| 1. |
- Bauer, A., et al.
(författare)
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Experimental and numerical investigation on cold flat rolling processes of DC04 sheets with special focus on residual stresses
- 2016
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- The process of cold flat rolling is a widespread industrial technique to manufacture semi-finished products, e.g., for the automotive or homewares industry. Basic knowledge of the process regarding dimensioning and adjustment of defined characteristics is already state of the art. However, a detailed consideration and analysis with respect to local inhomogeneous residual stresses in several process steps mostly remains disregarded. A broad understanding of the process due to the distribution of residual stresses in the workpiece and the direction of the stress tensors allows for a definition of the characteristics of the workpiece even before the actual manufacturing process. For that purpose, it is necessary to perform numerical investigations by means of the finite element analysis (FEA) of cold flat rolling processes. Within this contribution, several approaches for the calibration of the FEA with the real flat rolling process will be addressed and discussed. To ensure that the numerical consideration provides realistic results, this calibration is indispensable. General parameters such as geometry, height reduction, rolling temperature, process time, and the rolling speed are considered as well as a photogrammetric survey, and calculated residual stresses with results of X-ray diffraction (XRD) will be compared. In the course of the experiments, a good agreement between the stress results of the FEA and the XRD was found in the center of the specimen. In combination with the allocation of the stress orientations, the agreement close to the edges is also fine. Some issues that cause differences between the FEA and the experiment are dis-cussed.
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| 2. |
- Morgenstern, R., et al.
(författare)
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Plasma electrolytic oxidation of Titanium Aluminides
- 2016
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Due to their outstanding specific mechanical and high-temperature properties, titanium aluminides exhibit a high potential for lightweight components exposed to high temperatures. However, their application is limited through their low wear resistance and the increasing high-temperature oxidation starting from about 750 °C. By the use of oxide ceramic coatings, these constraints can be set aside and the possible applications of titanium aluminides can be extended. The plasma electrolytic oxidation (PEO) represents a process for the generation of oxide ceramic conversion coatings with high thickness. The current work aims at the clarification of different electrolyte components' influences on the oxide layer evolution on alloy TNM-B1 (Ti43.5Al4Nb1Mo0.1B) and the creation of compact and wear resistant coatings. Model experiments were applied using a ramp-wise increase of the anodic potential in order to show the influence of electrolyte components on the discharge initiation and the early stage of the oxide layer growth. The production of PEO layers with technically relevant thicknesses close to 100 μm was conducted in alkaline electrolytes with varying amounts of Na2SiO3•5H2O and K4P2O7 under symmetrically pulsed current conditions. Coating properties were evaluated with regard to morphology, chemical composition, hardness and wear resistance. The addition of phosphates and silicates leads to an increasing substrate passivation and the growth of compact oxide layers with higher thicknesses. Optimal electrolyte compositions for maximum coating hardness and thickness were identified by statistical analysis. Under these conditions, a homogeneous inner layer with low porosity can be achieved. The frictional wear behavior of the compact coating layer is superior to a hard anodized layer on aluminum.
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| 3. |
- Ossiansson, Mattias, et al.
(författare)
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Assessment of CrFeCoNi and AlCrFeCoNi High-Entropy Alloys as Bond Coats for Thermal Barrier Coatings
- 2022
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Ingår i: Journal of thermal spray technology (Print). - : Springer Nature. - 1059-9630 .- 1544-1016. ; 31, s. 1404-1422
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Tidskriftsartikel (refereegranskat)abstract
- 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 coatings’ 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).
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| 4. |
- Sieber, Maximilian, et al.
(författare)
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Wear-resistant coatings on aluminium produced by plasma anodising - A correlation of wear properties, microstructure, phase composition and distribution
- 2014
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 240, s. 96-102
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Tidskriftsartikel (refereegranskat)abstract
- In the recent decades, various process windows have been found for plasma anodising of aluminium surfaces to produce wear-resistant alumina coatings. The coatings offer a high hardness and provide an excellent bonding to the substrate material, thus preventing spallation under mechanical or tribological load. In the present study, coatings with a high abrasive wear resistance and a hardness of up to 12GPa were produced in an electrolyte of 5g/l sodium metasilicate and 5g/l potassium hydroxide at a current density of 30A/dm2. To understand the reasons for the high wear resistance, the morphology as well as the phase composition and distribution within the coating were examined globally and locally using X-ray diffraction with conventional and grazing incidence and electron backscatter diffraction. The analyses show that the coating globally is comprised of approximately one third of α-alumina, one third of γ-alumina and one third of amorphous alumina with locally varying phase content.
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| 5. |
- Simchen, F., et al.
(författare)
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Characterisation method of the passivation mechanisms during the pre-discharge stage of plasma electrolytic oxidation indicating the mode of action of fluorides in peo of magnesium
- 2020
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Ingår i: Coatings. - : MDPI. - 2079-6412. ; 10:10, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Plasma electrolytic oxidation (PEO) is a method to obtain protective coatings on metallic light-weight construction materials. Here, the workpiece receives a strong anodic polarisation in a suitable aqueous electrolyte, which leads to the formation of a passive layer and a gaseous shell. Afterwards, plasma electrolytic discharges appear on the substrate surface and convert it into a ceramic layer. The properties of the passive layer are influenced by the selected substrate/electrolyte combination and are essential for the PEO process-initiation and characteristics. In this work, a new method for the systematic investigation of the substrate/electrolyte interactions during the pre-discharge stage is presented. The procedure is carried out by a polarisation experiment and allows for a quantitative characterisation of the passivation behavior, based on a small electrolyte volume. The method is used to investigate a literature-known electrical conduction mechanism on passive films formed on magnesium, by cross-comparison between different Mg and Al materials. In addition, the influence of phosphate, glycerol, and fluoride on the passivation behaviour of the Mg alloy AZ31 in an alkaline environment is considered and quantified. The results provide an explanatory approach for the positive influence of toxic fluorides within the electrolyte on the morphology of PEO layers on magnesium.
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| 6. |
- Gröber, D., et al.
(författare)
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The effect of anodising on the fatigue performance of self-tapping aluminium screws
- 2015
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 75, s. 108-114
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Tidskriftsartikel (refereegranskat)abstract
- Self-tapping aluminium screws are an innovative joining technology for the assembly of lightweight components in industrial scale. It has been established in the past that porous anodic oxide coatings in many cases reduce the fatigue strength of specimens without notches. In the present work, the fatigue behaviour of notched specimens, i.e. self-tapping screws made from aluminium alloys EN AW-6056, 6082 (both in a conventional state and in a fine-grained state produced by equal channel angular pressing - ECAP) and 7068 with and without oxide coatings is examined. The coatings are produced by hard anodising and are necessary for the thread-forming process during assembly. While the coatings do not affect the static tensile strength, they reduce the fatigue strength for the specimens of the 6056 and the 6082 alloy. For the 7068 alloy a slight increase in fatigue strength is discovered on a low load horizon. The scatter of endured fatigue cycles until fracture of specimens is generally reduced by the anodic oxide coatings.
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| 7. |
- Kuhn, D., et al.
(författare)
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Localised anodic oxidation of aluminium material using a continuous electrolyte jet
- 2017
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Anodic oxidation of aluminium and its alloys is often used as protection against material wearout and corrosion. Therefore, anodic oxidation of aluminium is applied to produce functional oxide layers. The structure and properties of the oxide layers can be influenced by various factors. These factors include for example the properties of the substrate material, like alloy elements and heat treatment or process parameters, like operating temperature, electric parameters or the type of the used electrolyte. In order to avoid damage to the work-piece surface caused by covering materials in masking applications, to minimize the use of resources and to modify the surface in a targeted manner, the anodic oxidation has to be localised to partial areas. Within this study a proper alternative without preparing the substrate by a mask is investigated for generating locally limited anodic oxidation by using a continuous electrolyte jet. Therefore aluminium material EN AW 7075 is machined by applying a continuous electrolyte jet of oxalic acid. Experiments were carried out by varying process parameters like voltage or processing time. The realised oxide spots on the aluminium surface were investigated by optical microscopy, SEM and EDX line scanning. Furthermore, the dependencies of the oxide layer properties from the process parameters are shown.
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| 8. |
- Morgenstern, R., et al.
(författare)
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Influence of the heat treatment condition of alloy AlCu4Mg1 on the microstructure and properties of anodic oxide layers
- 2017
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Due to their outstanding specific mechanical properties, high-strength, age-hardenable aluminum alloys offer a high potential for lightweight security-related applications. However, the use of copper-alloyed aluminum is limited because of their susceptibility to selective corrosion and their low wear resistance. These restrictions can be overcome and new applications can be opened up by the generation of protective anodic aluminum oxide layers. In contrast to the anodic oxidation of unalloyed aluminum, oxide layers produced on copper-rich alloys exhibit a significantly more complex pore structure. It is the aim of the investigation to identify the influence of microstructural parameters such as size and distribution of the strengthening precipitations on the coating microstructure. The aluminum alloy EN AW-2024 (AlCu4Mg1) in different heat treatment conditions serves as substrate material. The influence of the strengthening precipitations' size and distribution on the development of the pore structure is investigated by the use of high-resolution scanning electron microscopy. Integral coating properties are characterized by non-destructive and light-microscopic thickness measurements and instrumented indentation tests.
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| 9. |
- Morgenstern, R., et al.
(författare)
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Plasma electrolytic oxidation of AMCs
- 2016
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- Aluminum Matrix Composites (AMCs) consisting of high-strength alloys and ceramic reinforcement phases exhibit a high potential for security relevant lightweight components due to their high specific mechanical properties. However, their application as tribologically stressed components is limited because of their susceptibility against fatigue wear and delamination wear. Oxide ceramic protective coatings produced by plasma electrolytic oxidation (PEO) can solve these problems and extend the possible applications of AMCs. The substrate material was powder metallurgically processed using alloy EN AW 2017 and SiC or Al2O3 particles. The influence of material properties like particle type, size and volume fraction on coating characteristics is clarified within this work. An alkaline silicate electrolyte was used to produce PEO coatings with technically relevant thicknesses under bipolar-pulsed current conditions. Coating properties were evaluated with regard to morphology, chemical composition, hardness and wear resistance. The particle type proved to have the most significant effect on the coating properties. Whereas compactness and thickness are not deteriorated by the incorporation of thermodynamically stable alumina particles, the decomposition of silica particles during the PEO processes causes an increase of the porosity. The higher silica particle content decreases also the coating thickness and hardness, which leads in particular to reduction of the wear resistance of the PEO coatings. Finally, different approaches for the reduction of the coating porosity of silica reinforced AMCs are discussed.
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| 10. |
- Sadeghi, A., et al.
(författare)
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Co-deposition behavior of alumina nanoparticles and properties of Ni-Al2O3 nanocomposite coatings
- 2015
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Ingår i: Surface and Interface Analysis. - : John Wiley & Sons. - 0142-2421 .- 1096-9918. ; 47:6, s. 738-744
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Tidskriftsartikel (refereegranskat)abstract
- The influence of adding alfa-Al2O3 nanoparticles with different concentrations into Watt's bath under the application of ultrasound during electrodeposition was investigated by means of electrochemical impedance spectroscopy (EIS) in the galvanostatic mode. The characteristics of the double layer during nickel deposition were affected by the existence of Al2O3 nanoparticles in the electrolyte. In this study, the results of the impedance were correlated with the layer properties, e.g. the mean grain size, the incorporation of particles in the deposit and the strengthening performance. It became obvious that there is a good relationship between the EIS data and layer properties, which makes the impedance spectroscopy a reliable tool for predicting the properties in dispersion coatings.
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