Structure Design of Soft Magnetic Materials Using Electron‐Beam‐Based Additive Manufacturing

Fe93.5Si6.5 (wt%) soft magnetic materials in toroidal shape are additively manufactured by means of electron beam powder bed fusion (PBF‐EB). Different hatching strategies are applied to realize specific patterns of molten material alternating with non‐molten powder particles. The specimens produced using different hatching strategies show identical relative densities but various structural features resulting in different magnetic properties. The magnetic performance of the specimens is characterized by determining hysteresis loops (B–H curves), power losses, and maximum magnetic flux density at frequencies between 50 and 1000 Hz. At constant mass, the different structures induced by using various hatching strategies have a strong influence on the hysteresis losses. These losses can be significantly reduced by applying a targeted structure design. The modified specimens show superior magnetic properties at sub‐kHz compared to some soft magnetic materials fabricated by means of conventional methods and laser powder bed fusion (PBF‐L).Fe93.5Si6.5 (wt%) toroidal cores with tailored structures fabricated by electron beam powder bed fusion using specifically developed hatching strategies (i.e., radial hatching and circle hatching) show promising magnetic properties (i.e., low power losses and high maximum magnetic flux density), outperforming some soft magnetic materials produced by conventional techniques and laser powder bed fusion. image China Scholarship Council http://dx.doi.org/10.13039/50110000454

Correlation Between Structural Features and Magnetic Performance of Fe93.5Si6.5 (wt.%) Soft Magnetic Materials

Laminated, powder filled, and dense bulk soft magnets are currently used for various electrical and electronic applications due to their characteristic magnetic properties. In order to systematically investigate the correlation between the structural features and the resulting magnetic performance of various soft magnetic materials, toroidal Fe93.5Si6.5 (wt.%) specimens with “layer structure”, “powder structure”, and “dense structure” are additively manufactured and characterized by means of electron beam powder bed fusion (PBF‐EB). The specimens with “layer structure” show outstanding magnetic performance in terms of low power losses and good maximum magnetic flux density at frequencies ranging from 50 to 1000 Hz, outperforming even some soft magnetic materials fabricated using conventional methods. Fe93.5Si6.5 (wt.%) specimens with various layered structures are produced using different processing strategies, allowing for sophisticated structural tailoring, and modifying the corresponding magnetic performance. Based on the results derived in this study, an ideal structure that can result in superior soft magnetic properties is proposed.Toroidal Fe93.5Si6.5 (wt.%) specimens with “layer structure”, “powder structure”, and “dense structure” fabricated by means of Electron Beam Powder Bed Fusion, imitating conventional laminated, powder‐filled and dense bulk soft magnets, show characteristic magnetic properties, based on which a brand‐new and ideal structure, displaying a “Honeycomb” structure, is proposed to further improve soft magnetic properties. image China Scholarship Council http://dx.doi.org/10.13039/50110000454

Electron-optical in-situ crack monitoring during electron beam powder bed fusion of the Ni-Base superalloy CMSX-4

Electron beam powder bed fusion (PBF-EB) of Ni-base superalloys such as CMSX-4 is a demanding process. Using conventional PBF-EB machines, process observation is done by mounting optical camera systems on viewing windows at the top of the build chamber. However, the concomitant metallization blocks optical observation methods with increasing build time. Therefore, build quality evaluation is normally done after the process utilizing visual inspection or subsequent metallurgical analysis. In this work, CMSX-4 is processed using a freely programmable PBF-EB machine with an electron optical (ELO) imaging system. It consists of a four-segment ELO detector and in-house developed imaging software. The ELO system works reliably for almost 30 h of build time and allows a layerwise monitoring of the build area. A comparison of in-situ ELO monitoring and the sample surfaces shows remarkable accordance. Furthermore, ELO imaging is applied to exemplarily document surface cracking over long build times. Therefore, the present study successfully demonstrates the application of ELO imaging for improved process control under the demanding test conditions of Ni-base superalloys.Open Access funding enabled and organized by Projekt DEAL.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Friedrich-Alexander-Universität Erlangen-Nürnberg (1041

Using Selective Electron Beam Melting to Enhance the High‐Temperature Strength and Creep Resistance of NiAl–28Cr–6Mo In Situ Composites

By increasing the density of interfaces in NiAl–CrMo in situ composites, the mechanical properties can be significantly improved compared to conventionally cast material. The refined microstructure is achieved by manufacturing through electron beam powder bed fusion (PBF‐EB). By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate‐like or an interconnected network of the (Cr,Mo) reinforcement phase which is embedded in a NiAl matrix. The microstructure of the different cell morphologies is investigated in detail using scanning electron microscope, transmission electron microscopy, and atom probe tomography. For both morphologies, the mechanical properties at elevated temperatures are analyzed by compression and creep experiments parallel and perpendicular to the building direction. In comparison to cast NiAl and NiAl–(Cr, Mo), the yield strength of the PBF‐EB fabricated specimens is significantly improved at temperatures up to 1,027 °C. While the columnar morphology exhibits the best improved mechanical properties at high temperatures, the equiaxial morphology shows nearly ideal isotropic mechanical behavior, which is a substantial advantage over directionally solidified material.The additive manufacturing of NiAl–28Cr–6Mo in situ composites improves the mechanical properties significantly compared to conventionally cast material. By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate‐like or an interconnected network of the (Cr,Mo) reinforcement phase. The yield strength of the PBF‐EB fabricated specimens is significantly improved at temperatures up to 1027 °C. image © 2023 WILEY‐VCH GmbH Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

