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  • 51. Kalousek, Radek
    et al.
    Spousta, Jiri
    Zlamal, Jakub
    Dub, Petr
    Sikola, Tomas
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Salamon, David
    Maca, Karel
    Rapid heating of zirconia nanoparticle-powder compacts by infrared radiation heat transfer2017Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, nr 3, s. 1067-1072Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Homogeneous rapid sintering of nanoparticle powder compacts of yttria-stabilized zirconia was achieved by the radiation heat transfer. Green bodies were prepared by cold isostatic pressing (CIP) at various pressures providing different porosity of samples before sintering. Pressure-less sintering was performed in air at a heating rate of 100 degrees C/min up to the 1500 degrees C/1 min. Scanning electron microscopy, mercury intrusion porosimetry, and Archimedes technique were used to characterize the microstructure and to determine the density of the green and sintered bodies. Contrary to expectations, our results reveal opposite dependence of the green- and sintered densities on the CIP pressure. Since the whole sintering process does not exceed 10 min, to propose what processes are responsible for observed results, our attention is focused on the radiation heat transfer from furnace heating elements into the ceramics. Our arguments are supported by numerical calculations of the electromagnetic field enhancement in/between particles.

  • 52. Kaluzhskikh, M. S.
    et al.
    Kazakov, S. M.
    Mazo, G. N.
    Istomin, S. Ya.
    Antipov, E. V.
    Gippius, A. A.
    Fedotov, Yu.
    Bredikhin, S. I.
    Liu, Yi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    High-temperature crystal structure and transport properties of the layered cuprates Ln(2)CuO(4), Ln=Pr, Nd and Sm2011Inngår i: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 184, nr 3, s. 698-704Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-temperature crystal structure of the layered cuprates Ln(2)CuO(4), Ln = Pr, Nd and Sm with tetragonal T'-structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a- and c-axis changing from TEC(a)/TEC(c)approximate to 1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln(2)CuO(4) shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO(2)-planes (TEC(Pr-O1)= 11.7 ppm K(-1)) in comparison with other cuprates: TEC (Nd-O1)=15.2 ppm K(-1) and TEC (Sm-O1)= 15.1 ppm K(-1). High-temperature electrical conductivity of Pr(2)CuO(4) is the highest one in the whole studied temperature range (298-1173 K): 0.1-108 S/cm for Pr(2)CuO(4), 0.07-23 S/cm for Nd(2)CuO(4) and 2 X 10(-4)-9 S/cm for Sm(2)CuO(4). The trace diffusion coefficient (D(T)) of oxygen for Pr(2)CuO(4) determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2 X 10(-13) Cm(2)/S (973 K) and 3.8 X 10(-10) Cm(2)/S (1173 K) which are in between those observed for the manganese and cobalt-based perovskites.

  • 53. Kamba, S.
    et al.
    Nuzhnyy, D.
    Vanek, P.
    Savinov, M.
    Knizek, K.
    Shen, Z.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Santava, E.
    Maca, K.
    Sadowski, M.
    Petzelt, J.
    Magnetodielectric effect and optic soft mode behaviour in quantum paraelectric EuTiO3 ceramics2007Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 80, nr 2, s. 27002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Infrared reflectivity and time-domain terahertz transmission spectra of EuTiO3 ceramics revealed a polar optic phonon at 6-300K whose softening is fully responsible for the recently observed quantum paraelectric behaviour. Even if our EuTiO3 ceramics show lower permittivity than the single crystal due to a reduced density and/ or small amount of secondary pyrochlore Eu2Ti2O7 phase, we confirmed a magnetic field dependence of the permittivity, also slightly smaller than in single crystal. An attempt to reveal the soft phonon dependence at 1.8K on the magnetic field up to 13T remained below the accuracy of our infrared reflectivity experiment.

  • 54. Kocjan, Andraz
    et al.
    Pouchly, Vaclav
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Processing of zirconia nanoceramics from a coarse powder2015Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, nr 4, s. 1285-1295Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have merged the benefits of coarse-grained and nanocrystalline powders by the consolidation and sintering of coarse, yet nanostructured, mesoporous Y-TZP powder. The powder was composed of loosely aggregated, nanoscale crystallites, which can be seen as secondary particles or agglomerates. Their homogeneous, defect-free packing proved to be a viable pathway for the processing of zirconia nanoceramics. The powder consolidation yielded homogeneous green bodies with hierarchical heterogeneities in terms of intra- and inter-particle pore packing. The hierarchical heterogeneities had a pronounced effect on the densification and grain growth. The intra-particle pore coalescence along with a frozen interparticle porosity, prolonged the pore-pinning effect, separating the densification and grain-growth mechanisms. Increased heating rates promoted the grain-growth and densification via a competitive mechanism of primary crystallite ordered coalescence, while by applying pressure, the crystallite growth was completely prevented, making such a coarse powder suitable for the fabrication of zirconia nanoceramics.

  • 55.
    Kocjan, Andraz
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Colloidal processing and partial sintering of high-performance porous zirconia nanoceramics with hierarchical heterogeneities2013Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 33, nr 15-16, s. 3165-3176Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-performance, porous, Y-TZP nanoceramics with hierarchical heterogeneities originating from uniform, intra- and inter-particle packing were prepared by colloidal processing and partial sintering of a mesoporous powder. The powder consisted of 100-150-nanometer-sized secondary particles initially composed of smaller, loosely aggregated, primary, nanoscale crystallites. Green bodies were prepared by centrifugal slip casting of weakly flocculated suspensions. During the initial stage of sintering, necking between the secondary particles was accompanied by intraparticle pore coalescence, while the pores originating from the secondary particle packing remained intact. Such microstructures with porosity levels between 46 and 18.3% and pore areas between 18 and 4 m(2)/g led to attractive properties, i.e., much reduced thermal conductivities of 0.63-1.88W m(-1) K-1, high bending strengths of 70-540 MPa and lowered elastic moduli of 32-156 GPa, making them potentially ideal as thermal insulators and/or load-bearing porous biomaterials owing to the possibility of further impregnation with bioactive ingredients.

  • 56. Kocjan, Andraž
    et al.
    Logar, Manca
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    The agglomeration, coalescence and sliding of nanoparticles, leading to the rapid sintering of zirconia nanoceramics2017Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikkel-id 2541Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Conventional sintering is a time- and energy-consuming process used for the densification of consolidated particles facilitated by atomic diffusion at high temperatures. Nanoparticles, with their increased surface free energy, can promote sintering; however, size reduction also promotes agglomeration, so hampering particle packing and complete densification. Here we show how the ordered agglomeration of zirconia primary crystallites into secondary particle assemblies ensures their homogeneous packing, while also preserving the high surface energy to higher temperatures, increasing the sintering activity. When exposed to intense electromagnetic radiation, providing rapid heating, the assembled crystallites are subjected to further agglomeration, coalescence and sliding, leading to rapid densification in the absence of extensive diffusional processes, cancelling out the grain growth during the initial sintering stages and providing a zirconia nanoceramic in only 2 minutes at 1300 degrees C.

  • 57.
    Leonova, Ekaterina
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Hakeem, Abbas S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Jansson, Kjell
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Stevensson, Baltzar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Esmaeilzadeh, Saeid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Edén, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Nitrogenrich La-Si-Al-O-N oxynitride glass structures probed by solid state NMR2008Inngår i: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 354, nr 1, s. 49-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the local structures of oxynitride La–Si–(Al)–O–N glasses by 29Si and 27Al magic-angle spinning (MAS) solid state Nuclear Magnetic Resonance (NMR). The glasses studied span an unprecedented range of compositions, up to >50 at.% lanthanum and nitrogen out of the cations and anions, respectively, and achievable through a recently introduced glass preparation route. Transmission as well as scanning electron microscopy verified homogeneous samples over length-scales down to 20 nm. As the nitrogen content of the glasses increased, 29Si NMR evidenced a progressive formation of Si–N bonds, with SiO2N2 tetrahedra dominating in the nitrogen-rich glass networks. In the oxygen-rich end of the series, aluminum is predominantly present in tetrahedral coordination as AlO4, whereas the glasses with highest nitrogen contents have a major fraction of AlO3N structural units. Trends in isotropic 29Si and 27Al chemical shifts and 27Al quadrupolar couplings are compared with results of La–Si–Al–O glasses and are discussed in relation to the glass compositions and their proposed structures.

  • 58.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    de Moraes, Elisangela Guzi
    Colombo, Paolo
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Preparation of nasal cavity-like SiC-Si3N4 foams with a hierarchical pore architecture2015Inngår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 5, nr 35, s. 27891-27900Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Rigid SiC-Si3N4 foams with hierarchical porosity were prepared through protein-based gel-casting followed by radiant sintering in a modified spark plasma sintering (SPS) set-up. The porous bodies sintered at 1500-1700 degrees C for only 10 minutes achieved a compressive strength of 15-21 MPa while keeping a porosity of 60-70 vol%. Gradient porous structures, with pore sizes ranging between 1 to 100 mm, were intersected by the growth of hybrid SiC and Si3N4 nanowires inside the pores resulting in a nasal cavity-like appearance. Gas permeability at room temperature (25 degrees C) and 600 degrees C was evaluated. Darcian permeabilities and non-Darcian permeabilities of all the prepared foams at room temperature fell within (0.354-1.55) x 10(-12) m(2) and (1.60-6.33) x 10(-8) m, respectively. Measurement of the Darcian and non-Darcian permeabilities at 600 degrees C were much higher, at 1.71 x 10(-11) m(2) and 2.68 x 10(-7) m, respectively. The microstructure, stability, gas flow properties and the green synthesis route reveal the potential of these ceramic foams to be used as industrial PM filters for airborne pollutions.

  • 59.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Guo, Peng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Guzi de Moraes, Elisângela
    Wan, Wei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zou, Ji
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Colombo, Paolo
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Structural study of disordered SiC nanowires by three-dimensional rotation electron diffraction2014Inngår i: Materials Research Express, ISSN 2053-1591, Vol. 1, nr 4, artikkel-id 045023Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structure of disordered SiC nanowires was studied by using the three-dimensional rotation electron diffraction (RED) technique. The streaks shown in the RED images indicated the stacking faults of the nanowire. High-resolution transmission electron microscopy imaging was employed to support the results from the RED data. It suggested that a 2H polytype is most possible for the nanowires.

  • 60.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hu, Jianfeng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zhang, J. -Z
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Xi'An University of Architecture & Technology, Xian, China.
    Ma, J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsing Hua University, Beijing, China.
    Densification as an exothermic process revealed by rapid high temperature consolidation of BaTiO3 nanopowder2014Inngår i: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 113, nr 4, s. 251-256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Densification is an exothermic process according to the classical sintering theories; however, it has never been explored experimentally. In the present work, such heat release was successfully detected from nanosized BaTiO3 nanopowder compact, which was rapidly consolidated by spark plasma sintering. A reduction of total power consumption was observed immediately when rapid densification occurred. The effects of the deviation of overall electric resistance on total power consumption were analysed. The temperature at which a falling inflection point of the power supply was observed can be used as an indicator of the minimum temperature required for densification. This would be of help for defining the 'kinetic window' for processing of nanoceramics in sintering practice.

  • 61.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Li, Wenjie
    Fasel, Claudia
    Shen, James
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Riedel, Ralf
    Sinterability of the oxynitride LaTiO2N with perovskite-type structure2014Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 586, s. 567-573Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on a thermal stability study, the sinterability of the oxynitride LaTiO2N was investigated by spark plasma sintering (SPS). The results show that LaTiO2N is thermodynamically unstable above ca. 400 degrees C in air and ca. 800 degrees C in argon. While it appears impossible to completely avoid decomposition during sintering, LaTiO2N ceramics with relative density of 74-94% and a residual LaTiO2N content of 57-90 wt% were prepared. By manipulating kinetics, a relative density of 94% was achieved at 1350 degrees C under an uniaxially applied pressure of 125 MPa. This density is higher than any other counterparts prepared by conventional sintering so far. SPS appears a feasible tool for manipulating the sintering kinetics. It enables the preparation of almost dense LaTiO2N bulks with adequate purity.

  • 62.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Y. S.
    Zou, J.
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Leifeng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Dense and strong ZrO2 ceramics fully densified in < 15 minManuskript (preprint) (Annet vitenskapelig)
  • 63.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). National University of Defense Technology, People’s Republic of China.
    Liu, Yongsheng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Northwestern Polytechnical University, People’s Republic of China.
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Leifeng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Adolfsson, Erik
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Dense and strong ZrO2 ceramics fully densified in <15 min2019Inngår i: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 118, nr 1-2, s. 23-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Crack-free zirconia ceramics were consolidated via sintering by intense thermal radiation (SITR) approach at 1600-1700 degrees C for 3-5 min. The resulted ceramic bulks can achieve a relative density up to 99.6% with a grain size of 300-1200 nm. Their bending strength, Vickers hardness and indentation toughness values are up to 1244 +/- 139 MPa, 13.3 +/- 0.3 GPa and 5.5 +/- 0.1 MPa m(1/2), respectively. Quantitative Raman and XRD analysis show the presence of minor m phase on the natural surface (<7%), fracture surface (<10%) and indentation areas (<15%). It reveals that the SITR method is efficient for rapidly manufacturing zirconia ceramics with desired density, fine grained microstructure and good mechanical properties that are strongly demanded in dental applications.

  • 64.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Yongsheng
    Zou, Ji
    Liu, Leifeng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Sintering by Intense Thermal Radiation (SITR): heat and mass transferArtikkel i tidsskrift (Fagfellevurdert)
  • 65.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Moraes, Elisângela Guzi de
    Guo, Peng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zou, Ji
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zhang, Junzhan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Xi′an University of Architecture and Technology, People’s Republic of China.
    Colombo, Paolo
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Rapid sintering of silicon nitride foams decorated with one-dimensional nanostructures by intense thermal radiation2014Inngår i: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 15, nr 4, artikkel-id 045003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silicon nitride foams were prepared by direct foaming and subsequent rapid sintering at 1600 °C. The intense thermal radiation generated under the pressureless spark plasma sintering condition facilitated necking of Si3N4 grains. The prepared foams possessed a porosity of ~80 vol% and a compressive strength of ~10 MPa, which required only ~30 min for the entire sintering processes. Rapid growth of one-dimensional SiC nanowires from the cell walls was also observed. Thermodynamic calculations indicated that the vapor–liquid–solid model is applicable to the formation of SiC nanowires under vacuum.

  • 66.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Rapid sintering of ceramics with gradient porous structure by asymmetric thermal radiation2015Inngår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 98, nr 12, s. 3631-3634Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, thermal radiation was employed for sintering silicon carbide foams that achieved a gradient porous structure. The simultaneous use of graphite and carbon fiber reinforced carbon composite (Cf/C) radiators resulted in an axial temperature gradient of ~600°C along the cylindrical sample, as confirmed by both numerical simulation and experimental measurement. By sintering the cylinder top at 1600°C for 5 min, the porous SiC body achieved an axial pore size gradient from ~106 ± 36 μm to ~250 ± 84 μm and an open porosity from 41.4 to 79.8 vol%. This work indicates the potential of sintering by intense thermal radiation technique for rapid manufacturing functionally graded materials through asymmetric assembly of thermal radiators.

  • 67.
    Li, Duan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Sintering by intense thermal radiation (SITR): A study of temperature distribution by simulation and experiments2015Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, nr 12, s. 3303-3309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The modeling and a confirming experimental study of a sintering process by using intense thermal radiation (SITR) is demonstrated. Experiments were conducted in a modified spark plasma sintering set-up for the purpose of rapid consolidation of porous SIC ceramics. A finite element method based software package, COMSOL Multiphysics, was employed to simulate the temperature distributions with two different die geometries. Experimental verifications were performed by sintering of SiC foams and measuring the temperature differences between two fixed points on the die and samples at 1000-1800 degrees C. SiC foams sintered under two geometries with 10 mm' dwell resulted in the formation of grain necks. The compressive strengths are 19.2 +/- 0.7 MPa (65.0 +/- 0.1 vol% porosity) and 15.3 +/- 1.9 MPa (69.0 +/- 0.3 vol% porosity), respectively. The simulation and experimental results showed that the temperature distributions are strongly related to these geometries.

  • 68. Li, Hezhen
    et al.
    Song, Lu
    Sun, Jialin
    Ma, Jing
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsinghua University, People’s Republic of China.
    Dental ceramic prostheses by stereolithography-based additive manufacturing: potentials and challenges2019Inngår i: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 118, nr 1-2, s. 30-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current method for making dental ceramic prostheses in a subtractive manner causes a severe waste of materials while requires excessive manual works that bring in the uncertainty for control of quality. The rapid development and commercialisation of additive manufacturing (AM) has aroused interest and wonders both in material and dental communities about their potentials and challenges in fabricating of ceramic prostheses in a materials-saving manner. In this work, AM approach was applied to fabricate the dental bridges and implants made of zirconia. The achieved geometries and dimensional accuracy are used to demonstrate the potential of this technique in fabricating of dental ceramic prostheses, whereas the observed macro and micro defects formed during the treatment process is used to reveal the challenges facing in order to adapt this technology into real dental practice. Suggestions are provided for future development of the technology, particularly on minimising the processing defects.

  • 69. Li, Hezhen
    et al.
    Song, Lu
    Sun, Jialin
    Ma, Jing
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Stereolithography-fabricated zirconia dental prostheses: concerns based on clinical requirements2020Inngår i: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With the recent rapid development of the additive manufacturing family of technologies, the interest in application potential of stereolithography on producing ceramic dental prostheses has aroused and been widely discussed. While someone claimed the birth of 'stereolithography-fabricated ceramic dental prostheses', an overall evaluation based on the clinical requirements is lacking, making the optimism a kind of unrealistic. In this article, the prototypes of ceramic dental prostheses and standard specimens produced by the ceramic stereolithography approach are compared with those made by the classic subtractive manufacturing method by following the critical clinical requirements. Concerns on the upcoming challenges and future improvement towards clinical applications are presented that include productivity, delivery time, dimensional tolerance, mechanical and aesthetic properties. It is concluded that it is far too early to call 'stereolithography-fabricated ceramic dental prostheses' as a success as usable and competitive products for clinical applications.

  • 70. Li, Kailun
    et al.
    Wang, Dianzheng
    Xing, Leilei
    Wang, Yafei
    Yu, Chenfan
    Chen, Jinhan
    Zhang, Tao
    Ma, Jing
    Liu, Wei
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsinghua University, China.
    Crack suppression in additively manufactured tungsten by introducing secondary-phase nanoparticles into the matrix2019Inngår i: International journal of refractory metals and hard materials, ISSN 0263-4368, Vol. 79, s. 158-163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, an effective strategy was developed to suppress cracking by introducing secondary-phase ZrC nanoparticles into a tungsten (W) matrix. Pure W and W-0.5wt%ZrC bulks were additively manufactured via the laser powder bed fusion (LPBF) technique, and their cracking behaviour was compared. It was observed that the crack density of W-ZrC was reduced by 88.7% compared with that of pure W. The grains in W-ZrC were obviously refined compared with the grains in pure W, which significantly increased the cracking resistance. In addition, ZrC diminished the oxygen impurities, further increasing the cracking resistance. This study provides a promising strategy for the additive manufacturing of high-quality W by introducing secondary-phase nanoparticles into the metal matrix.

  • 71. Li, Ming
    et al.
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Nygren, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Origin(s) of the apparent high permittivity in CaCu3Ti4O12 ceramics: Clarification on the contributions from internal barrier layer capacitor and sample-electrode contact effects2009Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 10, s. 104106/1-104106/8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CaCu3Ti4O12 ceramics with a range of resistivities have been prepared using both conventional sintering and spark plasma sintering. For all cases, the high effective permittivity is associated primarily with an internal barrier layer capacitor mechanism. Additional polarization associated with the electrode-sample interface may appear but its visibility depends on the grain boundary resistivity (Rgb) of the ceramic. If the Rgb is large, the electrode polarization is obscured by sample-related effects; if the Rgb is small, a separate impedance associated with the electrode polarization may be seen. Discrepancies in the literature regarding the magnitude and origin of the high effective permittivity are attributed to a combination of differences in processing conditions, electrode contact material and measuring frequency range

  • 72. Li, Wenjie
    et al.
    Li, Duan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Gao, Xin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Gurlo, Aleksander
    Zander, Stefan
    Jones, Philip
    Navrotsky, Alexandra
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Riedel, Ralf
    Ionescu, Emanuel
    A study on the thermal conversion of scheelite-type ABO(4) into perovskite-type AB(O,N)(3)2015Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, nr 17, s. 8238-8246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phase-pure scheelite AMoO(4) and AWO(4) (A = Ba, Sr, Ca) were thermally treated under an ammonia atmosphere at 400 to 900 degrees C. SrMoO4 and SrWO4 were shown to convert into cubic perovskite SrMoO2N and SrWO1.5N1.5, at 700 degrees C and 900 degrees C respectively, and to form metastable intermediate phases (scheelite SrMoO4-xNx and SrWO4-xNx), as revealed by X-ray diffraction (XRD), elemental analysis and FTIR spectroscopy. High-temperature oxide melt solution calorimetry reveals that the enthalpy of formation for SrM(O,N)(3) (M = Mo, W) perovskites is less negative than that of the corresponding scheelite oxides, though the conversion of the scheelite oxides into perovskite oxynitrides is thermodynamically favorable at moderate temperatures. The reaction of BaMO4 with ammonia leads to the formation of rhombohedral Ba3M2(O,N)(8) and the corresponding binary metal nitrides Mo3N2 and W4.6N4; similar behavior was observed for CaMO4, which converted upon ammonolysis into individual oxides and nitrides. Thus, BaMO4 and CaMO4 were shown to not provide access to perovskite oxynitrides. The influence of the starting scheelite oxide precursor, the structure distortion and the degree of covalency of the B-site-N bond are discussed within the context of the formability of perovskite oxynitrides.

  • 73. Li, Wenjie
    et al.
    Li, Duan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Gurlo, Aleksander
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Riedel, Ralf
    Ionescu, Emanuel
    Synthesis and rapid sintering of dense SrA(O,N)(3) (A = Mo, W) oxynitride ceramics2015Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 35, nr 12, s. 3273-3281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    SrMo(O,N)(3) and SrW(O,N)(3) oxynitride powders were synthesized via a solvothermal route followed by ammonolysis. Their rapid densification by spark plasma sintering with a heating rate of 300-400 degrees C/min under a uniaxial pressure of 100 MPa yielded dense monoliths. The lowest open porosity achieved was 0 vol% for SrMo(O,N)(3) and 7.6 vol% for SrW(O,N)(3). The compacted monoliths were characterized by elemental analysis, electron microscopy (SEM, TEM) coupled with energy dispersive X-ray spectroscopy (EDX), as well as X-ray diffraction (XRD). Rietveld refinement of the XRD patterns revealed in the case of the compacted SrMo(O,N)(3) the formation of small amount of ternary oxides (Sr3Mo2O7/SrMoO4/Sr3MoO6), molybdenum nitride (MO2N), as well as metallic Mo. On the contrary, SrW(O,N)(3) exhibited significant decomposition after consolidation, with SrWO4/Sr3WO6 being main components beside SrMo(O,N)(3), accompanied by tungsten nitride (WN) and metallic W. Thus, rapid SPS enables the densification of oxynitrides with high density and acceptable purity that were hardly achieved earlier.

  • 74. Lilja, Mirjam
    et al.
    Butt, Umer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Sandvik Coromant Sverige AB.
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Bjöörn, Dorota
    Nucleation and growth of hydroxyapatite on arc-deposited TiO2 surfaces studied by quartz crystal microbalance with dissipation2013Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 284, s. 1-6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding of nucleation and growth kinetics of biomimetically deposited hydroxyapatite (HA) on crystalline TiO2 surfaces is important with respect to the application and performance of HA as functional implant coatings. Arc-evaporation was used to deposit TiO2 coatings dominated by anatase phase, rutile phase or their mixtures. Subsequent formation of HA from phosphate buffered saline solution (PBS) was investigated in real-time using in situ quartz crystal microbalance with dissipation technique (QCM-D). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to characterize the presence, morphology and crystal structure of TiO2 coatings and the formed HA. Increasing temperature of the PBS, increasing flow rate and applying a higher ion concentration in solution were found to accelerate HA nucleation process and hence affect growth kinetics. Lower PBS temperature resulted in the formation of HA coatings with flake-like morphology and increasing HA porosity. All TiO2 coatings under study enabled HA formation at body temperature, while in contrast Ti reference surfaces only supported HA nucleation and growth at elevated temperatures. QCM-D technique is a powerful tool for studying the impact of process parameters during biomimetic coating deposition on coating structure evolution in real time and provides valuable information for understanding, optimizing as well as tailoring the biomimetic HA growth processes.

  • 75.
    Lin, C.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Xiao, Changhong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Shen, Zhijian James
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Nano Pores Evolution in Hydroxyapatite Microsphere during Spark Plasma Sintering2011Inngår i: Science of Sintering, ISSN 0350-820X, Vol. 43, nr 1, s. 39-46Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 76. Lin, Yuan-Hua
    et al.
    Lan, Jinle
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    High-temperature electrical transport behaviors in textured Ca3Co4O9-based polycrystalline ceramics2009Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 7, s. 072107/1-072107/3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Highly (00l) oriented Ca3Co4O9-based ceramics were fabricated by spark plasma sintering combined with a dynamic forging process. The grain orientation is effective in lowering the electrical resistivity and enhancing the thermoelectric power factor but with little influence on the Seebeck coefficient. A metallic-to-semiconducting transition temperature can be observed and the activation energy is almost independent of the La-doping. All of the Ca3Co4O9-based ceramic samples exhibit large thermoelectric power, and the figure of merit for La-doped Ca3Co4O9 sample can reach 0.26 at 975 K, which can be a promising candidate of p-type material for high-temperature thermoelectric application

  • 77. Lin, Yuan-Hua
    et al.
    Liu, Yong
    Zhang, Bo-Ping
    Nan, Ce-Wen
    Li, Jing-Feng
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för oorganisk kemi.
    Electrical transport properties of La2CuO4 ceramics processed by the spark plasma sintering2007Inngår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 90, nr 12, s. 4005-4008Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Highly dense La2CuO4 ceramics have been prepared by the spark plasma sintering technique. Temperature dependence of electrical conductivity indicates that La2CuO4 ceramics sintered at over 875 degrees C exhibit a metal-like behavior, which should be ascribed to the special La2CuO4 crystal structure and its correlation splitting of the half-filled d(x2-y2) band. Our experimental data indicate that all of the La2CuO4 samples exhibit positive thermoelectric power in the whole measuring temperature range, indicating that the majority of charge carriers are holes. It is desirable to obtain good thermoelectric performance for this system by optimizing the electrical properties and reducing the thermal conductivity.

  • 78. Liu, Chong
    et al.
    Xiang, Mingyu
    Fu, Zhengyi
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Xiong, Yan
    Microstructural refinement in spark plasma sintering 3Y-TZP nanoceramics2016Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 36, nr 10, s. 2565-2571Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A commercial 3Y-TZP nanopowder was consolidated by spark plasma sintering (SPS) techniques. By special die-upset designs, each possible influence from the electric field, uniaxial pressure and heating rate was peeled to identify its contribution. Besides density and grain growth, the evolution of pore structure was consulted to clarify the relationships between microstructural development and densification kinetics. The results showed that neither electric current nor fast heating had no decisive contributions while external force was a necessity for the microstructural refinement. The authors proposed that the essentially underlying mechanism was the intensive particle rearrangement, which involves no grain growth but particle close-packing through grain rotation and sliding. The full advantages of this mechanism can be taken in rapid heating conditions, which combined with the application of higher pressures, make the SPS family of techniques to have advancement in the preparations of nanoceramics over their conventional counterparts characterized by slow heating features.

  • 79.
    Liu, Jing
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för oorganisk kemi.
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för oorganisk kemi.
    Yan, Haixue
    Reece, Michael J.
    Kan, Yanmei
    Wang, Peiling
    Dielectric, piezoelectric, and ferroelectric properties of grain-orientated Bi3.25La0.75Ti3O12 ceramics2007Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, nr 10, s. 104107-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By dynamic forging during Spark Plasma Sintering (SPS), grain-orientated ferroelectric Bi3.25La0.75Ti3O12 (BLT) ceramics were prepared. Their ferroelectric, piezoelectric, and dielectric properties are anisotropic. The textured ceramics parallel and perpendicular to the shear flow directions have similar thermal depoling behaviors. The d(33) piezoelectric coefficient of BLT ceramics gradually reduces up to 350 degrees C; it then drops rapidly. The broadness of the dielectric constant and loss peaks and the existence of d(33) above the permittivity peak, T-m, show that the BLT ceramic has relaxor-like behavior.

  • 80.
    Liu, Jing
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Yao, Wenlong
    Zhao, Yonghao
    Mukherjee, Amiya K
    Visible and infrared transparency in lead-free bulk BaTiO3 and SrTiO3 nanoceramics2010Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, nr 7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multifunctional transparent ferroelectric ceramics have widespread applications in electro-optical devices. Unfortunately, almost all currently used electro-optical ceramics contain a high lead concentration. In this work, via coupling of spark plasma sintering with high pressure, we have successfully synthesized bulk lead-free transparent nanostructured BaTiO3 (abbreviated as BTO) and SrTiO3 (STO) ceramics with excellent optical transparency in both visible and infrared wavelength ranges. This success highlights potential ingenious avenues to search for lead-free electro-optical ceramics.

     

  • 81. Liu, Jingyin
    et al.
    Han, Guang
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Pan, Shaoxia
    Ge, Yanjun
    Feng, Hailan
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Biomineralization stimulated peri-titanium implants prepared by selective laser melting2015Inngår i: Journal of Materiomics, ISSN 2352-8478, Vol. 1, nr 3, s. 253-261Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Titanium implants prepared by selective laser melting (SLM), a method of additive manufacturing, were subjected to implantation in beagle dogs for two and four weeks. Argon ion beam-polished cross sections of the implants after in vivo tests were characterized by scanning electron microscope (SEM) to evaluate the bone–implant interface and the early peri-implant biomineralization with sufficiently improved resolution. Two bone mineralization mechanisms were disclosed. As early as two weeks after implantation, a layer of new bone was found to form directly on the implant surface and bone in-growth was also observed. Osseointegration was found to establish partly at the tip of the implants. After healing for four weeks it was found that osseointegration was established around the entire tip of the implants, whereas only partly at the third thread region of the implants. The experimental evidences observed reveal that an inherent highly porous surface of the titanium implants generated by selective laser melting is favorable for new bone apposition.

  • 82.
    Liu, Leifeng
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Ding, Qingqing
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zou, Ji
    Wu, Jing
    Chiu, Yu-Lung
    Li, Jixue
    Zhang, Ze
    Yu, Qian
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Dislocation network in additive manufactured steel breaks strength-ductility trade-off2018Inngår i: Materials Today, ISSN 1369-7021, E-ISSN 1873-4103, Vol. 21, nr 4, s. 354-361Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most mechanisms used for strengthening crystalline materials, e.g. introducing crystalline interfaces, lead to the reduction of ductility. An additive manufacturing process - selective laser melting breaks this trade-off by introducing dislocation network, which produces a stainless steel with both significantly enhanced strength and ductility. Systematic electron microscopy characterization reveals that the pre-existing dislocation network, which maintains its configuration during the entire plastic deformation, is an ideal modulator that is able to slow down but not entirely block the dislocation motion. It also promotes the formation of a high density of nano-twins during plastic deformation. This finding paves the way for developing high performance metals by tailoring the microstructure through additive manufacturing processes.

  • 83.
    Liu, Leifeng
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). University of Birmingham, UK; South University of Science and Technology of China, China.
    Eriksson, Mirva
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zou, Ji
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Qi
    Liu, Zhi
    Chiu, Yu-Lung
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Self-supported yttria-stabilized zirconia mesocrystals with tunable mesopores prepared by a chemi-thermal process2019Inngår i: Journal of Materiomics, ISSN 2352-8478, Vol. 5, nr 3, s. 350-356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mesoporous mesocrystals are highly desired in catalysis, energy storage, medical and many other applications, but most of synthesis strategies involve the usage of costly chemicals and complicated synthesis routes, which impede the commercialization of such materials. During the sintering of dense ceramics, coarsening is an undesirable phenomenon which causes the growth of the grains as well as the pores hence hinders the densification, however, coarsening is desired in the sintering of porous ceramics to expand the pore sizes while retaining the total pore volume. Here we report a chemi-thermal process, during which nanocrystallite aggregates were synthesized by hydrothermal process and then converted to the product by sintering. Through this strategy, we synthesized mesoporous self-supported mesocrystals of yttria-stabilized zirconia with tunable pore size and the process was then scaled-up to industrial production. The thermal conductivity measurement shows that the mesoporous powder is a good thermal isolator. The monolith pellets can be obtained by SPS sintering under high pressure and the mesoporosity is retained in the monolith pellets. This work features facile and scalable process as well as low cost raw chemicals making it highly desirable in industrial applications.

  • 84. Liu, Xihe
    et al.
    Zhao, Congcong
    Zhou, Xin
    Eibl, Florian
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsinghua University, People’s Republic of China.
    Liu, Wei
    Meiners, Wilhelm
    CNT-reinforced AlSi10Mg composite by selective laser melting: microstructural and mechanical properties2019Inngår i: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 35, nr 9, s. 1038-1045Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon nanotube (CNT)-AlSi10Mg composites were fabricated by selective laser melting (SLM). The influence of CNTs on the density, microstructure, and strength of SLM CNT-AlSi10Mg composites was investigated. The addition of CNTs over 0.1 wt-% significantly damaged the density due to the high surface energy of the CNTs. The network Si eutectic had no significant difference in either the SLM AlSi10Mg alloy or the CNT-AlSi10Mg composite. Reserved CNTs with a short scale were observed in the SLM CNT(0.5 wt-%)-AlSi10Mg composite. The ultimate tensile strength of the 0.05 wt-% CNT-AlSi10Mg composite was 441.2 +/- 0.9 MPa, which was higher than that of AlSi10Mg alloy. The grain boundary strengthening played an important role in the reinforcement of CNT-AlSi10Mg composite because of the refined grain.

  • 85. Liu, Xihe
    et al.
    Zhao, Congcong
    Zhou, Xin
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsinghua University, China.
    Liu, Wei
    Microstructure of selective laser melted AlSi10Mg alloy2019Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 168, artikkel-id 107677Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of laser power during selective laser melting (SLM) on the grain morphology and texture component in AlSi10Mg alloy has been investigated, using electron backscattered diffraction (EBSD). Both equiaxed and columnar grainswere observed. The formation of equiaxed grainswas attributed to the huge thermal gradient on the border of melt pool and the columnar to equiaxed transition (CET) occurred in front of the columnar grains. The grain size of lowlaser power samplewas found smaller than that of higher ones. A fine pseudoeutectic structure, in which Si existed as fibrous, was observed because of the high cooling rate. This paper, from a new angle, explained the formations of three different zones across the melt pool, which were differentiated by the morphology of Si phase. The three zones correspond to the three temperature zones, whichwere divided by liquidus and solidus temperature, during the heating by laser beam. The coarse zones are formed by reheating the basic metal to semi-solid state when the temperature is lower than the liquidus temperature but higher than the solidus temperature.

  • 86. Liu, Xihe
    et al.
    Zhou, Xin
    Xu, Ben
    Ma, Jing
    Zhao, Congcong
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsinghua University, China.
    Liu, Wei
    Morphological Development of Sub-Grain Cellular/Bands Microstructures in Selective Laser Melting2019Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, nr 8, artikkel-id 1204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, single-layer and bulk 316 L selective laser melting (SLM) experiments were conducted, fine submicron-scale geometric symmetrical cellular (hexagonal, pentagonal and square), elongated cellular and bands solidification morphologies were found in the laser-melt top surface. Meanwhile, morphological developed sub-grain patterns with quasi-hexagonal cellular, elongated cellular and bands structures (size similar to 1 m) coexisting inside one single macro-solidified grain were also identified. This demonstrated the transitions from quasi-hexagonal-cells to elongated cells/bands, and transitions reverse, occurred in the whole bulk under some circumstances during SLM. Based on the experimental realities, these morphologies are formed by the local convection and Benard instabilities in front of the solid/liquid interface (so-called mushy zones) affected by intricate temperature and surface tension gradients. Quasi-hexagonal cellular convective fields are then superimposed on macro-grain solidification to form the sub-grain patterns and micro-segregations. This explanation seems reasonable and is unifying as it can be expanded to other eutectic alloys with face center cubic (FCC) prevenient phase prepared by SLM, e.g., the Al-Si and Co-Cr-Mo systems.

  • 87. Liu, Yi
    et al.
    Eriksson, Mirva
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Jin, Zhihao
    Nygren, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Micro-hydrothermal reactions mediated grain growth during spark plasma sintering of a carbonate-containing hydroxyapatite nanopowder2014Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 34, nr 16, s. 4395-4401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A carbonate-containing hydroxyapatite nanopowder was consolidated by spark plasma sintering at the temperatures ranging from 650 to 1100 degrees C. It was found that the water released by dehydroxylation was trapped inside the nanopores in the densified HAp bodies over 900 degrees C. Based on the analysis by the X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscope, the water-nanopore system was evaluated and its effect on the grain growth was also investigated. It was revealed that the water existed inside the closed nanopores most probably resulted in the formation of local micro-hydrothermal environments inside bulk HAp ceramics during SPS. Therefore, the grain growth was enhanced by the local micro-hydrothermal reactions activated above 900 degrees C. In addition, abnormal grain growth was also observed when a higher temperature or higher heating rate was employed, which may be attributed to the local highly active hydrothermal reactions.

  • 88.
    Liu, Yi
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Dehydroxylation of hydroxyapatite in dense bulk ceramics sintered by spark plasma sintering2012Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, nr 11, s. 2691-2696Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dense transparent hydroxyapatite (HAp) nanoceramic samples were prepared by spark plasma sintering of a commercial available granulated nanopowder. This made it possible for investigating the dehydroxylation behaviours of HAp in fully dense bulks. Post-SPS thermal annealing was performed in a temperature interval of 800 to 1100 degrees C in air. The phase analysis and microstructural characterization revealed that the dehydroxylation in fully dense HAp was initiated above 900 degrees C and its kinetics seems to be determined by the water vapour diffusion. Accordingly, a gradient structure consisting of porous interiors and a peculiar surface topography reflecting the water vapour escaping patterns were observed in samples experienced severe dehydroxylation.

  • 89.
    Liu, Yi
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shi, Zhongqi
    Wang, Jiping
    Qiao, Guanjun
    Jin, Zhihao
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Reactive consolidation of layered-ternary Ti(2)AlN ceramics by spark plasma sintering of a Ti/AlN powder mixture2011Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 31, nr 5, s. 863-868Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A reactive consolidation process for preparing ternary Ti(2)AlN ceramics was investigated by spark plasma sintering (SPS). A Ti/AlN powder mixture with a molar ratio of 2:1 was consolidated at temperatures ranging from 800 to 1450 degrees C. The phase composition and microstructure evolution during the process were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with an energy dispersive spectroscopy (EDS). A series of intermediate phases, namely TiN, Ti(3)Al, Ti(3)AlN and TiAl were indentified, which revealed a reaction pathway towards the formation of Ti(2)AlN.

  • 90. Liu, Yihong
    et al.
    Liu, Guanghua
    Wang, Yong
    Shen, James Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Feng, Hailan
    Failure Modes and Fracture Origins of Porcelain Veneers on Bilayer Dental Crowns2014Inngår i: International Journal of Prosthodontics, ISSN 0893-2174, E-ISSN 1139-9791, Vol. 27, nr 2, s. 147-150Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aims of this study were to determine the fracture origins and crack paths in the porcelain of clinically failed bilayer ceramic restorations and to reveal the correlation between the porcelain failures and material properties. Three clinically failed crowns of each material (bilayer zirconia crowns, galvano-ceramic crowns, and porcelain-fused-to-metal crowns) were collected and underwent failure analysis. The fractures found in porcelain veneers showed several characteristics including wear, Hertzian cone crack, chipping off, and delamination. The results indicated that the fracture origins and features of the porcelain in bilayer ceramic restorations might be affected by the rigidity of core materials and thickness of copings.

  • 91. Liu, Yihong
    et al.
    Wang, Yong
    Wang, Dianzheng
    Ma, Jing
    Liu, Leifeng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Self-glazed zirconia reducing the wear to tooth enamel2016Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 36, nr 12, s. 2889-2894Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The wear behaviors of a newly developed grade of self-glazed zirconia against the enamel of freshly extracted teeth were investigated under simulated oral stresses and chemical environment. It was revealed that an inherently formed enamel-like surface on self-glazed zirconia that is very smooth on micrometer scale yet with nanoscale roughness has almost the same frictional coefficient against tooth enamel as the well-polished zirconia surface. The wear scars observed on the worn surface of enamel against self-glazed zirconia and well-polished zirconia surface revealed that in both cases fatigue wear is the dominating wear mechanism. It was concluded that the friction and wear performances of both the well-polished and self-glazed zirconia ceramics against natural enamel were very similar, which bears a very strong implication for the clinical safe use of the full contour zirconia restorations, yet the self-glazed zirconia provides sufficiently improved aesthetic appearance that ensures its potential for direct clinical uses.

  • 92.
    Ma, Jing
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Zhang, Junzhan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Liu, Wei
    Shen, Zhijian James
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    Suppressing pore-boundary separation during spark plasma sintering of tungsten2013Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, nr 1-3, s. 199-203Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A tungsten powder with bimodal particle size distribution is consolidated by spark plasma sintering (SPS). Effects are made for understanding the densification and grain growth mechanisms and their relations to the SPS processing parameters. By holding the sample at an intermediate temperature, i.e., 1200 degrees C for 5 min, where the densification is enhanced by particle close packing, the pore-boundary separation that yields the formation of entrapped pores inside individual grains at final stage of sintering is suppressed. This optimization of the SPS process is beneficial for preparing fine grained bulk tungsten with homogeneous microstructure from the powders produced in industrial-scale. The prepared tungsten with minimized porosity appears a potential candidate for plasma-facing materials in the divertor region in the International Thermonuclear Experimental Reactor (ITER).

  • 93. Mayerhoefer, Thomas G.
    et al.
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för materialkemi.
    SUBLeonova, Ekaterina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för fysikalisk kemi.
    Eden, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för fysikalisk kemi.
    Kriltz, Antje
    Popp, Juergen
    Consolidated silica glass from nanoparticles2008Inngår i: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 181, nr 9, s. 2442-2447Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dense silica glass was prepared by consolidating a highly dispersed silicic acid powder (particle size < 10 nm) with the Spark Plasma Sintering (SPS) technique. The glass was characterized by ellipsometry, transmission electron microscopy (TEM), infrared reflectance and transmittance spectroscopy, as well as by Raman, UV-Vis-NIR and solid-state nuclear magnetic resonance (NMR) spectroscopy. The prototypic sample showed a transmittance of about 63% compared to silica glass in the UV-Vis spectral range. Based on the results of infrared transmittance spectroscopy this lower transparency is due to the comparably high water content, which is about 40 times higher than that in silica glass. H-1 magic-angle spinning (MAS) NMR confirmed an increase in hydroxyl groups in tie sample prepared by SPS relative to that of the conventional SiO2 reference glass. Aside from the comparably high water content, we conclude from the similarity of the IR-reflectance and the Si-29 MAS NMR spectra of the SPS sample and the corresponding spectra of the conventionally prepared silica glass, that the short- and medium-range order is virtually the same in both materials. Raman spectroscopy, however, Suggests that the number of three- and four-membered rings is significantly smaller in the SPS sample compared to the conventionally prepared sample. Based on these results we conclude that it is possible to prepare glasses by compacting amorphous powders by the SPS process. The SPS process may therefore enable the preparation of glasses with compositions inaccessible by conventional methods. 

  • 94. Mazaheri, Mehdi
    et al.
    Mari, Daniele
    Schaller, Robert
    Cai, Yanbing
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Esmaeilzadeh, Saeid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    High-Temperature Mechanical Spectroscopy of Nitrogen-Rich Ca-alpha-SiAlON Ceramics2011Inngår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, nr 5, s. 1536-1545Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nitrogen-rich Ca-alpha-SiAlON ceramics made with different starting powder compositions have been studied by high-temperature mechanical spectroscopy in parallel with compressive deformation in a spark plasma sintering equipment. The mechanical loss spectra measured upon heating show a relaxation peak at about 1150 K and a high-temperature exponential background at higher temperatures (> 1400 K), which are attributed to the alpha-relaxation in the glassy phase and to grain-boundary sliding, respectively. A theoretical interpretation of the results shows that the peak position is mainly a function of glass viscosity. The amplitude of the peak is not only affected by the glassy phase quantity but also depends on the restoring force due to grain elasticity. Therefore, despite a higher amount of glassy phase specimens containing elongated grains may show a lower peak. The amplitude of the internal friction peak corresponding to alpha-relaxation can be used to predict the compression creep of silicon-nitride-based ceramics.

  • 95. Mazo, G. N.
    et al.
    Kazakov, S. M.
    Kolchina, L. M.
    Istomin, S. Ya.
    Antipov, E. V.
    Lyskov, N. V.
    Galin, M. Z.
    Leonova, L. S.
    Fedotov, Yu. S.
    Bredikhin, S. I.
    Liu, Yi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Influence of structural arrangement of R2O2 slabs of layered cuprates on high-temperature properties important for application in IT-SOFC2014Inngår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 257, s. 67-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Layered cuprates Pr2 - xSrxCuO4-delta with T* (x = 0.3, 0.4) and T (x = 1.0, 13) structures were prepared in air at 1273-1373 K. Oxygen content (4 - delta) of the as-prepared phases decreases from 3.96 (x = 03) and 3.98 (x = 0.4) to 3.69 (x = 1.0) and 3.49 (x = 1.3), respectively, as determined by chemical titration. Dilatometry measurements revealed non-linear expansion with low- and high-temperature regions occurring due to thermogravimetrically detected oxygen loss. Different expansion behaviors in low- and high-temperature regions of T- and T*-phases are attributed to various distributions of oxygen vacancies in their crystal structures. Both x = 0.4 and 1.0 ceramic samples exhibit lower conductivity values at high temperatures in comparison with undoped Pr2CuO4. The temperature dependences of the electrical conductivity at variable oxygen partial pressure (Po-2 = 10(-4)-0.21 atm) reveal different mechanisms of the holes generation in x = 0.4 and 1.0 compounds. The tracer diffusion coefficient of oxygen (D-T) in Pr1.6Sr0.4CuO3.98 determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) is in the range 6.7 x 10(-10)-5.7 x 10(-8) cm(2)/s at 973-1223 K. Obtained values are in between those for La2CuO4 and Pr2CuO4 with pure rock-salt and fluorite slabs in the crystal structure, respectively. This shows the importance of rock-salt slabs for high oxygen conductivity in R2MO4 oxides.

  • 96. Nan, Beiya
    et al.
    Liu, Yongsheng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Northwestern Polytechnical University, P. R. China.
    You, Qiangwei
    Wan, Jiajia
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Li, Hongxia
    Yuan, Bo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Sinosteel Luoyang Institute of Refractories Research Co., Ltd, P. R. China.
    Cheng, Laifei
    Wang, Gang
    Microstructure and Properties of Porous SiC Ceramics Modified by CVI-SiC Nanowires2019Inngår i: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 21, nr 5, artikkel-id 1800653Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sintered porous SiC ceramics are modified with SiC nanowires prepared via chemical vapor infiltration (CVI). SiC nanowires are successfully grown within sintered porous SiC ceramics following vapor-liquid-solid growth. The diameter of the SiC nanowires is in the range of 200 nm-1 mu m, and first decreases with increasing input gas ratio (alpha = 50, 60, 70, and 80) and increases thereafter. The diameter of the nanowires decreases from the surface to the interior areas of the porous SiC ceramics. SiC nanowires effectively improve the mechanical properties of the porous SiC ceramics, and sample Ni-50 has the highest flexural strength of 33.91 MPa and fracture toughness of 0.79 MPa center dot m(1/2), which increases by 90.4% and 49.1% compared to an unmodified sample, respectively. Additionally, the presence of SiC nanowires leads to porous SiC ceramics with altered porosity and microstructure, and higher thermal conductivity. The porous SiC ceramics modified by CVI SiC nanowires satisfy the requirements of gas filtration applications and the pressure drop increases with decreasing apparent porosity. The porous SiC ceramics modified with CVI SiC nanowire has higher permeability than those resulting from the introduction of CVI-SiC matrix or CVD-SiC coating into porous SiC ceramics.

  • 97.
    Olsén, Jon
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    An investigation into the effect of Hot Isostatic pressing on parts manufactured with Selective Laser meltingManuskript (preprint) (Annet vitenskapelig)
  • 98.
    Olsén, Jon
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Leifeng
    Koptyug, Andrey
    Rannar, Lars-Erik
    Micro- and macro-structural heterogeneities in 316L stainless steel prepared by electron-beam melting2018Inngår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 141, s. 1-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This is a study of the micro- and macrostructural variations in samples of stainless steel with the overall composition of the grade 316L, produced using electron beam melting. Electron beam melting is one of the processing methods under consideration for manufacturing some of the International Thermo- Nuclear Experimental Reactor In-Vessel components. Therefore further studies of the homogeneity of the material were conducted. Electron beam melting results in a complicated thermal history of the manufactured part giving a significant impact on the microstructure. A cellular structure that is often observed in samples prepared by selective laser melting was found in the top layers of the specimens. Further down, the structure changed until the cellular structure was almost non-existing, and the grain boundaries had become more pronounced. This revelation of a heterogeneous structure throughout the entire part is crucial for large-scale industrial applications like the Thermo- Nuclear Experimental Reactor to make sure that it is understood that the properties of the material might not be the same at every point, as well as to assure that the correct post-treatment is done. It is also exposed that a significant part of this change is due to molybdenum redistribution inside the sample when it diffuses from the cell boundaries into the cells, and into bigger agglomerates in the grain boundaries. This diffusion seems not to affect the microhardness of the samples.

  • 99.
    Olsén, Jon
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Rännar, Lars-Erik
    Investigation of the heterogeneous structure and its effect on mechanical properties of electron beam melting fabricated 316L stainless steelManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    316L stainless steel samples were prepared with Electron Beam Melting. Samples were produced to investigate what parameters and conditions govern the microstructural evolution during the process, as well as the effect of the microstructural variations on the tensile strength. The effects investigated in this study are the cooling speed of the melt, the heatwaves moving through the sample due to additional layers being melted on top, and the constant base temperature of around 800 °C. Several different samples were prepared to simulate different conditions that occur during the manufacturing of real parts. The microstructures of these samples were investigated and characterized using scanning electron microscope. The investigation showed that all these effects had different effects on the microstructure. The tensile strength was homogeneous throughout the material, with little variance in the values. The ultimate tensile strength was recorded to 562±4 MPa, the yield strength to 261±3 MPa, and the Elongation to 67.5±4.8 %. Further investigation into why the change in microstructure has no impact on tensile strength was done using transmission electron microscopy. It was revealed that the material was missing the dislocation networks that are responsible for the increased strength observed in samples prepared by the selective laser melting process.

  • 100.
    Olsén, Jon
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Zhou, Xin
    Zhong, Yuan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsinghua University, China.
    Liu, Leifeng
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Wang, Dianzheng
    Yu, Chenfan
    Wang, Yafei
    Li, Kailun
    Xing, Leilei
    Ma, Jing
    Cui, Daqing
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Liu, Wei
    Shen, Zhijian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Tsinghua University, China.
    Tailoring hierarchical structures in selective laser melted materials2017Inngår i: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 219, artikkel-id 012036Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    With selective laser melting the potential to manufacture a wide variety of geometries from different materials has presented itself. Interest in this technology keeps growing every year, and with that growth a deeper understanding of the process and resulting materials is urgently needed. In this paper we present a short overview of the structural elements that appear during selective laser melting, and explain how to tailor them to achieve specific structures and material properties. Melt-pools, texture and grains, subgrain cells, and inclusions are the elements discussed herein, and tailoring of these elements can have effects on density, and corrosion resistance, as well as mechanical properties in general.

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