TY - JOUR A1 - Ulrich, A. S. A1 - Kasatikov, S. A1 - König, T. A1 - Fantin, Andrea A1 - Margraf, J. T. A1 - Galetz, M. C. T1 - Decreased Metal Dusting Resistance of Ni-Cu Alloys by Fe and Mn Additions N2 - Ni-Cu alloys are promising for application at temperatures between 400–900 °C and reducing atmospheres with high C-contents. Typically, under such conditions, metallic materials in contact with the C-rich atmosphere are degraded by a mechanism called metal dusting (MD). Ni-Cu-alloys do not form protective oxide scales, but their resistance is attributed to Cu, which catalytically inhibits the C-deposition on the surface. Adding other alloying elements, such as Mn or Fe, was found to enhance the MD attack of Ni-Cu alloys again. In this study, the effect of the Mn and Fe is divided into two affected areas: the surface and the bulk. The MD attack on binary Ni-Cu alloys, model alloys with Fe and Mn additions, and commercial Monel Alloy 400 is experimentally demonstrated. The surface electronic structure causing the adsorption and dissociation of C-containing molecules is investigated for model alloys. Analytical methods such as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, electron probe microanalysis combined with wavelength-dispersive X-ray spectroscopy, X-ray diffraction analysis, and near-edge X-ray absorption fine structure measurements were used. The results are correlated to CALPHAD calculations and atomistic simulations combining density functional theory calculations and machine learning. It is found that the Cu content plays a significant role in the surface reaction. The effect of Mn and Fe is mainly attributed to oxide formation. A mechanism explaining the enhanced attack by adding both Fe and Mn is proposed. KW - Metal Dusting KW - XANES PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-608226 DO - https://doi.org/10.1007/s11085-024-10263-w SN - 2731-8397 SP - 1 EP - 14 PB - Springer Science and Business Media LLC AN - OPUS4-60822 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - 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 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 - Lepore, G. O. A1 - Widom, M. A1 - Kasatikov, S. A1 - Manzoni, Anna Maria T1 - How Atomic Bonding Plays the Hardness Behavior in the Al–Co–Cr–Cu–Fe–Ni High Entropy Family N2 - A systematic study on a face‐centered cubic‐based compositionally complex alloy system Al–Co–Cr–Cu–Fe–Ni in its single‐phase state is carried out, where a mother senary compound Al₈Co₁₇Cr₁₇Cu₈Fe₁₇Ni₃₃ and five of its suballoys, obtained by removing one element at a time, are investigated and exhaustively analyzed determining the contribution of each alloying element in the solid solution. The senary and the quinaries are compared using experimental techniques including X‐ray absorption spectroscopy, X‐ray diffraction, transmission electron microscopy, and first principles hybrid Monte Carlo/molecular dynamics simulations. Chemical short‐range order and bond length distances have been determined both at the experimental and computational level. Electronic structure and local atomic distortions up to 5.2 Å have been correlated to the microhardness values. A linear regression model connecting hardness with local lattice distortions is presented. KW - High entropy alloys KW - EXAFS KW - Short-range order KW - Microhardness KW - Alloy design KW - Transmission electron microscopy KW - Lattice distortion PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-593333 DO - https://doi.org/https://doi.org/10.1002/smsc.202300225 SN - 2688-4046 SP - 1 EP - 12 PB - Wiley CY - Weinheim AN - OPUS4-59333 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 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 - Andreoli, A. F. A1 - Fantin, Andrea A1 - Kasatikov, S. A1 - Bacurau, V. P. A1 - Widom, M. A1 - Gargarella, P. A1 - Mazzer, E. M. A1 - Woodcock, T. G. A1 - Nielsch, K. A1 - Coury, F. G. T1 - The impact of chemical short-range order on the thermophysical properties of medium- and high-entropy alloys N2 - The unusual behavior observed in the coefficient of thermal expansion and specific heat capacity of CrFeNi, CoCrNi, and CoCrFeNi medium/high-entropy alloys is commonly referred to as the K-state effect. It is shown to be independent of the Curie temperature, as demonstrated by temperature-dependent magnetic moment measurements. CoCrFeNi alloy is chosen for detailed characterization; potential reasons for the K-state effect such as texture, recrystallization, and second-phase precipitation are ruled out. An examination of the electronic structure indicates the formation of a pseudo-gap in the Density of States, which suggests a specific chemical interaction between Ni and Cr atoms upon alloying. Hybrid Monte Carlo/Molecular Dynamic (MC/MD) simulations indicate the presence of non-negligible chemical short-range order (CSRO). Local lattice distortions are shown to be negligible, although deviations around Cr and Ni elements from those expected in a fully disordered structure are experimentally observed by X-ray absorption spectroscopy. The determined bonding distances are in good agreement with MC/MD calculations. A mechanism is proposed to explain the anomalies and calorimetric experiments and their results are used to validate the mechanism. KW - Mechanical Engineering KW - Mechanics of Materials KW - General Materials Science PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-595869 DO - https://doi.org/10.1016/j.matdes.2024.112724 SN - 0264-1275 VL - 238 SP - 1 EP - 15 PB - Elsevier B.V. AN - OPUS4-59586 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -