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The basic principle of electron beam melting (EBM) technology is the additive generation of structures by the selective melting of metal powder layer by layer with an electron beam under vacuum conditions. The cooling rate of the EBM process can be reduced drastically by increasing the temperature of the powder bed to avoid the formation of solidification cracks by brittle materials such as tungsten (W). This refractory metal is a promising candidate as plasma facing material for future fusion reactors. The selection of tungsten is owing to its physical properties such as the melting point of 3420 °C, the high strength and high thermal conductivity, the low thermal expansion and low erosion rate. Disadvantages are the low ductility, and fracture toughness at room temperature. Furthermore, the manufacturing by mechanical machining, such as milling and turning, is extremely cost and time consuming. An interesting alternative process route to conventional manufacturing technologies is EBM. It allows the near-net shape fabrication of prototype structures with geometrical freedom and has proven its capability for mass production by the manufacturing of hip prostheses made of titanium.This manuscript describes the fabrication of tungsten parts via electron beam melting, with application to the manufacturing of divertor armour. The investigation comprises the microstructure examination, crystallographic texture, as well as mechanical characterization via tensile and Charpy impact testing. This is followed by the presentation of process routes to fabricate mock-ups with different designs and copper cooling structures.Furthermore, the different mock-ups were exposed to high heat flux (HHF) applying transient thermal loads to assess thermal shock and thermal fatigue performance of EBM tungsten.Post mortem analyses were performed quantifying the occurring damage with respect to reference tungsten grades by microscopical means.The achieved results demonstrate the high potential to process tungsten via electron beam melting.

As recent trends in manufacturing engineering disciplines show a clear development in the sustainable as well as economically efficient design of forming processes, monitoring techniques have been gaining in relevance. In terms of monitoring of product properties, most processes are currently open-loop controlled, entailing that the microstructure evolution, which determines the final product properties, is not considered. However, a closed-loop control that can adjust and manipulate the process actuators according to the required product properties of the component will lead to a considerable increase in efficiency of the processes regarding resources and will decrease postproduction of the component. For most forming processes, one set of component dimensions will result in a certain set of product properties. However, to successfully establish closed-loop property controls for the processes, a systematic understanding of the reciprocity of the dimensions after forming and final product properties must be established. This work investigates the evolution of dimensional accuracy as well as product properties for a series of forming processes that utilize different degrees of freedom for process control.

ABSTRACTAlthough finite element model based process simulations for the laser powder bed fusion additive manufacturing process have become more common in the recent years, the proposed approaches are often only viable for materials without complex phase transformations. Process simulations for materials such as the quench and tempering steel AISI 4140 typically lead to higher computational cost due to the finer mesh and time steps needed for more complex material models. This study proposes a novel multiscale approach to combine the advantages of the macroscale and mesoscale models into one framework, in order to reduce computational cost while retaining the high accuracy. The implementation of these multiscale methods was validated by experimentally analyzing multiple parameter combinations regarding bulk hardness and local microstructure differences. The results show an accurate prediction of bulk hardness and localised tempering effects while reducing the computational cost in order to simulate the component scale.

3D hybrid additive manufacturing describes the combined application of different additive manufacturing processes in order to manufacture a component with almost unlimited design freedom and free choice of materials. One challenge in the hybrid additive manufacturing lies in the different conditions of individual additive manufacturing processes. For example, in the combined application of the laser powder bed fusion (PBF-LB) of metals with the fused filament fabrication (FFF) of polymers, damage can occur in the plastic due to the higher processing temperatures of PBF-LB. Therefore, in this work a process strategy for the buildup of metallic structures in the PBF-LB process on polymer base structures was developed. By reducing the laser energy density in combination with increasing the height of the first layer, a processing window could be identified. The built hybrid components were investigated with micro-computed tomography and the effects of different processing parameters on the interface between the polymer and metal part are discussed. Finally, a strategy to increase the strength of the interface is presented.

High-speed steels (HSS) such as AISI M2 are generally used for cutting and forming tools or broaches with the highest demands on load bearability and hot-hardness. The requirements for high-speed steels are, on the one hand, extremely high hardnesses of over 800–900 HV and, on the other hand, the thermal stability of the microstructure up to 500 °C. This combination is achieved by complex precipitation-hardenable iron-based alloys. Common heat treatment practices for high-speed steels use salt baths or vacuum ovens, which are energetically unfavorable and require subsequent cleaning. The study consists of short-time hardening and short-time tempering on a laboratory scale by means of dilatometry and thereupon an implementation in an industrial induction hardening machine. The laboratory scale experiments demonstrate the feasibility of bringing sufficient alloying elements into solution by means of several heat treatment cycles despite short holding times of 1 s and less. Combined tests of short time hardening and tempering show a hardness of up to 850 HV10 that are competitive with the conventional heat treatment route. First attempts to transfer the process to an industrial setup exhibit some peculiarities in the process control, but reveal promising results with a surface hardness of up to 750 HV10.

The fabrication of polymer–metal hybrids in an additive process makes it possible to further improve the geometrical and material adaption in a multi-material design. In this work, PLA is fabricated through a fused filament fabrication process on AlSi10Mg structures manufactured by laser powder bed fusion. The mechanical connection is realised by form fit, for which different geometries are examined through tensile tests. Deep penetration of the PLA into the metallic structures is achieved by optimisation of the process parameters. The penetration depth is assessed through the use of micro-computed tomography. Finally, the interplay of mechanisms leading to a firm connection is discussed.

A novel maraging steel with vanadium supplement called Specialis® has been developed for additive manufacturing by powder bed fusion using a laser beam. This study characterized this material after processing and post-processing. An intensive process optimization was carried out by means of a single track melt pool analysis to investigate optimal parameter sets for manufacturing of dense parts. Furthermore, the development of post heat treatment strategies and their influence on mechanical and microstructural characteristics of the material was evaluated. Two main concepts of direct aging treatment (AT) and solution treatment followed by aging treatment (ST+AT) were tested by dilatometry, to analyse the material behaviour with different initial microstructures: as-built and recrystallized. Both heat treatments resulted in a considerable improvement of hardness after only 2 h of aging, increasing to approximately 700 HV and 760 HV respectively, which exceeded the peak hardness of commonly known maraging steel 18Ni300 (660 HV after 6 h). These results were confirmed by tensile tests, where a tensile strength of more than 2300 MPa was achieved. Alongside the precipitation hardening known for maraging steels, the increased hardness was a result of grain refinement due to the addition of vanadium.

This work presents a comprehensive investigation into the optimization of critical process parameters associated with metal fused filament fabrication (Metal-FFF) for the production of copper-based components. The study focused on three different commercial and one self-manufactured filament, each with unique chemical compositions. These filaments were systematically optimized and the density was characterized for all processing steps, as well as the electrical conductivity on the specimen scale. Remarkably, two of the studied filaments exhibited exceptional properties after sintering with forming gas (up to 94% density and 55.75 MS/m electrical conductivity), approaching the properties measured for established manufacturing methods like metal injection molding. Finally, the research was extended to component-scale applications, demonstrating the successful fabrication of inductors with integrated cooling channels. These components exhibited water tightness and were used in induction hardening experiments, validating the practical utility of the optimized Metal-FFF process. In summary, the results show great promise in advancing the utilization of Metal-FFF in industrial contexts, particularly in the production of high-performance copper components.

In this study, a novel process is presented in which direct induction heating with frequencies in the MHz range is used for the wire-feed additive manufacturing of the alloy AlSi7Mg. The high frequency of 1.5 MHz enables processing of 1.2 mm diameter wires without the need for indirect heating via a nozzle. The feasibility of the process is proven by the experimental identification of a proper process window regarding the influential parameters such as the distance between inductor and substrate, induction power and wire feed rate for the fabrication of single layers. Furthermore, a strategy for the successful fabrication of multi-layered cubes is developed. The microstructure of the cubes exhibits a characteristic variation along the build direction. Micro-computed tomography is used to reveal defects like lack of fusion and spherical pores in test cubes. The presented results are used to derive possible process improvements, which will allow the novel process to be used as a fast and powder-free alternative metal additive manufacturing route in future.

This study aims at a thorough characterization of the relationship of interstitially solved carbon and nitrogen on the γ → α′ transformation in PM steels, the accompanied volume change and the resulting hardness. Furthermore, the investigations include multiple porosity levels of 6.9, 7.2 and 7.35 g/cm3 to characterize porosity effects. Dilatometric samples were carburized and carbonitrided to seven distinct compositions to account for common compositions in the process of thermochemical case hardening heat treatment. The dilatometric samples were rapidly austenitized and quenched and the dilatometric response was evaluated. To fully characterize the martensitic transformation of PM steels, X-ray diffractometry evaluated the amount of retained austenite after quenching. Conclusive results of iterative quenching procedures along with elemental analysis after heat treatment give distinct evidence that PM steels underlie rapid decarburization. This effect ultimately leads to an erroneous evaluation of the martensite transformation kinetics, especially the often proposed effect of porosity on MS. However, a distinct effect on the accompanied volume change from austenite to martensite is proposed. To account for an interplay of solved carbon and nitrogen, an effective nitrogen contribution of 25% based on carbon equivalent is proposed. Utilizing the effective content, the impact of nitrogen can be projected on carbon within the range of common carbon and nitrogen contents, and a good predictability of the martensite transformation can be achieved. Regarding the resulting hardness, a dependency solely on carbon is suggested. The overall hardness shows a typical maximum at approximately 0.6–0.7 wt%, irrespective of the solved amount of nitrogen.

The exposure of operators, workers, residents and bystanders to pesticides is of high potential concern. Yet, reports on pesticide residues in the environment and near treated fields often spark debates if such findings might indicate a health risk. Although the underlying models are considered conservative, there are only limited field data on systemic exposure available. As a first step to improve the situation, we conducted a scoping review of state-of-the-art pesticide exposure biomonitoring studies in operators, workers, residents or bystanders. In contrast to existing reviews, we focused on target cultures of potential high pesticide exposure such as tree-grown produce, vine or hops. The search was conducted in Web of Science, Scopus and PubMed. Out of 17 eligible articles, a total of 11 studies met our search criteria, and 6 of them quantified the systemic exposure of humans. The analysis revealed that exposure was mainly driven by application of pesticides and reentry work, resulting in a higher exposure of operators and workers than of residents and bystanders. In nearly all cases, the systemic exposure was below the relevant toxicological reference values. The studies were subsequently analyzed to identify key criteria for a reliable design of a biomonitoring study on pesticide exposure.

Besides the optimisation of process parameters such as laser power or scan speed, the choice of the scan path represents a possibility to optimise the laser powder bed fusion process even further. The usual hatching strategy creates a homogeneous microstructure but makes it necessary to switch the laser off and on after each scan vector, which can slow down the fabrication. Moreover, the end of each scan vector is a location susceptible to the creation of keyhole pores. In this work, these disadvantages were meant to be avoided by using scan strategies that consist of longer paths and thus less end of track points. To this end, an open-source tool to tailor the LPBF G-code to geometric part features and advanced path configurations was developed and embedded into a co-visualization platform. With this tool, specimens built with four different types of paths were fabricated and the effect of these alternative scan strategies on pore distributions and path neighbourhood was investigated using micro-computed tomography. In the examined example geometry, a spiral scan pattern reduced the distance the laser had to jump between scanning by 78%. However, with the alternative path patterns, the defect architecture was strongly dependant on the part geometry and increased the overall porosity to 0.42%. Respective alleviation approaches are therefore necessary and are discussed in the remainder of this work.

As part of an international research project (HiPTSLAM), the development and holistic processing of high-performance tool steels for AM is a promising topic regarding the acceptance of the laser powder bed fusion (PBF-LB) technology for functionally optimized die, forming and cutting tools. In a previous work, the newly developed maraging tool steel FeNiCoMoVTiAl was qualified to be processed by laser powder bed fusion (PBF-LB) with a material density of more than 99.9% using a suitable parameter set. To exploit further optimization potential, the influence of dual-laser processing strategies on the material structure and the resulting mechanical properties was investigated. After an initial calibration procedure, the build data were modified so that both lasers could be aligned to the same scanning track with a defined offset. A variation of the laser-based post-heating parameters enabled specific in-situ modifications of the thermal gradients compared to standard single-laser scanning strategies, leading to corresponding property changes in the produced material structure. An increase in microhardness of up to 15% was thus obtained from 411 HV up to 471 HV. The results of the investigation can be used to derive cross-material optimization potential to produce functionally graded high-performance components on PBF-LB systems with synchronized multi-laser technology.

A zirconia-based potentiometric solid electrolyte gas sensor with internal solid state reference was used to study the response behavior of platinum cermet and indium tin oxide sensing electrodes. Target gases included both oxygen and carbon monoxide in nitrogen-based sample gas mixtures. It was found that with the indium tin oxide sensing electrode, the low-temperature behavior is mainly a result of incomplete equilibration due to contaminations of the electrode surface. On the other hand, some of these contaminant species have been identified as being pivotal for the higher carbon monoxide sensitivity of the indium tin oxide sensing electrode as compared to platinum cermet electrodes.

By combining results of adsorption/desorption measurements on powders and electrical conductivity studies on thick and thin films, the interaction of indium tin oxide with various ambient gas species and carbon monoxide as potential target gas was studied between room temperature and 700 °C. The results show that the indium tin oxide surfaces exhibit a significant coverage of water-related and carbonaceous adsorbates even at temperatures as high as 600 °C. Specifically carbonaceous species, which are also produced under carbon monoxide exposure, show a detrimental effect on oxygen adsorption and may impair the film’s sensitivity to a variety of target gases if the material is used in gas sensing applications. Consequently, the operating temperature of an ITO based chemoresistive carbon monoxide sensor should be selected within a range where the decomposition and desorption of these species proceeds rapidly, while the surface oxygen coverage is still high enough to provide ample species for target gas interaction.

Martensitic steels are tempered to increase the toughness of the metastable martensite, which is brittle in the as-quenched state, and to achieve a more stable microstructure. During the tempering of steels, several particular overlapping effects can arise. Classical dilatometric investigations can only detect effects by monitoring the integral length change of the sample. Additional in-situ diffractometry allowed a differentiation of the individual effects such as transformation of retained austenite and formation of cementite during tempering. Additionally, the lattice parameters of martensite and therefrom the tetragonality was analyzed. Two low-alloy steels with carbon contents of 0.4 and 1.0 wt.% and a high-alloy 5Cr-1Mo-steel with 0.4 wt.% carbon were investigated by dilatometry and in-situ diffractometry. In this paper, microstructural effects during tempering of the investigated steels are discussed by a comparative study of dilatometric and diffractometric experiments. The influence of the chemical composition on the tempering behavior is illustrated by comparing the determined effects of the three steels. The kinetics of tempering is similar for the low-alloy steels and shifted to much higher temperatures for the high-alloy steel. During tempering, the tetragonality of martensite in the steel with 1.0 wt% carbon shifts towards a low carbon behavior, as in the steels with 0.4 wt.% carbon.

The electrode processes governing response behavior of a solid electrolyte CO2 sensor have been studied using electrochemical impedance spectroscopy on symmetric cells exposed to various temperatures and gas compositions. It was shown that the electrochemical processes leading to potential formation at the Au/Na2CO3 electrode can be described by adapting models commonly used in the field of molten carbonate fuel cells.

The influence of various gas compositions on surface adsorbate species and electrical conductivity of indium tin oxide (ITO) powders and thick films was studied. By combining results of temperature dependent desorption (TPD) with electrical conductivity measurements it was shown that, after exposure to ambient air, the surfaces of both powders and films are covered with significant amounts of oxygen, water and carbon related species. While the influence of oxygen adsorbates has already been described for temperatures below 500 °C, desorption of some of these species could be detected at temperatures as high as 675 °C, with a significant influence on electrical film conductivity.

In this study, micron-sized pored membranes, based on the co-polymer polyvinylidene difluoride hexafluoropropylene (PVdF-HFP) were prepared via phase inversion techniques. The aim of the approach was to find less harmful and less toxic solvents to fabricate such films. Therefore, the Hansen solubility approach was used to identify safer and less toxic organic solvents for the phase inversion process, relative to present solvent mixtures, based on acetone, dimethyl formamide, dimethyl acetamide or methanol. With this approach, it was possible to identify cyclopentanone, ethylene glycol and benzyl alcohol as suitable solvents for the membrane preparation process. Physicochemical and mechanical properties were analyzed and compared, which revealed a uniform membrane structure through the cross section. Differences were observed at the top surface, in dependence of both preparation approaches, which are described in detail.