Corrosion Properties Of Alloys Research Articles

Chemical passivation as a method of improving the electrochemical corrosion resistance of Co-Cr-based dental alloy.

The purpose of the study was to evaluate corrosion resistance of Wirobond C® alloy after chemical passivation treatment. The alloy surface undergone chemical passivation treatment in four different media. Corrosion studies were carried out by means of electrochemical methods in saline solution. Corrosion effects were determined using SEM. The greatest increase in the alloy polarization resistance was observed for passive layer produced in Na2SO4 solution with graphite. The same layer caused the highest increase in corrosion current. Generally speaking, the alloy passivation in Na2SO4 solution with graphite caused a substantial improvement of the corrosion resistance. The sample after passivation in Na2SO4 solution without graphite, contrary to others, lost its protective properties along with successive anodic polarization cycles. The alloy passivation in Na3PO4 solution with graphite was the only one that caused a decrease in the alloy corrosion properties. The SEM studies of all samples after chemical passivation revealed no pit corrosion - in contrast to the sample without any modification. Every successive polarization cycle in anodic direction of pure Wirobond C® alloy enhances corrosion resistance shifting corrosion potential in the positive direction and decreasing corrosion current value. The chemical passivation in solutions with low pH values decreases susceptibility to electrochemical corrosion of Co-Cr dental alloy. The best protection against corrosion was obtained after chemical passivation of Wirobond C® in Na2SO4 solution with graphite. Passivation with Na2SO4 in solution of high pH does not cause an increase in corrosion resistance of WIROBOND C. Passivation process increases alloy resistance to pit corrosion.

Improvement of microstructure, mechanical and corrosion properties of biomedical Ti-Mn alloys by Mo addition

In previous studies, Ti-Mn alloys showed promising performance for biomedical applications, but their elongation required improvement. In this study, Mo was added to Ti-Mn alloys to promote mechanical twinning and improve their ductility. Four alloys for biomedical applications were designed and fabricated by cold crucible levitation melting: Ti-5Mn-3Mo (TMM-53), Ti-5Mn-4Mo (TMM-54), Ti-6Mn-3Mo (TMM-63), and Ti-6Mn-4Mo (TMM-64). The microstructure, mechanical properties, tensile deformation mechanisms, and electrochemical corrosion properties of the alloys were evaluated. Their hardness ranges from 336 to 373HV. Their Young's modulus ranges from 89 to 100GPa. Both hardness and Young's modulus tend to decrease with decreasing amount of athermal ω phase, which is caused by increasing alloying elements contents. Mo addition improves the elongation of TMM-53 and TMM-54 by promoting twinning. Conversely, it increases the tensile strength of TMM-63 and TMM-64. Particularly, TMM-54 shows an elongation of 34% with an ultimate tensile strength (UTS) of 935MPa. TMM-63 shows an elongation of 14% and a UTS of 1220MPa, associated to the formation of deformation-induced ω phase. Moreover, Mo addition decreases the corrosion rate of the Ti-Mn alloys to a level comparable to that of commercially-pure Ti.

