TY - JOUR A1 - Sommer, Konstantin A1 - Agudo Jácome, Leonardo A1 - Hesse, René A1 - Bettge, Dirk T1 - Revealing the nature of melt pool boundaries in additively manufactured stainless steel by nano-sized modulation N2 - In the current study, the 3D nature of the melt pool boundaries (MPBs) in a 316 L austenitic steel additively manufactured by laser-based powder bed fusion (L-PBF) is investigated. The change of the cell growth direction and its relationship to the MPBs is investigated by transmission electron microscopy. A hitherto unreported modulated substructure with a periodicity of 21 nm is further discovered within the cell cores of the cellular substructure, which results from a partial transformation of the austenite, which is induced by a Ga+ focused ion beam. While the cell cores show the modulated substructure, cell boundaries do not. The diffraction pattern of the modulated substructure is exploited to show a thickness ≥200 nm for the MPB. At MPBs, the cell walls are suppressed, leading to continuously connecting cell cores across the MPB. This continuous MPB is described either as overlapping regions of cells of different growing directions when a new melt pool solidifies or as a narrow planar growth preceding the new melt pool. KW - Additive manufacturing KW - Austenitic steel 316L KW - Melt pool boundary KW - Microstructural characterization KW - Transmission electron microscopy PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-547295 DO - https://doi.org/10.1002/adem.202101699 SN - 1527-2648 VL - 24 IS - 6 SP - 1 EP - 11 PB - Wiley-VCH CY - Weinheim AN - OPUS4-54729 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pu, Y. A1 - Lawrence, M. J. A1 - Celorrio, V. A1 - Wang, Q. A1 - Gu, M. A1 - Sun, Z. A1 - Agudo Jácome, Leonardo A1 - Russell, A. E. A1 - Huang, L. A1 - Rodriguez, P. T1 - Nickel confined in 2D earth-abundant oxide layers for highly efficient and durable oxygen evolution catalysts N2 - Low cost, high-efficiency catalysts towards water splitting are urgently required to fulfil the increasing demand for energy. In this work, low-loading (<20 wt%) Ni-confined in layered metal oxide anode catalysts (birnessite and lepidocrocite titanate) have been synthesized by facile ion exchange methodology and subjected to systematic electrochemical studies. It was found that Ni-intercalated on K-rich birnessite (Ni-KMO) presents an onset overpotential (ηonset) as low as 100 mV and overpotential at 10 mA cm−2 (η10) of 206 mV in pH = 14 electrolyte. By combining electrochemical methods and X-ray absorption and emission spectroscopies (XAS and XES), we demonstrate Ni sites are the active sites for OER catalysis and that the Mn3+ sites facilitate Ni intercalation during the ion-exchange process, but display no observable contribution towards OER activity. The effect of the pH and the nature of the supporting electrolyte on the electrochemical performance was also evaluated. KW - Confined catalyst KW - Low-loading KW - Layered manganese oxide KW - Oxygen evolution reaction KW - Transmission electron microscopy (TEM) PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-515027 DO - https://doi.org/10.1039/D0TA04031B SN - 2050-7496 SN - 2050-7488 VL - 8 IS - 26 SP - 13340 EP - 13350 PB - Royal Society of Chemistry CY - London AN - OPUS4-51502 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Suárez Ocano, Patricia A1 - Manzoni, Anna Maria A1 - Lopez-Galilea, I. A1 - Ruttert, B. A1 - Laplanche, G. A1 - Agudo Jácome, Leonardo T1 - Influence of cooling rate on the microstructure and room temperature mechanical properties in the refractory AlMo0.5NbTa0.5TiZr superalloy N2 - Refractory chemically complex alloys with bcc-based microstructures show great potential for high-temperature applications but most of them exhibit limited room-temperature ductility, which remains a challenge. One such example is the AlMo0.5NbTa0.5TiZr alloy, mainly consisting of a nano-scaled structure with an ordered B2 matrix and a high-volume fraction of aligned cuboidal and coherently embedded A2 precipitates. This work aims to investigate how the cooling rate after hot isostatic pressing of the AlMo0.5NbTa0.5TiZr alloy affects its microstructure and its resulting hardness and fracture toughness at room temperature. A slow cooling rate of 5 °C/min leads to a coarse microstructure consisting of aligned slabs (mean A2 precipitate ≈ 25 nm) with a nanohardness of about 8 GPa. In contrast, after the fastest cooling rate (30 °C/min), the A2 precipitates become more cubic with an edge length of ≈ 16 nm, resulting in an increase in nanohardness by 10 %. The fracture toughness is roughly independent of the cooling rate and its mean value (≈ 4.2 MPa∙m1/2) resembles that of some B2 intermetallics and other A2/B2 alloys. As the lattice misfit between the A2 and B2 phases is known to play a key role in microstructure formation and evolution, its temperature dependence between 20 and 900 °C was investigated. These findings offer insights into the evolution of the microstructure and room-temperature mechanical properties of the AlMo0.5NbTa0.5TiZr alloy, which could help the development of advanced chemically complex alloys. KW - High entropy alloy KW - Lattice misfit KW - Scanning electron microscopy KW - Transmission electron microscopy KW - X-ray diffraction KW - Refractory alloy PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-572809 DO - https://doi.org/10.1016/j.jallcom.2023.169871 SN - 0925-8388 VL - 949 SP - 169871 PB - Elsevier B.V. AN - OPUS4-57280 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gonzalez-Martinez, I. A1 - Weinel, Kristina A1 - Feng, W. A1 - Agudo Jácome, Leonardo A1 - Gemming, T. A1 - Büchner, B. T1 - Hybrid tungsten-carbon 2D nanostructures via in-situ gasification of carbon substrates driven by ebeam irradiation of WO2.9 microparticles N2 - Since the TEM has the capacity to observe the atomic structure of materials, in-situ TEM synthesis methods are uniquely suited to advance our fundamental understanding of the bottom-up dynamics that drive the formation of nanostructures. E-beam induced fragmentation (potentially identified as a manifestation of Coulomb explosion) and electron stimulated desorption (ESD) are phenomena that have received attention because they trigger chemical and physical reactions that can lead to the production of various nanostructures. Here we report a simple TEM protocol implemented on WO2.9 microparticles supported on thin amorphous carbon substrates. The method produces various nanostructures such as WC nanoparticles, WC supported films and others. Nevertheless, we focus on the gradual graphitization and gasification of the C substrate as it interacts with the material expelled from the WO2.9 microparticles. The progressive gasification transforms the substrate from amorphous C down to hybrid graphitic nanoribbons incorporating W nanoparticles. We think these observations open interesting possibilities for the synthesis of 2D nanomaterials in the TEM. KW - Transmission electron microscope (TEM) KW - in-situ synthesis KW - Tungsten carbide KW - Nanoribbons KW - Coulomb explosion PY - 2023 DO - https://doi.org/10.1088/1361-6528/acf584 SN - 0957-4484 VL - 34 IS - 49 SP - 1 EP - 15 PB - IOP Publishing AN - OPUS4-58279 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Famy, A. A1 - Agudo Jácome, Leonardo A1 - Schönhals, Andreas T1 - Effect of Silver Nanoparticles on the Dielectric Properties and the Homogeneity of Plasma Poly(acrylic acid) Thin Films N2 - For the first time, structure−electrochemical relationships of thin films of a plasma-polymerized acrylic acid/carbon dioxide AA/CO2 (75/25%) copolymer modified by implanted silver nanoparticles are discussed. The pulsed plasma polymerization of AA/CO2 was utilized and adjusted to obtain a maximal amount of COOH Groups forming an almost uncross-linked polymer structure. The prepared polymer layer is rinsed by a silver nitrate solution to impregnate Ag+ ions. This step is followed by its reduction of Ag+ with NaBH4 as a chemical route in comparison to the reduction by sunlight as an ecofriendly photoreduction method. The chemical composition and morphology of the topmost surface layer of the AA/CO2 polymer thin film were investigated by X-ray photoelectron spectroscopy and atomic force microscopy. Moreover, the molecular mobility, conductivity, and thermal stability of the polymer layer were analyzed using broadband dielectric spectroscopy. The dielectric properties of the AA/ CO2 polymer thin film were studied in the presence of Ag+ ions or Ag0. It was found that a cross-linked polymer layer with a smooth surface and high conductivity was obtained in the presence of Ag+/ Ag0. KW - Nanoparticles PY - 2020 DO - https://doi.org/10.1021/acs.jpcc.0c06712 SN - 1932-7447 VL - 124 IS - 41 SP - 22817 EP - 22826 PB - ACS AN - OPUS4-51468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gadelmeier, C. A1 - Agudo Jácome, Leonardo A1 - Suárez Ocano, Patricia A1 - Glatzel, U. T1 - Effect of stacking fault energy (SFE) of single crystal, equiatomic CrCoNi and Cantor alloy on creep resistance N2 - Compared to mechanisms like solid solution strengthening, the stacking fault energy (SFE) should be considered as a further factor that influences the material properties. The effect of SFE of alloys or individual elements on strength and resistance can vary considerably. In the high-temperature regime above 700 ◦C, there are still significant gaps in the knowledge about the effect of the SFE on the mechanical properties of single-phase alloys. The effect of SFE on creep resistance of two face-entered cubic equiatomic medium and high entropy alloys, CrCoNi and CrMnFeCoNi, respectively, is evaluated to fill parts of these gaps. Using the Bridgman solidification process, the alloys were produced as single crystals and crept under vacuum at 700 ◦C up to 1100 ◦C. This work shows a significant impact of the lower SFE of CrCoNi on the creep behavior compared to the results of previous investigations of CrMnFeCoNi. The creep resistance of the former is higher over the complete temperature range. At very high temperatures, the strengthening effect of the stacking faults is significantly present. The formation of tetragonal stacking faults and extended dislocation nodes can be identified as the reason for this effect. KW - Medium entropy alloy KW - MEA KW - HEA KW - Single crystal KW - CrCoNi PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-602620 DO - https://doi.org/10.1016/j.msea.2024.146779 SN - 0921-5093 VL - A 908 SP - 1 EP - 9 PB - Elsevier B.V. AN - OPUS4-60262 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - INPR A1 - Weinel, Kristina A1 - Hahn, Marc Benjamin A1 - Lubk, Axel A1 - Feng, Wen A1 - Martinez, Ignacio Gonzalez A1 - Büchner, Bernd A1 - Agudo Jácome, Leonardo T1 - Electron-beam-induced modification of gold microparticles in an SEM N2 - Electron-beam-induced conversion of materials in a transmission electron microscope uses the high power density of a localized electron beam of acceleration voltages above 100 kV as an energy source to transform matter at the sub-micron scale. Here, the e-beam-induced transformation of precursor microparticles employing a low-energy e-beam with an acceleration voltage of 30 kV in a scanning electron microscope is developed to increase the versatility and efficiency of the technique. Under these conditions, the technique can be classified between e-beam lithography, where the e-beam is used to mill holes in or grow some different material onto a substrate, and e-beam welding, where matter can be welded together when overcoming the melting phase. Modifying gold microparticles on an amorphous SiOx substrate reveals the dominant role of inelastic electron-matter interaction and subsequent localized heating for the observed melting and vaporization of the precursor microparticles under the electron beam. Monte-Carlo scattering simulations and thermodynamic modeling further support the findings. KW - Scanning electron microscopy KW - Electron-beam-induced modification KW - Heat transfer KW - Gold microparticles KW - Nanoparticles synthesis PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-609513 UR - https://arxiv.org/html/2408.02409v1 SP - 1 EP - 9 AN - OPUS4-60951 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Feng, Wen A1 - Gemming, Thomas A1 - Giebeler, Lars A1 - Qu, Jiang A1 - Weinel, Kristina A1 - Agudo Jácome, Leonardo A1 - Büchner, Bernd A1 - González-Martínez, Ignacio T1 - Influence of magnetic field on electron beam-induced Coulomb explosion of gold microparticles in transmission electron microscopy N2 - In this work we instigated the fragmentation of Au microparticles supported on a thin amorphous carbon film by irradiating them with a gradually convergent electron beam inside the Transmission Electron Microscope. This phenomenon has been generically labeled as “electron beam-induced fragmentation” or EBIF and its physical origin remains contested. On the one hand, EBIF has been primarily characterized as a consequence of beam-induced heating. On the other, EBIF has been attributed to beam-induced charging eventually leading to Coulomb explosion. To test the feasibility of the charging framework for EBIF, we instigated the fragmentation of Au particles under two different experimental conditions. First, with the magnetic objective lens of the microscope operating at full capacity, i.e. background magnetic field B = 2 T, and with the magnetic objective lens switched off (Lorenz mode), i.e. B = 0 