Corrosion Rate Of Alloy Research Articles

Corrosion of structural materials for salt melt technologies

Molten salt mixtures are considered media for many modern technologies using their ability to store thermal energy, thermal stability at high temperatures, low melting point, and other properties. The disadvantage of their use is high corrosion aggressiveness towards metal structural materials. In particular, impurities contained in salt mixtures can significantly increase the corrosion rates of alloys. This paper compares the corrosion behaviour of Inconel 625, 321, 316L and 316Ti alloys in a mixture of chloride and nitrate salt melts. The parameters in which both mixtures are stable and in melt form were chosen -400 °C, an inert argon atmosphere, and a pressure of 0.2 MPa. After exposure, the state and composition of the surfaces were analysed by XPS (X-ray photoelectron spectroscopy) and SEM (Scanning Electron Microscopy). These materials are better suitable for nitrate salt environments, where only very thin surface layers were formed without local types of corrosion. In chloride melts, Alloy 321 and Inconel 625 have shown greater resistance than 316L and 316Ti stainless steels.

Oxide formation mechanism of a corrosion-resistant CZ1 zirconium alloy

Tailoring microstructure and microchemistry by altering elemental compositions and thermomechanical treatment parameters enables superior corrosion performance in zirconium alloys for nuclear applications. However, our understanding of the relationship between various defects and the corrosion process remains limited in the newly developed zirconium alloys. Here we report the oxide formation mechanism of a CZ1 zirconium alloy with corrosion resistance surpassing many other zirconium alloy systems, such as Zircaloy-4 and Zr-1Nb-1Sn alloys. Autoclave experiments of CZ1 alloy and Zr-1Nb-1Sn model alloy were performed in 360 °C water for up to 820 d. We quantitively determined oxide phases by transmission Kikuchi diffraction (TKD) and examined lateral cracks, nano-porosity, and second-phase particles in oxide scales by transmission electron microscopy (TEM). Compared to the Zr-1Nb-1Sn model alloy, CZ1 alloy with lower Nb and Sn concentrations has shown smaller and lower-density lateral cracks but slightly larger oxide grains, reducing the diffusion route for oxidating species. Using analytical scanning and transmission electron microscopy, we demonstrate that due to the lower content of Sn (∼0.9 wt.%), there is less tetragonal ZrO2 phase formed in the oxide, and the level of tetragonal to the monoclinic phase transition is reduced. Although the Nb content (0.1 wt.%–0.3 wt.%) is lower than the solid solution limit of Nb in Zr, by introducing minor elements such as Fe, Cr, and Cu, there are still a reasonable number of second-phase particles to relieve the high stress associated with the metal-to-oxide transformation. These mechanisms have substantially changed the density and distribution of lateral cracks in the oxide, thus reducing the corrosion rate of zirconium alloys.

TK diagrams to determine the impact of pH variation on 3D printed CoCr alloy implant corrosion

Thermo-kinetic (TK) diagrams are developed for an additively manufactured (AM) CoCr alloy in 0.1 M Na2SO4 in the pH range of 4 to 9 at a constant temperature of 37 °C. The effect of 100 ppm chloride in these solutions was also investigated. TK diagrams can be used to estimate the corrosion rate of the AM CoCr alloy as a function of solution potential and pH. For instance, based on the potentiodynamic polarization results obtained at an optimized potential sweep rate (1.0 mV/s), the passive film had reduced stability at potential > 0.2 VSHE, within 5 < pH < 7, and in the presence of 100 ppm Cl−. Similarly, the CoCr alloy has poor corrosion resistance at potentials lower than 0.8 V vs SHE within 5 < pH < 7, which may be due to the conversion of Cr(OH)3 into soluble CrOH2+ species. The TK diagrams can be used to predict the corrosion rate of CoCr alloys during changes in pH, which may be important during wound healing for implants.

Effect of Mn addition on the microstructure, mechanical, and corrosion properties of an extruded biodegradable Zn-0.2Mg alloy

In this study, the effect of Mn addition on microstructural evolution, mechanical properties, and biocorrosion behaviors of as-extruded Zn-0.2 Mg alloy as candidates for degradable biomaterials were investigated. The microstructural observations indicated that the addition of Mn element significantly refined α-Zn grains, and the average size decreased from 17.23 μm to 7.14 μm. Moreover, Mn-rich intermetallic precipitated alongside eutectic Mg2Zn11 phases. A result of electron backscattered diffraction indicated that manganese has caused grains to rotate 19°, facilitating the activation of non-basal slip as the Schmid factor increases. Mechanical test results showed that the yield strength (YS), ultimate tensile strength (UTS), and elongation (El) of Zn-0.2Mg-0.5Mn alloy is improved by 35.92%, 31.51%, and 6.65%, respectively, compared with Zn-0.2 Mg alloy. The main mechanisms responsible for the improvement of mechanical properties were higher volume fraction of the particles, grain refinement, texture modification, and deformation twining formed by Mn addition. The electrochemical test in SBF solution at human body temperature revealed that the corrosion rate of Mn-containing alloy increased from 0.664 mm/year to 0.87 mm/year compared to the base alloy. It is evident from these results that the Zn-0.2Mg-0.5Mn alloy has a great deal of potential as a cardiovascular stent material.

Influence of Electron Mediator on Microbiologically Influenced Corrosion Behavior of 2024 Aluminum Alloy

In microbiologically influenced corrosion (MIC) caused by sulfate-reducing bacteria (SRB), extracellular electron transfer (EET) between metals and microorganisms affects the metal corrosion process. In this work, the effect of the electron mediator riboflavin on the EET-MIC behavior of 2024 aluminum alloy (AA2024) was investigated by electrochemical methods, surface analysis techniques, focused ion beam, scanning electron microscopy, and x-ray photoelectron spectroscopy techniques. The results showed that the electron mediator was significantly able to accelerate SRB attack against AA2024. SRB utilized to consume H+ to accelerate its own metabolism and promoted the corrosion of AA2024, resulting in the formation of corrosion product AlOOH and Al(OH)3. The addition of electron mediator riboflavin increased the electron transfer efficiency and affected the reaction rate constant to accelerate the corrosion rate of aluminum alloy. The addition of 10 ppm riboflavin led to denser corrosion product biofilms on the surface of the aluminum alloy, which accelerated the formation of NaAlO2. Cl− diffused into the film layer through the pores of the surface of the aluminum alloy and was adsorbed into the film layer to induce pitting corrosion on the surface of the aluminum alloy. A large amount of SRB was attached, which resulted in an increasing pit depth on the surface of the aluminum alloy. Riboflavin accelerated the electron transfer process from the surface of the aluminum alloy across the cell wall to the cytoplasm, which led to serious corrosion of the aluminum alloy. The distribution of SRB in biofilm and the longitudinal distribution of bacteria in the process of pitting corrosion showed that the addition of electron mediators increased the depth of pits in aluminum alloys. Bacteria in the pitting area gathered at the bottom of the biofilm, and the pits were rich in Ca, P, and other elements.

Surface Heparinization of a Magnesium-Based Alloy: A Comparison Study of Aminopropyltriethoxysilane (APTES) and Polyamidoamine (PAMAM) Dendrimers.

Magnesium (Mg)-based alloys are biodegradable metallic biomaterials that show promise in minimizing the risks of permanent metallic implants. However, their clinical applications are restricted due to their rapid in vivo degradation and low surface hemocompatibilities. Surface modifications are critically important for controlling the corrosion rates of Mg-based alloys and improving their hemocompatibilities. In the present study, two heparinization methods were developed to simultaneously increase the corrosion resistance and hemocompatibility of the AZ31 Mg alloy. In the first method, the surface of the AZ31 alloy was modified by alkali-heat treatment and then aminolyzed by 3-amino propyltriethoxy silane (APTES), a self-assembly molecule, and heparin was grafted onto the aminolyzed surface. In the second method, before heparinization, polyamidoamine dendrimers (PAMAM4-4) were grafted onto the aminolyzed surface with APTES to increase the number of surface functional groups, and heparinization was subsequently performed. The presence of a peak with a wavelength of about 1560 cm-1 in the FTIR spectrum for the sample modified with APTES and dendrimers indicated aminolysis of the surface. The results indicated that the corrosion resistance of the Mg alloy was significantly improved as a result of the formation of a passive layer following the alkali-heat treatment. The results obtained from a potentiodynamic polarization (PDP) test showed that the corrosion current in the uncoated sample decreased from 25 µA to 3.7 µA in the alkali-heat-treated sample. The corrosion current density was reduced by 14 and 50 times in samples treated with the self-assembly molecules, APTES and dendrimers, respectively. After heparinization, the clotting time for pristine Mg was greatly improved. Clotting time increased from 480 s for the pristine Mg sample to 630 s for the APTES- and heparin-modified samples and to 715 s for the PAMAM- and heparin-modified samples. Cell culture data showed a slight improvement in the cell-supporting behavior of the modified samples.

Effect of fluoride complexation by aluminium ions on the corrosion behaviour of aluminium cathodes used in zinc electrowinning

Fluoride (F−) impurity at 20 mg L−1 in the zinc sulphate electrolyte increased by 73% and 98% the corrosion rate of Al-1050 and Al-1070 alloys, respectively, which are used as cathode in zinc electrowinning process. The addition of aluminium ions, Al3+, to the electrolyte reduced the corrosion rate by about 21% for the Al-1050 alloy and about 28% for the Al-1070 alloy. The effect was ascribed to the formation of AlF2+ and AlF2+ complexes, thus decreasing fluoride activity. Electrochemical impedance spectroscopy demonstrated that the corrosion resistance of Al alloys is increased in the presence of Al3+. Scanning electron microscopy indicated uniform corrosion of the Al surface, the degree of which depends on fluoride concentration. The higher corrosion resistance of Al-1050 was related to its coarser microstructure, which is less susceptible to corrosion in a non-passivating media. The selection of effective complexing agent for fluoride ion and the consequent reduction in the corrosion rate of aluminum cathodes are relevant in scenario of increasing co-processing of secondary zinc sources.

Hydrothermal pre-treatment fortified binding strength and corrosion resistance of phenolic-amine crosslinking coating on biomedical magnesium alloy

Biomedical magnesium (Mg) alloys are promising biodegradable vascular stent materials, but their applications are limited by rapid degradation. In this study, we construct a composite consisting of a hydrothermal and a phenolic-amine cross-linked coating to reduce the corrosion rate of Mg alloys. The hydrothermal coating is prepared underneath the phenolic-amine crosslinking coating to serve as an embedded layer on the Mg-alloy substrate. The hydrothermally treated surface provides a corrosion-resistant coating with a dense microporous structure, thereby increasing the contact area and enhancing the reaction efficiency of the substrate. The adhesion and bonding strength of the composite coating and the substrate are fortified and the bearable loading force is increased from 40 N to 100 N, as compared to the samples without any hydrothermal transition layer. Moreover, the corrosion rate of the modified samples decreases from 0.35 mm/year to 0.06 mm/year. The results show that the composite coating, which includes a hydrothermal transition layer, can effectively improve the adhesion of the surface coating to the substrate and further enhance the corrosion resistance of the Mg alloy. This work provides a new approach for the surface modification of biomedical Mg alloys.

Machine learning-based design of biodegradable Mg alloys for load-bearing implants

For load-bearing applications, biodegradable Mg alloys require high strength and slow degradation rates to support bone regeneration. This study proposes a design guide of Mg-Zn-Mn-Sr-Ca (ZMJX) alloys for load-bearing Mg implants using machine learning. To this end, it quantitatively investigates the correlation between 4 alloying elements with content of 0–3 wt%, ultimate compressive strength (UCS) and in vitro corrosion rate (CR) in ZMJX alloys. Cascade-forward neural networks predict UCS and CR with high accuracy of over 0.95 for a total of 840 data points. Random forest regression identifies Zn as a major determinant of UCS and CR. Based on this, three chemical compositions are recommended with improved compressive strength and in vitro corrosion resistance by well-verified neural network models. The proposed Mg alloys have UCS of 244–305 MPa and CR of 0.31–0.83 mm/y according to the change of the Zn content. These results can not only provide deep insights into ZMJX alloys, but also recommend a compositional window for load-bearing Mg implants.

Electrochemical behavior and corrosion rate prediction study of alloy 690

Alloy 690 is a material commonly used in heat transfer tubes of steam generators (SGTs). The electrochemical corrosion behavior in different volumes (V) of NaCl–Na2S2O3 solution for different surface roughness (Ra) of alloy 690 was studied, and a BPNN model for predicting electrochemical corrosion parameters of alloy 690 was established (CP and CCD). The results show that Ra on the surface of alloy 690 destroys the passivation film and changes the oxygen vacancies in the passivation film, so that Cl− is more easily attached to the passivation film. Finally, accelerated electrochemical reactions on the surface of SGTs. When the solution is Na2S2O3, with the increase of Ra on the metal surface (0.0977≤ Ra ≤ 1.1661), the corrosion potential gradually decreases. BPNN can accurately predict the electrochemical corrosion rate of alloy 690 under different conditions, and the relative error is less than 10%. In this paper, an artificial intelligence model is established for the first time to predict the relationship between Ra and electrochemical corrosion, and the conclusion can be used to schedule the maintenance process of the SG, thereby reducing the risk of structural failure and maintenance costs.

Tailoring the microstructural characteristic and improving the corrosion rate of Mg-Gd-Ni alloy by heat treatment with different volume fraction of LPSO phase

The microstructure and corrosion behaviors of Mg-Gd–Ni alloys with various long period stacking ordered (LPSO) phase volume fraction and heat treatments were investigated. Compared with as-cast alloys, the corrosion rates increased significantly after heat treatment, and increased with increasing volume fraction of LPSO phase, which may be due to the transformation of continuous bulk reticular LPSO phase to discontinuous rod-like and the precipitation of the lamellar 14 H LPSO phase, changing the corrosion propagation paths and providing more galvanic corrosion points for alloy with high LPSO phase volume fraction, resulting in corrosion rate of MgGd3Ni3 alloy increased significantly by 58.1%.

Hot Corrosion Behavior of a New Powder Metallurgy Superalloy in Molten Na&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;-NaСl Salts

Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na2SO4+5%NaCl salts at 700 °C, 750 °C and 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Experimental results show that the average corrosion rate of Alloy 1 increases as the temperature elevates. The corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr2O3, TiO2, Al2O3 , NiO and Ni3S2 at each temperature, meanwhile NiCr2O4 and Cr2S3 appeared at 750 °C and 800 °C respectively. The cross-sectional morphologies and corresponding elemental maps indicate that lots of Ni-Ni3S2 eutectic appeared in corrosion layers and a large amount of sulfides and oxides appeared in internal substrate. According to these results, the combined mechanism of oxidation and sulfuration in Na2SO4-NaCl salts for Alloy 1 is confirmed. Compared to Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr2O3 and Al2O3 protective films on the alloy surface in which Co inhibited internal oxidation of Al and reduced internal diffusion of S through the third element effect.

Anomalous In Vitro Corrosion Behaviour of Rolled Mg-1 wt. % Zn Alloy Due to Buffer-Microstructure Interactions

In this study, the influence of microstructure and buffer system on the corrosion behaviour of Mg-1 wt. % Zn is examined. The grain size of the alloy was refined from 700 µm to under 15 µm by rolling with varying reduction percentages per pass. The effects of the rolling procedure on the resulting corrosion profile were analysed with immersion and electrochemical methods. Though the rolling procedure resulted in significant grain refinement, the as-cast samples had the lowest corrosion rate of 2.8 mm/yr, while those of the rolled samples were as high as 15.8 mm/yr. The HEPES buffer system did not control the pH or support the formation of insoluble precipitates as well as the NaHCO3/CO2 buffer system, leading to more severe localised pitting corrosion in samples immersed in HEPES buffered media. While reducing grain size generally corresponds to a lower corrosion rate in Mg alloys, this study provides evidence that other factors such as texture and buffer system must also be considered to accurately test candidate alloys for biodegradable orthopaedic applications.

Silk-Cellulose Nanocrystal Composite Coatings for Enhanced Corrosion Protection and Cytocompatibility

The clinical application of magnesium (Mg)-based alloys as biodegradable orthopedic implants is highly restricted because of their rapid corrosion rate in the physiological environment [1]. Polymeric coatings have been recognized as one of the most effective methods to tailor the corrosion rate of Mg alloys without changing their bulk properties, while providing them with other functionalities such as enhanced biocompatibility [2]. In this study, a composite polymeric coating based on silk fibroin (SF) and cellulose nanocrystal (CNC) was fabricated on AZ31 Mg alloy to enhance its corrosion resistance and cytocompatibility for biodegradable bone implant application. The coating was prepared by drop-cast method on AZ31 Mg alloy and fully characterized by various physiochemical techniques. The corrosion resistance of the coating and the effect of CNC inclusion on the corrosion protection performance of the coating were investigated through extensive electrochemical techniques (open circuit potential, polarization test, and electrochemical impedance spectroscopy) as well as in vitro immersion tests. In addition, the cytocompatibility of the coating in terms of cellular toxicity and adhesion was assessed toward human fetal osteoblast cells. SEM images revealed the formation of a defect-free and uniform SF-CNC coating with a thickness of 11.2 ± 2.5 µm on AZ31 alloy. The results of the electrochemical corrosion and in vitro immersion tests clearly demonstrated an enhanced corrosion resistance of the SF coating after the incorporation of CNCs. Compared to the unmodified Mg alloy, the SF-CNC coated AZ31 exhibited a remarkably improved cytocompatibility with a viability of 114% and excellent adhesion and spreading of human fetal osteoblast cells onto the coating surface. The findings of this work highlight the great potential of SF and CNC as bio-based nature-derived anticorrosive nanofillers for fabrication of protective and biocompatible coatings on Mg-based biodegradable orthopedic implants.

Anti-Corrosive and Anti-Bacterial Polymeric Coatings Consisting of PCL and Lawsone

The clinical application of magnesium (Mg)-based alloys as biodegradable orthopedic implants is highly restricted because of their rapid corrosion rate in the physiological environment [1]. Polymeric coatings have been recognized as one of the most effective methods to tailor the corrosion rate of Mg alloys without changing their bulk properties, while providing them with other functionalities such as enhanced biocompatibility and antibacterial properties [2]. In this study, a bi-layered anti-corrosive polymeric coating based on polycaprolactone (PCL) and lawsone, a natural corrosion inhibitor extracted from the leaves of Lawsonia inermis plant, was fabricated on AZ31 Mg alloy to improve its corrosion resistance. The result of electrochemical and in vitro immersion studies clearly demonstrated the corrosion inhibitory effect of lawsone and the enhanced corrosion resistance of AZ31 alloy by almost two orders of magnitude (inhibition efficiency of 98.3%) after being coated with PCL-lawsone. Moreover, coated AZ31 substrates exhibited significantly hampered local alkalization and excessive H2 generation. Apart from the corrosion inhibition properties, incorporation of lawsone imparted a strong antibacterial activity to the coating, which is helpful in the prevention of microbial infection and early implant failure. While most of the commonly used corrosion inhibitors are known to be toxic and have limited biomedical applications, no cytotoxic effect was observed for lawsone-containing coating toward human fetal osteoblast cells (viability of > 85%). The findings of this work highlighted the great potential of lawsone as a natural corrosion inhibitor for fabrication of corrosion protective, antibacterial, and biocompatible coatings on Mg-based biodegradable implants. References Wang, Jia‐Li, et al. "Biodegradable magnesium‐based implants in orthopedics—a general review and perspectives." Advanced science 7.8 (2020): 1902443. Asadi, Hamid, et al. "A multifunctional polymeric coating incorporating lawsone with corrosion resistance and antibacterial activity for biomedical Mg alloys." Progress in Organic Coatings 153 (2021): 106157.

Effect of stray current on corrosion behavior of Mg alloy sacrificial anode in buried pipeline

In this work, a self-designed stray current simulated system was employed in corrosion evaluation test, and the effect of stray current on corrosion behavior of Mg alloy was investigated. The anti-corrosion performance of Mg alloy directly related to its corrosion film. The corrosion film covered on Mg surface was incomplete, which was a mixture of porous MgO + Mg(OH)2, and the corrosion happened on the bare Mg substrate at the rupture of corrosion film. The pitting corrosion randomly occurred on α-Mg, and the anodic hydrogen evolution (AHE) further damaged the corrosion film. With the extension of time, the pits developed into severe localized corrosion and the corrosion rate was accelerated. The stray current was composed of direct current (DC) and low-frequency alternating current (AC), which promoted the rupture of corrosion film, hence the stray current significantly accelerated the corrosion rate of Mg alloy.

Corrosion resistance of 6061-T6 aluminium alloy and its feasibility of near-surface reinforcements in concrete structure

Abstract The durability of concrete structures is often reduced owing to the corrosion of reinforcement in an aggressive environment. Ordinary reinforcement methods, such as wrapping section steel or steel plate, are also vulnerable to corrosion. Using 6061-T6 aluminium alloy as near-surface reinforcement of the concrete structure is a feasible method. In this study, the corrosion resistance of 6061-T6 aluminium alloy bars was studied by simulating the coastal environment, atmospheric environment, and concrete internal environment with chloride solution, simulated acid rain solution, and saturated Ca(OH)2 solution. The corrosion rate of the 6061-T6 aluminium alloy in the above environments was tested using a weight loss method, and its corrosion resistance was evaluated using the metal corrosion resistance classification standard. Based on the electrochemical reaction mechanism, the polarisation properties and AC impedance spectra of steel and 6061-T6 aluminium alloy were compared, and the corrosion resistance mechanisms of steel and the 6061-T6 aluminium alloy in the above corrosive environments were obtained. The results show that the 6061-T6 aluminium alloy has better corrosion resistance than steel bars in chloride and atmospheric environments, with corrosion currents of 0.012 and 0.037 µA·cm−2, and 8-day corrosion rates of 0.051 and 0.031 mm·a−1, respectively. However, owing to the activity of the aluminium alloy, its corrosion resistance in an alkaline environment inside concrete is poor; the corrosion current is 0.22 µA·cm−2 and the 8-day corrosion rate is 16.166 mm·a−1. The research results can provide a reference for applying aluminium alloy bars as external prestressed concrete bars and near-surface steel bars.

Corrosion behavior of Ti60 alloy under continuous NaCl solution spraying at 600 °C

• The corrosion rate of Ti60 alloy in NaCL spray is lower than that under NaCL film. • A mixed corrosion including classical oxidation and active oxidation happened. • The mixed corrosion delayed active oxidation and formed dense Ti oxides scale, both of which decreased corrosion rate. The corrosion behavior of Ti60 alloy was investigated under continuous NaCl solution spraying at 600 °C. Results indicate that the corrosion rate of the Ti60 alloy is lower than that obtained with the solid NaCl deposit film in H 2 O + O 2 . The outer corrosion products are compact layers mainly containing Na 2 TiO 3 and nanocrystalline TiO 2 . The inner layer is mainly composed of Ti 2 O, TiO and SnO 2 . Ti 2 O has a lamellar structure, and TiO has a strip-shaped structure. A mixed corrosion mechanism including classic oxidation and active oxidation occurred under NaCl solution spraying environment: the first stage was controlled by the classic oxidation mechanism with the promotion by the active oxidation following parabolic curves, and the second stage was controlled by the active oxidation mechanism following a linear rise in the mass gain curve. The mixed corrosion mechanism between classic oxidation and active oxidation produced a relatively dense Ti oxides scale, which decreased the corrosion rate.

Electrochemical behavior of the double-layer diamond-like carbon/plasma electrolytic oxidation on AZ31 alloy: A comparison of different PEO interlayers

In the present study, a double-layer diamond-like carbon (DLC)/plasma electrolytic oxidation (PEO) coating was developed on the AZ31 substrate and its electrochemical behavior was studied. In this regard, after fabrication of PEO coatings using two different electrolytes (silicate (PEOSi) and phosphate (PEO-Ph) compounds), DLC thin films were synthesized on the substrates using the radio frequency plasma-enhanced chemical vapor deposition (RFPECVD) method. Results showed the successful formation of thin and crack-free DLC layer with the thickness of about 1 μm on the middle PEO layers. However, the structure and chemical stability of the final DLC layer was dependent on the PEO composition. Moreover, the electrochemical studies in buffer phosphate saline (PBS) at the normal body temperature (37 ± 0.5 °C) showed that while both PEO-Ph and PEO-Si layers significantly decreased the corrosion rate of substrate, PEO-Ph revealed better electrochemical performance. On the other hand, DLC/PEO-Si was more effective than DLC/PEO-Ph to decrease the corrosion rate of substrates owing to the greater bonding of DLC coating on PEO-Si layer. In summary, crack-free DLC/PEO coatings could be a promising candidate to prevent from the high corrosion rate of magnesium alloys, making it appropriate for biomedical applications.

Role of zirconium conversion coating in corrosion performance of aluminum alloys: An integrated first-principles and multiphysics modeling approach

A variety of chromate-free conversion coatings are being actively investigated to improve the corrosion performance of light-weight alloys for aerospace and defense applications. Advancing conversion coating, however, requires an in-depth understanding of the underlying corrosion mechanisms in order to rationally design sustainable coatings. Here, we present a multiscale modeling approach to predict corrosion performance of metallic materials, with a focus on localized corrosion of Cu-containing aluminum alloys coated with ZrO2 layer. First-principles and transition-state theory are used to implement the kinetics model, which includes electrolyte-metal interfacial reactions. The modeling framework systematically characterizes and couples multiple electrochemical and physical (e.g., transport) phenomena to explore interrelationships between pit morphology, surface chemistry, and local environment. This multiscale model can quantitatively link the corrosion rate of ZrO2-coated aluminum alloys with the evolution of interfacial reactions during immersion, which is very difficult to establish using in situ experiments. We have evaluated the presented multiscale model using available experimental data. The rate of corrosion and pit stability were quantitatively assessed for various environmental parameters and applied potentials. Results show that Zr-based conversion coating strongly enhances the corrosion performance of aluminum alloys due to zirconium involvement in interfacial kinetics.