Features of structure and properties of modified multicomponent alloys

Study of state of the problem of formation of structure and properties of compact enhance steels and alloys used for cast and deformed pieces of mechanical engineering and aerospace engineering. To solve this problem is provided a method of modifying metal melts dispersed nanosized refractory formulations range.The material of the study were multi-component (heat-resistant) nickel alloys for blades aviation gas turbine engines (GTE) and Si- Mn steels used for gas and oil pipes and welded structures responsible. The chemical composition of heat resisting nickel alloys,% wt .: Al-4,0%; Ti-2,5; Cr-11.0; Mo-3,8; W-3,8; Co-8,0; C-0,09; Fe-2,0; Ni- base. The chemical composition of 15GS and 16GS,% wt .: C-0.16 Si- Mn steels; Si-0,70; Mn-1,20; Cr <0,3; Ni <0,3; Cu <0, 3; S <0,040; P <0,035.Reasonable selection guidelines Nanodisperse complex modifiers in relation to the composition of alloys. Compositions designed nanomodifiers heat resisting nickel alloys, titanium based carbonitride powders of Ti (C, N); kremniymargantsovistyh for steel - based on titanium and aluminum. The formulations are patented modifiers.The laboratory and pilot-scale melting of the alloys with varying number of members of modifiers.An experimental set optimal amount of injected modifier 0,10..0,20% of the mass of the melt.The initial size of 60..100 nm nanopowders obtained by plasma-chemical synthesis. The study granulometry powder specific surface modifier particles picked Ti (C, N) and Ti; crystallographic parameters. Modifiers administered in tablet form in the melt. Installed temperature and time parameters modification. Duration complex modifiers make up for nickel alloys up to 5 minutes for the steel -15 min. In industrial conditions experienced cast castings for turbine engine blades and blanks for further deformation. The samples - witnesses investigated the structure, mechanical and corrosion properties of alloys in the original and modified state.As a result, a substantial modification achieved grain refinement Ni-alloys from 5..8mm to 0,5..1mm. and stalyah- Si- Mn 1.5. The phase composition of the alloy by X-ray electron microprobe analysis. The formation of dispersed carbide phases in the Ni-alloys, both inside and along the grain boundaries, as well as strengthening of intermetallic compounds dispersed Ni3Ti.Achieved increase of properties for Ni-alloys: σв 7%, δ-24%, KCU-46%; for Si- Mn steels: σв - 23%, δ-18%, KCU-40%

Method of estimation of corrosion stability of multicomponent alloys using equilibrium and polarization potential – pH diagrams

Purpose The purpose of this study is to develop a method of thermodynamic and kinetic evaluation of corrosion properties of alloys. Design/methodology/approach Method of estimation of corrosion-electrochemical behaviour of multicomponent alloys is proposed. The method takes into account both thermodynamic and kinetic data and is based on mutual construction of equilibrium and polarization potential – pH diagrams. The usage of the proposed method is illustrated in the example of the structural steel 20KT. Findings Passivation of steel 20KT is determined by formation of oxide film based on magnetite (Fe3O4); silicon, manganese and copper oxides as well as manganese sulphides can be locally included into the inner side of the passivation layer. An experimental potential – pH diagram of steel 20KT is constructed. Interpreting the results of polarization measurements revealed good agreement between equilibrium and polarization potential – pH diagrams. Originality/value It is shown in the example of structural steel 20KT that for interpretation of experimental potential – pH diagrams, one should compare them with corresponding equilibrium diagrams for multicomponent alloys rather than with Pourbaix diagrams for pure metals. The corrosion properties of steel 20KT are estimated using equilibrium and polarization potential – pH diagrams.

The effects of zirconium and beryllium on microstructure evolution, mechanical properties and corrosion behaviour of as-cast AZ63 alloy

Alloying elements are able to strongly modify the microstructure characteristics of Mg–Al–Zn alloys which dominate mechanical and corrosion properties of the alloys. In this research, the individual effects of Zr and Be additions on the microstructure, mechanical and corrosion properties of as-cast AZ63 alloy were explored. The results revealed that the addition of Zr leads to microstructure refinement in as-cast AZ63 alloy, resulting in improved tensile and hardness properties. 0.0001 and 0.001wt% Be containing cast AZ63 alloy exhibited microstructure coarsening, while morphological alteration from sixford symmetrical to irregular shape grain was observed for the alloy containing 0.01 and 0.1wt% Be. No specific Be compound was detected. In addition, mechanical properties of AZ63 alloy containing Zr was improved due to the microstructure modification, while Be containing alloy responded reverse behaviour. The corrosion resistance of AZ63 alloy was improved after the addition of Zr and Be due to the grain refinement and passivation effects, respectively. However, when the Zr content exceeds 0.5wt%, the formation of Al2Zr affected the corrosion resistance. In other words, AZ63–0.5Zr alloy provided the lowest corrosion rate.