T. We observe that the presence or absence of the magnetic field noticeably affects the critical current density at which EBIF occurs. This strongly suggests that magnetic field effects play a crucial role in instigating EBIF on the microparticles. The dependence of the value of the critical current density on the absence or presence of an ambient magnetic field cannot be accounted for by the beam-induced heating model. Consequently, this work presents robust experimental evidence suggesting that Coulomb explosion driven by electrostatic charging is the root cause of EBIF. KW - Electron beam-induced fragmentation KW - Coulomb explosion KW - X-ray diffraction KW - Lorenz transmission electron microscopy PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-600247 DO - https://doi.org/10.1016/j.ultramic.2024.113978 SN - 1879-2723 VL - 262 SP - 1 EP - 8 PB - Elsevier CY - Amsterdam AN - OPUS4-60024 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Suárez Ocaño, Patricia A1 - Agudo Jácome, Leonardo T1 - Oxidation Behavior of the AlMo0.5NbTa0.5TiZr Chemically Complex Alloy N2 - The chemically complex alloys that contain mostly refractory elements (rCCAs), may be highly resistant to heat and load, which makes them attractive candidates for use at extremely high temperatures associated with technological applications such as aeroengine turbines. However, the oxidation behavior remains an emerging field within the CCA community. The fully heat treated AlMo0.5NbTa0.5TiZr rCCA contains a dual-phase microstructure that resembles the γ/ γ’ pattern of the well-known Ni-base superalloys, however with a continuous Al-Zr-Ti-rich B2 ordered matrix embedding Mo-Nb-Ta-rach bcc precipitates. The question thus arises what is the oxidation behavior of this rCCA alloy? In this study, this question is addressed via in situ and ex situ X-ray diffraction (XRD) in dry and humid air in the 800–1000 °C regime. Electron microscopic investigations complement the findings. In situ synchrotron experiments were carried out at the KMC2 beamline of the Helmholtz Zentrum Berlin (HZB), with a wavelength of 1.5418 Å at 800 and 950 °C under dry and humid (≈ 40% rH, laboratory air) air for 12 h. Scanning and transmission electron microscopy was performed before and after exposure to spatially resolve the scale development ex situ. In general, 12 h exposure led to an oxide scale which internal oxidation reaches several tens of microns, and which is dominated by Zr-, Ti- and Mo-containing oxides although aluminum oxide was also always present. Main differences are observed between temperatures, while the humidity played a lesser role. T2 - International Conference on High Entropy Materials (ICHEM) 2023 CY - Knoxville, TN, USA DA - 18.06.2023 KW - High entropy superalloy KW - High temperature oxidation KW - In situ synchrotron diffraction KW - Electron microscopy PY - 2023 AN - OPUS4-63857 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Manzoni, Anna Maria A1 - Mohring, Wencke A1 - Hesse, René A1 - Agudo Jácome, Leonardo A1 - Stephan-Scherb, C. T1 - Early material damage in equimolar CrMnFeCoNi in mixed oxidizing/sulfiding hot gas atmosphere N2 - The challenges to use more varied fuels at medium and high temperatures above 500 °C need to be addressed by tuning the materials toward a better resistance against increased corrosion. As a first step the corrosion processes need to be better understood, especially in the case of the unavoidable and highly corrosive sulfur-based gases. Herein, oxidation/sulfidation of an equimolar CrMnFeCoNi high-entropy alloy is studied at an early stage after hot gas exposure at 600 °C for 6 h in 0.5% SO2 and 99.5% Ar. The oxidation process is studied by means of X-ray diffraction, scanning and transmission electron microscopy, and supported by thermodynamic calculations. It is found that the sulfur does not enter the bulk material but interacts mainly with the fast-diffusing manganese at grain boundary triple junctions at the alloy surface. Submicrometer scaled Cr–S–O-rich phases close to the grain boundaries complete the sulfur-based phase formation. The grains are covered in different Fe-, Mn-, and Cr-based spinels and other oxides. KW - High entropy alloy KW - Sulfiding KW - Corrosion KW - Transmission electron microscopy PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543495 DO - https://doi.org/10.1002/adem.202101573 SN - 1527-2648 SP - 1 EP - 8 PB - Wiley-VCH CY - Weinheim AN - OPUS4-54349 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -