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  • 1. Dalou, Celia
    et al.
    Füri, Evelyn
    Deligny, Cécile
    Piani, Laurette
    Caumon, Marie-Camille
    Laumonier, Mickael
    Boulliung, Julien
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Redox control on nitrogen isotope fractionation during planetary core formation2019In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 29, p. 14485-14494Article in journal (Refereed)
    Abstract [en]

    The present-day nitrogen isotopic compositions of Earth's surficial (N-15-enriched) and deep reservoirs (N-15-depleted) differ significantly. This distribution can neither be explained by modern mantle degassing nor recycling via subduction zones. As the effect of planetary differentiation on the behavior of N isotopes is poorly understood, we experimentally determined N-isotopic fractionations during metal-silicate partitioning (analogous to planetary core formation) over a large range of oxygen fugacities (Delta IW -3.1 < logfO(2) <Delta IW -0.5, where Delta IW is the logarithmic difference between experimental oxygen fugacity [fO(2)] conditions and that imposed by the coexistence of iron and wustite) at 1 GPa and 1,400 degrees C. We developed an in situ analytical method to measure the N-elemental and -isotopic compositions of experimental run products composed of Fe-C-N metal alloys and basaltic melts. Our results show substantial N-isotopic fractionations between metal alloys and silicate glasses, i.e., from -257 +/- 22% to -49 +/- 1% over 3 log units of fO(2). These large fractionations under reduced conditions can be explained by the large difference between N bonding in metal alloys (Fe-N) and in silicate glasses (as molecular N-2 and NH complexes). We show that the delta N-15 value of the silicate mantle could have increased by similar to 20 parts per thousand during core formation due to N segregation into the core.

  • 2.
    Eriksson, Mirva
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Radwan, Mohamed
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Spark plasma sintering of wc, cemented carbide and functional graded materials2013In: International journal of refractory metals & hard materials, ISSN 0263-4368, ISSN 0263-4368, Vol. 36, p. 31-37Article in journal (Refereed)
    Abstract [en]

    Spark plasma sintering (SPS) is an extremely fast solidification technique for compounds that are difficult to sinter within the material group's metals, ceramics, or composites thereof. SPS uses a uniaxial pressure and a very rapid heating cycle to consolidate these materials. The heating is generated by Joule effect when a strong, pulsed electric current passes the conductive graphite die and also through the sample, if conductive. Cemented carbides (hard metals) are mostly used for metal cutting and drilling, wood cutting or rock drilling tools and are consolidated either by pressureless sintering (PLS), hot pressing (HP), or hot isostatic pressing (HIP). With SPS the main benefit is the ability to control the WC grain size due to the short sintering times at high temperature. In addition, unwished reactions between WC and cobalt to form other phases are minimized. By SPS the amount of cobalt can be reduced towards zero in fully dense WC materials. With this technique it is easy to prepare gradient materials where a ductile weldable metal can be joined with the cemented carbide part.

  • 3.
    Guo, Hua
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Peking University, People's Republic of China. .
    Ping, He
    Hu, Jiangtao
    Song, Xiaohe
    Zheng, Jiaxin
    Pan, Feng
    Controllable synthesis of LiFePO4 in different polymorphs and study of the reaction mechanism2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 27, p. 14294-14300Article in journal (Refereed)
    Abstract [en]

    Lithium iron phosphate, a widely used cathode material in Lithium Ion Batteries (LIBs), crystallizes typically in an olivine-type phase, alpha-LiFePO4 (aLFP). However, the new phase beta-LiFePO4 (bLFP), which can be transformed from aLFP at high temperature with high pressure, can be produced through a simple liquid-phase reaction. The mechanism of controllable synthesis of the two polymorphs of lithium iron phosphate has not been studied thoroughly. In this paper, with thorough experiments, we demonstrate that controllable synthesis of LFP with different crystal polymorphs can be obtained by controlling certain conditions. The phosphoric acid ratio in the reactants and the reaction time play key roles in the controllable syntheses. Higher phosphoric acid ratios and shorter reaction times would result in a higher bLFP content, while a lower amount of phosphoric acid and a longer reaction time would be beneficial to aLFP formation. To illustrate the mechanism for this phenomenon, the detailed reaction process was researched via X-ray diffraction, from which a possible mechanism associated with the evolution of crystal structures was demonstrated. The solvent content is also important for the process: some water content would lead to nanoplate-shaped aLFP particles appearing. Their influence on the reaction could be attributed to the change of thermodynamics and kinetics, which leads to different crystal nucleation, growth and phase-change processes.

  • 4.
    Hu, Jianfeng
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ordered coalescence of nano crystallites contributing to the rapid anisotropic grain growth in silicon nitride ceramics2013In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, no 3, p. 270-273Article in journal (Refereed)
    Abstract [en]

    Microstructural characterization is performed on two dense Si3N4 ceramic samples consolidated by spark plasma sintering (SPS): one fabricated using alpha-Si3N4 and the other using beta-Si3N4 as the starting powder. A novel mechanism is revealed where ordered coalescence of nano beta-crystallites accelerate the rapid beta-Si3N4 anisotropic grain growth. The rapid alpha- to beta-Si3N4 phase transformation via a high supersaturation of dissolved Si3N4 in the melt favors this mechanism. The high heating rate by SPS is essential for achieving such supersaturation.

