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  • 151. Xihe, Liu
    et al.
    Congcong, Zhao
    Xin, Zhou
    Wei, Liu
    Zhijian, Shen
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, People´s Republic of China.
    Eibl, Florian
    Meiners, Wilhelm
    Influence of Carbon Nanotubes on Defects in AlSi10Mg Alloy Fabricated by Selective Laser Melting2019In: Xiyou jinshu cailiao yu gongcheng, ISSN 1002-185X, Vol. 48, no 5, p. 1637-1644Article in journal (Refereed)
    Abstract [zh]

    Pure AlSi10Mg alloy and carbon nanotubes (CNTs)-AlSi10Mg composite with different CNTs additions were fabricated by selective laser melting (SLM). The CNTs-AlSi10Mg composite is strengthened when the CNTs content is lower than 0.05 wt%. With the increasing CNTs content, however, the strength is decreased significantly because of the poor density. In order to understand the influence of CNTs on the defects in SLMed AlSi10Mg alloy, nano-CT technology was used to get the 3D information of the defects. The results indicate that the volume fraction of large defects (with diameter larger than 50 mu m) in the total volume of defects is increased from 12% to 46% in CNTs(0.5wt%)-AlSi10Mg composite. The number of gas pores in CNTs(0.5wt%)-AlSi10Mg composite are significantly increased. The diameter of gas pores in CNTs(0.5wt%)-AlSi10Mg composite are larger than that in pure AlSi10Mg alloy. The agglomeration of CNTs in the powder and gas adsorption are the fundamental reasons for the increase of the two types of defects.

  • 152.
    Xiong, Yan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Hubei University of Technology, China.
    Fu, Zhengyi
    Pouchly, Vaclav
    Maca, Karel
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Preparation of Transparent 3Y-TZP Nanoceramics with No Low-Temperature Degradation2014In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 97, no 5, p. 1402-1406Article in journal (Refereed)
    Abstract [en]

    The progresses of the relative density, average grain size (GS), and maximum pore size entering into the final sintering stage are investigated in 3mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) compacts in the range of 87%similar to 99% theoretical density. It is found that during conventional pressureless sintering, the pores in the compact enlarged dramatically, which appears to be the major obstacle for preparing fully dense nanoceramics. Transparent 3Y-TZP nanoceramics with an average GS of 87nm were prepared by exploiting microstructural refinement on nanoscale. The yields a maximal optical transmittance of 67% and shows no noticeable low-temperature degradation after 100h aging at 134 degrees C under a hydrothermal pressure of two bars.

  • 153.
    Xiong, Yan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hu, Jianfeng
    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).
    Dynamic Pore Coalescence in Nanoceramic Consolidated by Two-Step Sintering Procedure2013In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 33, no 11, p. 2087-2092Article in journal (Refereed)
    Abstract [en]

    Two-step sintering (TSS) concept was adopted in the consolidation of 3 mol% yttria doped zirconia nanopowder. Partially densified bodies with 87% theoretical density (TD) were firstly prepared using high-pressure spark plasma sintering (SPS) technique and followed by second-step pressureless sintering. The samples achieved only 96% TD final density after 30 h soaking. It was found that the densification process was impeded by dynamic pore coalescence with a pore growth factor of 10. The phenomenon was explained by the coalescence of interconnected small pores generated by differential sintering of nanoceramic green compacts. Such pore coalescence was accompanied with particle movement, which resulted in sintering state deviating from the frozen state. Present results indicated that the active range for particle rearrangement was greatly extended during nanoceramic sintering and the efficiency of TSS approach was greatly dependent on the homogeneity of green bodies

  • 154.
    Xiong, Yan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hu, Jianfeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Pouchly, Vaclav
    Maca, Karel
    Preparation of Transparent Nanoceramics by Suppressing Pore Coalescence2011In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, no 12, p. 4269-4273Article in journal (Refereed)
    Abstract [en]

    Microstructural developments in nanoceramics were investigated in 3Y-TZP compacts with relative density (RD) exceeding 93%. Special attentions were paid to the evolutions of pore structures. It was found that the densification process of nanoceramic compacts with apparently close porosity was greatly jeopardized by pore coalescence. This observation was interpreted by the coalescence of locally interconnected pores originated from inhomogeneous packing of particles. The pore coalescence can be suppressed by application of an external pressure. The processing principle was demonstrated by spark plasma sintering (SPS) with extended holding at a minimized sintering temperature. The highly dense 3Y-TZP nanoceramics containing no large pores became optically transparent.

  • 155. Yang, X.
    et al.
    Li, Duan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ren, Z. H.
    Zeng, R. G.
    Gong, S. Y.
    Zhou, D. K.
    Tian, H.
    Li, J. X.
    Xu, G.
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Han, G. R.
    Colossal dielectric performance of pure barium titanate ceramics consolidated by spark plasma sintering2016In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, no 79, p. 75422-75429Article in journal (Refereed)
    Abstract [en]

    A facile sol-gel-hydrothermal method was developed to prepare well-dispersed BaTiO3 (BT) nanocrystals with a size of about 20 nm. By using such nanopowder, dense BT nanoceramics were densified via spark plasma sintering (SPS). Dielectric measurements reveal that pure BT nanoceramics have an extremely high permittivity up to 6 x 10(4) and a low dielectric loss. On the basis of microstructure characterization and dielectric measurement, it was proposed that the polaron dipoles configured by oxygen vacancies and Ti3+ cations within the grains could contribute to the colossal dielectric permittivity of the ceramics. By using the thermally activated polaron hopping model, a large activation energy EA has been determined (0.135 eV) below the Curie temperature, possibly due to the coupling of polaron dipoles and intrinsic ferroelectric dipoles. This simple method offers the possibility to produce pure BT nanoceramics with a colossal permittivity.

  • 156. Yoon, Songhak
    et al.
    Dornseiffer, Juergen
    Xiong, Yan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gruener, Daniel
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Iwaya, Shoichi
    Pithan, Christian
    Waser, Rainer
    Spark plasma sintering of nanocrystalline BaTiO(3)-powders: Consolidation behavior and dielectric characteristics2011In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 31, no 9, p. 1723-1731Article in journal (Refereed)
    Abstract [en]

    BaTiO(3) nanopowders prepared by two different wet chemical routes, one based on microemulsion-mediated synthesis (M-BT) and the other one on the alkoxide-hydroxide method (A-BT) were consolidated by spark plasma sintering (SPS). The densification process, the linear shrinkage rates and the relative densities achieved were strongly dependant on the synthetic route. The results show that fully densified BaTiO(3) ceramics with a grain size of about 200 nm can be obtained in both cases by controlling the sintering temperature during the SPS process. The study of dielectric properties revealed that M-BT derived ceramics show higher permittivity values compared to those obtained for A-BT. The influence of the barium/titanium ratio on the sintering behavior and the dielectric properties is discussed.

  • 157. Yoon, Songhak
    et al.
    Dornseiffer, Juergen
    Xiong, Yan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grüner, Daniel
    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).
    Iwaya, Shoichi
    Pithan, Christian
    Waser, Rainer
    Synthesis, spark plasma sintering and electrical conduction mechanism in BaTiO(3)-Cu composites2011In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 31, no 5, p. 773-782Article in journal (Refereed)
    Abstract [en]

    BaTiO(3)-Cu composite powders were prepared via an alkoxide-mediated synthesis approach. As-synthesized BaTiO(3) nanoparticles were as small as 40 nm and coated partially larger Cu particles of approximately 1 mu m in size. Thermogravimetric analysis (TGA) and dilatometry revealed a gradual increase in weight loss and retarded shrinkage with the increase of Cu addition. BaTiO(3)-Cu composites were successfully densified by spark plasma sintering (SPS). The microstructures show an average grain-size for BaTiO(3) of around 100 nm and a crystallite size of about 1 mu m for the Cu inclusions. The AC conductivity of the BaTiO(3)-Cu composites increased with increasing Cu content or with temperature. The dominant electrical conduction mechanism in SPSed BaTiO(3)-Cu composites changed from migration of oxygen vacancies to band conduction of trapped electrons in oxygen vacancies with the increase of Cu content.

  • 158. Yoon, Songhak
    et al.
    Pithan, Christian
    Waser, Rainer
    Dornseiffer, Juergen
    Xiong, Yan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gruner, Daniel
    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).
    Iwaya, Shoichi
    Electronic Conduction Mechanisms in BaTiO3-Ni Composites with Ultrafine Microstructure Obtained by Spark Plasma Sintering2010In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 93, no 12, p. 4075-4080Article in journal (Refereed)
    Abstract [en]

    Spark plasma sintering (SPS) was used to densify BaTiO3-Ni composite powders to relative densities above 92.8%. With the increasing Ni content, a decrease in relative density is observed, suggesting that Ni hampers the consolidation process. The microstructures of the BaTiO3-Ni composites were of duplex character. The crystallite size of the BaTiO3-grains was around 100 nm in average. The ceramic matrix phase of BaTiO3 surrounded Ni inclusions of approximately 1 mu m in diameter that were completely incorporated without the formation of any elongated metallic filaments. The ac conductivity of these BaTiO3-Ni composites increased with increasing Ni content and with temperature. The dominant conduction mechanisms in SPSed BaTiO3-Ni composites showed quite a complicated behavior. A gradual change from band conduction of trapped electrons in oxygen vacancies to a hopping-type motion of small polarons between Ti4+ and Ti3+ is suggested to occur, when the Ni content increases. The influence of oxygen vacancies and other lattice defects on the electrical properties of BaTiO3-Ni composites is discussed.

  • 159. You, Qiangwei
    et al.
    Liu, Yongsheng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Polytechnical University, Xi’an, Shanxi, PR China.
    Wan, Jiajia
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Li, Hongxia
    Yuan, Bo
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Sinosteel Luoyang Institute of Refractories Research Co., Ltd, PR China.
    Cheng, Laifei
    Wang, Gang
    Microstructure and properties of porous SiC ceramics by LPCVI technique regulation2017In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 43, no 15, p. 11855-11863Article in journal (Refereed)
    Abstract [en]

    A new gradient pore structure in porous SiC ceramics was fabricated by low pressure chemical vapor infiltration (LPCVI). Effects of deposition duration on the mechanical properties and permeability of porous SiC ceramics were investigated. Results demonstrated that pore diameter and shapes decreased from the surface to the interior along with LPCVI duration. Porous SiC ceramics with deposition duration of 160 h exhibited flexural strength of 48.05 MPa and fracture toughness of 1.30 MPa m(1/2), where 221% and 189% improvements were obtained compared to porous SiC ceramics without LPCVI, due to CVI-SiC layer strengthening effect. Additionally, at the same gas velocity, pressure drop increase rate was faster due to apparent porosity and pore size change.

  • 160. Yuan, Bo
    et al.
    Li, Hong-Xia
    Wang, Gang
    Yu, Jian-Bin
    Ma, Wei-Kui
    Liu, Lei-Feng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Yong-Sheng
    Shen, Zhi-Jian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Preparation and properties of porous silicon carbide based ceramic filter2016In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 684, p. 613-615Article in journal (Refereed)
    Abstract [en]

    Porous silicon carbide ceramics with high open porosity and large pore size are usually applied as filters for the cleaning of hot dust gases. However, the large porosity and large pore size will decrease the mechanical properties. In the present study, porous SiC ceramics were prepared using bentonite as bonding phase. The effects of sintering temperature on the microstructure and the compressive strength were studied. Bentonite could melt and spread on the surface of silicon carbide particles at all the sintering temperatures. However, the bonding effects were very different at different temperatures.

