg-Er alloy

The study investigated precipitate evolution and its effect on corrosion properties in Al-Mg-Er alloy welded joints fabricated by metal inert gas (MIG) and laser welding (LW) techniques. It was observed that the morphology and size of precipitates in different joints varied significantly, with 40 μm elongated precipitates occurring in the heat-affected zone (HAZ) of the MIG joint, contrasted with abundant 2 μm precipitates in the weld metal (WM) of the laser joint. Large pits were observed in the MIG-HAZ, exhibiting dimensions of 17.4 μm in length and up to 7.1 μm in depth. Contrastingly, the LW-WM revealed smaller and shallower pits around 2.2 μm in length and 0.3 μm in depth. Polarization curves revealed that the corrosion potential of MIG-HAZ was the most negative, indicating its inferior corrosion resistance, which aligned with the corrosion morphology findings. Coarsened Al6(Mn,Fe) precipitates in the MIG-HAZ notably reduced corrosion resistance, as they hindered the formation of a stable passive film. Conversely, the LW-WM featured the Al2Er0.307Mg0.693 phase around Al6(Mn,Fe), which enhanced corrosion resistance compared to the base metal due to the fine and dispersed distribution of precipitates.

Revealing the Impact of Micro-SiO2 Filer Content on the Anti-Corrosion Performance of Water-Borne Epoxy Resin.

Due to green development in recent years, water-borne epoxy resins (WBE) have become increasingly popular since they generate the lowest level of volatile organic compounds (VOC) during curing. However, because of the large surface tension of water, it is easy to produce voids and cracks during the curing process of the coating. An electrochemical strategy was used in this study to assess the impact of different SiO2 content on the corrosion performance of a WBE coating, in which micron spherical SiO2 particles were synthesized in a liquid phase reduction. The results showed that the synthesized micron spherical SiO2 particles were about 800 ± 50 nm in diameter and in an amorphous state. By hydrophilizing the surfaces of these SiO2 particles, uniform dispersion in an aqueous solvent and a WBE can be achieved. It is important to note that adding a small or excessive amount of SiO2 to a coating will not improve corrosion resistance and may even reduce corrosion resistance. With the appropriate modification of SiO2, corrosion resistance of composite coatings is greatly enhanced, as is the adhesion between the coatings and the metallic substrates. Because the appropriately modified SiO2 can effectively fill the pores that are formed during the curing process, a corrosive medium is less likely to react with the matrix when the medium comes into contact with the matrix. Based on their incorporation content of 3 wt.%, their corrosion resistance is the best after 16 cycles of AC-DC-AC accelerated corrosion tests.

Influence of grain refinement on strength and corrosion resistance of 316LN steel welded joint

The cost of repairs for corrosion damage can be decreased with corrosion prevention. All industries, including those in the oil and gas sectors, as well as the majority of human endeavors, are impacted by corrosion. Optimal corrosion management techniques may increase efficiency and cut costs when corrosion is taken into account along the entire value chain. The influence of smaller grains on sensitization microstructure, strength, and corrosion of TIG-welded 316LN SS joints was summarized in this investigation. The welded metal structure and electrochemical resistance of 316LN steel after TIG welding and appropriate heat treatment have been summarized by using Electron Back Scatter Diffraction and Tafel plot test methods. This study summarized the understanding of the effect of TIG welding and appropriate annealing on the deformed and welded structure of 316LN steel. The corrosion rate drastically increases after TIG welding (HAZ zone) of forged samples as compared to base metal (un-welded zone) samples. The mechanism behind the reduction of corrosion resistance is the Depletion of the chromium oxide film. From the results findings, the corrosion rate decreased after TIG welding of forged samples. In the corrosion plot, shifting the intensity of the corrosion current to the passive direction indicates the formation of Cr2O3 after the annealing of welded and forged samples. From the EBSD micrographs, it was observed that the appropriate annealing after welding and forging produces fewer pits as compared to the base metal. Results also indicates that both the mechanical characteristics and corrosion resistance deteriorate as a result of sensitization.

Electrochemical properties of electroless Ni plated super duplex stainless in 3.5% NaCl solution

Si wafers used in semiconductors require precise machining; therefore, they are processed using an STS304 saw wire, which is made of an austenitic stainless steel with excellent strength and corrosion resistance. However, the recently developed super duplex stainless steel (SDSS) exhibits superior performance compared to STS304 and is suitable for use as a saw wire. SDSS is a stainless steel composed of austenite and ferrite, with the ratio varying depending on the temperature during heat-treatment. Ferrite has better wear resistance than austenite; therefore, Ni plating was applied to ferritized SDSSs to improve the saw wire performance, and the electrochemical properties were analyzed. The nickel layer increased with time, forming a non-uniform coating until 180 s, followed by uniform plating. This was confirmed by the changes in the surface roughness and surface images. With the formation of a uniform nickel-plating layer, the distinction between austenite and ferrite became visible, resulting in decreased surface roughness. When the time exceeded 240 s, the difference in roughness increased owing to the difference between in the reactivities of austenite and ferrite. This difference in the surface roughness influenced the electrochemical behavior. The uneven nickel-plating layer exhibited a potential change of over 200 mV during the initial open-circuit potential (OCP) stage (prior to 800 s). In a potentiodynamic polarization test, plating for more than 300 s resulted in a reduced corrosion resistance owing to overplating. Increasing the thickness of the Ni layer altered the electrochemical behavior from SDSS to nickel. By analyzing the surface conditions and electrochemical properties, a uniform nickel-plating layer, exhibiting the characteristics of SDSS, was observed at 240 s. Therefore, the optimal duration for electrolytic nickel plating of ferritized SDSS was 240 s

Microstructure evolution of lean duplex stainless steel produced by a short process

A short process of direct cold rolling of continuous casting billets following solution treatment is proposed, and the effect of cold-rolled reduction on the microstructure evolution and corrosion resistance of lean duplex stainless steel (LDSS) 2101 is investigated. The results show that when the cold-rolled reduction increased to 50%, the strain-induced martensite (SIM) engulfed the austenite along the annealing twin boundaries (TBs). Furthermore, the galvanic corrosion of the martensite and matrix combined with the decreasing fraction of the low-Σ CSL boundaries results in a significant reduction in corrosion resistance at 50% cold-rolled reduction. Additionally, the majority of metastable pits were generated within the ferrite grains and at the α/γ phase boundaries.

Microstructure evolution and corrosion properties of ECAPed Mg–Pb-9.2Al-0.8B alloys

Effect of grain refinement on corrosion behavior of Mg–Pb-9.2Al-0.8B alloy by equal-channel angular pressing (ECAP). By measuring open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS), the corrosion behavior of as-cast and ECAP samples in 3.5 wt % NaCl solution were compared and analyzed. The results showed that sample obtained fine crystal after ECAP, and grain refining reduced the corrosion resistance of the alloy. In the polarization test, the Icorr value was the largest, and the type changed from local corrosion to uniform corrosion. Two factors weaken the corrosion resistance: The first is that β-Mg17Al12 phase is homogenized by the tissue and disappears, thus losing the barrier of corrosion propagation, resulting in reduced corrosion resistance. The second is that Mg + Pb eutectic phase produced by thermal deformation is the first to be corroded. As a result, the corrosion resistance of the alloy decreases after ECAP.

Effect of subcritical-temperature heat treatment on corrosion of SLM SS316L with different process parameters

This study focuses on regulating the 316 L stainless steel manufactured by selective laser melting (SLM) microstructure and analyzing the influence between it and the corrosion resistance behaviors. The results show after the same subcritical-temperature heat treatment (950 °C). For the high-parameter (HP) samples, the high-density dislocation of the cellular substructures and the molten pool boundaries are eliminated. The nano inclusions are further evenly distributed, which enhances the corrosion resistance. However, the melt pool boundary of low-parameter (LP) samples is no longer eliminated, and nano-inclusions are agglomerated, resulting in reduced corrosion resistance.

Metal Oxide Coating On Biodegradable Magnesium Alloys

Magnesium is a biodegradable metal that has potential in orthopaedics. It has several advantages over other metallic materials because it is biocompatible and degradable now being used for biomedical applications, including elimination of stress shielding effects, enhancing degradation properties and enhancing biocompatibility concern in vivo, eliminating the second surgery for implant removal. Bioabsorbable magnesium (Mg) and related alloys have been limited in their usage because of its lower corrosion resistance. Surface alteration and functionality, in addition to basic alloying, is an important technique to deal with Mg and its alloys' reduced corrosion resistance. Magnesium's rapid depreciation however is a double-edged sword because it's critical to match bone renewal to material corrosion. As a result, calcium phosphate coatings have been proposed as a way to slow down corrosion. There are various possible calcium phosphate phases and their coating methods and can give a few distinct properties to various applications. Despite magnesium's lower melting point and greater reactivity, calcium phosphate coatings require precise settings to be effective. Because of their toxicity, non-biodegradability, and much higher cost, the recently used inorganic conversion coatings are less appealing and their application is limited. Conversion coatings are a viable alternative technology that is based on a cost- effective, environmentally friendly, and biodegradable organic component. Surface chelating functional groups in these compounds allow them to link with the magnesium/surface hydroxide layer while also providing anchoring groups for the polymer topcoat. Nanoreservoirs with multilayer inhibitors for active self-healing corrosion resistance thrive in this environment. This study examines the organic conversion coatings for Mg and its alloys in depth.

Effects of Carbon Content on the Properties of Novel Nitrogen-Free Austenitic Stainless Steel with High Hardness Prepared via Metal Injection Molding

A novel nitrogen-free austenitic stainless steel with a hardness of >200 HV was developed using metal injection molding (MIM), and the effects of graphite addition on the sintering behavior, mechanical properties, and corrosion resistance of heat-treated samples were investigated. The results show that a certain amount of graphite addition increases the relative density to >98%. In samples with the addition of 0–500 ppm graphite, large grain-boundary precipitates reduced corrosion resistance and ductility. In contrast, when graphite addition was increased to 750–1500 ppm, fine precipitates, which exhibited coherent lattice relationships with the matrix, were uniformly distributed within the grain and grain boundaries; this significantly improved the mechanical properties and corrosion resistance. The tensile strength and elongation intervals were 546.94–608.62 MPa and 29.68–24.63%, respectively. To prevent overburning, samples with a graphite content higher than 3000 ppm were sintered at a lower temperature, resulting in a higher porosity and lower performance.

Towards understanding of corrosion behaviors of Q235A pipeline steel subjected to simulated direct stray current interference in different electrolytes

Electrochemical corrosion induced by leakage current from the running rail in DC subway system, the stray current corrosion, is a threat that can't be ignored to the transportation pipeline near the metro line system. In view of the corrosion problem caused by stray current in the subway, this paper discusses the evaluation of simulated direct stray current interference on Q235A metal in two types of electrolytes (solution or soil environments), which is often employed as the pipeline steel. Instrumental methods employed in this study to conduct the electrochemical analysis includes Tafel polarization, electrochemical impedance spectroscopy, SEM scanning and EDS scanning to analyze the main electrochemical parameters for the assessment of corrosion resistance during the stray current corrosion process, which is carried out in electrolyte solution and soil environment, respectively. The EIS of electrolyte solution and soil environment (10 min–30 min) exhibits the same equivalent electronic circuit. The electrochemical results were also compared with two different experimental environments to exhibit a degree of similarity. Results also show that the charge transfer resistance Rct decreases and corrosion current density icorr increases in both electrolyte solution and soil environment, which indicates a reduction of corrosion resistance during the experimental period of this study.

Microstructure, mechanical properties, and corrosion performance of additively manufactured CoCrFeMnNi high-entropy alloy before and after heat treatment

Equiatomic CoCrFeMnNi, one of the well-known high-entropy alloys, possesses attractive mechanical properties for many potential applications. In this research, the effects of heat treatment on additively manufactured CoCrFeMnNi materials were studied. A pilot experiment was conducted to select two selective laser melting (SLM) conditions of different laser scanning speeds based on the density and porosity of obtained materials. Thereafter, microstructure, tensile properties, impact fracture, microhardness, and corrosion resistance were investigated for the materials obtained under the two selected SLM conditions, with and without heat treatment. It was discovered that while the texture with a strong <100> alignment was observed in both as-built and heat treated materials, the texture of heat treated materials was stronger. Also, heat treatment drastically improved the ductility of as-built CoCrFeMnNi by 23 – 59% for the selected SLM conditions, while the ultimate tensile strength showed only negligible change. The increase of ductility was believed to result from the release of residual strain and the increase of average grain size after heat treatment. Moreover, heat treatment was able to bring noticeable improvement in energy absorption for the as-built CoCrFeMnNi, reflected by 11 – 16% more energy absorption. Besides, all studied materials showed signs of ductile fracture, but more signs of brittle fracture, such as cleavage facets, were found in the as-built materials as compared with the heat-treated materials. In addition, higher laser scan speed was found to cause moderate reduction in corrosion resistance. Effect of heat treatment was also negative and mild for lower scanning speed case. However, the highest reduction in corrosion resistance was observed after heat treatment of the high laser scanning speed case.

The Influence of Different Type Materials of Grit Blasting on the Corrosion Resistance of S235JR Carbon Steel

The aim of this paper is to evaluate the corrosion rate expressed in material loss per unit of time and the surface properties of carbon steel type S235JR blasted with different types of materials (quartz, alumina, and red garnet with a particle size between 60 and 80 mesh (0.25–0.60 mm)). The estimation of corrosion rate was determined by electrochemical methods, such as open circuit potential (OCP), polarization resistance (Rp), corrosion rate (Vcorr), and gravimetric method by immersing the samples in 3.5% NaCl solution for a period of 336 h. All surfaces were characterized before and after corrosion tests using ex-situ characterizations, such as optical microscopy and roughness analysis. The results indicate that S235JR non-sandblasted exhibited higher polarization resistance, the lowest corrosion rate, and the lowest roughness values. While for the S235JR sandblasted groups, reduced corrosion resistance and increasing roughness values were noted. From the sandblasted groups, the lowest corrosion resistance and the highest value of roughness are attributed to the S235JR surface sandblasted with quartz. The S235JR surface sandblasted with quartz shows a decrease in corrosion resistance approximately two times lower than the non-sandblasted surface and an increasing of roughness approximately six times greater than the non-sandblasted surface.