Microstructure and Hot Corrosion Properties of Surface Plasma Alloyed Ti2AlNb-Based Alloys

Some unsatisfactory characteristics of Ti2AlNb-based alloys restrict its practical application, such as the insufficient high temperature oxidation, corrosion resistance and poor wear resistance. The double glow plasma surface chromizing can improve their wear resistance, however the hot corrosion properties of surface plasma chromised Ti2AlNb-based alloys were little investigated. The microstructure, composition and surface hot corrosion morphologies of Ti2AlNb-based alloy were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD of alloying layer indicated that the Cr-Nb alloy phase was the main composition, including the compact and uniform Cr2Nb phase, which was benefit to improve the hot corrosion properties of alloy.

Effect of Hot Extrusion and Cyclic Extrusion Compression Progress on the Microstructures and Properties of Mg-Zn-Y-Nd Alloy

Magnesium alloys are promising candidate materials for cardiovascular stents due to their good biocompatibility and degradation property in human body. However, in vivo tests also show that improvement in mechanical property and corrosion resistance is necessary for wide application. In this study, hot extrusion and cyclic extrusion compression (CEC) were used on Mg-Zn-Y-Nd alloy, the effects of hot extrusion and CEC process on the microstructures, mechanical properties and corrosion properties of alloy were studied. The results showed that the microstructures of CEC treated Mg-Zn-Y-Nd alloy became finer and more homogenous, some nanoparticles which came from the cluster phase uniformly precipitated inside grains, alloy had good mechanical properties and corrosion resistance. The immersion test results in SBF solution at 37 for 24h showed that the alloy after CEC treatment is uniform corrosion.

A study on the mechanical and corrosion properties of lead added magnesium alloys

The purpose of this study was to investigate the effect adding Pb at different ratios had on the corrosion properties of Mg alloys. Pb, at a rate of 0.2%, 0.5%, and 1%, was added to Mg-10% Al–12Si. The microstructure characterisation, mechanical and corrosion properties of alloys, produced using a casting method was investigated. Light Optical Microscopy (LOM), X-Ray Diffraction (XRD) analyses and a Scanning Electron Microscope (SEM) were used to conduct the microstructure characterisation of investigated alloys. Corrosion tests were performed by suspending the samples of certain sizes into the 3.5% NaCl solutions measuring the weight loss, and also by potentiodynamic polarisation measurements in the same solution. According to corrosion experiment results, Ikor decreased with the addition of Pb, causing an increase in the corrosion resistance.

Effect of the chemistry and structure of the native oxide surface film on the corrosion properties of commercial AZ31 and AZ61 alloys

The purpose of this study has been to advance in knowledge of the chemical composition, structure and thickness of the thin native oxide film formed spontaneously in contact with the laboratory atmosphere on the surface of freshly polished commercial AZ31 and AZ61 alloys with a view to furthering the understanding of protection mechanisms. For comparative purposes, and to more fully describe the behaviour of the native oxide film, the external oxide films formed as a result of the manufacturing process (as-received condition) have been characterised. The technique applied in this research to study the thin oxide films (thickness of just a few nanometres) present on the surface of the alloys has basically been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Corrosion properties of the alloys were studied in 0.6 M NaCl by measuring charge transfer resistance values, which are deduced from EIS (electrochemical impedance spectroscopy) measurements after 1 h of exposure. Alloy AZ61 generally showed better corrosion resistance than AZ31, and the freshly polished alloys showed better corrosion resistance than the alloys in as-received condition. This is attributed to a combination of (1) higher thickness of the native oxide film on the AZ61 alloy and (2) greater uniformity of the oxide film in the polished condition. The formation of an additional oxide layer composed by a mixture of spinel (MgAl 2O 4) and MgO seems to diminish the protective properties of the passive layer on the surface of the alloys in as-received condition.

The Effect of Anions on the Passive Film Properties and Localized Corrosion Behavior of Alloy C-22

This paper investigates corrosion behavior of Alloy C-22 in hot concentrated brines. The passive film behavior and localized corrosion properties of alloy C-22 as a function of nitrate and sulfate anions in concentrated chloride brines was investigated. Cyclic potentiodynamic polarization tests were used to study the general corrosion behavior of the alloy, Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (M-S) were used to examine the electronic properties of the passive films, and constant potential tests were done to study crevice corrosion initiation, propagation and stifling of the alloy. The aim was to investigate the correlation between the electronic properties of the alloy's passive film and the localized corrosion susceptibility of the alloy. The results showed that anions had major impact on the repair- repassivation behavior but did not cause significant effect on the properties of passive film when it was intact.

Metallurgical, surface, and corrosion analysis of Ni–Cr dental casting alloys before and after porcelain firing

Objectives A porcelain veneer is often fired on nickel–chromium casting alloys used in dental restorations for aesthetic purposes. The porcelain-fused-to-metal (PFM) process brings the temperature to over 950 °C and may change the alloy's corrosion properties. In this study, the metallurgical, surface, and corrosion properties of two Ni–Cr alloys were examined, before and after PFM firing. Methods Two types of alloy were tested—a high Cr, Mo alloy without Be and a low Cr, Mo alloy with Be. Before the PFM firing, specimens from both alloys were examined for their microstructures, hardness, electrochemical corrosion properties, surface composition, and metal ion release. After the PFM firing, the same specimens were again examined for the same properties. Results Neither of the alloys showed any differences in their electrochemical corrosion properties after the PFM firing. However, both alloys exhibited new phases in their microstructure and significant changes in hardness after firing. In addition, there was a slight increase in CrO x on the surface of the Be-free alloy and increased Mo–Ni was observed on the surface of both alloys via X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). This might be one of the reasons why both alloys had increased Ni and Mo ion release after firing. Significance The PFM firing process changed the alloys’ hardness, microstructure, and surface composition. No significant changes in the alloys’ corrosion behavior were observed, however, the significant increase in metal ion release over a month may need to be further investigated for its clinical effects.

The effect of temperature oscillation on the passive corrosion properties of Alloy 22

A temperature-oscillating heated electrode technique (TOHET) was developed for investigating the temperature effect on the passive corrosion properties of Alloy 22 (UNS N06022, Ni–22Cr–13Mo–3W–3Fe), which has been selected as the corrosion-resistant material (CRM) of the waste package outer barrier for the high level nuclear waste (HLNW) repository at Yucca Mountain, NV, USA. Cyclic and potentiostatic polarization tests were conducted on a temperature-controlled hot surface of Alloy 22, which was immersed in simulated Yucca Mountain ground waters. The current recorded during cyclic polarization tests was sensitive to temperature changes when the temperature amplitude was greater than 2 °C. Corrosion potential increased from −293 mV to −256 mV (Ag/AgCl) when temperature was decreased from 102 °C to 72 °C. Current variation was also observed during a potentiostatic test at −150 mV over which temperature oscillated between 65 °C and 95 °C. The log–linear plot of passive current density vs. temperature exhibited a linear relationship. In summary, the TOHET method is a valuable technique for studying the effects of temperature on the corrosion rate of passive alloys.

Effect of Sulfate on the Passive and Crevice Corrosion Properties of Alloy 22 in 4 M Sodium Chloride

Abstract The study of the electrochemical behavior of Alloy 22 (UNS N06022) was carried out in 4 M sodium chloride (NaCl) and 4 M NaCl with sulfate additions of 0.4 M and 0.04 M between 45°C and 10...

Influence of Solution pH, Anion Concentration, and Temperature on the Corrosion Properties of Alloy 22

We introduce an acid addition technique for the rapid assessment of the influence of solution pH, anion (such as chloride) concentration, and temperature on the dissolution of metals. We demonstrate the technique with the characterization of the dissolution of alloy 22 (Ni–22Cr–13Mo–3W–3Fe) exposed to chloride-containing hydrochloric, sulfuric, and nitric acid environments as a function of pH (from pH 5 to pH ) and temperature (25–90°C). A combination of electrochemical techniques (electrochemical impedance spectroscopy and linear polarization resistance) and atomic force microscopy are used to characterize the influence of the various solutions on the dissolution of alloy 22. Below 50°C, corrosion rates are less than independent of acid type, pH, and temperature. In contrast, between 50°C and the upper explored limit of 90°C, dissolution rates in sulfuric and hydrochloric acid scale approximately linearly with temperature at rates that depend on the solution pH. In nitric acid, corrosion rates are lower at comparable pH values due to the oxidizing effects of nitrates. An increase in the open-circuit potential in conjunction with electrochemical impedance spectroscopy data suggests that nitrates promote a stable passive oxide film that inhibits alloy dissolution in all environments tested.

