Anodic Dissolution Behavior Research Articles

Suitability of electrolytes and anodic dissolution behavior of 17-4 PH stainless steel

17-4 PH SS alloy finds widespread applications in turbine blades, power plants, marine and chemical industries. However, some of its mechanical properties such as high tensile and fatigue strength, good toughness, high hardness and formability make its machinability poor. Thus, non-conventional machining processes such as electrochemical micromachining (ECMM), which removes the material by chemical dissolution, has better potential to fabricate micro features of high surface quality. However, the ECMM behavior of 17-4 PH SS alloy has not been exhaustively explored yet. It is very important to understand the regular dissolution patterns to improve machining stability and machined surface quality. Therefore, the present work aims at studying the suitability of different electrolytes in ECMM process for the fabrication of micro features with better dimensional accuracy and surface quality on 17-4 PH SS alloy. The electrolytes used in the experimentation are an aqueous solution of NaBr, NaCl, NaNO3and a compound aqueous solution of NaCl + NaNO3. The performance characteristics such as radial overcut, dimple depth and some aspects of surface integrity have been investigated. Experimental results showed that better dimensional accuracy and surface quality have been achieved with NaCl + NaNO3electrolyte owing to the combined properties of passive and non-passive electrolytes.

Anodic dissolution of aluminum in AlCl3-[BzMIM]Cl ionic liquid

• The anodic dissolution behaviors of aluminum in AlCl 3 —1-benzyl-3-methylimidazolium chloride ionic liquid were studied for the first time. • The mechanism of passivation generation was explained in detail, and the passivation products were identified. • The corrosion behaviors of aluminum in AlCl 3 -[BzMIM]Cl ionic liquid were analyzed by electrochemical tests. • To provide the theoretical basis for the extraction of aluminum from AlCl 3 -[BzMIM]Cl ionic liquid. The anodic dissolution behaviors of aluminum in AlCl 3 -[BzMIM]Cl (1-benzyl-3-methylimidazolium chloride) ionic liquid was investigated using coulometric weight loss experiments, linear sweep voltammetry, potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that passivation occurred during the anodic dissolution of aluminum, and the passivation film was identified as the formation of AlCl 3 precipitates and local solidification of electrolyte on the electrode surface. The potentiodynamic polarization analysis showed that an increase in temperature caused a positive shift in corrosion potential ( E corr ), an increase in corrosion current density ( i corr ) and a decrease in polarisation resistance ( R P ). Impedance measurements indicated that the anodic dissolution process of aluminum in AlCl 3 -[BzMIM]Cl ionic liquids consisted of charge transfer, confinement of the passivated film on the electrode surface and diffusion-induced Warburg impedance.

Anodic Dissolution Behavior of Passive Layer During Hybrid Electrochemical Micromachining of Ti6Al4V in NaNO3 Solution

AbstractTitanium and its alloys are considered as difficult to cut material classes, and their processing through the traditional machining methods is a painful task. These materials have an outstanding combination of properties like high specific strength, excellent corrosive resistance, and exceptional biocompatibility; therefore, they have broad fields of application like aerospace, micro-electromechanical system, and biomedical. Electrochemical micromachining (ECMM) is a vital process for the production of microdomain features in difficult-to-machine materials. The machining issue with ECMM for titanium and their alloys is the passive layer formation, which hinders the dissolution and causes stray removal. To overcome these issues, a hybrid ECMM approach has been proposed by using a diamond abrasive tool combined with ECMM. This study focuses on the detailed characterization of the passive layer formed using the hybrid approach. Through the use of abrasive tool, the abrasive grits scoop the passive layer by the mechanical grinding action, formed in microdrilling on the Ti6Al4V alloy to expose a new surface for further dissolution. The microholes were produced incorporating the abrasive tool and then compared by the holes created using a cylindrical tool (tool without abrasive). The taper and the stray dissolution of the microholes were also compared, produced at different applied potentials. The minimum average entry overcut and exit overcut of the hole were obtained as 29 μm and 3 μm, respectively, also a microhole with the lowest taper of 2.7 deg, achieved by the use of the abrasive microtool.

Electrodissolution Processes and Their Application in Manufacturing for Shaping and Finishing of Advanced Materials

Controlled material removal by anodic dissolution at high rates forms the basis of non-conventional metal shaping and finishing processes such as Electrochemical Machining (ECM), Electrochemical Micromachining (EMM), and Electropolishing (EP). These processes are employed in the manufacturing and processing industries for a variety of applications ranging from the machining of complex shaped components for heavy industries to the fabrication of microstructures in thin films and foils and microfinishing of superconducting radiofrequency cavities (1-3). Application of these processes for the production of reliable, reproducible, and high-yielding components require an understanding of the parameters that influence the anodic dissolution processes.ECM, EMM, and EP can be understood and theoretically modeled based on the same principles provided the scaling effects related to each process are considered (2). In the first part of this presentation, the high rate anodic dissolution behavior of different materials including refractory materials are described which helps in establishing the basic concepts that govern ECM/EMM/EP processes. Electrochemical reactions taking place at high anodic potentials depend on the metal-electrolyte combination and the operating conditions. These reactions include active metal dissolution, passivity, oxygen evolution, and the phenomena of passive film breakdown leading to the transpassive metal dissolution. In passivating electrolytes (containing oxidizing anions), oxygen evolution and metal dissolution take place simultaneously. The current density dependence of meat dissolution efficiency in such electrolytes provides minimized stray cutting in ECM. Mass-transport, current distribution, and surface film properties play a significant role in the metal removal rate and surface finish. Whereas the formation of a salt film on the dissolving anode in ECM electrolytes is well established, the identification of the rate-controlling species during electropolishing of metals in concentrated acid solutions remains a controversial issue.The second part of the presentation deals with the applications of these processes in the manufacturing of advanced products for the aerospace, biomedical, electronics, and photovoltaics industries. Different ECM techniques such as die-sinking, combined tool machining, EC drilling, and EC deburring are described that are used in the manufacturing of complicated shaped parts such as turbine blades. Maskless EMM methods such as Jet EMM, micro-drilling, and wire EMM are applied to fabricate precision microstructures. For process enhancement, assisted techniques such as laser, abrasive, vibration, and ultrasonic are incorporated with maskless EMM. For through mask electrochemical micromachining (TMEMM), an understanding of mass transport in a cavity and shape evolution modeling is critical. The use of laser patterned oxide film mask for Ti patterning is presented as an interesting application of TMEMM (4). A few case-studies on electropolishing are described which include the fabrication of STM probes and Nitinol stents, and microfinishing of print bands. In the microprocessor industry, a significant effort was invested in the development of EP and electrochemical mechanical planarization (ECMP) approaches as a no-contact or low-contact planarization processes for the integration of ULK/copper interconnects. The development work, including processing details and planarization efficiency of EP and ECMP, are reviewed. A critical evaluation of the current status of EP/ECMP vis a vis the chemical mechanical planarization (CMP) process is presented.References J. McGeough, Principles of Electrochemical Machining, Chapman and Hall, Wiley, London, 1974.M. Datta, Electrodissolution Processes: Fundamentals and Applications, CRC Press/Taylor and Francis, Boca Raton, 2020.E. J. Taylor and M. Inman, Electrochemical Surface Finishing, The Electrochemical Society Interface, Fall 2014, p47.P.-F. Chauvy, P. Hoffmann, D. Landolt, Electrochemical Micromachining of Titanium Through a Laser Patterned Oxide Film, Electrochem. Solid-State Lett., 4(5), C31 (2001).

Preparation of zirconium metal through electrolysis of zirconium oxycarbonitride anode

• A single phase zirconium oxycarbonitride was prepared through carbothermal reduction route using ZrO 2 and graphite powder as raw materials. • The zirconium oxycarbonitride has good chemical stability in NaCl-KCl melt and also exhibits good anodic dissolution. • Zirconium metal was produced by electrolysis using zirconium oxycarbonitride as anode in NaCl-KCl melt, which indicated that zirconium oxycarbonitride was a suitable consumable material for the electrolytic preparation of zirconium. A single phase zirconium oxycarbonitride was prepared through a carbothermal reduction route at 1600 °C in nitrogen atmosphere using ZrO 2 and graphite powder as raw materials. The hot-pressed zirconium oxycarbonitride block has good stability in the NaCl-KCl melt. The anodic dissolution behavior of zirconium oxycarbonitride and the reduction mechanism of zirconium ion in NaCl-KCl melt were studied by linear sweep voltammetry, electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The results show that zirconium in the anode is oxidized to Zr 2+ ions and dissolved in the molten salt. The zirconium ions diffuse to the cathode and are reduced to zirconium metal by transferring two electrons in one step. Potentiostatic electrolysis at −2.9 V was performed between a Mo rod cathode and ZrC x O y N z anode. The cathode product was detected to be zirconium metal, which indicated that zirconium oxycarbonitride was a suitable consumable anode for the electrolytic preparation of zirconium metal.

(Invited) Micro-Electrochemistry of Pit Initiation at Non-Metallic Inclusions of Stainless Steels and Roles of Alloying Elements in Improving Corrosion Resistance

A micro-electrochemical system for in situ high-resolution optical microscopy was developed and applied to the real-time observation of pit initiation at MnS inclusions in Type 304 stainless steel in NaCl solutions. Metastable and stable pits were found to be initiated at the MnS/steel boundaries during potentiodynamic polarization. After polarization, it was confirmed that deep trenches were generated at the boundaries. Therefore, metastable and stable pits were determined to be initiated in the trenches. From the real-time observation, it was found that the initial rounded form of metastable and stable pits became polygonal in shape within 1 s. After that, the dissolution proceeded in the depth direction with no change in the appearance of the pit as observed externally. In the case of the metastable pitting, the duration of this stage was approximately 1.5 s, and then the pit repassivated, and the polygonal metastable pit remained. The in-depth growth stage for stable pitting was relatively longer (approx. 3.5 s), and the pit grew deeply into the steel matrix and wrapped beneath the inclusion, leading to the formation of a large occluded cavity, in which the corrosivity considerably exceeded the critical conditions for autocatalytic pit growth. The anodic dissolution behavior of CrS, TiS, and Ti4C2S2 inclusions was compared with that of MnS. The dissolution potential of CrS inclusions was in the transpassive region of stainless steels. Stable pits were initiated in this potential region. In contrast, TiS and Ti4C2S2 inclusions did not dissolve in the passive or the trans-passive regions of stainless steels, and no pits were initiated at these inclusions in NaCl solutions. The calculations made from the potential-pH diagrams for CrS, TiS, and Ti4C2S2 systems indicated that Cr-oxide or Ti-oxide enriched surface films would form, and this was confirmed by surface analysis. The Cr-oxide or Ti-oxide enriched layers on the inclusions inhibited the anodic dissolution of the inclusions in the passive or trans-passive regions of stainless steels. In contrast, MnS inclusions dissolved in NaCl solutions, and pits were initiated at the inclusions. While MnS inclusion surfaces were covered by Mn-oxides, the corrosion resistance of Mn-oxides was not sufficient to prevent inclusion dissolution and subsequent pit initiation. The oxide enriched surface layers on the sulfide and carbo-sulfide inclusions were shown to significant enhance pit initiation resistance at the inclusions. In addition to the above findings, the roles of the addition of Ce and Mo were studied. From the results of micro-scale polarization, thermodynamic calculations, and scanning electron microscopy, it was suggested that the Ce3+ ions inhibit trench formation at the inclusion/steel matrix boundary, resulting in improved pitting corrosion resistance at sulfide inclusions. And also, the active dissolution rate of the steel was suppressed by Mo alloying. This suggests that, even after trenching at high potentials, Mo alloying inhibits the initiation of pitting inside the trenches.

(Invited) Measurement of Passivation on Fe-6Cr Using an Ellipso-Microscope Combined with a Channel Flow Electrode Method

An electrochemical ellipso-microscopy cell was expanded by combination with a channel flow electrode method. Fe-6 wt% Cr was potentio-dynamically polarized to passive region in acidic 0.15 M Na2SO4 solution. During the polarization, the electrolyte solution was flowed at various flow rates under laminar flow condition, and the Fe-6Cr sample surface was monitored by the ellipso-microscope. Simultaneously, two detector electrodes in the solution downstream were potentio-statically polarized to detect Fe and Cr species dissolved from the sample. Dissolution rates of Fe and Cr species in active region were depended on the flow rate. When AES analysis was conducted after the polarization of Fe-6Cr, depth profiles revealed that Cr enrichment in the outermost layer of passive film. Cr ratio in metal cations on the passive film increased with increaseing in flow rate. These behaviors implied that the corrosion resistance of passive film formed under solution convection was improved by oxidized products generated in active region. In the presentation, Fe-6Cr anodic dissolution behavior and enrichment of Cr species are discussed.

Distinction in electrochemical behaviour of Ti6Al4V alloy produced by direct energy deposition and forging

The relationship between microstructural characteristics and anodic dissolution behaviour plays a crucial role in the process control of the electrochemical machining technology (ECM). An additive-manufactured Ti6Al4V alloy produced by direct energy deposition (DED) exhibited a finer lamellar α+β structure within the considerably coarser columnar prior-β grains as compared to the traditional forged Ti6Al4V alloy consisting of equiaxed α and transformed β phases. The electrochemical anodic behaviour of DED-produced Ti6Al4V alloy was investigated in a 15-wt.% NaCl solution and compared with that of the forged Ti6Al4V alloy. Electrochemical measurements showed that the DED-produced Ti6Al4V exhibited higher resistance to corrosion and lower electrochemical machinability than did the forged Ti6Al4V alloy. The high phase boundary density, originating from the refinement of constituent phases, increased the stability of the passive film formed on the surface of the DED-produced Ti6Al4V, thereby improving the corrosion resistance, while the high fraction of β phase in the Ti6Al4V deposit decreased the rate of anodic dissolution. The lower composition difference of solutes of DED-produced Ti6Al4V was beneficial to its higher resistance to corrosion. The fine and lath-type α phases led to a competitively high level of microscopic flatness of the Ti6Al4V alloy after the electrochemical dissolution.

Oxidation and Corrosion of Al<sub>86</sub>Ce<sub>10</sub>Fe<sub>4</sub> Metallic Glass

High temperature oxidation of Al86Ce10Fe4 amorphous alloy at 630°C in static air for 15, 60, 300, 600, 1,200, 3,000, 6,000 and 12,000 minutes was studied. The morphology, composition and microstructure of the oxide films were investigated using SEM, EDS and XRD. The hardness and corrosion resistance of the oxide films were determined by micro-indentation and polarization technique. The results indicate oxidation at 630 °C instigates nucleation, growth and coarsening of fcc-Al, Al11Ce3 and Al13Fe5 crystalline phases inside the Al86Ce10Fe4 matrix, reducing the hardness of the alloy, and oxidation of the alloy surface, forming crystallized Al2O3 and AlFeO3 chemical compounds. Active anodic dissolution behavior and diffusion-controlled cathodic polarization of the oxidized alloy were observed. The corrosion resistance of the oxide films rates in the level of 10-7 ~10-5 [A/cm2]. The results demonstrate Al86Ce10Fe4 amorphous alloy, as a new-developed high temperature high strength glass, exhibits potential application for aerospace and national defense in terms of its high mechanical strength, high temperature endurance, and satisfactory oxidation and corrosion resistance.

Effect of Grain Size on the Anodic Dissolution of Lean Duplex UNS S32202 Austenitic-Ferritic Stainless Steel

The effect of grain size on the anodic dissolution of lean duplex UNS S32202 dual-phase austenitic-ferritic stainless steel was evaluated. Grain coarsening was achieved by heat treatment, and grain size and grain boundary densities determined by automatic image analysis after etching. Potentiodynamic electrochemical testing in acidic chloride medium allowed isolating the anodic dissolution behavior of the crystallographic phases of the material. A relationship between grain boundary density (for grain sizes in the micrometer range) and dissolution rate has been found, showing that reducing grain size enhances active corrosion rates in environments that promote active behavior. This leads to new possibilities of industrial adjustment of the corrosion behavior of duplex stainless steels via grain size control.

Investigation of anodic dissolution behaviour of intermetallic compound in Sn-3Ag-0.5Cu solder alloy by cyclic voltammetry

Purpose The purpose of this paper is to study the mechanism of electrochemical dissolution of SAC305 solder in mild acid solution. Design/methodology/approach Cyclic voltammetry (CV) was used to obtain electrochemical dissolution peaks followed by chronoamperometery (CA) to investigate the dissolution mechanism at each peak. Structural and microstructural characterization was performed to verify the CA analysis. Potentiodynamic polarization was performed afterwards to determine the corrosion potential of every phase in SAC305. Findings The early cycle of CV exhibits only dissolution peaks of β-Sn until intermetallic compound (IMC) peaks emerged at a later cycle. CA performed for 24 h at selected potentials reveals that β-Sn can be removed completely from the sample without disrupting the IMC network at a suitable potential. This was later verified by XRD and SEM. Potentiodynamic polarization determined the corrosion potential of IMC as −0.36 V. Originality/value The mechanism of anodic dissolution of SAC305 was studied and proposed.

On-Line Monitoring of the Stability of Electrodes in Non-Aqueous Media

Stability of electrochemical systems is particularly important in applications. No matter if it is a fuel cell, a battery, a supercapacitor, a construction subject to corrosion or an electrode used for synthesis, economic considerations require a certain lifetime of these systems. Depending on the systems, instability can have several causes, like changes in the mechanical or crystal structure of electrodes, oxidation of materials, decomposition of electrolytes, loss of percolation and electrical conductivity, or material loss due dissolution. Many of these processes happen slowly, causing only minimal performance loss within laboratory timescales. Their studies involve therefore usually long-term measurements with ex situ analysis. In situ, real-time analysis requires very sophisticated and usually coupled analysis methods. In this work we show a powerful approach to study dissolution phenomena in non-aqueous electrochemical systems. A scanning electrochemical flow cell (SFC) combined with on-line inductively coupled plasma mass spectrometric (ICP-MS) analysis has proven to be a very valuable tool for the study of stability of electrocatalysts in aqueous solutions. This coupled technique is mainly connected to the works of Dr. Mayrhofer and Dr. Cherevko. It was very appealing to develop this method further and make it useable in organic systems too. This task might seem for the first glance to be almost trivial, however, the harsh conditions caused by the organic electrolytes limit the usability of materials to contrive these systems to a huge extent. Furthermore, the ICP-MS is standardized mainly for aqueous media and a lot of experimental work has to be devoted for the optimization of the device for each individual organic solvent. Most of the chemicals used are sensitive to atmospheric components, like O2, H2O, CO2 or even N2. Therefore, the experiments have to be carried out in a glovebox that ensures a controlled and very clean atmosphere. Platinum is often considered to be a model electrode and catalyst material. This metal is probably the most thoroughly studied one in electrochemistry, however, it still shows many interesting yet not well understood features. This is also true for the stability of the metal during potential cycling. The electrochemical stability window of organic electrolytes is usually much higher than that of water enabling the simultaneous cycling and downstream analysis of dissolution in a higher potential range. As a result, even the electrochemistry of platinum shows hitherto unveiled phenomena regarding its dissolution mechanism. In this work, we focus on the effect of water contamination, anions, cations and organic solvent molecules on the anodic and cathodic dissolution behavior of platinum. To demonstrate the benefits of this novel method on the field of non-aqueous electrochemistry the stability of other non-aqueous systems will be discussed shortly, too.

Thermodynamic properties of praseodymium on the liquid cadmium electrode and evaluation of anodic dissolution behavior in LiCl-KCl eutectic

The electrochemical and thermodynamic properties of Pr on a liquid Cd electrode and the formation of Cd-Pr intermetallic compounds were systematically studied by a series of electrochemical techniques in LiCl-KCl eutectic. The activity coefficient of Pr in the liquid Cd was determined by galvanostatic intermittent titration and in-situ open circuit chronopotentiometry at various temperatures. The measurement of electromotive force was conducted to calculate the partial molar Gibbs free energies of Pr in two phase coexisting states. In addition, the thermodynamic parameters of seven Cd-Pr intermetallic compounds such as the Gibbs free energy, enthalpy and entropy of formation were also determined. The deposited Cd-Pr alloy sample was prepared by galvanostatic electrolysis and further characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). The dissolution behavior of Cd-Pr alloy as an anode material was also evaluated by monitoring the variation of anodic potential.

Magnetic Field Effect on Anodic Dissolution Behavior of Iron in Sodium Perchlorate Solution

It has been reported that magnetic field affects the anodic dissolution and passivation behavior of iron in acidic, neutral, slightly alkaline solutions. Perchlorate solution has been used in the mechanistic study of anodic dissolution mechanism of iron. In this study, the effects of 0.4T magnetic field on the electrochemical behavior and corrosion morphologies of iron in sodium perchlorate solution were studied by optical microscope (OM), scanning electron microscope (SEM) and several electrochemical methods such as potentiodynamic polarization curve and potentiostatic polarization. Magnetic field was placed horizontally and parallel to the working electrode. The anodic polarization curves show that magnetic field did not have strong effect on anodic current at the potential before the transpassivation potential. In the transpassivation range, magnetic field increased the anodic current, increased the slope of the i/E curve. After the potentiodynamic polarization curve measurements up to 2.0V(SCE), severe electrode thinning was observed under both 0T and 0.4T. Macroscopically uniform dissolution was observed on the electrode after measurements under 0T, while locally accelerated thinning was found on the iron electrode after the measurements under 0.4T, showing the accelerating effect of magnetic field on the anodic dissolution at the edges of the electrode along the horizontal direction, as the result of uneven distribution of the actual magnetic field flux density. Potentiostatic polarization measurements show that magnetic field decreased the anodic current density in the passive range, where the electrode was not significantly affected by magnetic field due to low current density. The accelerating or inhibiting effect of magnetic field can be interpreted based on the magnetohydynamic driving force and the magnetic field gradient driving force theory. Figure 1

Anodic Polarization Behavior of Iron in Phosphoric Acid Solution Under the Action of Magnetic Field

The effect of magentic field on anodic dissolution, passivation and dissolution-passivation transition of iron in sulfuric acid solutions have been investigated. The change of anodic dissolution in the dissolution-passivation transition region and the resultant shrinkage of the passive region due to applied magnetic field have been reported. Uneven dissolution of iron electrode after anodic dissolution in sulfuric acid solutions have been reported. In the represent work, the effect of magnetic field on anodic behavior of iron in 0.5 mol/L phosphoric acid is investigated. Potentiodynamic polarization curves and potentiostatic polarization measurements are conducted at 0T and 0.4T. The anodic polarization curves at 0T and 0.4T are shown in Fig. 1, and the electrode surfaces after the measurements are shown in Fig. 2. The anodic polarization curve at 0T exhibits typical anodic dissolution, dissolution-passivation transition, steady passivation and transpassivation behavior. There is no sgnificant effect of magentic field on the active dissolution at potentials lower than Emax, 0T. Magnetic field moves the dissolution-passivation transition potential to a more noble potential therefore narrows the steady passivation range. There is no passive range in the anodic polarizaiton curve at 0.4T, showing only the drastic drop of current at Emax, 0.4T and then an increase of current soon. There is a quasi-linear potential-current density relationship in a wide potential range, i.e. -0.45 to 0.90V(SCE) at 0T, and -0.45 to 1.85V (SCE). The electrode surfaces after the potentiodynamic polarization measurements up to 2.0V(SCE) at 100 mV/min are observed, indicating severe anodic dissolution. The uneven electrode surface shows the locally accelerated anodic dissolution at the left and right edges of the electrode. From the center of the electrode along the horizontal direction to the edge, the uneven dissolution of the electrode surface presents an aggravating tendency. The results are consistent with thoese observed for iron in sulfuric acid at 0.4T magnetic field. When potentiostatic polarization starts at 1.2V at 0T, passive state can be reached and the further applied 0.4T magnetic field decreased the measured current density, showing the potential-dependent rate determining step and the resultant magnetic field effect on selective electrochemical processes. Figure 1

Effect of stress-relief annealing on anodic dissolution behaviour of additive manufactured Ti-6Al-4V via laser solid forming

Stress-relief annealing is one of the most frequently used heat treatments for additive manufactured components. The effects of the stress-relief annealing on anodic dissolution behaviour of laser solid formed Ti-6Al-4V in a 15wt.% NaCl electrolyte was investigated. The annealed Ti-6Al-4V exhibited comparatively improved resistance to dissolution compared with as-deposited one. The reduced micro-segregation resulted in the superior corrosion resistance for the annealed Ti-6Al-4V, owing to the formation of a more stable passive film and the weakened galvanic effect. The selective dissolution of α phase was lightened with the decreasing concentration difference of solutes between the refined α and β phases.

Glass-forming ability, thermal stability, mechanical and electrochemical behavior of Al-Ce-TM (TM = Ti, Cr, Mn, Fe, Co, Ni and Cu) amorphous alloys

Abstract Al86Ce10TM4 amorphous alloys (TM = Ti, Cr, Mn, Fe, Co, Ni and Cu; where the alloys are denoted by A1~A7, respectively) were fabricated using melt-spin fast-quenching method. The glass-forming ability (GFA), thermal stability (TS), and mechanical and corrosion behavior of the as-spun alloys were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy - energy dispersive spectroscopy (SEM-EDS), differential scanning calorimetry (DSC), micro-indentation and electrochemical techniques. It was found Al and Ce microalloyed with Ti, Cr, Mn, Fe, Co, Ni and Cu, respectively enhance glass formation, thus the as-spun Al86Ce10TM4 alloys form an amorphous matrix embedded with short range ordered (SRO) Al-TM, Al-Ce and Al-Ce-TM quasi-crystalline clusters due to a strong heteroatomic interaction related to a covalent character of atomic bonds (for A1~A7) or/and inlaid with face-centered-cubic aluminum (FCC-Al) nano-crystallites which were precipitated during the melt-spin quenching (for A1~A3). The GFA of the alloys ranks in the sequence of A4 > A5 > A6 > A7 > A2 > A3 > A1 which can be assessed by the supercooled liquid region ΔTm (=Tm-Tx), the reduced glass transition temperature Trg (=Tg/Tm), and other criteria such as γ′ = Tx/(Tg + Tm), δ′ = Tx/(Tm − Tg), β′ = TxTg/(Tm + Tx)2, and ω′ = Tm(Tm + Tx)/(Tx(Tm − Tx)); while the TS of the alloys lists in the series of A5 > A6 ~ A4 > A7 > A3 > A2 > A1 that can be evaluated by the first crystallization activation energy Ec, first crystallization activation enthalpy ΔH⁎, frequency factor Ko, fragility parameter m, and theoretical glass transition temperature Tg⁎. The hardness of the alloys A1~A7 accounts to 707, 809, 940, 863, 762, 809, and 715 MPa, respectively, attributing to a composite structure consisting of an amorphous matrix tessellated with SRO quasi-crystalline clusters or/and FCC-Al nano-crystallites. In addition, the alloys exhibit high corrosion resistance in the rate of 10−7–10−8 A/cm2 with a large passivation scope except that the alloy A7 presents a corrosion rate of 10−6 A/cm2 with an active anodic dissolution behavior. The results manifest the Al86Ce10TM4 alloys can be fabricated into a unique composite consisting of an amorphous matrix embedded with SRO quasi-crystalline or/and nano-crystalline phases which confers high mechanical hardness and corrosion resistance for potential engineering applications.

Corrosion Electrochemical Kinetic Study of Copper in Acidic Solution using Scanning Electrochemical Microscopy

The cathodic hydrogen evolution and anodic dissolution behavior of pure copper in acidic solution were investigated by tip generation/substrate collection mode of scanning electrochemical microscopy. The cupric ion generated by copper anodic dissolution without complexation with Cl− was directly monitored and quantitatively analyzed in the potential range between 0.266 V and 0.516 V vs NHE. Based on COMSOL simulation and Tafel linear fitting, the standard rate constants and transfer coefficients of hydrogen evolution reaction, copper oxidation to cupric ion and copper ion are 1.28 × 10−4 cm/s and 0.29, 5.69 × 10−4 cm/s and 0.42, 1.31 × 10−4 cm/s and 0.76, respectively. Moreover, both the proton reduction and oxygen reduction reactions strongly depend on the electrode potential, which should be carefully considered and distinguished for polarization curve analysis of Cu in an acidic solution.

Distinction in anodic dissolution behavior on different planes of laser solid formed Ti-6Al-4V alloy

Microstructure, electrochemical impedance, and Tafel and potentiodynamic polarizations were characterized to investigate the electrochemical anodic dissolution behavior of Ti-6Al-4V alloy produced by the laser solid forming (LSF) additive manufacturing process with a specific focus on the distinction on different planes. Electrochemical measurements show that the anodic dissolution characteristic of LSFed Ti-6Al-4V reveals anisotropic behavior on different planes. The horizontal-plane (XOY plane) is more resistant to corrosion than the vertical-plane (XOZ plane) in 15 wt% NaCl solution. Additionally, the vertical-plane shows a lower initial machining potential for the process of electrochemical machining compared to the horizontal-plane. The microstructure of Ti-6Al-4V alloy deposit is composed of dominant α-laths and small amounts of β phase, and its horizontal-plane has higher content of the β phase, lower content of the α phase, slightly finer α-laths, and more uneven α-lath width distribution compared to the vertical-plane. These differences in the microstructural characteristics produce the distinctions observed in the electrochemical anodic dissolution behavior of LSFed Ti-6Al-4V alloy on the vertical- and horizontal-planes.

Qualitative use of potentiodynamic polarization and anodic hydrogen evolution in the assessment of corrosion susceptibility in AA2198‐T851 Al–Cu–Li alloy

In this study, the corrosion behavior of the AA2198‐T851 and its friction stir weldment was used to show the qualitative use of potentiodynamic polarization and the effect of anodic hydrogen evolution (AHE). The results showed that some details can be revealed in the anodic arm of the polarization curves of an Al alloy above the breakdown potential with changes in cell configuration and electrolytes. In addition, AHE interferes with the measured current density in the anodic arm, which in turn can be used to assess the extent of corrosion susceptibility and changes in anodic dissolution behavior of the alloy.