  • 161. Yuan, Bo
    et al.
    Wang, Gang
    Li, Hongxia
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Yongsheng
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fabrication and microstructure of porous SiC ceramics with Al2O3 and CeO2 as sintering additives2016In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 42, no 11, p. 12613-12616Article in journal (Refereed)
    Abstract [en]

    In the present study, porous silicon carbide ceramics were prepared via spark plasma sintering at relatively low temperatures using Al2O3 and CeO2 as sintering additives. Sacrificial template was selected as the pore forming mechanism, and gelcasting was used to fix the slurry in a short time. The evolution process of the microstructures during different steps was observed by SEM. The influence of the sintering temperature and sintering additives on the shrinkage and porosity of the samples was studied. The microstructures of different samples were characterized, and the mechanical properties were also evaluated.

  • 162. Yuan, Jia
    et al.
    Li, Duan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johanns, Kurt E.
    Fasel, Claudia
    Durst, Karsten
    Kleebe, Hans-Joachim
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Riedel, Ralf
    Ionescu, Emanuel
    Preparation of dense SiHf(B)CN-based ceramic nanocomposites via rapid spark plasma sintering2017In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 37, no 16, p. 5157-5165Article in journal (Refereed)
    Abstract [en]

    Dense SiHf(B)CN-based ceramic nanocomposites were prepared by spark plasma sintering (SPS) using high heating rates (similar to 450 degrees C/min.) and high pressures (>= 100 MPa). The obtained nanocomposites were investigated by X-ray diffraction, Raman spectroscopy and electron microscopy concerning their phase evolution and microstructure. The hardness and the elastic modulus of dense SiHfCN were found to be 26.8 and 367 GPa, respectively. Whereas the SiHfBCN samples exhibited a hardness of 24.6 GPa and an elastic modulus of 284 GPa. The investigation of the oxidation of the prepared dense ceramic nanocomposites at high temperature revealed that the parabolic oxidation rates of SiHfCN were comparable to those of ultra-high temperature ceramics (UHTCs, e.g. HfC-20 vol% SiC); whereas the parabolic oxidation rates of SiHfBCN were several orders of magnitude lower than those. The results obtained within this study indicate the feasibility of SPS for rapid preparation of dense though nano-scaled Hf-containing ceramic nanocomposites that are promising candidates for high-temperature applications in harsh environments.

  • 163. Yuan, Y.
    et al.
    Greuner, H.
    Boeswirth, B.
    Linsmeier, Ch.
    Luo, G. -N
    Fu, B. Q.
    Xu, H. Y.
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Liu, W.
    Surface modification of molten W exposed to high heat flux helium neutral beams2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 437, no 1-3, p. 297-302Article in journal (Refereed)
    Abstract [en]

    High heat flux tests with central heat flux of 10.5 MW/m(2) using helium neutral beams have been carried out on rolled tungsten. The energy of helium particles is 33 keV and the particle flux is 2 x 10(21) m(-2) s(-1). An 80 x 65 x 3 mm(3) rolled tungsten plate is firstly exposed to a 4.6 s pulse resulting in partially molten surfaces. Thereafter the tungsten plate is irradiated by several helium pulses with fluences of 1.2-2.5 x 10(22)/m(2) and peak temperatures from 1450 to 2590 degrees C. The experiments show that: (1) helium-induced surface modification of the resolidified tungsten surface is very different from that of the non-molten surface; (2) the surface morphology of molten surface is closely related to the orientation of the resolidified grain; (3) the evolution of surface modifications, for both of the molten and non-molten tungsten surfaces, indicates a strong dependence on the surface temperature and local helium fluence.

  • 164. Zhang, Hongtao
    et al.
    Yan, Haixue
    Eriksson, Mirva
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    The grain size effect on the properties of Aurivillius phase Bi3.15Nd0.85Ti3O12 ferroelectric ceramics2009In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 20, no 38, p. 385708/1-385708/5Article in journal (Refereed)
  • 165. Zhang, Ranran
    et al.
    Elkhooly, Tarek A.
    Huang, Qianli
    Liu, Xujie
    Yang, Xing
    Yan, Hao
    Xiong, Zhiyuan
    Ma, Jing
    Feng, Qingling
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    A dual-layer macro/mesoporous structured TiO2 surface improves the initial adhesion of osteoblast-like cells2017In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 78, p. 443-451Article in journal (Refereed)
    Abstract [en]

    A dual-layer TiO2 surface with hierarchical macro and mesoporous structure was prepared by a combinational approach of micro-arc oxidation followed by evaporation-induced self-assembly of nano-crystallites. The mesoporous layer contains pores with an average size of <10 nm and consists of anatase TiO2 nanocrystallites. The dual-layer hierarchical macro/mesoporous structured TiO2 surface improves the hydrophilicity and fibronectin adsorption ability in comparison with the sole macroporous or smooth TiO2 surface. With the formation of an additional mesoporous layer on macroporous TiO2 surface, the attached number of human osteogenic sarcoma cells (SaOS-2) increases in the initial incubation of 4 h but it does not show significant difference after 24 h compared to that attached on the macroporous or smooth surfaces. Whereas, it was noticed that SaOS-2 cells have larger spread area and more stress fibers on the macro/mesoporous structured surface than those on the other surfaces. To understand the intracellular mechanism of the initial cell adhesion on the macro/mesoporous surface, the Rho/ROCK pathway was investigated to reveal the topography-induced biological functions by introducing the ROCK inhibitor Y-27632 during cell culture. In the presence of Y-27632, cells on the macroporous surface and macro/mesoporous surface both show stellate appearance, with poor assembly stress fibers and long cell membrane protrusions. Cells on the smooth surface have larger spread areas compared to the former two surfaces. And the attached cells significantly reduced but there are no differences among the three surfaces. It reveals that the ROCK inhibitor invalidates the promotion of initial cell adhesion on the macro/mesoporous structure. This study may shed light on the mechanism behind the enhancement effect of macro/mesoporous structure for initial cell adhesion.

  • 166. Zhang, Ranran
    et al.
    Elkhooly, Tarek A.
    Huang, Qianli
    Liu, Xujie
    Yang, Xing
    Yan, Hao
    Xiong, Zhiyuan
    Ma, Jing
    Feng, Qingling
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Effects of the hierarchical macro/mesoporous structure on the osteoblast-like cell response2018In: Journal of Biomedical Materials Research. Part A, ISSN 1549-3296, E-ISSN 1552-4965, Vol. 106, no 7, p. 1896-1902Article in journal (Refereed)
    Abstract [en]

    To improve the success of medical devices, implants with strong surface bioactivity are urgently required. Coatings with a macroporous structure produced by micro-arc oxidation possess advantages, such as strong adhesion to substrate and excellent resistance to wear and corrosion. Mesoporous structures contain pores with sizes of 2-50 nm, which can endow the biomaterials with the ability to enhance osteogenesis and to be loaded with diverse drugs. Thus, in this study, we aimed to evaluate the effects of both macroporous and mesoporous structures using a hierarchical macro/mesoporous structure to modify the titanium implant surface. The behaviors of SaOS-2 human osteosarcoma cells on the macro/mesoporous structure, including initial adhesion, proliferation, alkaline phosphatase (ALP) activity, and collagen secretion, were investigated. Cells that attached on the macro/mesoporous surface showed the highest cell numbers and greatest spreading area after incubation for 1, 2, and 4 h compared with the polished smooth substrate and macroporous surface in the presence of fetal bovine serum (FBS). However, in the absence of FBS, cell adhesion on the polished substrate, macroporous structure, and macro/mesoporous structure did not differ significantly. Cell proliferation on the macroporous and macro/mesoporous surfaces increased compared with that on the smooth substrate surface. Furthermore, ALP activity and collagen secretion were enhanced on the macro/mesoporous structure. Our findings provided important insights into the cellular responses to macro/mesoporous structures in the field of implant surface modification.

  • 167. Zhang, Ranran
    et al.
    Huang, Qianli
    Liu, Xujie
    Yang, Xing
    Yan, Hao
    Xiong, Zhiyuan
    Xu, Nan
    Ma, Jing
    Feng, Qingling
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    ZnO nanostructures enhance the osteogenic capacity of SaOS-2 cells on acid-etched pure Ti2018In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 215, p. 173-175Article in journal (Refereed)
    Abstract [en]

    Zinc oxide (ZnO) has attracted a great deal of interest due to its electronic and optical properties, and has potential applications in biomedical field, while few studies have been conducted to investigate its biocompatibility. In this study, we prepared nanostructured ZnO on acid-etched pure Ti surface through a moderate hydrothermal treatment in ammonia solution (pH = 12.6). By changing Zn precursor concentration and hydrothermal duration, it was feasible to synthesis flake-like ZnO nanostructures with variable spacings. The adhesion, proliferation and alkaline phosphatase (ALP) activity of SaOS-2 cells were enhanced on the ZnO nanostructures when the Zn precursor concentration was 0.02 M and the hydrothermal duration was 4 h, compared to those on the acid-etched pure Ti without ZnO nanostructures. Narrower spacings (< 70 nm) between ZnO nanostructures are considered to contribute to this enhancement. Together, the results indicate that the superposition of ZnO nanostructures on titanium surfaces may be beneficial for the enhanced biological performance.

  • 168. Zhang, Ranran
    et al.
    Liu, Xujie
    Xiong, Zhiyuan
    Huang, Qianli
    Yang, Xing
    Yan, Hao
    Ma, Jing
    Feng, Qingling
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Novel micro/nanostructured TiO2/ZnO coating with antibacterial capacity and cytocompatibility2018In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, no 8, p. 9711-9719Article in journal (Refereed)
    Abstract [en]

    Insufficient osseointegration between implants and bone, and peri-implant infection are the two most common factors contributing to implantation failure. As such, implant materials should ideally be designed with antibacterial capacity while maintaining cytocompatibility. Combining Zn, a known antibacterial agent, with micro/nanostructures on the implant surface to promote osseointegration, potentially reduces peri-implant infection. To this end, in the present study, we developed novel bifunctional micro/nanostructured titanium oxide/zinc oxide (TiO2/ZnO) coating by micro-arc oxidation (MAO) followed by hydrothermal treatment. The release rate of the Zn2+ ions was reduced by heat treatment which established a balance between antibacterial capacity and cytocompatibility. The results demonstrate a simple approach for developing a Zn-based material that balances antibacterial capacity and cytocompatibility as a promising coating material for Ti implants.

  • 169. Zhang, Ranran
    et al.
    Liu, Xujie
    Xiong, Zhiyuan
    Huang, Qianli
    Yang, Xing
    Yan, Hao
    Ma, Jing
    Feng, Qingling
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, Beijing, China.
    The immunomodulatory effects of Zn-incorporated micro/nanostructured coating in inducing osteogenesis2018In: Artificial cells nanomedicine and biotechnology, ISSN 2169-1401, Vol. 46, p. S1123-S1130Article in journal (Refereed)
    Abstract [en]

    Micro/nanostructured TiO2/ZnO coating has been shown to possess multiple functions, including antibacterial activity and bioactivity. Osteoblast-like SaOS-2 cells were employed for evaluating the in vitro osteogenic capacity of this coating and positive results were obtained. However, traditional principles of osseointegration focus only on the osteogenic differentiation alone. The effects of immunomodulation on the osteogenic activity have been largely ignored. In this study, the inflammatory responses of macrophages on the micro/nanostructured TiO2/ZnO coating were investigated. The extract media of macrophage cell line RAW264.7 cultured on the TiO2/ZnO coating were collected as indirect co-culture conditioned media. The osteogenic activity of SaOS-2 cells in the conditioned media was investigated. Adhesion, ALP activity and extracellular mineralization of cells grown in the conditioned media extracted from the micro/nanostructured TiO2/ZnO coating were found to be enhanced, compared to those grown in the conditioned media extracted from the macroporous TiO2 coating. The immune microenvironment produced by the micro/nanostructured TiO2/ZnO coating showed excellent capacity to promote osteogenesis, indicating that this coating could be a promising candidate for implant surface modification in orthopaedic and dental applications. Furthermore, this work could help us understand the interplay between the host immune system and the osteoimmunomodulatory properties of the biomaterials, and optimize the design for coating biomaterials.

  • 170. Zhang, Ranran
    et al.
    Xu, Nan
    Liu, Xujie
    Yan, Hao
    Ma, Jing
    Feng, Qingling
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, People’s Republic of China.
    Dose-dependent enhancement of bioactivity by surface ZnO nanostructures on acid-etched pure titanium2019In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 118, no 3, p. 121-125Article in journal (Refereed)
    Abstract [en]

    Zinc (Zn) is found to be essential in biologic osseous functions, and deficiency of Zn may cause delayed skeletal growth and osteoporosis. Additionally, Zn-based coatings are reported to be effective to promote the bioactivity of implants. In this study, we employed the hydrothermal treatment to incorporate Zn into the surface of acid-etched pure Ti. The process was conducted in ammonia solution with an increased Zn precursor concentration (0.0002M, 0.002M and 0.02M, respectively). XPS analysis demonstrated that the nanostructures were composed of ZnO. Proliferation and alkaline phosphatase (ALP) activity of osteoblast-like SaOS-2 cells were enhanced dose-dependently, compared to those on the acid-etched pure Ti without ZnO nanostructures. This study addresses a favourable surface modification method to improve the bioactivity of implants.

  • 171. Zhang, Ranran
    et al.
    Xu, Nan
    Liu, Xujie
    Yang, Xing
    Yan, Hao
    Ma, Jing
    Feng, Qingling
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Micro/nanostructured TiO2/ZnO coating enhances osteogenic activity of SaOS-2 cells2019In: Artificial cells nanomedicine and biotechnology, ISSN 2169-1401, Vol. 47, no 1, p. 2838-2845Article in journal (Refereed)
    Abstract [en]

    Although titanium implants account for a large proportion of the commercial dental market, their bioactivity are inadequate in many applications. A micro- and nano- scale hierarchical surface topography of the implant is suggested for rapid osseointegration from the biomimetic perspective. Moreover, Zinc (Zn) is an essential element in the skeletal system. Thus, a micro/nanostructured TiO2/ZnO coating, produced by micro-arc oxidation, and hydrothermal treatment, and heat treatment, was designed to endow the implant surface with enhanced osteogenic capacity. Physiochemical properties and biological effects of this coating were investigated in our study. The annealed micro/nanostructured TiO2/ZnO coating exhibited higher hydrophilicity and fibronectin adsorption ability compared to the micro-arc oxidation modified TiO2 coating. SaOS-2 cells grown on the annealed micro/nanostructured TiO2/ZnO coating showed increased alkaline phosphatase activity and collagen secretion, and immunofluorescence labeling revealed an upregulation of osteopontin, collagen type iota and osteocalcin. The micro/nanostructure and incorporation of Zn were considered to perform positive effect on the enhanced osteogenic activity of SaOS-2 cells. In conclusion, the micro/nanostructured TiO2/ZnO structure is simple, stable, and easy to produce and scale up, has promising applications in the surface modification of titanium implants.

  • 172. Zhang, Xin
    et al.
    Yu, Xiangwen
    Zhou, Beiying
    Luo, Wei
    Jiang, Wan
    Jiang, Weihui
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wang, Lianjun
    Sinterability Enhancement by Collapse of Mesoporous Structure of SBA-15 in Fabrication of Highly Transparent Silica Glass2015In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 98, no 4, p. 1056-1059Article in journal (Refereed)
    Abstract [en]

    Highly transparent silica glass was prepared from mesoporous silica SBA-15 powders at low temperature using Spark Plasma Sintering. It was found that the combined effect of pressure and temperature resulted in collapse of porous structure of SBA-15 and transformation to transparent glass. A sinterability enhancement mechanism involving generation of incremental surface area from pore collapse during sintering process was proposed to interpret the fully densification at low temperature.

  • 173. Zhang, Youdong
    et al.
    Han, Jian-min
    Zheng, Gang
    Lin, Hong
    Bai, Wei
    Zhao, Jing
    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).
    Fatigue behaviours of the zirconia dental restorations prepared by two manufacturing methods2017In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 116, no 7, p. 368-375Article in journal (Refereed)
    Abstract [en]

    The fatigue behaviours were evaluated on a novel zirconia dental restoration known as self-glazed zirconia (SG), prepared by a precision additive 3D gel deposition approach, compared with a conventional zirconia (CZ) restoration, shaped by CNC milling of zirconia blanks made by cold isostatic pressing. Eight fixed partial dentures made by each method were subjected to fracture test, without or with the application of 5-million fatigue cycles, respectively. The processing defects, grain size, and t-m phase transformation were examined by SEM and XRD. The results revealed that the fracture force of the SG restorations was higher than that of the CZ restorations in both cases, which ascribed to the fact that more voids and larger grains in the conventional versus in the SG restorations. The t-m phase transformation was observed only on the fracture surfaces of both materials subjected to fatigue test. Both zirconia restorations meet the clinical requirement.

  • 174.
    Zhao, Jing
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Peking University, PR China.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsing Hua University, PR China.
    Si, Wenjie
    Wang, Xinzhi
    Bi-colored zirconia as dental restoration ceramics2013In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, no 8, p. 9277-9283Article in journal (Refereed)
    Abstract [en]

    Machinable zirconia blocks with gradient colors are fundamental for fabrication of full-contour esthetic dental restorations. The aim of this study was to process and evaluate bi-colored zirconia ceramics as a pilot dental material by using well-established techniques. Two commercially available partially stabilized zirconia granules, one undoped and one doped with 0.202 wt% Fe2O3, resulted in white and yellow colors after sintering, respectively. Bi-colored zirconia was fabricated by two-step dry pressing of both zirconia granules one above the other to form green bodies, followed by cold isostatic pressing (CIP) and, a two-step pressureless sintering finally at 1450 degrees C. The dilatometer results showed that the Fe2O3 doped zirconia sintered slightly rapid, but the difference of shrinkage between two powders was <1%. Sintered bars achieved full density, 6.018 g/cm(3) (similar to 99%TD), without cracks in the similar to 1 mm color gradient zone. The microstructures were characterized by scanning electron microscopy (SEM) and careful observation of both surface and interior provided no obvious structural difference of either grains or pores among the three distinct regions, comprising white, yellow and color gradient zone. Vickers hardness of hi-colored zirconia was similar to 13.1 GPa, with no obvious difference in the three regions. The four-point bending strength of the hi-colored zirconia bars was 745.5 +/- 159.6 MPa, which appeared noticeably lower than that of the single-colored references being above 1000 MPa. Fractographic analysis revealed that in most of the cases (60%) the fracture was initiated at the color gradient zone, where large voids with high coordination numbers, agglomerates with critical size and concentration of irregular grains with porous surfaces were observed. Above all, bi-colored zirconia ceramics prepared by the improved technique could meet the basic requirements of dental materials. The ways of minimizing the defects within hi-colored blocks should be developed for the production of esthetic zirconia ceramics of high strength and reliability.

  • 175.
    Zhao, Jing
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Peking University School and Hospital of Stomatology, PR China.
    Wang, Xinzhi
    Si, Wenjie
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, PR China.
    Effect of resin cement selection on the microtensile bond strength of adhesively veneered 3Y-TZP2013In: Acta Odontologica Scandinavica, ISSN 0001-6357, E-ISSN 1502-3850, Vol. 71, no 5, p. 1105-1111Article in journal (Refereed)
    Abstract [en]

    Objective. The aim of this study was to investigate the effect of resin cement selection on the microtensile bond strength (mu TBS) of adhesively veneered 3Y-TZP. Materials and methods. 3Y-TZP discs were fabricated from commercial powders and treated by sandblasting and zirconia primer. Porcelain discs were sectioned from a feldspathic block and conditioned with 5% HF and silane agent. Pre-treated surfaces of zirconia and porcelain discs were bonded together using one of the three following resin cements: Multilink N (MN), Panavia F (PA) or RelyX Unicem (RU), respectively. After light-curing the joined discs were cut into microbars where 15 microbars per group were randomly chosen for mu TBS test until failure occurred (24 h storage in water in advance, crosshead speed of 0.5 mm/min). The data were analysed by one-way ANOVA and Tukey's test (p < 0.05). Fractured zirconia surfaces were examined using both a stereomicroscope and scanning electron microscope to identify the failure mode. Results. Significant differences in the mu TBS values among three groups were found (p < 0.001) and the descending order was PA, RU and MN. No zirconia or feldspathic failure occurred, but the zirconia/cement interfaces suffered from fracture for all samples. Cement cohesive failure and/or feldspathic/cement interfacial failure sometimes were involved. Failures were mainly adhesive for RU, while they were mixed for MN and PA. Conclusion. When using the adhesive veneering method, Panavia F offers better bond strength than Multilink N or RelyX Unicem, which is probably due to the content of the 10-methacryloyloxydecyl dihydrogenphosphate (10-MDP) monomer.

  • 176.
    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).
    Wikman, Stefan
    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).
    Intragranular cellular segregation network structure strengthening 316L stainless steel prepared by selective laser melting2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 470, p. 170-178Article in journal (Refereed)
    Abstract [en]

    A feasibility study was performed to fabricate ITER In-Vessel components by Selective Laser Melting (SLM) supported by Fusion for Energy (F4E). Almost fully dense 316L stainless steel (SS316L) components were prepared from gas-atomized powder and with optimized SLM processing parameters. Tensile tests and Charpy-V tests were carried out at 22 degrees C and 250 degrees C and the results showed that SLM SS316L fulfill the RCC-MR code. Microstructure characterization reveals the presence of hierarchical macro-, micro- and nano-structures in as-built samples that were very different from SS316L microstructures prepared by other established methods. The formation of a characteristic intragranular cellular segregation network microstructure appears to contribute to the increase of yield strength without losing ductility. Silicon oxide nano-inclusions were formed during the SLM process that generated a micro-hardness fluctuation in the building direction. The combined influence of a cellular microstructure and the nano-inclusions constraints the size of ductile dimples to nano-scale. The crack propagation is hindered by a pinning effect that improves the defect-tolerance of the SLM SS316L. This work proves that it was possible to manufacture SS316L with properties suitable for ITER First Wall panels. Further studies on irradiation properties of SLM SS316L and manufacturing of larger real-size components are needed.

  • 177.
    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
    Kvetkova, Lenka
    Lofaj, Frantisk
    Wang, Dianzheng
    Olsén, Jon
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cui, Daqing
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Manipulating the sub-grain cellular network structure during selective laser meltingManuscript (preprint) (Other academic)
  • 178.
    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)
  • 179.
    Zhong, Yuan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rännar, Lars-Erik
    Liu, Leifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Koptyug, Andrey
    Wikman, Stefan
    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).
    Additive manufacturing of 316L stainless steel by electron beam melting for nuclear fusion applications2017In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 486, p. 234-245Article in journal (Refereed)
    Abstract [en]

    A feasibility study was performed to fabricate ITER In-Vessel components by one of the metal additivemanufacturing methods, Electron Beam Melting®(EBM®). Solid specimens of SS316L with 99.8% relativedensity were prepared from gas atomized precursor powder granules. After the EBM®process the phaseremains as austenite and the composition has practically not been changed. The RCC-MR code used fornuclear pressure vessels provides guidelines for this study and tensile tests and Charpy-V tests werecarried out at 22C (RT) and 250C (ET). This work provides thefirst set of mechanical and micro-structure data of EBM®SS316L for nuclear fusion applications. The mechanical testing shows that theyield strength, ductility and toughness are well above the acceptance criteria and only the ultimatetensile strength of EBM®SS316L is below the RCC-MR code. Microstructure characterizations reveal thepresence of hierarchical structures consisting of solidified melt pools, columnar grains and irregularshaped sub-grains. Lots of precipitates enriched in Cr and Mo are observed at columnar grain boundarieswhile no sign of element segregation is shown at the sub-grain boundaries. Such a unique microstructureforms during a non-equilibrium process, comprising rapid solidification and a gradient‘annealing’process due to anisotropic thermalflow of accumulated heat inside the powder granule matrix. Relationsbetween process parameters, specimen geometry (total building time) and sub-grain structure are dis-cussed. Defects are formed mainly due to the large layer thickness (100mmÞwhich generates insufficientbonding between a few of the adjacently formed melt pools during the process. Further studies shouldfocus on adjusting layer thickness to improve the strength of EBM®SS316L and optimizing total buildingtime.

  • 180.
    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.

  • 181. Zhou, Xin
    et al.
    Li, Kailun
    Zhang, Dandan
    Liu, Xihe
    Ma, Jing
    Liu, Wei
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Textures formed in a CoCrMo alloy by selective laser melting2015In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 631, p. 153-164Article in journal (Refereed)
    Abstract [en]

    Unique crystal textures formed by selective laser melting of a CoCrMo alloy were characterized by electron backscattered diffraction. Preferred crystallographic orientations were found for individual grains in the solid alloy microstructure. Along the building or radial grain growth direction in the rapidly cooling melt pool the formed columnar grains were not purely < 001 > or < 111 >, as reported before, but a concurrence of < 001 > and < 011 >. Along the scanning direction, a (011) < 100 > texture was limited to the outmost surface whereas in the solid bulk the preferred orientation was a < 001 > fiber texture.

  • 182. Zhou, Xin
    et al.
    Liu, Xihe
    Zhang, Dandan
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, People's Republic of China.
    Liu, Wei
    Balling phenomena in selective laser melted tungsten2015In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 222, p. 33-42Article in journal (Refereed)
    Abstract [en]

    Selective laser melting (SLM) of pure tungsten was carried out and the relevant consolidation issues were investigated. It was observed that balling of melted droplets at the laser focal points and entrapped cavities hindered the preparation of fully dense parts. An analysis of the balling mechanism reveals that SLM of tungsten is a process where melt spreading and solidification compete with each other and the final result is determined by intrinsic tungsten properties and the set laser processing parameters. Melted tungsten droplets wetted its own solid substrate at a low speed driven by capillary force, but solidified simultaneous at a high speed driven by the existing steep temperature gradient. Melted droplets solidified before spreading completely and kept their globular geometry instead of creating a flat layer. Tungsten bodies reaching a density of 14.8-15.2 g/cm(3) were prepared with an open irregular porosity and surface roughness. With a second laser scanning the balling W droplets were remelted at the building surface resulting in a much smoother appearance with less porosity and indicated a way to further improve relative density, near 16 g/cm(3) (82.9% theoretical density). Oxidation must be avoided, as any oxide contamination enriched preferably around the melt pool edge, changing the surface tension gradient and the thermocapillary convection thereby increasing balling.

  • 183. Zhou, Xin
    et al.
    Wang, Dianzheng
    Liu, Xihe
    Zhang, DanDan
    Qu, Shilian
    Ma, Jing
    London, Gary
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Liu, Wei
    3D-imaging of selective laser melting defects in a Co-Cr-Mo alloy by synchrotron radiation micro-CT2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 98, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Microstructure defects set the mechanical property limits for solid Co-Cr-Mo alloy prepared by selective laser melting (SLM). Previous studies were mainly based on 2D SEM images and thus not able to provide information of the 3D morphologies of the complex defects. In this paper, the remaining porosities in Co-Cr-Mo alloy parts prepared by selective laser melting were presented in relation to the laser processing parameters. In order to understand the defect forming mechanism, accurate 3D images of defects inside SLM fabricated Co-Cr-Mo samples were provided by synchrotron radiation micro-CT imaging of 300 pm thick slices cut from a 10 mm cube. With 3D reconstructed images distinctive morphologies of SLM defects spanning across the consolidated powder layers were generated. The faults can be classified as single layer or multi-layers defects. The accidental single layer defects form as gaps between adjacent laser melt tracks or melt track discontinuousness caused by inherent fluid instability under various disturbances. The first formed single layer defect generates often a multi-layer defect spanning for 2-3 subsequent powder layers. By stabilizing the melt pool flow and by reducing the surface roughness through adjusting processing parameters it appears possible to reduce the defect concentrations.

  • 184.
    Zou, Ji
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Chinese Academy of Sciences, Shanghai.
    Liu, Jingjing
    Zhang, Guo-Jun
    Huang, Shuigen
    Vleugels, Jef
    Van der Biest, Omer
    Shen, Zhijian James
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hexagonal BN-encapsulated ZrB2 particle by nitride boronizing2014In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 72, p. 167-177Article in journal (Refereed)
    Abstract [en]

    A facile method based on an in situ reaction, called nitride boronizing, was first developed to directly coat ZrB2 particles with a nano-scale hexagonal boron nitride (h-BN) film. The crystallinity of the BN coating and the diameters of the ZrB2 particles could be tailored by changing the reaction conditions. A mechanism was proposed from thermodynamic calculations to clarify the formation of a core-shell nanostructure, i.e. the shock heat generated by the exothermal reaction. The core-shell ZrB2 powders showed excellent sinterability and the advantage in producing dense h-BN texture-free composites. Even when sintered at 2000 degrees C for 20 min and under a uniaxial pressure of 60 MPa, no texture created by h-BN was observed. The isotropic bending strength (similar to 300 MPa) of ZrB2-37 vol.% BN ceramics from core-shell precursor powders were investigated and compared with ceramics of the same nominal composition, but densified from commercial powders containing highly aligned h-BN grains. The nitride boronizing approach could be explored to synthesize other h-BN-coated IVB group transition metal borides.

  • 185.
    Zou, Ji
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Shanghai Institute of Ceramics, China; KU Leuven, Belgium.
    Liu, Jingjing
    Zhao, Jian
    Zhang, Guo-Jun
    Huang, Shuigen
    Qian, Bin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vleugels, Jef
    Van der Biest, Omer
    Shen, James Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A top-down approach to densify ZrB2-SiC-BN composites with deeper homogeneity and improved reliability2014In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 249, p. 93-101Article in journal (Refereed)
    Abstract [en]

    A novel top down approach was developed to fabricate dense ZrB2-SiC-BN (ZSN) composites with a fine-grained (<1 mu m) microstructure using coarse-grained (similar to 10 mu m) ZrN and Si precursors that reacted with fine (similar to 0.5 mu m) B4C powders at 1850 degrees C. The results show that the reaction and densification mechanisms acting during sintering could be separated or happen simultaneously by changing the pressure loading strategy. Loading cycles not only have a substantial influence on the microstructure homogeneity and the strength reliability of as sintered composites, but might alter the electric current path during the Spark Plasma Sintering process as well. A residual compressive stress of 361 MPa, generated upon the SiC grains in the ZSN composites, was measured by Raman spectroscopy. The fine SiC grains tended to form larger clusters in the dense microstructure if the loading cycle is inappropriate, which was further employed to interpret the observed scattering of strength values in one batch of ZSN. The 48ZrB(2)-24SiC-28BN (number in vol%) composite has an average strength of 473 MPa, which was 94% of that of in situ densified ZrB2-SiC ceramics (ZS). Considering the corresponding Youngs modulus was only half of that for ZS, the in situ ZSN composite owns a better mechanical strain tolerance.

  • 186. Zou, Ji
    et al.
    Zhang, Guo-Jun
    Shen, Zhi-Jian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Tsinghua University, China.
    Binner, Jon
    Ultra-low temperature reactive spark plasma sintering of ZrB2-hBN ceramics2016In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 36, no 15, p. 3637-3645Article in journal (Refereed)
    Abstract [en]

    Starting from ZrN and amorphous boron, dense ZrB2 ceramics with 37 vol% hexagonal BN were consolidated by spark plasma sintering. Benefiting from the moderate exothermic reaction between ZrN and B and the resultant fine powder generated, ZrB2-BN ceramics with relative density of 94% could be reached at 1100 degrees C, further improved to 97% by 1550 degrees C. The effects of sintering temperature and holding time on the densification behavior, microstructural evolution and mechanical properties of ZrB2-BN ceramics were investigated. ZrB2-37 vol%BN ceramics densified at 1700 degrees C exhibited attractive mechanical performance: a three-point bending strength of 353 MPa, a Vicker's hardness of 6.7 GPa and a Young's modulus of 197.5 GPa. Note that its strength dropped sharply to 191 MPa measured at 1300 degrees C. The combination of low sintering temperature (1100-1550 degrees C), low Young's modulus (180-200 GPa) and relatively high strength (200-350 MPa) make reactively sintered ZrB2-BN composites as promising matrix for continuous fiber reinforced composites.

  • 187.
    Zou, Ji
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhong, Yuan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eriksson, Mirva
    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).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tougher zirconia nanoceramics with less yttria2019In: Advances in Applied Ceramics: Structural, Functional and Bioceramics, ISSN 1743-6753, E-ISSN 1743-6761, Vol. 118, no 1-2, p. 9-15Article in journal (Refereed)
    Abstract [en]

    Reducing the grain size in zirconia ceramics has shown to decrease its toughness by size-dependent stabilisation of the tetragonal phase that, in turn, hinders the stress-induced phase transformation from tetragonal to monoclinic. The stability of the tetragonal phase increases with the decrease of grain size but decreases with the reduction of the amount of yttria added, implying the need for adjustment of the yttria content when a nano-grained structure is of concern. In this study, low-yttria compositions were investigated. The ceramics were prepared with two sintering methods namely spark plasma sintering (SPS) and pressureless sintering. A clear tendency was noted for the indentation toughness increase with the reduction of yttria content, and a higher toughness achieved in as-SPSed samples in comparison with the annealed samples. The origins of the increased toughness were discussed in terms of yttria content, carbon contamination and increased oxygen vacancies after sintering at reducing atmosphere in SPS.

  • 188.
    Zou, Ji
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhong, Yuan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhang, Jun-Zhan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Xi'an University of Architecture & Technology, China.
    Ekelund, Magnus
    Shen, Zhi-Jian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Separating macrostresses from microstresses in Al2O3-15 vol%SiC particulate reinforced composites2015In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 109, p. 84-88Article in journal (Refereed)
    Abstract [en]

    Macrostresses and microstresses coexist in ceramics, but are difficult to distinguish. In this work, these two types of residual stresses were separated by comparing the stress levels on the mechanically and argon beam polished surfaces of Al2O3-15 vol%SiC particulate reinforced composites. Stresses were measured using the shift of a Raman peak of beta-sic, the shift of a luminescence line of alpha-Al2O3 and a self-consistent approach. The critical grain size of SiC, over which will result in the crack formation in Al2O3 matrix, was calculated to be 13.5-26.4 mu m. New microcracldng did not form in Al2O3 grains during progressive mechanical polishing.

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