A novel rapid alloy development method towards powder bed additive manufacturing, demonstrated for binary Al-Ti, -Zr and -Nb alloys

Powder bed fusion (PBF) methods offer the best material properties among metal additive manufacturing (AM) processes. Yet, alloy development for PBF is only at its infancy and has a great untapped potential. This originates from the high solidification rate within the melt pool and to exploit the full potential of materials produced by PBF methods, a diligent work lies ahead. This paper presents a high-throughput method to rapidly screen large compositional alloy intervals experimentally for their PBF feasibility, which can drastically reduce the time needed for alloy development and provide valuable data for modelling. Our method consists of two steps; co-sputtering and electron beam re-melting. First step produces an alloy gradient film on a sheet substrate. The film is then re-molted to produce a PBF mimicked microstructure. The method is successfully demonstrated on binary systems; Al-Ti,-Zr and-Nb and produced gradients in compositional ranges of 3-50 wt%Ti, 1-15 wt%Zr and 2-15 wt%Nb over a length of 200 mm. From the produced materials, the alloying efficiency could be investigated and determined regarding hardness and grain refinement. Zr shows the highest strength contribution per at% and the best grain refinement at low levels. However, at higher levels grain refinement efficiency decreases for Zr. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).Funding Agencies|Norsk Hydro ASA; Carl Tryggers Foundation for Scientific Research [CTS 15:219, CTS 14:431]</p

High entropy alloy thin films on SS304 substrates: Evolution of microstructure and interface modulated by energetic condensation in nanoscale

High entropy alloys (HEAs), as a novel material in the 21st century, possess several advantages, such as excellent corrosion &amp; oxidation resistance and high mechanical properties. HEA thin films show these favourable properties with lower material costs than their bulk counterparts. Studying the HEA film-substrate interface represents challenges but is of extreme importance for the understanding of growth mechanisms with important implications for film adhesion. However, most HEA films were deposited on monocrystalline silicon substrates with limited practical applicability. Further, where commercial stainless steel, aluminium or titanium alloy substrates were used, the microstructure and chemistry at the interface were neglected. Here, we deposited AlCrFeCoNiCu0.5 HEA thin films on stainless steel 304 (SS304) substrates using cathodic arc deposition with different substrate biases. The crystallography and microstructure were investigated using an X-ray and electron-microscopy based chatacterization. A transition of an incoherent to semi-coherent interface was observed from 0 V to -50 V of the substrate bias. Energy dispersive spectroscopy demonstrated a transition of Cr2O3 to aluminum oxide across the interface. The nanoindentation tests revealed the significant improvement of mechanical properties of SS304 with HEA coatings. High-strength HEA (8.0 ± 0.2 GPa) thin films with semi-coherent interfaces were manufactured on SS304

Periodic Open Cellular Raney‐Copper Catalysts Fabricated via Selective Electron Beam Melting

Herein, the possibility of generating Raney‐Copper catalysts with high geometric complexity is demonstrated. For this, periodic open cellular structures (POCS) composed of a highly brittle Al–Cu alloy containing 29.4 at% copper are fabricated by selective electron beam melting (SEBM) for application in chemical reaction engineering. After selective leaching of aluminum in an NaOH solution, the POCS show a core–shell structure with a nanoporous copper surface layer and a solid core. The fabrication and dealloying processes as well as the microstructure are studied. Moreover, the SEBM‐processed Raney‐type copper catalysts show a high catalytic activity in methanol synthesis

No Structure-Switching Required: A Generalizable Exonuclease-Mediated Aptamer-Based Assay for Small-Molecule Detection

The binding of small molecules to double-stranded DNA can modulate its susceptibility to digestion by exonucleases. Here, we show that the digestion of aptamers by exonuclease III can likewise be inhibited upon binding of small-molecule targets and exploit this finding for the first time to achieve sensitive, label-free small-molecule detection. This approach does not require any sequence engineering and employs prefolded aptamers which have higher target-binding affinities than structure-switching aptamers widely used in current small-molecule detecting assays. We first use a dehydroisoandrosterone-3-sulfate-binding aptamer to show that target binding halts exonuclease III digestion four bases prior to the binding site. This leaves behind a double-stranded product that retains strong target affinity, whereas digestion of nontarget-bound aptamer produces a single-stranded product incapable of target binding. Exonuclease I efficiently eliminates these single-stranded products but is unable to digest the target-bound double-stranded product. The remaining products can be fluorescently quantified with SYBR Gold to determine target concentrations. We demonstrate that this dual-exonuclease-mediated approach can be broadly applied to other aptamers with differing secondary structures to achieve sensitive detection of various targets, even in biological matrices. Importantly, each aptamer digestion product has a unique sequence, enabling the creation of multiplex assays, and we successfully demonstrate simultaneous detection of cocaine and ATP in a single microliter volume sample in 25 min via sequence-specific molecular beacons. Due to the generality and simplicity of this assay, we believe that different DNA signal-reporting or amplification strategies can be adopted into our assay for target detection in diverse analytical contexts

Practically applicable water oxidation electrodes from 3D-printed Ti6Al4V scaffolds with surface nanostructuration and iridium catalyst coating

Bundesministerium für Bildung und Forschun