Corrosion Current Density Values Research Articles

Electrochemical synthesis, physical properties and corrosion behavior of electropolymerized polyaniline films developed on 316L stainless steel

AbstractPolyaniline (PANI) films may be developed on metallic substrates by a variety of electrochemical techniques. In the present work, PANI films were electrodeposited on AISI 316L stainless steel substrates by cyclic voltammetry (CV), chronoamperometry (CA), and chronopotentiometry (CP) with the objective of comparing the efficacy of each method, based on the integrity of the developed films. Cyclic voltammetry and anodic polarization were used to determine optimal electrodeposition parameters for the development PANI films using the CA and CP methods. The structure and morphology of the coatings were characterized by scanning electron microscopy, energy‐dispersive x‐ray spectroscopy, Fourier‐transform infrared spectroscopy, and ultraviolet–visible spectroscopy. Among the evaluated techniques, CV led to the formation PANI films with the best homogeneity as well as the lowest number of defects, such as cracks or pores. Subsequently, the corrosion resistance of AISI 316L steels with and without PANI was compared in a physiological saline solution (0.9% NaCl). Potentiodynamic polarization tests indicated that the PANI‐coated samples exhibited lower corrosion current density values (0.012 vs. 0.018 μA/cm2) and lower passive current density values (0.04 vs. 0.06 μA/cm2) in comparison to the bare AISI 316L steel. Additionally, long‐term monitoring by electrochemical impedance spectroscopy revealed that PANI films consistently exhibited superior polarization resistance up to 32 days of exposure in the 0.9%NaCl solution (233,000 vs. 207,000 Ωcm2).

Corrosion behaviour of the magnesium-cerium binary alloy designed for degradable medical implants

ABSTRACT Magnesium (Mg) alloys containing rare earths (RE) gained special attention as promising candidates for degradable implant applications. Cerium (Ce) is one of the RE elements which can be tolerated by the human physiological system when used as an alloying element in Mg alloys. In this current research work, Mg-Ce binary alloys (0%, 0.5%, 1%, 1.5%, and 2% Ce by weight) were prepared by the stir-casting method. The developed alloys were characterised, and corrosion performance was assessed by immersion experiments in normal saline solution and by electrochemical experiments. The degradation rate of the developed alloys was measured as decreased with the increased Ce content up to 1.5%. From the polarisation studies, lower corrosion current density values 3.5 × 10−5 A/cm2 and 4.1 × 10−5 A/cm2 were observed for Mg-1.5%Ce and Mg-2%Ce alloys, respectively compared with the other samples. The surface morphologies after removing the corrosion products revealed more degraded regions for Mg and alloys with lower Ce content (0.5% and 1%) compared with 1.5% and 2% Ce. From the results, it is concluded that developing an Mg-Ce alloy with an optimum fraction of Ce (1.5%) is promising to produce degradable Mg-based medical implants with controlled degradation.

Step-by-Step Tuning of Tribological and Anticorrosion Performance of Zinc Phosphate Conversion Coatings through Effective Integration of Spherical P-Doped MoS2 Nanoparticles.

Surface coatings with enhanced mechanical stability, improved tribological performance, and superior anticorrosion performance find immense application in various industrial sectors. Herein, we report the development of multifunctional composite zinc phosphate coatings by the effective integration of a structurally and morphologically tuned P-doped MoS2 nanoparticle additive (3P-MoS2) into the zinc phosphate matrix to offer attractive characteristics suitable for industrial applications. The integration of spherical nanoparticles as additive leads to the formation of homogeneous and compact coatings with a densely packed crystalline microstructure having enhanced microhardness, distinctive leaf-like morphology, and comparatively smooth topographical features. The attractive lubricity of the additive (3P-MoS2), coupled with its spherical morphology, facilitates a transition from sliding to rolling friction and contributes significantly toward the performance enhancement of the tuned composition of the composite zinc phosphate coating (0.3-PMS). Thus, the tuned 0.3-PMS coating delivers the lowest specific wear rate (1.334 × 10-5 mm3/Nm) and coefficient of friction (0.114) that significantly outperform bare-zinc phosphate coating. Further, the electrochemical corrosion study results indicate the improvement in corrosion resistance behavior of the composite zinc phosphate coatings with reduced corrosion current density (icorr) and charge transfer resistance (Rct) values, as compared to the bare-zinc phosphate coating. The effect of passivation in conjunction with the barrier protection characteristics of the composite coatings induced by the optimal composition of the integrated additive nanoparticles (3P-MoS2) can efficiently prevent the infiltration of corrosive ions and thereby significantly reduce the rate of corrosion.

Insights into the role of tungsten on corrosion behavior of high-strength Ti alloys

High-performance titanium alloys with good corrosion resistance are expected to be applied in marine environments. In this work, we developed a Ti20W alloy using powder metallurgy and hot extrusion, which combined remarkable mechanical properties and good corrosion resistance. The Ti20W alloys exhibited ultrahigh strength (>1400 MPa) and good ductility (>7%), and the specific yield strength was comparable to the common high-strength Ti alloys. The ultrahigh-strength Ti20W alloys had characteristics of the solid solution of W atoms and the precipitation of fine α phases. Compared with Ti6Al4V alloy, the Ti20W alloys showed lower corrosion current density values in 3.5 wt% NaCl solution, which was attributed to the solid solution of W elements and the finer α phases. The W oxides, particularly WO3, acted as the barrier to effectively block the penetration of Cl− into the inner oxide layer, thereby enhancing the corrosion resistance. The fine α phases could be bridged by the surrounding matrix oxides during the passivation process, which contributed to decreasing the galvanic corrosion between the α phases and the matrix, further improving the corrosion resistance.

Effects of Cr3C2 addition on microstructure and corrosion properties of Cr3C2/15–5PH composite coatings on 12Cr13 by laser cladding

The application of laser cladding technology to prepare iron-based composite coatings has significant advantages in improving the surface properties of 12Cr13 stainless steel. 15–5PH composite coatings reinforced with Cr3C2 particles of different contents (0–25 wt%) were prepared on the 12Cr13 surface by the coaxial powder feeding laser cladding system. The microstructure, phase composition, element distribution, corrosion resistance and corrosion mechanism of the composite coatings were analyzed and studied by optical microscope, scanning electron microscope, X-ray energy dispersive spectrometer, X-ray diffractometer and electrochemical workstation. The results indicated that the Cr3C2/15–5PH composite coatings exhibited good macroscopic morphology and dilution rate under appropriate laser cladding process parameters. The addition of Cr3C2 particles changed the main phase from α-Fe to γ-Fe and formed new carbide phases (M7C3 and Cr23C6). The Cr3C2/15–5PH composite coatings exhibited a typical microstructure with rapid solidification characteristics, and the addition of Cr3C2 significantly changed the grain size. The distribution of Fe, Ni, and Cr elements in the composite coatings was uniform, and the relative content of Cr elements increased and remained at high level. The 15-5PH composite coating with 15 wt% Cr3C2 exhibited a lower corrosion current density and higher impedance modulus values. The surface of this composite coating had no obvious corrosion pits, and the passive film effectively retarded the further corrosion by the Cl- ions on the surface during the electrochemical corrosion process. By preparing a 15–5PH composite coating with 15 wt% Cr3C2 on the surface of 12Cr13, the corrosion resistance of the surface can be effectively improved.

Durability of Alkali activated concrete made using multiple precursors as primary binders

Alkali-activated binders (AABs) have been and continue to be extensively explored as an alternative to ordinary Portland cement (OPC), addressing environmental and sustainability issues. A large number of studies that were conducted earlier focused mainly on the mechanical properties and some durability aspects of industrial waste-based AABs. However, chloride migration and diffusion causing reinforcement corrosion in AAB-based concrete (AAC) have not been thoroughly investigated. The present study focuses on the durability of AAC produced using multiple precursors that included industrial waste materials and natural minerals such as limestone powder (LSP), red mud (RM), silicomanganese fume (SMF), and natural pozzolan (NP) activated by alkali. Firstly, the dosages of all four precursors were optimized through trials and then NP was partially replaced by 10, 20 and 30% OPC to enhance the performance of the AABs. The AAC mixtures were prepared and cured under different conditions and tested for compressive strength and durability characteristics related to chloride permeability, chloride migration, chloride diffusion, and chloride-induced reinforcement corrosion to evaluate the performances of the mixtures. The results show that the composition of the AABs and curing regimes significantly influenced the performance of the AAC. The inclusion of the OPC resulted in a very significant enhancement of the strength and durability characteristics of the AAC. In addition, there is a sharp increase in the performance of the AAC mixtures when the OPC content of the precursor was increased from 10 to 20%, irrespective of the curing method. Therefore, an optimum dosage of the OPC in the precursor can be considered as 20%, allowing utilization of 80% waste materials and natural minerals as the precursor with much higher strength and durability characteristics than traditional OPC concrete, thus saving energy and reducing environmental pollution leading to a cleaner production of concrete. Lastly, electrochemically measured corrosion potential (Ecorr ) and corrosion current density (Icorr ) values for the reinforcing bars (rebars) embedded in AAC mixtures were found to be misleading, as confirmed by visual inspection of the extracted rebars in addition to gravimetric test results. Hence, there is a need for further research to develop corrective measures before the utilization of the electrochemical-reinforced corrosion monitoring methods in the case of AACs.

Facile route for processing natural polymers for the formulation of new low-cost hydrophobic protective hybrid coatings for carbon steel in petroleum industry

This research helps with the creation, assessment, and characterization of a new hybrid protective coating for carbon steel alloy in acid conditions. The findings of this study will be useful for both chemical and petrochemical companies as well as scientists. This study aims to protect C-steel in acid pickling solution 1.0M HCl and formulate new hydrophobic protective hybrid organic–inorganic coatings from biopolymers chitosan and plant resin guar gum. Eight coating samples of chitosan in the absence and the presence of guar gum, silica and two heterocyclic compounds are prepared at feasible operational conditions using hot melt method. The aiding additives improved compatibility between coating constituents as confirmed by using different methods of analysis. This new processing approach has addressed the problems of using chitosan in corrosion control such as solubility in acid media and low mechanical strength. Coating samples of chitosan and its composites with the heterocyclic compounds (2-Hydrazinyl-6-methyl-4, 5-dihydro pyrimidine-4-on) or (2-Hydrazinyl-6-phenyl-4, 5-dihydro pyrimidine-4-on) are potent biocides. Coating shifts corrosion potential of carbon steel by 30 mV to more noble direction relative to the active potential 520 mV of bare carbon steel surface. Impedance and polarization measurements indicate that coating samples protect metal surface as mixed-type inhibitor by adsorption mechanism. There is a good agreement between percentages protection %P of coating calculated using the values of charge transfer resistance, Rct, and corrosion current density, icorr. All %P values are above 99% for all coating samples. Guar gum plant resin increases gloss of the coating film. Silica fills the pores in the polymeric film and increases the stuffiness of the polymeric coating film by modifying the particle size. All coated samples have high contact angle ranging from 150° to 165° indicating low wettability and high hydrophobicity of coating film on the metal surface.

Tribocorrosion behaviour of additively manufactured β-type Ti–Nb alloy for implant applications

β-type Ti–Nb alloys are promising materials for load-bearing implant applications with improved mechanical biofunctionality and biocompatibility. In this work, the electrochemical and tribo-electrochemical behaviour of laser powder bed fusion (LPBF) produced β-type Ti–42Nb alloy processed via Gaussian and top hat laser was investigated and compared with commercial grade β-type Ti–45Nb and α+β-type Ti–6Al–4V ELI. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization experiments were performed in phosphate-buffered saline (PBS) for corrosion behaviour. Tribocorrosion behaviour was studied under open circuit potential (OCP) conditions in PBS by using a reciprocating pin-on-disk tribometer. The passivation nature of the LPBF alloys is more decisive than the microstructural particularities for electrochemical behaviour. The overall corrosion response is similar due to the protective nature of the passive films formed on Ti alloys. Ti–6Al–4V ELI exhibits the best corrosion performance among all tested alloys with lower corrosion and passivation current density values. However, LPBF-produced alloys exhibit less reactive surfaces with better passive film properties compared to Ti–45Nb. In addition, EIS results revealed that passive film resistance values are higher for LPBF-produced alloys than conventionally produced Ti–45Nb. LPBF-produced alloys exhibit better tribo-electrochemical behaviour compared to Ti–45Nb. The differences in volume loss are mainly attributed to the microhardness of the alloys and the volume loss is dominated by mechanical wear. The alloys produced with LPBF show promising corrosion and tribocorrosion performance to be a potential candidate for load-bearing implant applications.

The Effect of Sulfuric Acid Anodization on the Electrochemical Properties of Aluminum Alloy AlSi10Mg Prepared by Selective Laser Melting

Aluminum alloy, AlSi10Mg, prepared by selective laser melt (SLM) fabrication was anodized in 9.8% sulfuric acid (Type II) at 15 V for a total of 23 min. Experiments were performed to study the potentiostatic anodization process and its effects on the oxide coating morphology, thickness, and electrochemical properties of the alloy. Prior to anodization, the alloy microstructure is composed of aluminum cells encapsulated in a silicon network. Anodizing the abraded and polished AlSi10Mg surface produced a porous oxide layer with a thickness of 5 μm. The oxide coating weight was 698 ± 29 mg/ft2. The oxide coating forms in the aluminum cells that are isolated from one another by the silicon eutectic phase. In electrochemical tests, the anodic and cathodic potentiodynamic polarization currents were suppressed by factors of 15× and 215×, respectively, as compared to the unanodized controls. The data indicate the anodic oxide coating suppresses the cathodic more than the anodic reaction rate. Linear polarization resistance (R p) values increased by 279× after anodization. The corrosion current density values (j corr) decreased by 133× after anodization. Taken together, the electrochemical data indicate the anodic oxide coating (unsealed) increases the corrosion resistance of the SLM alloy by two orders of magnitude.

Study on corrosion characteristics and mechanism of laser powder bed fusion of Mg–Zn–Zr alloy

Laser Powder Bed Fusion (LPBF) presents novel opportunities for the processing and manufacturing of magnesium (Mg) alloys. However, Mg alloys consistently face challenges with poor corrosion resistance. Consequently, it becomes imperative to delve into the corrosion behavior and mechanisms of Mg alloys formed through LPBF. This paper investigated the electrochemical corrosion behavior, the distribution of corrosion products, and the corrosion mechanism of LPBF ZK60 Mg alloy. The results show that the corrosion current density (Icorr) value of LPBF ZK60 Mg alloy is 3.76 μA∙cm−2. The hydrogen evolution in Hank's solution steadily increases with immersion time and reaches a stable state after 24 h. The corrosion rates calculated based on hydrogen evolution and weight loss are 2.1 mm/y and 2.4 mm/y, respectively. The corrosion resistance of LPBF ZK60 Mg alloy is predominantly affected by three factors: uneven microstructure, internal crack defects, and precipitate phases. The melt pool boundary is identified as a corrosion-vulnerable zone, which extends into the columnar crystal zone after corrosion. Crevice corrosion occurs at microcracks, and the precipitate phases within the grains and matrix induces galvanic corrosion. These findings suggest that the corrosion resistance of LPBF ZK60 Mg alloy may be regulated through targeted measures, such as eliminating cracks, achieving microstructure homogenization, and controlling the precipitate phases (including quantity, composition, and distribution).

Metronidazole mediated potassium iodide as high-performance deterioration retardant for mild steel in an acidic media

As corrosion scientists all over the world struggle to discover new metal deterioration retardant which can close the performance gap created by the legislative banned toxic inhibitors, we present in this research work an azole based drug and its mediation performance with a synergistic agent as ‘green’ metal degradation retardant. The anti-deterioration performance of the azole-based drug, metronidazole (MTN) and its different concentration combinations with potassium iodide (KI) were examined with materials degradation analysis tools such as functional group, nanoindentation, weight loss and electrochemical techniques. MTN alone performed well as an anti-deterioration retardant exhibiting retardation efficiencies (η%) in the range between 73 to 85% at different temperatures and analytical techniques. However, with the introduction of KI, an escalation in (η%) was obtained in the region of 92 to 97%. In addition, improved polarization resistance of chemical retardants on substrate cross sections was achieved, manifested by the resultant elevation in values of polarization resistances (Rp) from 1.54 Ω.cm2 of the blank to 30.61 Ω.cm2 of the optimum concentration, charge transfer resistances, (Rct) improved likewise from 6.03 to 144.07 Ω.cm2 and depreciation in the values of corrosion current densities (Icorr) from 8863.86 to 228.89 µA.cm2. This work describes a method of improving the metal deterioration retardation potentials of an azole compound, bringing out new knowledge on the degradation inhibition properties of MTN and the adsorption process taking place between the substrate and the belligerent environment. We hope it opens the door for the utilization of a mixture of MTN and KI as additives for the formulation of sealants, paints, conversion coatings and primers for ferrous alloys. It also encourages more investigations, to find additives such as suitable activating and accelerating agents for MTN to make It exercise the same or more anti-corrosion potents possessed by the banned hexavalent chromium (vi), benzothiazoles (BTA) and others. Some of these potents are the ability of MTN to function at a wide region of pH and in the moment of coating failure, what can enable an azole-containing coating, to undergo some chemical activities and still maintain the substrate surface integrity?

Effect of titanium on the structural, mechanical and surface properties of CoCrFeMnNiTix high entropy alloy fabricated by selective laser melting

In this study, the effect of titanium (Ti) on the microstructure, mechanical properties, wear resistance and corrosion behavior of CoCrFeMnNi high-entropy alloy (HEA) was examined. The selective laser melting (SLM) method was used to produce HEAs without Ti addition (HEA-1) and with Ti additions of 3 and 5 wt% (HEA-2 and HEA-3, respectively). While the HEA-1 sample exhibited a single-phase face-centered cubic (FCC) structure, the HEA-2 and HEA-3 samples exhibited intermetallic phase structures (Sigma and Laves) along with FCC. The addition of Ti and the presence of intermetallic phases in the HEA-2 sample revealed an improvement in mechanical properties without reducing the ductility value of the structure. However, in parallel with the increasing Ti ratio, the formation of more brittle intermetallic phases in the microstructure of the HEA-3 alloy caused a significant increase in strength but a decrease in ductility. Microstructural examinations revealed that all alloys had a cellular/dendritic structure and the relative densities of the samples were above 99%. While the ultimate tensile stress (UTS) of the HEA-1 sample was 548 MPa and the UTS of the HEA-3 alloy was 832.1 MPa, elongation values were obtained as 48% and 2%, respectively. HEA-2 sample exhibited more ideal results with an elongation value of approximately 22% and UTS values of 760.8 MPa. It was observed that the addition of Ti significantly increased the wear resistance in sliding conditions due to the increase in the hardness of the alloy. The highest hardness and lowest wear rate were obtained with HEA-3 coded samples. The HEA-1 sample exhibited the best corrosion rate, with higher corrosion potential (Ecorr) and lower corrosion current density (Icorr) values. The highest corrosion rate was observed in the HEA-3 sample.

Corrosion Behavior of Carbon Steel in LiCl/H2O Mixtures

The corrosion behavior of 1018 carbon steel in LiCl/H2O mixtures has been evaluated by using potentiodynamic polarization curves, electrochemical noise and electrochemical impedance spectroscopy techniques. Two different concentrations of LiCl were employed, namely 35 and 40 wt. %, and the testing temperatures included 25, 35 and 70 °C. It was found that the steel showed a passive zone; the corrosion current density value increased with an increase in the solution temperature and concentration. The pitting potential value decreased with an increase in the testing temperature and the solution concentration. The corrosion process was under charge transfer control. This mechanism was unaltered either by the solution temperature or concentration. The charge transfer resistance value decreased with an increase in both the solution temperature and concentration. A localized, pitting type of corrosion dominated the corrosion morphology at 25 and 35 °C, whereas at 70 °C, the main type of attack was a mixed type of corrosion.

Exploring cinnamon extract’s potential as a green corrosion inhibitor for X65 carbon steel in sulfuric acid: a comprehensive investigation

The effectiveness of cinnamon extract as an environmentally friendly corrosion inhibitor for X65 carbon steel (X65CSt) in a 1 mol/L H2SO4 solution was examined using electrochemical, chemical, and computational techniques. This inhibitor has many advantages, it is safe, environmentally friendly, harmless to human health, and economically feasible. The anticorrosion efficacy rises with rising the concentration of the cinnamon extract and reducing temperature and reaches 95.83% at 450 mg l−1 of cinnamon extract using potentiodynamic polarization. All the investigated methods confirm the anticorrosion ability of cinnamon extract as indicated by the reduced the corrosion current density values and mass loss as well as the greater charge transfer resistance. In addition, the values of the pitting potentials were also transformed in a more noble direction implying the resistance of pitting attack. The polarization technique categorized the cinnamon extract as a mixed inhibitor. The mechanism of inhibition was demonstrated in terms of adsorption of the main components of cinnamon extract onto the surface of X65CSt. of the adsorption of the main components of the cinnamon extract on the surface of the X65CSt and this adsorption is of combined type between both physical and chemical modes, as determined by the computed values of free energy of adsorption, which range between −46.96 and −37.42 kJ. mol−1. The adsorption is exposed to Langmuir isotherm. The four components of cinnamon extract were investigated through density functional theory, Monte Carlo, and Molecular dynamic simulation. The quantum parameters and the adsorption of these components on the Fe(110) reveals that cinnamaldehyde and cinnamic acid inhibitors are more effective as corrosion inhibitors.

Investigating the effect of Zr content on electrochemical and tribological properties of newly developed near β-type Ti-alloys (Ti–25Nb-xZr) for biomedical applications

In order to create alloys with exceptional properties for orthopedic uses, this study focuses on the impact of zirconium (Zr) content on the structural, electrochemical, and tribological qualities of nanostructured Ti–25Nb-xZr [x = 5, 10, 15, 20, 25, and 30 atomic (at.) %] alloys. The structural evolution was investigated using XRD and SEM techniques. The mechanical characteristics of the produced alloys, including Vickers hardness and Young's modulus, were measured. In addition, the corrosion tests were performed using the OCP, EIS, and PD methods in Ringer's solution within the independent pH range at 37 °C. A ball-on-disc tribometer was used to investigate the tribological behavior of the alloys under various loads and wet conditions using the Ringer solution. It has been verified that Zr content (at. %) in the alloys had an impact on their morphologies, structural evolution, and mechanical characteristics. According to the morphological analysis, the particle and crystallite size decreases with increasing Zr content. Young's modulus and Vickers hardness show the same tendency. The EIS data demonstrated that a single passive film formed on the alloy surfaces, and the addition of Zr enhanced the corrosion resistance of the passive films. The polarization curves demonstrate that the alloys had low corrosion current densities and large passive areas without the passive films disintegrating. Likewise, the inclusion of Zr resulted in a reduction in the corrosion and passive current density values. All of these results suggested that the titanium alloys exhibit a more noble electrochemical activity caused by Zr. From the tribological perspective, it was found that the friction coefficient of the alloys reduced with increasing Zr content.

Effect of a Substrate’s Preheating Temperature on the Microstructure and Properties of Ni-Based Alloy Coatings

Laser cladding is a new technology to fabricate a coating on the surface of a metal substrate. The properties on copper substrates are usually not very good due to the high thermal conductivity and reflectivity. The appropriate preheating temperature is helpful to fabricate coatings with good quality and properties, especially for copper substrates. In order to investigate the effect of different preheating temperatures, four coatings with different preheating temperatures (100, 200, 300 and 400 °C) were fabricated via a laser on a copper substrate. The microstructures and properties of four coatings were investigated using SEM, XRD, EDS, a Vickers microhardness meter, a wear tester and an electrochemical workstation. The results show that the elements from Ni-based alloy powder were uniformly distributed among the binding region, which obtained a good metallurgical bonding. The microstructure was mainly composited of cellular, dendrite and plane crystals, and the main reinforced phases were γ (Fe, Ni), Cr0.09Fe0.7Ni0.21, WC and Ni3B. The values of average microhardness of the four coatings were 614.3, 941.6, 668.1 and 663.1 HV0.5, respectively. The wear rates of the four coatings were 9.7, 4.9, 12.5 and 13.3 × 10−5 mm3·N−1·m−1, respectively, which were less than that of the copper substrate (4.3 × 10−3 mm3·N−1·m−1). The decrease in wear rate was due to the existence of the reinforced phases, such as WC, Ni3B, M7C3 (M=Fe, Cr) and Cr0.09Fe0.7Ni0.21. The fine crystals in the coating preheated at 200 °C also improved the wear resistance. Additionally, the minimum values of corrosion current density were 3.26 × 10−5, 2.34 × 10−7, 4.02 × 10−6 and 4.21 × 10−6 mA·mm−2, respectively. It can be seen that the coating preheated at 200 °C had higher microhardness, lower wear rates and better corrosion resistance due to the existence of reinforced phases and fine and uniform crystals.

Corrosion behavior and oxide layer of selective-laser-melted Al-Mg-Sc-Zr alloy in marine atmospheric environment with different Cl−concentration

In this study, the corrosion response of the Al-Mg-Sc-Zr alloy produced by selective laser-melting in marine atmospheric environments with different Cl− concentrations was studied by electrochemical and immersion. Microstructural observations showed the microstructural of Al-Mg- Sc -Zr alloy featured a double grain microstructure, making up a coarse and fine grain area. TEM showed that some white precipitates enriched with Zr and Sc were dispersed in the samples. The potentiodynamic polarization test indicated increasing the Cl− concentration led to a negative shift of corrosion potential and narrowed the potential range of the passive zone, which also caused the increase of corrosion current density value. The electrochemical impedance spectroscopy showed that higher Cl− concentration was greatly detrimental to generating a compact and dense oxide film on the Al-Mg-Sc-Zr alloys, as indicated by decreasing the resistance of the corrosion product layer and charge transfer resistance. The immersion test demonstrated that the samples suffered serious pit corrosion when the Cl− content increased to 1.5 and 3.5 wt%, showing a larger size and more depth of corrosion pits. This study is expected to provide data to determine the reliability of the SLM-manufactured Al-Mg-Sc-Zr alloy in marine atmospheric conditions.

Effect of co on mechanical and electrochemical properties of powder synthesized cellular Ti-Al alloy

ABSTRACT This work describes the effect of Co content on the compressive and electrochemical behaviour of cellular Ti4AlxCo (x = 2%, 4%, 6% and 8 wt%) alloy. Cellular products were prepared through powder metallurgy route by adding 70 v% of ammonium bicarbonate as space holder in Ti4AlxCo powder mixture. Relative density of the final products slightly upsurged due to increment of Co amount and it was found in the range of 0.32–0.35. Microstructure represented the interconnecting pores which will be advantageous to circulate the body fluid, if used as a bone implant. Plastic collapse stress of Ti4Al8Co was about 45% higher than Ti4Al2Co. Also, the elastic modulus was under the range of modulus of natural bone (11 ± 1 GPa). In Tafel plot, value of corrosion current density shifted from 8 μA/cm2 to 15 μA/cm2 by increasing the Co content from 2 wt% to 8 wt% which indicates the hampering of corrosion resistance. Corrosion rate followed the linear relationship with Co content. Best fitted electrochemical circuit showed the double layer oxide formation during corrosion. Micrographs of corroded cellular samples also represent that the surface of material is more prone to corrosion containing higher amount of Co.

Experimental and DFT studies on corrosion behaviors of laser-cladded (FeCoNi)75−xCrxB15Si10 high-entropy alloy coatings

The effects of Cr doping on microstructure evolutions and corrosion behaviors of laser-cladded (FeCoNi)75−xCrxB15Si10 (denoted as Crx hereafter, x = 0, 4, 8, 12, 16 at%) high-entropy alloy coatings (HEACs) were investigated. The composition and shape of the borides in interdendrite regions are modified by adding Cr, alleviating the localized corrosion behavior. The corrosion resistance of the HEACs increases continuously as a function of Cr level in 3.5 wt% NaCl solution. The Cr16 coating outperforms the previously reported Ni alloys, stainless steel, and some other high entropy alloys in terms of corrosion resistance, with the highest pitting potential (0.233 V), the lowest corrosion current density value of 9.9 × 10−9 A/cm2 and passive current density (2.138 ×10−8 A/cm2). Based on the experimental analysis and density functional theory (DFT) simulations, the corrosion mechanisms of the Crx HEACs were discussed. The exceptional corrosion resistance of the Cr16 coating can be attributed to its high oxygen adsorption energy and thus facilitates the rapid formation of protective and compact passive films with few defects.

Electrochemical behavior and surface stability of dental zirconia ceramics in acidic environments

Dental zirconia ceramics, widely employed in dentistry for their biocompatibility and mechanical properties, face challenges in long-term viability within the oral cavity. This study focuses on analyzing the electrochemical behavior of a commercial dental zirconia ceramic type in acidic environments. Through extensive electrochemical investigations, including Electrochemical Impedance Spectroscopy (EIS) and cyclic polarization resistance (Cpol), corrosion resistance was assessed. Despite indications of material dissolution, our results demonstrate significant corrosion resistance, as reflected in low corrosion current density (Icorr) values. Notably, the study reveals the development of a protective oxide layer at the ceramic-electrolyte interface, contributing to material stability. XRD analysis confirms the presence of stable crystallographic phases (t-ZrO2) even after exposure to acidic media. Surface characterizations utilizing scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) affirm minimal surface damage and maintained elemental composition. These findings illuminate the intricate electrochemical behavior of dental zirconia ceramics in challenging environments, underscoring their potential for durable dental restorations. This interdisciplinary research bridges dentistry and materials science, providing valuable insights for optimizing material properties and advancing dental materials and restorative techniques.