TY - JOUR A1 - Fantin, Andrea A1 - Cakir, Cafer Tufan A1 - Kasatikov, S. A1 - Schumacher, G. A1 - Manzoni, Anna Maria T1 - Effects of heat treatment on microstructure, hardness and local structure in a compositionally complex alloy JF - Materials Chemistry and Physics N2 - Unlike conventional alloys, high entropy alloys are characterized by one or more solid solution phase(s) without a clearly defined solvent, all element contribute to the matrix in a way that is still not entirely understood. In addition, it is not known to what extent classic thermodynamic rules can be applied to these multi-element alloys, especially concerning the question about what factor incites the matrix to undergo a phase transformation. This work tackles directly some of these aspects on a chosen alloy, Al8Cr17Co17Cu8Fe17Ni33 (at.%), which presents a high temperature single-phase γ state and a two-phase state with γ′ precipitates, above and below 900 ◦C, respectively. A combined investigation via microstructural observations, hardness testing, X-ray absorption and photoelectron spectroscopy was carried out above the γ′ formation temperature. Hardness values are independent of the annealing temperatures, microstructural analysis shows no phase formation and X-ray absorption spectroscopy does not reveal observable changes in neither local atomic nor electronic structure, indicating that approaching γ′ formation temperature is not influenced by atomic or electronic rearrangements. Interestingly, short-range chemical order remains quantitatively compatible at any annealing temperature in the single-phase γ state, and the observed preferred pairs Al–Cu and Al–Ni in the γ state match with the γ’ precipitates composition below 900 ◦C. KW - High entropy alloys KW - EXAFS KW - Short range order KW - Vickers hardness PY - 2022 DO - https://doi.org/10.1016/j.matchemphys.2021.125432 SN - 0254-0584 VL - 276 SP - 125432 PB - Elsevier B.V. AN - OPUS4-53760 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fantin, Andrea A1 - Orazio Lepore, G. A1 - Manzoni, Anna Maria A1 - Kasatikov, S. A1 - Scherb, T. A1 - Huthwelker, T. A1 - d'Acapito, F. A1 - Schumacher, G. T1 - Short-range chemical order and local lattice distortion in a compositionally complex alloy JF - Acta Materialia N2 - This work presents an X-ray absorption spectroscopy study on a single-phase state of the Al8Cr17Co17Cu8Fe17Ni33 compositionally complex alloy, focused on the local crystal structure around each alloying element. The comparison of 1st shell bond lengths, obtained by the analysis of extended X-ray absorption fine structure (EXAFS) measured at the K-edges of each alloying element, indicates that Al8Cr17Co17Cu8Fe17Ni33 crystallizes in a distorted arrangement of an fcc lattice. A modest bond length dependence of the alloying elements with increasing atomic number is observed, with minima and maxima at Cr/Co, and Al/Cu, respectively. 1st shell bond lengths spread over ~0.03 Å; consequently, such variations cannot result in lattice distortions greater than ~0.04 Å. EXAFS results clearly indicate short-range order in the alloy: pairing of Al with Ni and Cu is favored, correlating well with a g’ precipitate composition (Al-Ni-Cu rich) reported in previous work, while Al-Cr bonding is unfavored and no Al-Al pairs are observed. Electronic structure information was obtained through comparison between near-edge regions of alloying Elements and corresponding pure metals. Intensity comparison of K-edge features agree with a charge variation of p states in Al8Cr17Co17Cu8Fe17Ni33, where Ni and Cu act as p states electron acceptors, suggesting an orbital hybridization with Al, responsible for a shrinkage in Al metallic radius in the alloy by 0.17 Å. KW - High entropy alloys KW - EXAFS KW - Compositionally complex alloys PY - 2020 DO - https://doi.org/10.1016/j.actamat.2020.04.034 VL - 193 SP - 329 EP - 337 PB - Elsevier Ltd. AN - OPUS4-50830 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Scherb, Tobias A1 - Kimber, S. A. J. A1 - Stephan, Christiane A1 - Henry, P. F. A1 - Schumacher, G. A1 - Escolástico, S. A1 - Serra, J. M. A1 - Seeger, J. A1 - Just, J. A1 - Hill, A.H. A1 - Banhart, J. T1 - Nanoscale order in the frustrated mixed conductor La5.6WO12-Delta JF - Journal of Applied Crystallography N2 - This article reports a comprehensive investigation of the average and local structure of La5.6WO12-δ, which has excellent mixed proton, electron and oxide ion conduction suitable for device applications. Synchrotron X-ray and neutron powder diffraction show that a cubic fluorite supercell describes the average structure, with highly disordered lanthanum and oxide positions. On average, the tungsten sites are sixfold coordinated and a trace [3.7 (1.3)%] of anti-site disorder is detected. In addition to sharp Bragg reflections, strong diffuse neutron scattering is observed, which hints at short-range order. Plausible local configurations are considered and it is shown that the defect chemistry implies a simple 'chemical exchange' interaction that favours ordered WO6 octahedra. The local model is confirmed by synchrotron X-ray pair distribution function analysis and EXAFS experiments performed at the La K and W L-3 edges. It is shown that ordered domains of similar to 3.5 nm are found, implying that mixed conduction in La5.6WO12-δ is associated with a defective glassy-like anion sublattice. The origins of this ground state are proposed to lie in the nonbipartite nature of the face-centred cubic lattice and the pairwise interactions which link the orientation of neighbouring octahedral WO6 sites. This 'function through frustration' could provide a means of designing new mixed conductors. KW - neutron diffraction KW - x-ray diffraction KW - proton conductors PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-366756 DO - https://doi.org/10.1107/S1600576716006415 SN - 1600-5767 VL - 49 IS - Issue 3 SP - 997 EP - 1008 PB - International Union of Crystallography CY - Chester, UK AN - OPUS4-36675 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lahiri, D. A1 - Sharma, S.M. A1 - Verma, A.K. A1 - Vishwanadh, B. A1 - Dey, G.K. A1 - Schumacher, G. A1 - Scherb, T. A1 - Riesemeier, Heinrich A1 - Reinholz, Uwe A1 - Radtke, Martin A1 - Banerjee, S. T1 - Investigation of short-range structural order in Zr69.5Cu12Ni11Al7.5 and Zr41.5Ti41.5Ni17 glasses, using X-ray absorption spectroscopy and ab initio molecular dynamics simulations JF - Journal of synchrotron radiation N2 - Short-range order has been investigated in Zr69.5Cu12Ni11Al7.5 and Zr41.5Ti41.5Ni17 metallic glasses using X-ray absorption spectroscopy and ab initio molecular dynamics simulations. While both of these alloys are good glass formers, there is a difference in their glass-forming abilities (Zr41.5Ti41.5Ni17 > Zr69.5Cu12Ni11Al7.5). This difference is explained by inciting the relative importance of strong chemical order, icosahedral content, cluster symmetry and configuration diversity. KW - Multi-component alloy KW - Glass-forming ability KW - XAFS KW - Local structure KW - AIMD simulation PY - 2014 DO - https://doi.org/10.1107/S1600577514017792 SN - 0909-0495 SN - 1600-5775 VL - 21 IS - 6 SP - 1296 EP - 1304 PB - Blackwell Publishing CY - Oxford AN - OPUS4-31837 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Liu, Y. A1 - Schumacher, G. A1 - Riesemeier, Heinrich A1 - Banhart, J. T1 - Change in atomic coordination in a heavily deformed metallic glass JF - Journal of applied physics N2 - The local structure around Ni and La atoms in Al85Ni10La5 amorphous powder after ball milling was investigated by X-ray absorption spectroscopy. A continuous decrease in coordination number of Ni and La as a function of milling time was observed, while the nearest neighbour distance and the mean square atomic displacement did not change, pointing at the creation of free volume around the Ni and La atoms. These structural changes resemble those of a liquid upon temperature increase. The results are described by a shear band model in which the coordination numbers of Ni and La are different within and outside a shear band. KW - X-ray-diffraction KW - Shear bands KW - Electron-irradiation KW - Positron lifetime KW - Structural model KW - Amorphous-alloys KW - Deformation KW - Temperature KW - EXAFS KW - State PY - 2014 DO - https://doi.org/10.1063/1.4879682 SN - 0021-8979 SN - 1089-7550 VL - 115 IS - 20 SP - 203510-1 - 203510-8 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-32409 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grothausmann, R. A1 - Zehl, G. A1 - Manke, I. A1 - Fiechter, S. A1 - Bogdanoff, P. A1 - Dorbandt, I. A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Hentschel, Manfred P. A1 - Schumacher, G. A1 - Banhart, J. T1 - Dreidimensionale Charakterisierung von Katalysatornanopartikeln JF - International journal of materials research N2 - We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells. KW - Radiography KW - Tomography KW - Neutrons KW - Polymer electrolyte membrane fuel cell (PEMFC) KW - Fuel cell stack PY - 2012 SN - 1862-5282 VL - 103 IS - 1 SP - 135 EP - 136 PB - Carl Hanser CY - München AN - OPUS4-25976 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grothausmann, R. A1 - Zehl, G. A1 - Manke, I. A1 - Fiechter, S. A1 - Bogdanoff, P. A1 - Dorbandt, I. A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Hentschel, Manfred P. A1 - Schumacher, G. A1 - Banhart, J. T1 - Nanometer-Tomographie: kleinste Katalysatorteilchen erblicken - Mit Elektronen und Computern die mobile Brennstoffzelle erforschen JF - Materials and corrosion KW - Electron tomography KW - Polymer electrolyte membrane fuel cell (PEMFC) KW - Reconstruction algorithm KW - DIRECTT PY - 2012 DO - https://doi.org/10.1002/maco.201290007 SN - 0947-5117 SN - 1521-4176 VL - 63 IS - 2 SP - 1 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-26348 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grothausmann, R. A1 - Zehl, G. A1 - Manke, I. A1 - Fiechter, S. A1 - Bogdanoff, P. A1 - Dorbandt, I. A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Hentschel, Manfred P. A1 - Schumacher, G. A1 - Banhart, J. T1 - Quantitative structural assessment of heterogeneous catalysts by electron tomography JF - Journal of the American chemical society N2 - We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells. KW - Electron tomography KW - Reconstruction algorithm KW - Catalyst KW - Fuel cell PY - 2011 DO - https://doi.org/10.1021/ja2032508 SN - 0002-7863 SN - 1520-5126 VL - 133 IS - 45 SP - 18161 EP - 18171 PB - American Chemical Society CY - Washington, DC AN - OPUS4-24833 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mechler, S. A1 - Schumacher, G. A1 - Koteski, V. A1 - Riesemeier, Heinrich A1 - Schäfers, F. A1 - Mahnke, H.-E. T1 - Local structure and site substitution in amorphous and quasicrystalline Zr-Ti-Ni-(Cu) alloys JF - Applied physics letters N2 - Local structures of amorphous and quasicrystalline phases in Zr–Ti–Ni and Zr–Ti–Ni–Cu alloys have been studied by means of x-ray absorption spectroscopy. The amorphous phases show a high degree of icosahedral short-range order. In all investigated systems local order around Cu and Ni atoms was found to be nearly identical pointing to site substitution of Ni by Cu as the reason for an improved glass forming ability when Ni is partly substituted by Cu. The results strengthen an icosahedral cluster based approach for the structure of metallic glasses and indicate the importance of the medium-range order on glass formation. KW - Copper alloys KW - Frustration KW - Glass structure KW - Metallic glasses KW - X-ray absorption spectra PY - 2010 DO - https://doi.org/10.1063/1.3467265 SN - 0003-6951 SN - 1077-3118 VL - 97 IS - 4 SP - 041914-1 - 041914-3 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-22122 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schumacher, G. A1 - Darowski, N. A1 - Zizak, I. A1 - Klingelhöffer, Hellmuth A1 - Neumann, W. T1 - Two-stage relaxation of damage structure in strongly creep-deformed single crystal superalloy SC16 measured by means of X-ray diffraction JF - Scripta materialia KW - Superalloys KW - SC16 KW - Creep-deformation KW - Relaxation KW - X-ray diffraction PY - 2009 DO - https://doi.org/10.1016/j.scriptamat.2008.09.009 SN - 1359-6462 SN - 1872-8456 VL - 60 IS - 2 SP - 88 EP - 91 PB - Elsevier CY - Oxford AN - OPUS4-18304 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -