[en] HTSL final conductors require flat cross sections instead of rounded cross sections. Therefore, a gentle process was developed which comprises several calibrated drawing steps for modifying round cross sections to elliptical cross sections to flat cross sections

No abstract available

[en] Arterial spin labeling blood perfusion signal relies on the difference between a label and a control image. Background suppression pulses are commonly used to improve the contrast, yet these are based on estimates of tissue relaxation times. The aim of this study is to improve the perfusion contrast by individualizing the timing of these background suppression pulses by means of T1 mapping. The optimized timing of the background suppression pulses is obtained by rapid T1 mapping employing the variable flip angle technique. Ten healthy volunteers were included in this study. To compare the results, visual grading and the Wilcoxon signed-rank test was used comparing three categories of image quality. The readers confirmed that the images of the proposed method generally show a higher signal-to-background ratio and cortical structures are better visible. Noise was mostly comparable to the standard method. Relative blood flow was statistically significant higher in the modified method. The individually optimized background suppression pulses improve the image appearance and allow for a better visualization of cortical structures. The proposed technique however prolongs scan time, which can be seen as negative result, yet needs to be further evaluated. Background suppression timing in ASL can vary. Both the label and control condition can be modified for T1 mapping. Adapting the pulse timing improves the signal-to-background ratio.

[en] The lap shear test is a common method for determining the interlaminar shear strength of material compounds due to its simplicity with regard to specimen production and experimental realization. However, the obtained results strongly depend on the material pairing and the specimen geometry, which have a significant influence to the stress state within the interface during the experiment. A torsion test method using butt-bonded hollow cylinders seems more appropriate due to the expected more homogeneous shear stress distribution. The aim of this work is to compare both testing methods by experimental and numerical investigations. A comparative study with thermally joined aluminum-polyamide hybrid compounds was performed. The corresponding simulations were carried out with the commercial FE-software Abaqus™, using a user defined material model for the thermoplastic joining partner and the built-in cohesive behavior contact property for modelling interfacial damage. (paper)

[en] Thermal-spray coatings of austenitic materials are mainly used under corrosive conditions. The relatively poor wear resistance strongly limits their use. In comparative studies between nitrocarburized and untreated thermal-spray coatings, the influence of the nitrogen and carbon enrichment on the properties of the coatings and the microstructure was investigated. The cross-section micrograph of the nitrocarburized coating shows the S-phase formation in the surface layer region. The depth profile of the nitrogen and carbon concentration was determined by glow discharge optical emission spectroscopy (GDOS) analysis. A selective enrichment of the surface layer region with nitrogen and carbon by means of thermochemical heat treatment increases the wear resistance. The interstitially dissolved nitrogen and carbon causes the formation of strong compressive residual stresses and high surface hardness. Increases in the service life of existing applications or new material combinations with face-centred cubic friction partners are possible. In the absence of dimensional change, uniform as well as partial nitrogen enrichment of the thermal spray coating is possible. Nitrocarburized coatings demonstrate a significant improvement in adhesive wear resistance and extremely high surface hardness. (paper)

[en] High Entropy Alloys (HEA) are gaining increasing interest due to their unique combination of properties. Especially the combination of high mechanical strength and hardness with distinct ductility makes them attractive for numerous applications. One interesting alloy system that exhibits excellent properties in bulk state is AlCoCrFeNiTi. A high strength, wear resistance and high-temperature resistance are the necessary requirements for the application in surface engineering. The suitability of blended, mechanically ball milled and inert gas atomized feedstock powders for the development of atmospheric plasma sprayed (APS) coatings is investigated in this study. The ball milled and inert gas atomized powders were characterized regarding their particle morphology, phase composition, chemical composition and powder size distribution. The microstructure and phase composition of the thermal spray coatings produced with different feedstock materials was investigated and compared with the feedstock material. Furthermore, the Vickers hardness (HV) was measured and the wear behavior under different tribological conditions was tested in ball-on-disk, oscillating wear and scratch tests. The results show that all produced feedstock materials and coatings exhibit a multiphase composition. The coatings produced with inert gas atomized feedstock material provide the best wear resistance and the highest degree of homogeneity. (paper)

[en] Different manufacturing approaches have been investigated regarding their suitability to process high-entropy alloys (HEAs). However, comprehensive investigations on the influence of the production route on the microstructure, phase formation and properties have not been conducted yet. For the current study the alloy AlCoCrFeNiTi_0.5 is considered. Previous investigations have proven the formation of phases with predominantly body centred cubic structure for this alloy. Castings are produced by arc-melting. Feedstock material for coating deposition and powder metallurgical processing is produced by inert gas atomisation. For the processing high-velocity-oxygen-fuel (HVOF) thermal spraying and spark plasma sintering (SPS) are applied. Due to the significantly differing process conditions and temperature-time profiles, differences of microstructure, phase formation and resulting properties can be observed. Wear investigations under various conditions have been conducted. Especially under sliding and reciprocating wear conditions the structural defects formed for the thermally sprayed coating cause a reduction of wear resistance. The formation of structural defects could be avoided by SPS. However, the additional tetragonal phase causes a reduction of the wear resistance. The current study contributes to a better understanding of the interaction between process, microstructure and properties. (paper)

[en] In 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. (paper)

[en] The interlaminar strength of mechanically interlocked polymer-metal-interfaces strongly depends on the metal surface topography. Hence, this contribution assesses standardized surface roughness parameters as well as fractal dimension for interlaminar strength prediction of EN AW-6082/polyamide 6 polymer-metal-hybrids. Seven different metal surface topographies generated by mechanical blasting, alkaline etching, thermal spraying as well as laser structuring are investigated. Interlaminar strength testing is carried out with regard to tensile and shear strength using butt-bonded hollow cylinder specimens. The surface roughness profiles are recorded with a tactile stylus profiler. The fractal dimension of the metal surface is derived from cross-sectional images. The measured interlaminar strength values show good correlation to the fractal dimension, moderate correlation to the root mean square slope of the surface roughness profile and no correlation to surface roughness height parameters. (paper)

[en] The cleaning of silicon (Si) surfaces is a very important issue for the fabrication of novel semiconductor devices on the nanoscale. Established methods for the removal of organic impurities and the native or chemical oxide are often combined with high temperature desorption steps. However, devices with small feature sizes will be unfunctional if, for example, out-diffusion of dopants is not prevented. In this paper we present two possible processes for low-temperature cleaning: an atomic hydrogen source, based on dissociative adsorption of hydrogen at a heated tantalum (Ta) surface and a hydrogen DC plasma source as a part of an UHV cluster tool. The influence of atomic hydrogen on carbon and oxide removal is surveyed and the existing model for native oxide etching with an argon/hydrogen DC plasma is adapted