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369 results on '"Leineweber, Andreas"'

1. Dealing with Fe in Secondary Al-Si Alloys Including Metal Melt Filtration

Author

Becker, Hanka, Leineweber, Andreas, Hull, Robert, Series Editor, Jagadish, Chennupati, Series Editor, Kawazoe, Yoshiyuki, Series Editor, Kruzic, Jamie, Series Editor, Osgood Jr., Richard, Series Editor, Parisi, Jürgen, Series Editor, Pohl, Udo W., Series Editor, Seong, Tae-Yeon, Series Editor, Uchida, Shin-ichi, Series Editor, Wang, Zhiming M., Series Editor, Aneziris, Christos G., editor, and Biermann, Horst, editor

Published
2024
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40. Ni3Sn4 and FeAl2 as vacancy variants of the W-type ("bcc") structure.

Author

Leineweber, Andreas

Subjects
*ATOMIC displacements, *CRYSTAL structure, *LATTICE constants, *SOLID solutions, *CRYSTAL orientation, *DISLOCATIONS in metals
Abstract

Systematization of the vast number of known crystal structures of intermetallic phases is a challenge. One previously proposed group is referred to here as vacancy variants of the W-type structure. Members of this group, may, however, not be easily recognized because of the structural irregularity introduced by the vacancies. Descriptions of the experimentally observed crystal structures of Ni3Sn4 and FeAl2 in terms of vacancy variants of the W-type structure are, respectively, derived by establishing a lattice correspondence with the W-type structure, allowing, in particular, identification of the vacant sites. In both cases only small deviatoric strains are required to obtain the experimentally encountered lattice parameters, and generally small atomic displacements occur from the ideal positions, thus demonstrating significance of the lattice correspondence. The lattice correspondences allow, for both Ni3Sn4 and FeAl2, relating reported microstructure evidence (directions/planes occurring in orientation relationships and crystal habits but also on twinning and slip) with such typical for metals and solid solutions with W-type ("bcc") structures. This demonstrates that the established lattice correspondences have a significance going beyond a descriptive one, but the underlying W-type structures reveal themselves in the materials' behavior. [ABSTRACT FROM AUTHOR]

Published
2023
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42. Magnetic phase separation in the EuPdSn2 ground state.

Author

Martinelli, Alberto, Ryan, Dominic, Sereni, Julian, Ritter, Clemens, Leineweber, Andreas, Čurlík, Ivan, Freccero, Riccardo, and Giovannini, Mauro

Abstract

The chemical bonding, structural and magnetic properties of EuPdSn2 have been investigated by DFT, synchrotron X-ray and neutron powder diffraction and 151Eu Mössbauer spectroscopy. As a result, no structural transition is observed in the thermal range of 5–290 K, whereas ferromagnetic and antiferromagnetic orderings are found to coexist below 12 K and compete in the ground state. This magnetic phase separation is likely triggered by the minimization of the global energy resulting from the coexistence of the different magnetic configurations. Chemical bonding analysis in position space reveals the presence of heteroatomic 4a- and 5a-bonds, involving each species, and two-atomic Eu–Pd polar covalent interactions building up graphite-like distorted honeycomb layers. [ABSTRACT FROM AUTHOR]

Published
2023
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45. Ni3Sn4and FeAl2as vacancy variants of the W-type (“bcc”) structure

Author

Leineweber, Andreas

Abstract

Systematization of the vast number of known crystal structures of intermetallic phases is a challenge. One previously proposed group is referred to here as vacancy variants of the W-type structure. Members of this group, may, however, not be easily recognized because of the structural irregularity introduced by the vacancies. Descriptions of the experimentally observed crystal structures of Ni3Sn4and FeAl2in terms of vacancy variants of the W-type structure are, respectively, derived by establishing a lattice correspondence with the W-type structure, allowing, in particular, identification of the vacant sites. In both cases only small deviatoric strains are required to obtain the experimentally encountered lattice parameters, and generally small atomic displacements occur from the ideal positions, thus demonstrating significance of the lattice correspondence. The lattice correspondences allow, for both Ni3Sn4and FeAl2, relating reported microstructure evidence (directions/planes occurring in orientation relationships and crystal habits but also on twinning and slip) with such typical for metals and solid solutions with W-type (“bcc”) structures. This demonstrates that the established lattice correspondences have a significance going beyond a descriptive one, but the underlying W-type structures reveal themselves in the materials’ behavior.

Published
2023
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50. Phase Stability of Iron Nitride Fe4N at High Pressure—Pressure-Dependent Evolution of Phase Equilibria in the Fe–N System

Author

Wetzel, Marius Holger, Rabending, Tina Trixy, Friák, Martin, Všianská, Monika, Šob, Mojmír, and Leineweber, Andreas

Subjects
phase stability, Technology, Microscopy, QC120-168.85, QH201-278.5, Engineering (General). Civil engineering (General), Article, TK1-9971, phase transitions, high pressure, Descriptive and experimental mechanics, phase equilibria, Electrical engineering. Electronics. Nuclear engineering, TA1-2040, iron nitride, phase diagrams
Abstract

Although the general instability of the iron nitride γ′-Fe4N with respect to other phases at high pressure is well established, the actual type of phase transitions and equilibrium conditions of their occurrence are, as of yet, poorly investigated. In the present study, samples of γ′-Fe4N and mixtures of α Fe and γ′-Fe4N powders have been heat-treated at temperatures between 250 and 1000 °C and pressures between 2 and 8 GPa in a multi-anvil press, in order to investigate phase equilibria involving the γ′ phase. Samples heat-treated at high-pressure conditions, were quenched, subsequently decompressed, and then analysed ex situ. Microstructure analysis is used to derive implications on the phase transformations during the heat treatments. Further, it is confirmed that the Fe–N phases in the target composition range are quenchable. Thus, phase proportions and chemical composition of the phases, determined from ex situ X-ray diffraction data, allowed conclusions about the phase equilibria at high-pressure conditions. Further, evidence for the low-temperature eutectoid decomposition γ′→α+ε′ is presented for the first time. From the observed equilibria, a P–T projection of the univariant equilibria in the Fe-rich portion of the Fe–N system is derived, which features a quadruple point at 5 GPa and 375 °C, above which γ′-Fe4N is thermodynamically unstable. The experimental work is supplemented by ab initio calculations in order to discuss the relative phase stability and energy landscape in the Fe–N system, from the ground state to conditions accessible in the multi-anvil experiments. It is concluded that γ′-Fe4N, which is unstable with respect to other phases at 0 K (at any pressure), has to be entropically stabilised in order to occur as stable phase in the system. In view of the frequently reported metastable retention of the γ′ phase during room temperature compression experiments, energetic and kinetic aspects of the polymorphic transition γ′⇌ε′ are discussed.

Published
2021

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