  • 5.
    Lin, C.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Nano Pores Evolution in Hydroxyapatite Microsphere during Spark Plasma Sintering2011In: Science of Sintering, ISSN 0350-820X, Vol. 43, no 1, p. 39-46Article in journal (Refereed)
    Abstract [en]

    Micron-spherical granules of hydroxyapatite (HAp) nanoparticles were prepared by powder granulation methods. Through subsequent sintering, porous HAp microspheres with tailored pore and grain framework structures were obtained. Detailed microstructure investigation by SEM and TEM revealed the correlation of the pore structure and the necking strength with the sintering profiles that determine the coalescence features of the nanoparticles. The partially sintered porous HAp microspheres containing more than 50% porosity consisting of pores and grains both in nano-scale are active in inducing the precipitation of HAp in simulated body fluid. The nano-porous HAp microspheres with an extensive surface and interconnecting pores thus demonstrate the potential of stimulating the formation of collagen and bone and the integration with the newly formed bones during physiological bone remodeling.

  • 6. Liu, Leifeng
    et al.
    Ding, Qingqing
    Zhong, Yuan
    Zou, Ji
    Wu, Jing
    Chiu, Yu-Lung
    Li, Jixue
    Zhang, Ze
    Yu, Qian
    Shen, Zhijian
    3D dislocation network in additive manufactured steel breaks strength-ductility trade-offManuscript (preprint) (Other academic)
  • 7.
    Zhong, Yuan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sub-grain structure in additive manufactured stainless steel 316L2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis focuses on exploring the sub-grain structure in stainless steel 316L prepared by additive manufacturing (AM). Two powder-bed based AM methods are involved: selective laser melting (SLM) and electron beam melting (EBM). It is already known that AM 316L has heterogeneous property and hierarchy structure: micro-sized melt pools, micro-sized grains, nano-sized sub-grain structure and nano-sized inclusions. Yet, the relation among these structures and their influence on mechanical properties have not been clearly revealed so far. Melt pool boundaries having lower amount of sub-grain segregated network structures (Cellular structure) are weaker compared to the base material. Compared with cell boundaries, grain boundaries have less influence on strength but are still important for ductility. Cell boundaries strengthen the material without losing ductility as revealed by mechanical tests. Cellular structure can be continuous across the melt pool boundaries, low angle sub-grain boundaries, but not grain boundaries. Based on the above understanding, AM process parameters were adjusted to achieve customized mechanical properties. Comprehensive characterization were carried out to investigate the density, composition, microstructure, phase, magnetic permeability, tensile property, Charpy impact property, and fatigue property of both SLM and EBM SS316L at room temperature and at elevated temperatures (250°C and 400°C). In general, SLM SS316L has better strength while EBM SS316L has better ductility due to the different process conditions. Improved cell connection between melt pools were achieved by rotating 45° scanning direction between each layer compared to rotating 90°. Superior mechanical properties (yield strength 552 MPa and elongation 83%) were achieved in SLM SS316L fabricated with 20 µm layer thickness and tested in the building direction. Y2O3 added oxide dispersed strengthening steel (ODSS) were also prepared by SLM to further improve its performance at elevated temperatures. Slightly improved strength and ductility (yield strength 574 MPa and elongation 90%) were obtained on 0.3%Y2O3-ODSS with evenly dispersed nanoparticles (20 nm). The strength drops slightly  but ductility drops dramatically at elevated temperatures. Fractographic analysis results revealed that the coalescence of nano-voids is hindered at room temperature but not at elevated temperatures. The achieved promising properties in large AM specimens assure its potential application in nuclear fusion. For the first time, ITER first wall panel parts with complex inner pipe structure were successfully fabricated by both SLM and EBM which gives great confidence to application of AM in nuclear industry. 

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  • 8.
    Zhong, Yuan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zou, Ji
    Li, Xiaodong
    Olsén, Jon
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Oxide dispersion strengthened austenitic steel prepared by selective laser melting with superior strength and ductilityManuscript (preprint) (Other academic)
  • 9.
    Zhong, Yuan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rännar, Lars-Erik
    Wikman, Stefan
    Koptyug, Andrey
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cui, Daqing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Additive manufacturing of ITER first wall panel parts by two approaches: Selective laser melting and electron beam melting2017In: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 116, p. 24-33Article in journal (Refereed)
    Abstract [en]

    Fabrication of ITER First Wall (FW) Panel parts by two additive manufacturing (AM) technologies, selective laser melting (SEM) and electron beam melting (EBM), was supported by Fusion for Energy (F4E). For the first time, AM is applied to manufacture ITER In-Vessel parts with complex design. Fully dense SS316L was prepared by both SLM and EBM after developing optimized laser/electron beam parameters. Characterizations on the density, magnetic permeability, microstructure, defects and inclusions were carried out. Tensile properties, Charpy-impact properties and fatigue properties of SLM and EBM SS316L were also compared. ITER FW Panel parts were successfully fabricated by both SLM and EBM in a onestep building process. The SLM part has smoother surface, better size accuracy while the EBM part takes much less time to build. Issues with removing support structures might be solved by slightly changing the design of the internal cooling system. Further investigation of the influence of neutron irradiation on materials properties between the two AM technologies is needed.

1 - 9 of 9
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