Electrochemical Behavior of Al–Al9Co2 Alloys in Sulfuric Acid

Al–Co alloys of various Co contents (2–20 wt.% Co) were fabricated by vacuum arc melting (VAM) with the scope to investigate the influence of cobalt on the microstructure and corrosion resistance of Al in 1 M H2SO4. The obtained microstructures were directional, consisting of Al9Co2 platelets (grown to coarse acicular plates as the Co content increased) uniformly dispersed in an Al-matrix. Alloying Al with Co did not decrease the rate of uniform corrosion of Al but it considerably increased its passivation ability. Moreover, all Al–Co alloys displayed lower uniform corrosion rate and notably higher passivation ability than market leading Al-alloys. The underlying mechanisms during anodic polarization in 1 M H2SO4 were identified and correlated with the microstructure. High Co content alloys (7–20 wt.% Co) presented superior passivation ability in 1 M H2SO4 as compared to the low Co content alloys

A Critical Review on Al-Co Alloys: Fabrication Routes, Microstructural Evolution and Properties

Al-Co alloys is an emerging category of metallic materials with promising properties and potential application in various demanding environments. Over the years, different manufacturing techniques have been employed to fabricate Al-Co alloys, spanning from conventional casting to rapid solidification techniques, such as melt spinning, thus leading to a variety of different microstructural features. The effect of the fabrication method on the microstructure is crucial, affecting the morphology and volume of the precipitates, the formation of supersaturated solid solutions and the development of amorphous phases. In addition, the alloy composition has an effect on the type and volume fraction of intermetallic phases formed. As a result, alloy properties are largely affected by the microstructural outcomes. This review focuses on highlighting the effect of the fabrication techniques and composition on the microstructure and properties of Al-Co alloys. Another goal is to highlight areas in the field that are not well understood. The advantages and limitations of this less common category of Al alloys are being discussed with the scope of future prospects and potential applications

Cyclic Polarization of Corrugated Austenitic Stainless Steel Rebars in Acid Rain: Effect of Fly Ash, pH and Steel Type

The present work studies the effect of fly ash content (0–25 wt.%), pH (8, 12.5), and steel type (316L, 304L) on the cyclic polarization of stainless steel rebars in electrolytes, simulating fresh concrete exposed to acid rain and corroded concrete cover that has exposed the reinforcement to direct acid rain attack. At the same time, it tries to elucidate the corrosion inhibition activities of a Greek lignite fly ash that is a high-Ca fly ash with a questionable effect on the corrosion resistance of concrete. A higher pH results in lower corrosion rates for both steels and all fly ash content. However, different passivity trends are noted for the two steels as a function of pH. The partial replacement of Ca(OH)2 with fly ash up to 20 wt.% has a beneficial effect on the electrochemical behavior of the stainless steel rebars, in terms of both uniform and localized corrosion resistance. However, this trend is reversed at 25 wt.% FA. The reasons for such trends are explored via microstructural examinations of the steels after polarization and XRD analysis of fly ash, as well as reinforced concrete containing fly ash

Effect of Fly Ash on the Electrochemical Performance of 316L Stainless Steel Concrete Reinforcement in Saline Environments Attacked by Acid Rain

The present study investigates the effect of fly ash (FA) as a corrosion inhibitor on the electrochemical performance of 316L stainless steel concrete reinforcement in a simulating concrete pore solution exposed to a coastal environment that is severely polluted by acid rain (AR). The corrosion behavior of 316L stainless steel is examined by means of cyclic (reverse) polarization in order to evaluate the susceptibility of 316L rebars to localized corrosion. A slightly alkaline solution simulating corroded concrete that has exposed the reinforcement directly to acid rain attack (pH ≈ 8) was chosen as electrolyte. The solution contained Ca(OH)2 partially replaced by FA (0 wt.% - 25 wt.%), an acid rain simulating solution and 3.5 wt% NaCl. The beneficial effect of FA partially replacing Ca(OH)2 (up to 20 wt.% FA) on the corrosion resistance of 316L rebars was manifested by slower corrosion kinetics, nobler corrosion potentials and less susceptibility to localised corrosion. However, these trends were reversed at 25 wt.% FA. The above performance was compared with the corrosion performance in the same electrolyte but without the addition of 3.5 wt.% NaCl

Accelerated corrosion performance of AISI 316L stainless steel concrete reinforcement used in restoration works of ancient monuments

The accelerated corrosion performance of AISI type 316L stainless steel rebars in solutions simulating concrete exposed to various environments was studied by means of cyclic polarization, before and after a four month salt spray test. B500A structural steel rebars were also tested for comparison reasons. Although 316L showed some susceptibility to localized corrosion during polarization in saturated Ca(OH)2 containing 3.5 wt.% NaCl, four months of salt spraying did not significantly affect its polarization behavior. Salt spraying for 4 m did not have any significant effect on the macrostructural state of 316L reinforced concrete

Accelerated corrosion performance of AISI 316L stainless steel concrete reinforcement used in restoration works of ancient monuments

The accelerated corrosion performance of AISI type 316L stainless steel rebars in solutions simulating concrete exposed to various environments was studied by means of cyclic polarization, before and after a four month salt spray test. B500A structural steel rebars were also tested for comparison reasons. Although 316L showed some susceptibility to localized corrosion during polarization in saturated Ca(OH)2 containing 3.5 wt.% NaCl, four months of salt spraying did not significantly affect its polarization behavior. Salt spraying for 4 m did not have any significant effect on the macrostructural state of 316L reinforced concrete

Electrochemical Behavior of Nickel Aluminide Coatings Produced by CAFSY Method in Aqueous NaCl Solution

Combustion-assisted flame spraying (CAFSY) is a novel method that allows in-flight synthesis of alloys during flame spraying. The in-flight synthesis of alloys by the CAFSY method during flame spraying combines two different methods: the self-propagating high-temperature synthesis (SHS) and flame spraying (FS). The present work studies the corrosion performance (by cyclic polarization and chronoamperometry in aerated 3.5 wt.% NaCl) of NiAl coatings fabricated by the CAFSY technique in relation to main process parameters (composition of the initial feedstock, spraying distance, substrate temperature, postdeposition heat treatment) and their effect on the microstructure and porosity of the coatings. Most of the coatings exhibited limited susceptibility to localized corrosion. In all cases, the steel substrate remained intact despite corrosion. Interconnected porosity was the main parameter accelerating uniform corrosion. Localized corrosion had the form of pitting and/or crevice corrosion in the coating that propagated dissolving Al and Al-rich nickel aluminides along coating defects. Substrate preheating and postdeposition heat treatment negatively affected the corrosion resistance. A short spraying distance (1.5 inch) increased the corrosion resistance of the coatings

Solid particle erosion response of aluminum reinforced with tungsten carbide nanoparticles and aluminide particles

The main concept behind this work is to further enhance the attractive properties of aluminum by fabricating Al - WC composites and evaluating them in terms of their solid particle erosion response. Aluminum Matrix Composites (AMCs) were produced by the addition of submicron sized WC particles (up to 2.5vol %) into a melt of Al1050. Casting was assisted by the use of K2TiF6 as a wetting agent and mechanical stirring in order to minimize particle clustering. Extensive presence of in-situ intermetallic phases (Al4W, Al5W, Al12W, Al3(Ti,W), Al3Ti) was observed in the cast products. Particle distribution was reasonably uniform comprising both clusters and isolated particles. Solid particle erosion experiments were carried out for impact angles of 30°, 60° and 90°, using angular Al2O3 particles as the eroding medium and under 5 bar spraying pressure. The erosion rate was calculated by measuring the mass loss and the eroded surfaces were examined with SEM-EDX. Increased erosion resistance was observed for low particle additions (≤ 1.0 vol%WC). Finally, a possible erosion mechanism was proposed based on the material’s microstructural and morphological characteristics

Solid particle erosion response of aluminum reinforced with tungsten carbide nanoparticles and aluminide particles

The main concept behind this work is to further enhance the attractive properties of aluminum by fabricating Al - WC composites and evaluating them in terms of their solid particle erosion response. Aluminum Matrix Composites (AMCs) were produced by the addition of submicron sized WC particles (up to 2.5vol %) into a melt of Al1050. Casting was assisted by the use of K2TiF6 as a wetting agent and mechanical stirring in order to minimize particle clustering. Extensive presence of in-situ intermetallic phases (Al4W, Al5W, Al12W, Al3(Ti,W), Al3Ti) was observed in the cast products. Particle distribution was reasonably uniform comprising both clusters and isolated particles. Solid particle erosion experiments were carried out for impact angles of 30°, 60° and 90°, using angular Al2O3 particles as the eroding medium and under 5 bar spraying pressure. The erosion rate was calculated by measuring the mass loss and the eroded surfaces were examined with SEM-EDX. Increased erosion resistance was observed for low particle additions (≤ 1.0 vol%WC). Finally, a possible erosion mechanism was proposed based on the material’s microstructural and morphological characteristics

Microstructure and surface degradation of Al reinforced by Al

In the present effort, Al-AlxW composites have been prepared by vacuum arc melting (VAM), conventional casting (CAST) and free sintering (PM) with the objective to determine an effective fabrication route in terms of low cost, ease of manufacture and property boosting. The produced Aluminium Matrix Composites (AMCs) contain several types of in-situ aluminides. Their morphology, stoichiometry and distribution strongly depend on the fabrication route. The particulate aluminide reinforcements have a beneficial effect on the wear response of the monolithic matrix. VAM-AMCs show the highest resistance to wear. A wear mechanism is proposed