Alloys In Corrosive Environments Research Articles

Probing passivity of corroding metals using scanning electrochemical probe microscopy

AbstractPassive films are essential for the longevity of metals and alloys in corrosive environments. A great deal of research has been devoted to understanding and characterizing passive films, including their chemical composition, uniformity, thickness, porosity, and conductivity. Many characterization techniques are conducted under vacuum, which do not portray the true in‐service environments passive films will endure. Scanning electrochemical probe microscopy (SEPM) techniques have emerged as necessary tools to complement research on characterizing passive films to enable the in situ extraction of passive film parameters and monitoring of local breakdown events of compromised films. Herein, we review the current research efforts using scanning electrochemical microscopy, scanning electrochemical cell microscopy (or droplet cell measurements), and local electrochemical impedance spectroscopy techniques to advance the knowledge of local properties of passivated metals. The future use of SEPM for quantitative extraction of local film characteristics within in‐service environments (i.e., with varying pH, solution composition, and applied potential) is promising, which can be correlated to nanostructural and microstructural features of the passive film and underlying metal using complementary microscopy and spectroscopy methods. The outlook on this topic is highlighted, including exciting avenues and challenges of these methods in characterizing advanced alloy systems and protective surface films.

Preparation of corrosion‐resistant composite coating on AZ91D magnesium alloy through hydrothermal method

AbstractThe high corrosion susceptibility of magnesium alloy has become a practical problem which restricts its wide application in many fields. To improve its surface properties, a composite coating has been successfully prepared on the surface of AZ91D magnesium alloy using a one‐step hydrothermal method. The coating surface possesses a dense structure in the form of scales and has an adhesion strength of 3B. The effect of different preparation conditions on the coating thickness and corrosion resistance is discussed. The coating heated at 180°C for 2 h showed the best corrosion resistance in a 3.5 wt% sodium chloride solution, with a reduction in corrosion current density of 5 orders of magnitude compared to the bare sample. This solution significantly improved the corrosion resistance of the magnesium alloy and helped to further realize the application of magnesium alloys in corrosive environments.

Green Corrosion Inhibitors Based on Plant Extracts for Metals and Alloys in Corrosive Environment: A Technological and Scientific Prospection

The use of inhibitors is one of the most efficient methods to protect metals against corrosion, which affects many sectors and generates a significant effect on the world economy. This paper presents a prospection using plant extracts as green corrosion inhibitors, aiming at the use of environmentally friendly input. For this, the authors used scientific articles and patents, with recovery of 335 articles and 42 patents related to the subject, as the source. Most technological solutions consist of extracts prepared from leaves of interest plant species, with tests carried out in acidic corrosive environments, with carbon steel (SAE1020) being the most researched material to be protected. Among the identified technologies, some point to corrosion inhibition greater than 80%. The scientific and patent literature points to the excellent performance of these compounds added to the other data collected in the present study, indicating that the exploration of this area is on the rise and very promising. Special highlight is given to the studies and development of green inhibitors in Brazil, considering the potentialities of its high vegetable biodiversity.

Corrosion cracking in Mg alloys based bioimplants

Recently, magnesium alloys have garnered a lot of interest as a potentially useful material for applications involving biodegradable implants. Cracking or fracture of metal-based implants under the combined action of corrosion and mechanical stresses, namely stress corrosion cracking (SCC) is an obviously critical criterion before any new material might be deployed as implants. Cracking or fracture of metal-based implants occurs under the simultaneous action of corrosion and mechanical stresses. This article gives a review of the existing literature on the SCC of magnesium alloys in corrosive environments, including simulated body fluid and the accompanying fracture process. It also indicates the knowledge gap that exists in this area of research. In addition, a high-level review of the preventative measures that may be taken to avoid potential corrosion fatigue failures in magnesium alloys is provided.

On Mechanical Response of Aluminum Alloys in Corrosive Environment

Al6061T6 and Al7075T6 aluminum alloys are subjected to accelerated salt spray corrosion to evaluate the amount of degradation and the effect on mechanical behavior. The specimens were stored in a closed chamber with continuous salt spray for a period of 250 hours and 500 hours, respectively. It was observed that the oxide layer was unprotective after prolonged salt spray resulting in pitting continued with exfoliation corrosion. The tensile test results show that there was a remarkable decrease in tensile properties with exposure time. A significant reduction in tensile strength, yield strength, elongation at yield, elongation at break, and overall toughness in both the alloys was observed at 500 hours. The impact strength decreased by 14.4 % and 26.47 %, Rockwell hardness (HRB) reduced by 12.2% and 20.71% for respective alloys at 500 hours of exposure. However, there was an increasing trend in elastic stiffness which attributed to decrease in ductility. Furthermore, it was comparatively observed that Al7075T6 is more susceptible to corrosion than Al6061T6.

Experimental and theoretical aspects of crack assisted failures of metallic alloys in corrosive environments – A review

Failure analysis is one of the complex tasks in engineering materials since it involves analyses of the interdependency of factors like environmental conditions, materials properties and loading conditions etc., causing catastrophic failure of engineering components in real-time applications. In recent times, the advances in characterization techniques have led to the precise findings of the cause of the failures in several cases. However, specific failure analysis-based case studies report that the couple load effects of two or more parameters influencing the failures of engineering components are complex to identify. Moreover, it is difficult to formulate a mathematical model involving the interdependency factors to study the failure behaviour of the engineering materials. Especially in aerospace industry, the crack initiation and propagation in metallic alloys are more complex since the various factors like environmental conditions combined with loading parameters cause unpredictable failures. Hence, there is a need to study the effect of environmental conditions combined with different loading systems on the crack propagation of metallic alloys. The review concludes that still a comprehensive analytical modelling approach is required to relate the interdependencies of couple loads such as humidity and temperature of metallic alloys in corrosive environment.

Improvement on corrosion resistance of micro-arc oxidized AZ91D magnesium alloy by a pore-sealing coating

Micro-arc oxidation is a low-cost and environmentally friendly technology for improving the corrosion resistance of magnesium alloys. However, the inherent porous structure limits the application of magnesium alloy micro-arc oxidation coatings in corrosion resistance. Herein, we investigated the corrosion resistance and friction resistance of the magnesium alloy micro-arc oxidation coating after being sealed by hydrothermal treatment and heat treatment. SEM, FTIR, XRD and XPS were performed to investigate the surface morphology and chemical composition of the prepared coating. The potentiodynamic polarization curve and electrochemical impedance spectroscopy confirmed that the prepared sample has good corrosion resistance in 3.5 wt% NaCl aqueous solution. In addition, the samples with coating also exhibit good friction resistance. After friction test, the samples still maintain good corrosion resistance. This method not only promotes the application of magnesium alloys in corrosive environments, but also has great potential for industrial production.

Simulating Polarization Curves of Commonly Identified Intermetallic Particles from High Strength Aluminum Alloys Via First Principles

In this talk, first principles density functional theory (DFT) implemented in the Vienna Ab-initio Simulation Package (VASP) is coupled with micro-kinetic modeling to simulate the polarization curves of some commonly identified intermetallic particles (IMPs). First principles DFT calculation is used to characterize the adsorption energies for the cathodic reaction intermediates on intermetallic surfaces. The species include atomic oxygen (O) and hydroxyl (OH) as intermediates for the oxygen reduction reaction. We will show that when coupling the ground state energy calculations with an appropriate micro-kinetic model[1–4], we can simulate simple polarization curves of the IMPs. One of the most desirable properties obtained from the simulated polarization curve is corrosion potential of the IMPs. Corrosion potential can indicate the relative nobilities of IMPs with respect to the alloy matrix. Experimentally the corrosion potential of IMPs on the range of microns are measured via a micro-capillary cell technique. On the simulation side, however, a method that can be directly compared to experimental data has not yet been fully realized. Whereas attempts to estimate corrosion potentials from the surface work functions obtained by DFT calculations have been made in recent literature [7]. we contend here that a model founded in electrode kinetics will be more successful in bridging simulation and experiment. We started with Al7FeCu2, one of the most commonly identified cathodic IMP in high strength aluminum alloy. Our simulated for this IMP is -336.7 mV vs NHE, which is in good agreement with experimental data: -307 mV vs NHE[5]. We also aim to extend our current model to more reactive IMPs that contain Mg, such as Mg2Si and MgZn2, since these particles are measured to be more anodic than the aluminum matrix. For Mg containing particles, the cathodic reaction is the hydrogen evolution reaction (HER), and the reaction mechanism on the atomic scale has been proposed by Taylor[6]. Results for both anodic and cathodic particles based on the above DFT plus microkinetic model will be presented in this presentation. Reference: [1] C.D. Taylor, S. Li, A. Samin, S. Li, A. Samin, Oxidation versus salt-film formation: Competitive adsorption on a series of metals from first-principles, Electrochim. Acta. (2018). doi:10.1016/j.electacta.2018.02.150.This. [2] J.K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J.R. Kitchin, T. Bligaard, H. Jónsson, Origin of the overpotential for oxygen reduction at a fuel-cell cathode, J. Phys. Chem. B. 108 (2004) 17886–17892. doi:10.1021/jp047349j. [3] H. Ma, X.Q. Chen, R. Li, S. Wang, J. Dong, W. Ke, First-principles modeling of anisotropic anodic dissolution of metals and alloys in corrosive environments, Acta Mater. 130 (2017) 137–146. doi:10.1016/j.actamat.2017.03.027. [4] H.A. Hansen, V. Viswanathan, J.K. Nørskov, Unifying Kinetic and Thermodynamic Analysis of 2 e – and 4 e – Reduction of Oxygen on Metal Surfaces, J. Phys. Chem. C. 118 (2014) 6706–6718. doi:10.1021/jp4100608. [5] N. Birbilis, R.G. Buchheit, Electrochemical Characteristics of Intermetallic Phases in Aluminum Alloys, J. Electrochem. Soc. 152 (2005) B140. doi:10.1149/1.1869984. [6] C.D. Taylor, A First-Principles Surface Reaction Kinetic Model for Hydrogen Evolution under Cathodic and Anodic Conditions on Magnesium, J. Electrochem. Soc. 163 (2016) C602–C608. doi:10.1149/2.1171609jes. [7] Y. Zhu, J. Poplawsky, S. Li, R. Unocic, C. D. Taylor, J. Locke, E. Marquis, G. S. Frankel, Probe to the localized corrosion on/around nm-scale hardening precipitates in Al-Cu-Li alloys, in preparation.

First-principles modeling of anisotropic anodic dissolution of metals and alloys in corrosive environments

There have been extensive experimental observations of the anisotropic corrosion behavior of metals and alloys, and their mechanisms were assumed to be correlated with the so-called surface energy or the work function. However, to date, a specified mechanism or theory to interpret anisotropic corrosion behavior remains unclear. Here, we determine the anisotropic anodic dissolution of metals and alloys in corrosive environments by developing a formula to specify the relationship between the electrode potential (U) and the current density (I) by considering the basic parameters of our defined surface energy density (Esurf/ρ) and the work function (Φ). Therefore, we build an ab initio model to evaluate the anisotropic anodic dissolution behavior of metals and alloys using the inputs obtained within density functional theory. This theory is further validated in the case of variations in the crystallographic planes of Mg. Moreover, some selected alloying additions such as Ga, Cd, Hg, In, As, and Cr are theoretically elucidated to effectively reduce the anodic dissolution rates of the Mg matrix to some extent, in close agreement with available experimental observations. This model is capable of predicting the anisotropic anodic dissolution behavior, providing a promising perspective for designing better corrosion-resistant alloys.

Corrosion Prevention by Applied Coatings on Aluminum Alloys in Corrosive Environments

Corrosion Prevention by Applied Coatings on Aluminum Alloys in Corrosive Environments

An electrochemical study of corrosion protection by in situ oxidative polymerization in phenylenediamine crosslinked sol–gel hybrid coatings

The three isomers of phenylenediamine have been used as crosslinking agents for epoxide decorated silica colloids generated by high water content sol–gel chemistry techniques. The resulting materials were used as corrosion protection thin films for aluminum alloys in corrosive environments. These hybrid epoxy-amine crosslinked sol–gel materials have demonstrated an order of magnitude improvement over similar materials crosslinked with aliphatic diamines along with novel electrochemical and coloration behavior. The processes behind these performance improvements are explored and two possibly complementary mechanisms are identified, namely exposure-triggered toughening of the materials through oxidative polymerization of the phenylenediamines and an increase in corrosion inhibition via the formation of electroactive phenylenediamine oligomers.

Cyclic Deformation of Newly Developed Magnesium Cast Alloys in Corrosive Environment

The moderate corrosion rate exhibits by Mg-RE alloys make it candidate material for biodegradable implant. Owing to the operating environment, implants are subjected to stochastic cyclic load and chemical condition. The alloys response to the subjected condition determines its degree of applicability. This work studies the cyclic deformation of newly developed Mg10GdxNd alloys both in air and under corrosive environment. The corrosion fatigue test was carried out in Ringer-Acetate solution and was evaluated using mechanical hysteresis and pH-value measurements. The microstructural changes in correlation to the deformation parameters and fracture surfaces were characterized using SEM. Results show that alloying Mg10Gd with Neodymium improved its fatigue live both in air and corrosive medium. Chilled casted Mg10Gd and Mg10GdxNd were found to undergo brittle fracture in both media. Loading in Ringer-Acetate was found to reduce the fatigue life of the investigated alloys due to the interaction of corrosion and fatigue processes on the microstructure of the alloys. EDX analysis suggests that the improved fatigue life observed on the Mg10GdxNd is connected to the new ternary Mg-Gd-Nd phase observed in the microstructure.

Corrosion behavior of β titanium alloys for biomedical applications

The corrosion behavior of biocompatible β titanium alloys Ti–13Mo–7Zr–3Fe (TMZF) and Ti–35Nb–7Zr–5Ta (TiOsteum) was investigated in 0.9% NaCl and 5 M HCl solutions. Extra-low-interstitial Ti–6Al–4V, which is also a candidate material for biomedical applications, was studied for comparison. The as-received TiOsteum and TMZF alloys exhibited single-phase β and α + β microstructures, respectively, so the latter was also investigated in the solutionized and quenched condition. In 0.9% NaCl solution, all three alloys exhibited spontaneous passivity and very low corrosion rates. Ti–6Al–4V and the as-received TMZF exhibited active-passive transitions in 5 M HCl whereas TiOsteum and TMZF in the metastable β condition showed spontaneous passivity. Potentiodynamic polarization tests, weight loss and immersion tests revealed that TiOsteum exhibited the best corrosion resistance in 5 M HCl. Analysis of surfaces of the corroded specimens indicated that the α/β phase boundaries were preferential sites for corrosion in Ti–6Al–4V while the β phase was preferentially attacked in the two-phase TMZF. The performance of the alloys in corrosive environment was discussed in terms of the volume fraction of the constituent phases and partitioning of alloying elements between these phases.

Influence of Pre-oxidation on the Corrosion and Mechanical Strength of Fe–25Cr and Fe–25Cr–20Ni Alloys at 973 K

The influence of pre-oxidation on the corrosion and mechanical strength of Fe–25Cr and Fe–25Cr–20Ni alloys was investigated in N2–0.1SO2 at 973 K with and without mechanical loadings. About 0.1μm-thick Cr2O3 scales formed on the Fe–25Cr alloy by pre-oxidation in Ar. However, spinel oxides of (Fe,Cr)3O4 remained on the Cr2O3 and voids formed at the oxide/metal interface on Fe–25Cr–20Ni after pre-oxidation in Ar. The preformed oxides are very effective in preventing corrosion of the alloy surfaces. The preformed oxides are also beneficial to increase the strength of the alloys in corrosive environments. The effects of pre-oxidation on Fe–25Cr are stronger than those of Fe–25Cr–20Ni due to the different characteristics of the preformed oxides.

Modification of 27Cr cast iron with alloying yttrium for enhanced resistance to sliding wear in corrosive media

Yttrium has been found to be beneficial to the wear resistance of (Cr, Al)-containing alloys in corrosive environments. In this study, the performance of chill-cast 27Cr white iron alloyed with yttrium during sliding wear in different media, including tap water, dilute NaOH, and HNO3 solutions, was investigated. Compared to Y-free 27Cr cast iron, the Y-containing cast iron showed improved wear resistance. The study demonstrated that chill-cast 27Cr white iron containing 1 wt pct yttrium performed the best and that too much yttrium, however, deteriorated the material. In order to understand the beneficial role that yttrium played, mechanical properties of Y-containing and Y-free cast irons and their passive films were investigated. The electron work function, corrosion, and anodic polarization behavior of the materials were also studied. It was clarified that the beneficial role of yttrium was attributable to improved passivation capability with enhanced passive film. For comparison, sandcast 27Cr white iron was also investigated.

Erosion behavior of aluminide coating modified with yttrium addition under different erosion conditions

Oxygen-active elements have recently been found beneficial to the wear resistance of (Cr, Al)-containing alloys in corrosive environments. In this work, the performance of aluminide coating modified with yttrium, a typical oxygen-active element, under different erosion conditions was evaluated. Compared to yttrium-free coating and the mild steel substrate, the yttrium-containing coating showed considerably enhanced erosion resistance under the following erosion conditions: dry sand erosion at different temperatures; erosion in tap water containing 30% silica sand; erosion in a dilute NaCl solution containing 30% silica sand; and erosion in a dilute H 2SO 4 solution containing 30% silica sand. The study demonstrated that yttrium significantly improved the resistance of aluminide coating to both corrosive erosion and dry sand erosion. Yttrium effects on mechanical properties, micro-wear behavior and corrosion properties were also investigated. It was clarified that the protective role that yttrium played was attributable to its beneficial effect on corrosion behavior rather than the mechanical properties.

BASIC DIAGRAMS OF CYCLIC CRACK GROWTH RESISTANCE OF TITANIUM ALLOYS

Abstract— Basic diagrams of the cyclic crack growth resistance of two of the most investigated titanium alloys, namely Ti-6A1–4V and Ti-6A1–6V-2Sn, are presented. Diagrams are plotted for, in-air, distilled water and 3.5% NaCl solution, which are necessary for lifetime calculations of structural elements made of these metals. The dependency of cyclic crack growth resistance on the yield strength is established. It is shown that cyclic crack growth resistance of titanium alloys in corrosive environments is determined not only by the stress-strain state but also by the electrochemical conditions at the corrosion fatigue crack tip, which for aqueous environments can be characterized integrally by the hydrogen index of the environment and the electrode potential of the metal. Therefore, cyclic corrosion crack growth resistance testing should be performed under constant electrochemical conditions at the corrosion fatigue crack tip or these conditions should be taken into account. A new method of plotting the basic cyclic corrosion crack growth resistance diagrams of titanium alloys is considered.

Platinum Alloys in Corrosive Environments

Platinum Alloys in Corrosive Environments