| 1. |
- Cedervall, Johan, et al.
(författare)
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Low temperature magneto-structural transitions in Mn3Ni20P6
- 2016
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Ingår i: Journal of Solid State Chemistry. - : Academic Press Inc.. - 0022-4596 .- 1095-726X. ; 237, s. 343-348
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Tidskriftsartikel (refereegranskat)abstract
- X-ray and neutron powder diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure can be described as cubic with space group Fm3¯m (225) without any nuclear phase transformation within studied temperature interval from room temperature down to 4 K. The magnetic structure of Mn3Ni20P6 is complex with two independent magnetic positions for the Mn atoms and the compound passes three successive magnetic phase transitions during cooling. At 30 K the spins of the Mn atoms on the Wyckoff 4a site (Mn1) order to form a primitive cubic antiferromagnetic structure with propagation vector k=(0 0 1). Between 29 and 26 K the Mn atoms on the Wyckoff 8c site (Mn2) order independently on already ordered Mn1 magnetic structure forming a commensurate antiferromagnetic structure with propagation vector k=(0 0 12) and below 26 K, both Mn positions order to form an incommensurate helical structure with propagation vector k=(0 0 ~0.45). Magnetization vs. temperature curve of Mn3Ni20P6 shows a steep increase indicating some magnetic ordering below 230 K and a sharp field dependent anomaly in a narrow temperature range around 30 K.
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| 2. |
- Cedervall, Johan, et al.
(författare)
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Magnetic structure of the magnetocaloric compound AlFe2B2
- 2016
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 664, s. 784-791
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Tidskriftsartikel (refereegranskat)abstract
- The crystal and magnetic structures of AlFe2B2 have been studied with a combination of X-ray and neutron diffraction and electronic structure calculations. The magnetic and magnetocaloric properties have been investigated by magnetisation measurements. The samples have been produced using high temperature synthesis and subsequent heat treatments. The compound crystallises in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285 K through a second order phase transition. At temperatures below the magnetic transition the magnetic moments align along the crystallographic a-axis. The magnetic entropy change from 0 to 800 kA/m was found to be - 1.3 J/K kg at the magnetic transition temperature.
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| 3. |
- Cedervall, Johan, et al.
(författare)
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Magnetostructural transition in Fe5SiB2 observed with neutron diffraction
- 2016
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 235, s. 113-118
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Tidskriftsartikel (refereegranskat)abstract
- The crystal and magnetic structure of Fe5SiB2 has been studied by a combination of X-ray and neutron diffraction. Also, the magnetocrystalline anisotropy energy constant has been estimated from magnetisation measurements. High quality samples have been prepared using high temperature synthesis and subsequent heat treatment protocols. The crystal structure is tetragonal within the space group I4/mcm and the compound behaves ferromagnetically with a Curie temperature of 760 K. At 172 K a spin reorientation occurs in the compound and the magnetic moments go from aligning along the c-axis (high T) down to the ab-plane (low T). The magnetocrystalline anisotropy energy constant has been estimated to 0.3 MJ/m3 at 300 K.
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| 4. |
- Cedervall, Johan, et al.
(författare)
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On the structural and magnetic properties of the double perovskite Nd2NiMnO6Nd2NiMnO6
- 2019
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Ingår i: Journal of Materials Science: Materials in Electronics. - : Springer Science and Business Media LLC. - 1573-482X .- 0957-4522. ; 30:17, s. 16571-16578
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Tidskriftsartikel (refereegranskat)abstract
- The structural, electronic and magnetic properties of phase pure and stoichiometric samples of the double perovskite Nd 2NiMnO 6 have been investigated with a combination of X-ray and neutron diffraction, X-ray photoelectron spectroscopy and magnetometry. It is found that the monoclinic space group P2 1/ n best describes the crystal structure of Nd 2NiMnO 6. Photoectron spectroscopy revels a mixed valence of the transition metal sites where Ni has 3+/2+ oxidation states and Mn has 3+/4+. The compound orders ferromagnetically at ∼195 K. The magnetic structure was determined from the refinement of the neutron diffraction data. The results suggests that the B-site magnetic moments align along the crystallographic a-direction.
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| 5. |
- Cedervall, Johan, et al.
(författare)
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Phase stability and structural transitions in compositionally complex LnMO 3 perovskites
- 2021
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 300
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Tidskriftsartikel (refereegranskat)abstract
- Entropy stabilised materials have possibilities for tailoring functionalities to overcome challenges in materials science. The concept of configurational entropy can also be applied to metal oxides, but it is unclear whether these could be considered as solid solutions in the case of perovskite-structured oxides and if the configurational entropy plays a stabilising role. In this study, compositionally complex perovskite oxides, LnMO3 (Ln = La, Nd, Sm, Ca and Sr, M = Ti, Cr, Mn, Fe, Co, Ni, and Cu), are investigated for their phase stability and magnetic behaviour. Phase-pure samples were synthesised, and the room temperature structures were found to crystallise in either Pnma or R3¯c space groups, depending on the composition and the resulting tolerance factor, while the structural transition temperatures correlate with the pseudo cubic unit cell volume. The techniques used included diffraction with X-rays and neutrons, both ex- and in-situ, X-ray photoelectron spectroscopy, magnetometry as well as electron microscopy. Neutron diffraction studies on one sample reveal that no oxygen vacancies are found in the structure and that the magnetic properties are ferrimagnetic-like with magnetic moments mainly coupled antiferromagnetically along the crystallographic c-direction. X-ray photoelectron spectroscopy gave indications of the oxidation states of the constituting ions where several mixed oxidation states are observed in these valence-compensated perovskites.
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| 6. |
- Coll Ferrari, Maria Teresa, et al.
(författare)
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Effect of Austenitising Temperature and Cooling Rate on Microstructure in a Hot-Work Tool Steel
- 2014
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Ingår i: Proceedings of the 6th International Swedish Production Symposium. - 9789198097412 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- The effects on microstructucture of austenitising temperature and cooling rate during hardening were studied for a hot-work tool steel. Transformation temperatures were determined by dilatometry, scanning electron microscopy was used to characterise the microstructure and both retained austenite contents and their lattice parameters were measured by neutron diffraction. For lower cooling rates, lower austenitising temperatures produce larger amounts of both retained austenite and bainite. Retained austenite in bainitic structures is higher in carbon than in martensitic structures. Consequently, lowering the austenitising temperature will affect microstructure and properties.
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| 7. |
- Gebresenbut, Girma Hailu, 1982-, et al.
(författare)
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Effect of pseudo-Tsai cluster incorporation on the magnetic structures of R-Au-Si (R = Tb, Ho) quasicrystal approximants
- 2022
-
Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 106:18
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Tidskriftsartikel (refereegranskat)abstract
- In cluster-based quasicrystals, tetrahedra located in conventional Tsai clusters may be replaced by single rare-earth (R) ions at the cluster centers (pseudo-Tsai clusters). In this study, we investigate the effect of the pseudo-Tsai cluster incorporation on the magnetic structures of two approximants, the Tsai-type Tb-Au-Si [denoted TAS(0)] and Ho-Au-Si [denoted HAS(52)] with partial replacement of conventional Tsai clusters by pseudo-Tsai clusters, up to 52%. The mixture of Tsai and pseudo-Tsai clusters can be considered a different source of randomness/disorder other than the conventional chemical mix sites (Au/Si). The effect of the latter has been previously discussed regarding the origin/cause of spin-glass-like ordering and Anderson localization of electronic states in quasicrystals and approximant crystals. Single crystal neutron diffraction experiments at 2 K were performed and bulk physical properties (magnetization and specific heat) were investigated. In addition, earlier collected powder neutron diffraction data of TAS(14) with 14% replacement was reanalyzed in light of the results on TAS(0) and HAS(52). We find that the arrangement of ordered magnetic spins in the icosahedral shells of these phases is similar, while the cluster-center R magnetic states are different. In the case of TAS(14), the cluster-center Tb magnetic moments seem to affect the arrangement of surrounding icosahedral magnetic moments, and the magnetic structure of the icosahedral shell deviates from that of TAS(0). In the case of HAS(52), however, the icosahedral R magnetic moments are less affected by the cluster-center R, while the averaged cluster-center R magnetic moments are significantly diminished. We discuss these results considering the magnetic ordering effect on the bulk physical properties.
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| 8. |
- Gebresenbut, Girma, 1982-, et al.
(författare)
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Long range ordered magnetic and atomic structures of the quasicrystal approximant in the Tb-Au-Si system
- 2014
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:32, s. 322202-
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Tidskriftsartikel (refereegranskat)abstract
- The atomic and magnetic structure of the 1/1 Tb(14)Au(70)Si(16) quasicrystal approximant has been solved by combining x-ray and neutron diffraction data. The atomic structure is classified as a Tsai-type 1/1 approximant with certain structural deviations from the prototype structures; there are additional atomic positions in the so-called cubic interstices as well as in the cluster centers. The magnetic property and neutron diffraction measurements indicate the magnetic structure to be ferrimagnetic-like below 9Â K in contrast to the related Gd(14)Au(70)Si(16) structure that is reported to be purely ferromagnetic.
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| 9. |
- Höglin, Viktor, et al.
(författare)
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Detailed study of the magnetic ordering in FeMnP0.75Si0.25
- 2015
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 221, s. 240-246
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic and crystallographic properties of FeMnP0.75Si0.25 in the hexagonal Fe2P-type structure have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The room temperature diffractograms reveal co-existence of two distinct structural phases in the samples with small, but significant, differences only in the unit cell dimensions. The volume ratio between the two phases is governed by the annealing conditions. One of the phases orders ferromagnetically (TC = 250 K) and the other in an incommensurate antiferromagnetic structure at low temperatures (qx = 0.363(1), TN = 150 K).
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| 10. |
- Höglin, Viktor, et al.
(författare)
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The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5
- 2011
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 184:9, s. 2434-2438
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Tidskriftsartikel (refereegranskat)abstract
- The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5 has been studied by means of neutron and X-ray powder diffraction. Single phase samples of nominal composition FeMnP0.5Si0.5 have been prepared by the drop synthesis method. The compound crystallizes in the Fe2P-type structure (P-62m) with the magnetic moments aligned along the a-axis. It is found that the Fe atoms are mainly situated in the tetrahedral 3g site while the Mn atoms prefer the pyramidal 3f position. The material is ferromagnetic (TC=382 K) and at 296 K the total magnetic moment is 4.4 µB/f.u. It is shown that the magnetic moment in the 3f site is larger (2.5 µB) than in the 3g site (1.9 µB).
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| 11. |
- Ivanov, Sergey, et al.
(författare)
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Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1-xScx)(2/3)W1/3O3 solid solutions
- 2019
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Ingår i: European Physical Journal B. - : SPRINGER. - 1434-6028 .- 1434-6036. ; 92:8
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Tidskriftsartikel (refereegranskat)abstract
- Ceramic samples of the multiferroic perovskite Pb(Fe1-xScx)(2/3)W1/3O3 with 0 <= x <= 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (Fm3(_)m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B and B '' sites. As the non-magnetic Sc3+ ions replace the magnetic Fe3+ cations, the antiferromagnetic state of PbFe2/3W1/3O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B ' and B '' sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1-xScx)(2/3)W1/3O3 and possibly also in the undoped PbFe2/3W1/3O3.
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| 12. |
- Karlsson, Dennis, et al.
(författare)
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Structure and phase transformations in gas atomized AlCoCrFeNi high entropy alloy powders
- 2022
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 893
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the crystal structure and phase stability of gas atomized equiatomic AlCoCrFeNi powder was investigated. This alloy is usually described as a high entropy alloy forming a solid solution phase stabilized by a high mixing entropy. However, thermodynamic calculations show that the high entropy phase is stable only at very high temperatures close to the melting point and that a mixture of several phases are the most stable state at lower temperatures. This suggest that kinetic effects may influence the phase composition of atomized powder. The unique features of X-ray diffraction, neutron diffraction as well as transmission electron microscopy were used to study the atomic structure of the atomized powder in detail. The results show that the powder crystallises in an ordered B2 (CsCl-type) structure with a preferred site occupation of Al and Fe on the (1/2 1/2 1/2) position and Co and Ni on the (0 0 0) position. During heat-treatment of the powder, the B2 phase decomposes into fcc and sigma phases and the final phase composition is highly dependent on the heating rate. The effect of heat-treatment on the atomized powder was also investigated and revealed a significant phase transformation with e.g. the formation of sigma phase preferably at the surface of the powder particles. The phase content was also dependent on the size fraction of the powder particles. Sintering of green bodies made with different heat cycles showed that the phase composition of the starting material had a significant impact on the final phase composition and microstructure of the sintered components. The results illustrate the importance of well-defined powder materials for powder consolidation, especially additive manufacturing (binder jetting) of high entropy alloys.