In vitro biocorrosion of Co–Cr–Mo implant alloy by macrophage cells

We hypothesized that macrophage cells and their released reactive chemical species (RCS) affect Co–Cr–Mo alloy's corrosion properties and that alloy corrosion products change macrophage cell behavior. A custom cell culture corrosion cell was used to evaluate how culture medium, cells, and RCS altered alloy corrosion in 3-day tests. Corrosion was evaluated by measuring total charge transfer at a constant potential using a potentiostat and metal ion release by atomic emission spectroscopy. Viability, proliferation, and NO (nitric oxide) and IL-1β (interlukin-1β) release were used to assess cellular response to alloy corrosion products. In the presence of activated cells, total charge transfers and Co ion release were the lowest ( p<0.05). This was attributed to an enhancement of the surface oxide by RCS. Cr and Mo release were not different between cells and activated cells. Low levels of metal ions did not affect cell viability, proliferation, or NO release, though IL-1β released from the activated cells was higher on the alloy compared to the controls. These data support the hypothesis that macrophage cells and their RCS affect alloy corrosion. Changes in alloy corrosion by cells may be important to the development of host responses to the alloy and its corrosion products.

In vitro biocorrosion of Ti-6Al-4V implant alloy by a mouse macrophage cell line.

Corrosion of implant alloys releasing metal ions has the potential to cause adverse tissue reactions and implant failure. We hypothesized that macrophage cells and their released reactive chemical species (RCS) affect the alloy's corrosion properties. A custom cell culture corrosion box was used to evaluate how cell culture medium, macrophage cells and RCS altered the Ti-6Al-4V corrosion behaviors in 72 h and how corrosion products affected the cells. There was no difference in the charge transfer in the presence (75.2 +/- 17.7 mC) and absence (62.3 +/- 18.8 mC) of cells. The alloy had the lowest charge transfer (28.2 +/- 4.1 mC) and metal ion release (Ti < 10 ppb, V < 2 ppb) with activated cells (releasing RCS) compared with the other two conditions. This was attributed to an enhancement of the surface oxides by RCS. Metal ion release was very low (Ti < 20 ppb, V < 10 ppb) with nonactivated cells and did not change cell morphology, viability, and NO and ATP release compared with controls. However, IL-1beta released from the activated cells and the proliferation of nonactivated cells were greater on the alloy than the controls. In summary, macrophage cells and RCS reduced the corrosion of Ti-6Al-4V alloys as hypothesized. These data are important in understanding host tissue-material interactions.

Influence of heat treatment and surface conditioning on filiform corrosion of aluminium alloys AA3005 and AA5754

The effect of high-temperature heat treatment combined with different cleaning and pre-treatment practices on filiform corrosion resistance has been investigated for aluminium alloys AA3005 and AA5754. High-temperature heat treatment severely reduces the filiform corrosion resistance of alloy AA3005, while the corrosion properties of alloy 5754 are only moderately affected. The drastic loss of filiform corrosion resistance of alloy AA3005 after high-temperature heat treatment is attributed to preferential microstructural changes in a heavily deformed, micrograined surface layer caused by large surface shear strain during rolling. The enhanced deformation of the near-surface region promotes precipitation of a fine dispersion of intermetallic particles during subsequent heat treatment. The higher density of intermetallic particles combined with lower supersaturated solid solution levels of manganese in the surface layer as compared to the bulk structure makes the heat-treated AA3005 material susceptible to superficial corrosion attacks and results in poor filiform corrosion resistance. Application of a commercial acid cleaning/chromating pre-treatment did not restore the filiform corrosion resistance of heat-treated alloy AA3005. Alloy AA5754, containing lower levels of manganese and iron than AA3005, did not undergo similar preferential microstructural changes during heat treatment. A moderate increase in the amount of filiform corrosion of heat-treated AA5754 samples is attributed to poor protective properties of the thick, magnesium enriched, thermally formed surface oxide on this alloy. Any cleaning/pre-treatment practice that removes the thermally formed oxide on this alloy results in a very high filiform corrosion resistance.

Alloy Corrosion

The corrosion properties of alloys are of enormous practical importance: modern life would be very different without stainless steels. Alloy corrosion is also an intriguing field of scientific study that combines electrochemical kinetics with fashionable aspects of the morphological evolution of surfaces and even a dash of ancient history, via the studies of Forty and Lechtman on “depletion gilding” practiced by Early Andeans during pre-Columbian times in South America.The basic alloy corrosion process, as used by the metalsmiths to gold-coat artifacts, is de-alloying. This is defined as the selective electrolytic dissolution of one or more components from a metallic solid solution. For this to happen, there must be a significant difference in the equilibrium metal/metal-ion electrode potentials for the two metals, taking into account any complex ions that might be formed in the electrolyte. For example, we can expect de-alloying in Au-Cu alloys, but not in Au-Pt alloys.De-alloying shows sharp parting limits, expressed as critical atom percentages of the more reactive component above which that component can be removed from the alloy by electrochemical dissolution in an oxidizing environment such as nitric acid. Parting limits range from about 20 at.% to 60 at.%. This concept is still used in noble metal technology to separate noble metals from base metals. For example, an alloy of 55 at.% gold and 45 at.% silver does not de-alloy, but if it is re-melted with additional silver so that the atom fraction of Ag is greater than 60%, the gold can be separated almost completely by nitric acid immersion.

Oxidation and corrosion behaviour of Fe–Cr and Fe–Cr–Al alloys with minor alloying additions

The oxidation and corrosion properties of alloys based on Fe–40Cr and Fe–35Cr–5Al were studied using gravimetric and potentiodynamic techniques. The properties were modified by microalloying with ruthenium and rare-earth metals (REM). A high resistance to breakaway oxidation was characteristic of all the high chromium alloys assessed. Good oxidation resistance in the Fe–35Cr–5Al alloys was found to be contingent on (i) the rapid establishment of a stable protective aluminium oxide layer in the early stages, and (ii) the development of a secondary chromium oxide layer for long-term stability. Microalloying with 0.2 wt.% Ru promoted the formation of a chromium-rich layer at the substrate interface. The consequence of this differed in each case. In the Fe–35Cr–5Al alloy, the result was improved oxidation resistance, accompanied by segregation of the Ru to the aluminium oxide layer. In the Fe–40Cr alloy, the Ru addition was associated with an initially higher oxidation rate and an increased tendency to spalling. REMs, added as 0.05 wt.% mischmetal to the Fe–35Cr–5Al alloy, also lowered the oxidation rate, as expected. Relative to the Fe–40Cr composition, the substitution of 5 wt.% Al for 5 wt.% Cr had a negligible effect on the aqueous corrosion resistance in 10% H 2SO 4, but led to inferior pitting resistance in a 3.5% NaCl solution. As previously shown with stainless steels based on Fe–40Cr, small additions of ruthenium can also enhance the corrosion and pitting resistance of Fe–35Cr–5Al.

Passivity, pitting and corrosion of anodically polarized Fe-Ni alloys in 0.5 M H2SO4 containing Cl?

Iron-nickel alloys containing 0, 20, 40, 60, 80 and 100% Ni (wt%) have been anodically polarized in 0.5 M H2SO4 containing Cl−, and the conditions for passivity, pitting and corrosion with respect to alloy composition and Cl− concentration broadly defined. Breaks occur in the values of the corrosion properties at about 30% and 70% Ni. It is considered that the corrosion properties of alloys containing up to 30% Ni are determined by the ferrite in the alloy and the low corrosion resistance of its surface film, that alloys containing 30 to 70% Ni have a corrosion resistant film probably similar to a nickel ferrite spinel, and that alloys containing over 70% Ni have properties similar to nickel and probably have a surface film based on a solid solution of iron in NiO.