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Aluminium-copper alloys of the 2xxx type receive their excellent mechanical properties by the formation of copper-rich precipitates during hardening. Size, distribution and crystal structure of the formed precipitates determine the final strength of those alloys. Adding traces of certain elements, which bind to vacancies, significantly influences the decomposition behaviour, i.e. the diffusion of the copper atoms. For high-purity ternary alloys (Al-1.7 at.% Cu-X), we investigate the interaction of copper and trace element atoms (X=In, Sn, and Pb) with quenched-in vacancies by Positron Annihilation Lifetime Spectroscopy (PALS). By employing Vickers microhardness, Differential Scanning Calorimetry (DSC) and Small Angle X-Ray Scattering (SAXS) we obtain a comprehensive picture of the decomposition process: opposite to predicted binding energies to vacancies by ab-initio calculations we find during ageing at room and elevated temperature a more retarded clustering of copper in the presence of In rather than for Sn additions, while Pb, having the highest predicted binding to vacancies, shows nearly no retarding effect compared to pure Al-Cu. If the latter would be due to a limited solubility of lead, it had to be below 2 ppm. Transmission Electron Microscopy (TEM) as imaging method complements our findings. Annealing the quenched Al-1.7 at.% Cu-X-alloys containing 100 ppm In or Sn at 150∘C leads to finely distributed TH'-precipitates on the nanoscale, since due to the trace additions the formation temperature of TH' is lowered by more than 100∘C. According to TEM small agglomerates of trace elements (In, Sn) may support the early nucleation for the TH'-precipitates.

The effect of titanium addition beyond the solubility limit was investigated in order to proof the precipitation hardening possibility of the Cantor alloy CoCrFeMnNi. As high entropy alloys are currently in the focus of interest, this method is a highly suitable possibility to further improve their remarkably properties. After appropriate heat treatment consisting of homogenisation, solution and precipitation annealing a significant increase in hardness was detected. The high hardness was caused by nanometer sized precipitates, which were identified by TEM-analysis.

The quality of powder used in powder bed-based additive manufacturing plays a key role concerning process performance and end part properties. Even though this is a generally accepted fact, there is still a lack of a comprehensive understanding of the powder property-part property relationship. However, numerous investigations focusing on selected powder properties and their corresponding influence on process aspects or final part properties have been published in recent years. Still, generalized statements on powder requirements for a defined process performance are not available. This can be attributed to the fact that the community has not yet come to an agreement which characterization techniques are most suitable for powder characterization in the additive manufacturing context and in most cases only selected aspects have been investigated for special powder materials. The aim of this review is to assess these building blocks of knowledge and to provide an overview on the current state of the art.

Für die Beurteilung des Ausscheidungszustandes in Aluminiumbasislegierungen mittels Transmissionselektronenmikroskopie (TEM) ist eine Orientierung der Probe in [100]-Richtung der Matrix erforderlich. TEMs, deren Objektivlinsen für hohe Auflösungen optimiert sind, haben meist begrenzte Kippwinkel für die Probe. Es muss daher bereits bei der Probenahme der geforderten Kristallorientierung Rechnung getragen werden. Mittels Elektronenrückstreubeugung wurde in einem grobkörnigen Material ein günstig orientiertes Korn ausgewählt und in einer geeigneten Richtung mittels In-situ Lift-out Methode im Focused Ion Beam Gerät präpariert. Die finale Korrektur der Orientierung im TEM beträgt dann unter 12°.

In this study, the evolution of the electrical resistivity of metal powders during densification and the resulting current flow through punch, powder compact, and die is investigated. The evaluation of the accompanying Joule heating identifies the graphite punches as main heating element providing more than 90% of the heat. The high electrical resistance of the punches and the low resistance of the graphite die as parallel electrical load to the specimen determine the current flow in the tool. For powder particles with intact oxide layers, virtually no current flows through the compact. On the other hand, for a powder resistivity below 10−3 Ocm about 50% of the current flows through the compact. This fraction is constant despite further decreasing resistivity of the compact during densification. A constant current through the specimen has important implications for the microscopic temperature distribution and the understanding of the so-called 'spark plasma effects'.

The operating conditions of future nuclear reactors, both fission and fusion, still pose a number of materials challenges. In this context, the novel class of high-entropy alloys (HEA) attracts attention due to good mechanical properties and corrosion resistance as well as an - mostly hypothesized -improved irradiation resistance. In the present work the single-phase fcc HEA CoCrFeMnNi, produced by means of powder metallurgy, was ion-irradiated with Fe ions at RT, 300°C and 410°C up to 0.6 and 1 dpa, respectively, along with the austenitic stainless steel 316 serving as a benchmark. Transmission electron microscopy and nanoindentation were applied to study the irradiation-induced hardening and the evolution of the microstructure. While similar hardening is observed for the HEA compared to the benchmark material 316 at RT and 410°C, substantially higher hardening was observed at 300°C. The origin of the hardening will be discussed based on the microstructural evidence.

Porous electrodes for alkaline water electrolysis were prepared by spark plasma sintering, a short-time sintering technique, in combination with a space holder method. After removal of the space holders, highly porous layers of polycrystalline Ni and of a nanocrystalline Ni-Fe alloy were obtained on a metallic substrate. Both porosity and thickness of the electrocatalytic layers can be controlled by the space holder volume content and the sintering process conditions, for example, the applied pressure and temperature. The active surface of the electrode can be increased significantly by a roughness factor of up to 1,120 determined by double layer charging. The porous layers are efficient towards oxygen evolution reaction (OER), whereas activity is greatly influenced by the chemical composition. The porous Ni-Fe electrodes exhibit an extremely low OER-overpotential of 230 mV at 0.3 A cm−2 in highly concentrated KOH (29.9 wt.-%) at 333 K. Beside the high surface area, the efficiency of the porous Ni-Fe layer is characterized by a high intrinsic activity resulting in a low Tafel slope of around 23 mV dec−1 at low and 50 mV dec−1 at high current densities as well as a high turnover frequency (TOF) of approximately 3.4 s−1 at 0.3 V. The porous Ni electrodes have a lower intrinsic activity with higher Tafel slopes and lower TOF. Moreover, an excellent stability and activity under realistic operating conditions of intermittent electrolysis (up to 1 A cm−2) for 100 h was proven for the porous Ni-Fe electrode.

Solid-state hydrogen storage in metal hydrides offers highest volumetric energy storage densities and low working gas pressures at the same time. Recently developed metal hydride composites (MHC) consist of a hydride-forming metal alloy and a secondary phase, typically graphite, to realize form-stable composites and short loading and unloading times (

We report a combined experimental and first principles study of an extremely immiscible alloy of Mo with 1 and 2 at.% Na, which was produced by high-energy ball milling. The microstructure of the as-milled and annealed state were examined by various methods, including atom-probe tomography (APT), transmission electron microscopy, and energy-dispersive (EDX) analysis. Despite the complete immiscibility of the Mo-Na system in the solid and even in the liquid state, APT measurements clearly evidence the formation of a true nanocrystalline solid-solution microstructure with insignificant Na clustering for samples with 1 at.% Na. In agreement with our x-ray diffraction experiments, first principles calculations expose that the Na atoms do not expand the Mo lattice, which is in contrast to predictions using Vegard's rule. Heating at 700 °C induces only slight grain growth while the solid solution remains remarkably stable without any decomposition. On the contrary, after annealing at 900 °C first Na segregations at triple junctions and significant grain growth are observable, although the solid solution still retains most of the dissolved Na.

For the first time, we report on micro- and nanostructured Ti surfaces produced by ultrashort-pulse laser processing followed by sputter deposition of Pt aiming at efficient cathode electrodes for alkaline water electrolysis. We studied the laser processing-induced surface morphology, the elemental composition of the surface, the specific surface increase, the wetting behavior as well as the activity of the hydrogen evolution reaction. It is demonstrated that ultrashort-pulse laser structuring in combination with thin layer catalyst deposition can dramatically boost the performance of cathodes for the hydrogen evolution reaction due to the enormous increase in specific surface in combination with superhydrophilic and superwetting properties leading to a rapid gas bubble detachment.

Positron annihilation lifetime spectroscopy is applied to study the crystal defects in CoCrFeMnNi high entropy alloy. The material is measured in the as‐received (electro eroded; non‐etched) state; it shows a defect‐related positron lifetime of 220 ps, corresponding most likely to divacancies, with a relatively high concentration. Furthermore, this sample is annealed in the temperature range up to 1000 K and positron lifetime is measured after each annealing step. The average positron lifetime is found to decrease with annealing and reaches 121 ps after annealing at 1000 K, indicating the existence of some remaining defects in the material. To show whether the observed defects are present in the bulk sample or only in the surface area, another sample is deeply etched and shows only one lifetime component of 112 ps, which is assigned to the defect‐free bulk lifetime in this alloy. This study indicated that the investigates high entropy alloy (in etched state) does not contain open‐volume defects within the sensitivity range of positron annihilation. Here, the defects observed in the non‐etched sample are present in the subsurface region, which are assumed to be generated most probably during wire‐erosion of the samples. In addition, X‐ray diffraction results indicate that the crystal structure is FCC with a lattice constant of (3.597 ± 0.002) Å, which is not affected by annealing.

The main mechanism for the strengthening of aluminium‐copper alloys of the 2xxx type is hardening by copper‐rich precipitates. However, their size, distribution, and crystal structure determine the final mechanical properties of the material. It has been shown that alloying additionally small amounts of cadmium, indium, or tin influences the precipitation behavior as well as the final strength of Al‐Cu alloys. The binding energy of quenched‐in vacancies to trace elements in the aluminium matrix is recognized as an influence on the diffusion behavior of the copper atoms and thus the preferred type of precipitate changes. A precondition for this influence is the transition of trace elements into solid solution during the solution heat treatment. In the present work, solubility and interaction with quenched‐in vacancies is analyzed for the elements In, Sn, Sb, Bi, and Pb in high‐purity binary alloys using differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS) as well as scanning and transmission electron microscopy (SEM, TEM). The results confirm on one hand literature data and deliver on the other hand new structural details. A subsequent anneal at moderate temperature leads to finely distributed precipitations on the nanoscale.