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| 13. |
- Larsen, Simon R., et al.
(författare)
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Revealing the Magnetic Structure and Properties of Mn(Co,Ge)2
- 2022
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 61:44, s. 17673-17681
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Tidskriftsartikel (refereegranskat)abstract
- The atomic and magnetic structures of Mn(Co,Ge)2 are reported herein. The system crystallizes in the space group P63/mmc as a superstructure of the MgZn2-type structure. The system exhibits two magnetic transitions with associated magnetic structures, a ferromagnetic (FM) structure around room temperature, and an incommensurate structure at lower temperatures. The FM structure, occurring between 193 and 329 K, is found to be a member of the magnetic space group P63/mm'c'. The incommensurate structure found below 193 K is helical with propagation vector k = (0 0 0.0483). Crystallographic results are corroborated by magnetic measurements and ab initio calculations.
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| 14. |
- Marattukalam, Jithin James, et al.
(författare)
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The effect of laser scanning strategies on texture, mechanical properties, and site-specific grain orientation in selective laser melted 316L SS
- 2020
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting has been used to demonstrate the striking effect of laser scanning strategies on the crystalline texture in 316L SS. The aligned crystal orientation along the tensile direction (Z-axis) could be varied using the scanning strategy. A strong 〈100〉 single crystalline-like texture is obtained in the direction of the laser scan and a 〈110〉 texture was observed in the build direction when using a bidirectional scan without rotation. Fiber texture was observed along the tensile direction when the bi-directional laser scanning vectors were rotated by 67° (Rot-scan) for each layer. The study highlights a correlation between laser scanning strategies with resulting textures, microstructure, and mechanical properties in as-printed bulk 316L SS. The hardness, Young's modulus, and ultimate tensile strength were significantly influenced by the final microstructure, crystallographic texture, and porosity. Furthermore, the applied laser scanning strategies made it possible to tailor crystallographic textures locally within the component. This was demonstrated by printing characters with a fiber texture, in a matrix with ⟨100⟩ texture parallel to the Z-axis.
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| 15. |
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| 16. |
- Pacheco, Victor, et al.
(författare)
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On the relationship between laser scan strategy, texture variations and hidden nucleation sites for failure in laser powder-bed fusion
- 2022
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Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 26
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Tidskriftsartikel (refereegranskat)abstract
- While laser powder-bed fusion has overcome some of the design constraints of conventional manufacturing meth-ods, it requires careful selection of process parameters and scan strategies to obtain favorable properties. Here we show that even simple scan strategies, complex ones being inevitable when printing intricate designs, can inadvertently produce local alterations of the microstructure and preferential grain orientation over small areas - which easily remain unnoticed across the macroscale. We describe how a combined usage of neutron imaging and electron backscatter diffraction can reveal these localized variations and explain their origin within cm-sized parts. We explain the observed contrast variations by linking the neutron images to simulated data, pole figures and EBSD, providing an invaluable reference for future studies and showing that presumably minor changes of the scan strategy can have detrimental effects on the mechanical properties. In-situ tensile tests reveal that fracture occurs in a region that was re-melted during the building process.
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| 17. |
- Pacheco, Victor
(författare)
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Processing–Structure–Properties Relationship in Metal Additive Manufacturing
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The last three decades have seen the transition of additive manufacturing, from applications exclusively in rapid-prototyping to an emerging production method in the manufacturing industry that is rapidly gaining more relevance. Within additive manufacturing methods, selective laser melting (SLM) is one of the most widely used and mature technologies and is the focus of this thesis. In particular, this work aims at characterizing novel microstructures and/or alloys produced with SLM and to understand how the process parameters influence the microstructure and properties.Hitherto, the most prevalent material selection approach for SLM has been the use and optimization of well-known alloys, such as steels, Ni- and Ti-based alloys, among others. Favorable microstructures are usually achieved with a combination of appropriate parameters and post-processing techniques. Another approach, especially interesting from a research perspective, is the exploration of materials and microstructures suited for the inherent characteristics of SLM. In alignment with the latter strategy, three types of materials are successfully produced and analyzed in this work: the amorphous Zr-based AMZ4 alloy, 316L stainless steel with strong preferential orientation (i.e., similar orientation of the crystalline structure of the grains) and the intermetallic MnAl(C) with strong preferential orientation. The latter contains a ferromagnetic phase with potential applications as a permanent magnet.SLM was found to be an effective method to produce the amorphous phase in the Zr59.3Cu28.8Al10.4Nb1.5 system (AMZ4). The laser power and oxygen impurities were found to have a central role in the formation of crystalline particles in the amorphous matrix. These crystalline particles and the oxygen impurities reduced the thermal stability of the alloy in comparison to specimens fabricated by suction casting. For the more conventional 316L stainless steel, it was demonstrated that the scan strategy can be used to influence the type of texture, with a notable effect on the mechanical properties. In the case of MnAl(C), it was established that the high temperature polymorph – ε-phase, can be retained during the printing process. This phase can be subsequently transformed to the ferromagnetic τ-phase with annealing procedures. It was observed that a strong preferred orientation of the ε-phase can be achieved, although it did not translate into a strong texture in the τ-phase (after the heat treatments). The research methodology used in this thesis and the findings regarding the processing–structure–properties relationship in SLM provide an important reference for future studies of novel materials and microstructures produced by additive manufacturing.
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| 18. |
- Paul-Boncour, Valerie, et al.
(författare)
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TbMgNi4-xCox-(H,D)2 System. II : Correlation between Structural and Magnetic Properties
- 2023
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 8:33, s. 30727-30735
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of TbMgNi4-xCox intermetallic compounds and selected hydrides and deuterides of this system have been studied by various techniques, including magnetic measurements, in situ X-ray and neutron powder diffraction. The intermetallic compounds crystallize in a SnMgCu4-type structure and magnetically order below a Curie temperature (T-C), which increases exponentially with the Co content. This can be due to the ordering of the Co sublattice. On the other hand, the insertion of D or H in TbMgNiCo3 strongly decreases T-C. The X-ray diffraction measurements versus temperature reveal cell volume minima at T-C for the compounds with x = 1-3 without any hints of the structure change. The analysis of the neutron diffraction patterns for the intermetallics with x = 2 and 3 indicates a slightly canted ferrimagnetic structure below T-C. The Tb moments refined at 16 K are 4.1(2) (mu B)/Tb for x = 2, and 6.2(1) mu B/Tb for x = 3, which are smaller than the free ion value (9.5 mu B/Tb). This reduction can be due to the influence of temperature but also reveals the crystal field effect. As Ni and Co occupy statistically the same Wyckoff site, an average Ni/Co moment was refined, leading to 1.7(2) (mu B)/atom for x = 2 and 1.8(1) mu B/atom for x = 3 at 16 K. This moment is slightly canted compared to the Tb moment.
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| 19. |
- Roberts, Matthew, et al.
(författare)
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Design of a new lithium ion battery test cell for in-situ neutron diffraction measurements
- 2013
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 226, s. 249-255
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a new cell design for the construction of lithium ion batteries with conventional electrochemical performance whilst allowing in situ neutron diffraction measurement. A cell comprising of a wound cathode, electrolyte and anode stack has been prepared. The conventional hydrogen-containing components of the cell have been replaced by hydrogen-free equivalents. The electrodes are fabricated using a PTFE binder, the electrolyte consists of deuterated solvents which are supported in a quartz glass fibre separator. Typical battery performance is reported using the hydrogen-free components with a specific capacity of 140 mA h g(-1) being observed for LiFePO4 at a rate of 0.2 C. Neutron diffraction patterns of full cells were recorded with phase change reactions monitored. When aluminium packaging was used a better signal to noise ratio was obtained. The obtained atomic positions and lattice parameters for all cells investigated were found to be consistent with parameters refined from the diffraction pattern of a powder of the pure electrode material. This paper highlights the pertinent points in designing cells for these measurements and addresses some of the problems.
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