Electrochemical properties of Al-6060 alloy after industrial-scale ECAP

Equal-channel angular pressing (ECAP) as the most famous method of severe plastic deformation has the potential for up-scaling from laboratory to industrial. Therefore, it is important to examine practice-relevant properties of large billets deformed by this process. Mechanical properties and corrosion resistance essentially influence the service life of construction components. Mechanical properties of an Al-6060 alloy after industrial-scale ECAP (cross-section of the billet 50×50 mm) have been analyzed by P. Frint [4, 17]. The effect of one pass of industrial-scale ECAP on the electrochemical properties of an Al-6060 alloy by means of potentiodynamic polarization tests in 0.1M NaCl solution is investigated. The corroded surfaces were analyzed by means of optical microscopy. In order to characterize the homogeneity of the corrosion behaviour of the ECAP-processed material, all analyzes were taken in different zones perpendicular to the extrusion axis. The results indicate that one ECAP pass does not deteriorate the electrochemical behaviour of the Al-6060 alloy.Вплив одноразового рівноканального кутового пресування на електрохімічні властивості сплаву Al-6060 досліджено методом потенціодинамічної поляризації в 0,1М розчині NaCl. Поверхню після корозії обстежено за допомогою оптичної мікроскопії. Для опису гомогенності характеру корозії матеріалу проаналізовано різні зони, перпендикулярні осі пресування. Виявлено, що воно не змінює електрохімічну поведінку сплаву.Влияние однократного равноканального углового прессования на электрохимические свойства сплава Al-6060 исследовано методом потенциодинамической поляризации в 0,1М растворе NaCl. Поверхность после коррозии обследовано с помощью оптической микроскопии. Для описания гомогенности характера коррозии материала проанализированы разные зоны, перпендикулярные оси прессования. Выявлено, что оно не изменяет электрохимическое поведение сплава

Validation of Simple Shear Tests for Parameter Identification Considering the Evolution of Plastic Anisotropy

The evolution of plastic anisotropy plays a key role for an accurate computational springback prediction in complex, multistage forming processes. In many studies, the identification of material parameters is based on experimental results from shear testing because this technique allows for large plastic deformations without facing stability problems that occur, for instance, during uniaxial tensile testing. However, little is known about the   comparability of different shear test setups. In this study, we systematically compare two quite different and widelyused setups for the simple shear test, the Miyauchi setup and the Twente setup. In the shear tests performed on an AA6016 aluminum alloy sheet, we observed a good agreement for the flow stresses measured with the two different   setups. We then use the mechanical data for the identification of a phenomenological model of the evolution of plastic anisotropy, and we demonstrate the importance of consistent and reliable experimental data studying a model for combined isotropic-kinematic hardening

Development of a brazing process for the production of water- cooled bipolar plates made of chromium-coated metal foils for PEM fuel cells

Beside lithium batteries, PEM fuel cells are the most promising strategy as a power source to achieve the targets for introducing and increasing the usage of electric vehicles. Due to limited space and weight problems, water cooled, metallic bipolar plates in a fuel cell metal stack are preferred in motor vehicles. These plates are stamped metal sheets with a complex structure, interconnected media-tight. To meet the multiple tasks and requirements in use, complex and expensive combinations of materials are currently in use (carbon fiber composites, graphite, gold-plated nickel, stainless and acid resistant steel). The production of such plates is expensive as it is connected with considerable effort or the usage of precious metals. As an alternative, metalloid nitrides (CrN, VN, W2N, etc.) show a high chemical resistance, hardness and a good conductivity. So this material category meets the basic requirements of a top layer. However, the standard methods for their production (PVD, CVD) are expensive and have a slow deposition rate and a lower layer thicknesses. Because of these limitations, a full functionality over the life cycle of a bipolar plate is not guaranteed. The contribution shows the development and quantification of an alternative production process for bipolar plates. The expectation is to get significant advantages from the combination of chromium electrodeposition and thermochemical treatment to form chromium nitrides. Both processes are well researched and suitable for series production. The thermochemical treatment of the chromium layer also enables a process-integrated brazing

Silicate and Hydroxide Concentration Influencing the Properties of Composite Al2 O3-TiO2 PEO Coatings on AA7075 Alloy

This work evaluates the effect of sodium meta-silicate pentahydrate (SMS) and potassium hydroxide concentrations on properties of Al2O3-TiO2 coatings produced through plasma electrolytic oxidation in a solution containing 3 g L−1 potassium titanyl oxalate, (PTO), using a unipolar waveform with constant current density. The surface and cross-section characteristics of PEO coatings including morphology, elemental distribution, and phase composition were evaluated using FESEM, EDS, and XRD techniques. Voltage-time response indicated the concentration of SMS and KOH had a significant effect on the duration of each stage of the PEO process. More cracks and pores were formed at the higher concentrated solutions that resulted in the incorporation of solution components especially Si into the coating inner parts. Ti is distributed throughout the coatings, but it had a dominant distribution in the Si-rich areas. The coating prepared in the electrolyte containing no silicate consisted of non-stoichiometric γ-Al2O3 and/or amorphous Al2O3 phase. Adding silicate into the coating electrolyte resulted in the appearance of α-Al2O3 besides the dominant phase of γ-Al2O3. The corrosion behaviour of the coatings was investigated using the EIS technique. It was found that the coating prepared in the presence of 3 g L−1 SMS and 2 g L−1 KOH, possessed the highest barrier resistance (~10 MΩ cm2), owing to a more compact outer layer, thicker inner layer along with appropriate dielectric property because this layer lacks the Si element. It was discovered that the incorporation of Ti4+ and especially Si4+ in the coating makes the dielectric loss in the coating

Synthesis of Nickel-Carbon Nanohorn Composite Filmsby an Electrodeposition Technique

In this work, electrodeposition of nickel-single walled carbon nanohorns composite is obtained from a sulfamate bath. Electrodeposition of nickel-nanohorn composites is carried out from a sulfamate bath containing up to 2 g/l of dispersed single walled nanohorns with diameter 30 to 50 nm. Deposits with embedded nanohorns, homogeneously dispersed in metal matrix, are obtained. Structure of the deposits and contents of carbon nanohorns particles in these layers were investigated with respect to the possibility of agglomeration of SWNH particles and bath composition (concentration of SWNH in the electrolyte). Morphology of the coatings and the effects of codeposited particles on metal matrix structure are also reported. Microhardness of the composites has been investigated: Martens hardness is highly influenced by the incorporation of particles

Analytical methods to characterize heterogeneous raw material for thermal spray process: cored wire Inconel 625

International audienceIn wire arc spraying, the raw material needs to exhibit sufficient formability and ductility in order to be processed. By using an electrically conductive, metallic sheath, it is also possible to handle non-conductive and/or brittle materials such as ceramics. In comparison to massive wire, a cored wire has a heterogeneous material distribution. Due to this fact and the complex thermodynamic processes during wire arc spraying, it is very difficult to predict the resulting chemical composition in the coating with sufficient accuracy. An Inconel 625 cored wire was used to investigate this issue. In a comparative study, the analytical results of the raw material were compared to arc sprayed coatings and droplets, which were remelted in an arc furnace under argon atmosphere. Energy-dispersive X-ray spectroscopy (EDX) and X-ray fluorescence (XRF) analysis were used to determine the chemical composition. The phase determination was performed by X-ray diffraction (XRD). The results were related to the manufacturer specifications and evaluated in respect to differences in the chemical composition. The comparison between the feedstock powder, the remelted droplets and the thermally sprayed coatings allows to evaluate the influence of the processing methods on the resulting chemical and phase composition

A comparative study of oxidation kinetics and thermal cyclic performance of thermal barrier coatings (TBCs)

The present study was carried out to investigate the isothermal oxidation behavior, thermal cyclic performance and oxidation kinetics of thermal barrier coatings (TBCs) systems consisting of CoNiCrAlY metallic bondcoats produced by Atmospheric plasma spraying (APS) and high velocity oxy fuel spraying (HVOF) on Inconel 718 substrate. Yttria stabilized zirconia (YSZ) ceramic top coats was produced by APS process as for the insulation layer. The oxidation behavior of the coatings were investigated under isothermal oxidation conditions at 1000 °C, 1100 °C and 1200 °C for 8, 24, 50 and 100 h. The results of the experimental studies on the oxidation kinetics and microstructural evolution of APS and HVOF sprayed thermal barrier coatings (TBCs) are compared and discussed in the paper. The microstructural changes at the metallic/ceramic interface and growth behavior of the thermally grown oxide (TGO) layers during the isothermal oxidation and thermal cyclic tests were analyzed in detail. © 2018 Elsevier B.V

Assessment of CrFeCoNi and AlCrFeCoNi High-Entropy Alloys as Bond Coats for Thermal Barrier Coatings

High-entropy alloys (HEAs) represent a relatively new group of multicomponent alloys that have shown great potential for applications requiring tribological and oxidation resistant properties. Consequently, thermally sprayed coatings of different HEA chemistries have received increasing research attention. In this paper, atomized equimolar CrFeCoNi and AlCrFeCoNi feedstocks were used for high velocity air-fuel spraying (HVAF) to produce overlay coatings using two different nozzle configurations. The microstructure, phase constitution and hardness of the coatings were analyzed along with the primary aim of testing the coatings for their oxidation behavior. The performance of the two HEA chemistries was compared with two commercial MCrAlY coatings that are well-established bond coat materials for thermal barrier coatings (TBCs). An investigation was conducted to test the coatingsâ\u80\u99 performance as bond coats by applying suspension plasma sprayed yttria-stabilized zirconia top coats and evaluating the thermal cycling behavior of the TBCs. The AlCrFeCoNi-coating was found to demonstrate a lower oxidation rate than the CrFeCoNi-coating. However, the AlCrFeCoNi-coating was found to form more rapid oxide scales compared with the commercial bond coat material that also contained reactive elements. © 2022, The Author(s)