The Experts below are selected from a list of 26826 Experts worldwide ranked by ideXlab platform
Byungnam Kim - One of the best experts on this subject based on the ideXlab platform.
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high optical quality non cubic yb3 doped ca10 po4 6f2 yb fap laser ceramics
Optical Materials Express, 2021Co-Authors: Hiroaki Furuse, Naohiro Horiuchi, Koji Morita, Taiga Okabe, Homare Shirato, Daichi Kato, Byungnam KimAbstract:We fabricated an advanced transparent Yb-doped hexagonal fluorapatite ceramic with an average grain size of only 90 nm; we also demonstrated its laser oscillation. To the best of our knowledge, this is the smallest grain size for laser ceramics. The in-line transmittance was 86.1% at 1 µm for 0.79-mm-thick ceramics (corresponding to a loss coefficient of 0.45 cm-1). Although the ceramic crystal grains were randomly oriented, scattering at the grain boundary was suppressed because the grains were considerably smaller than the wavelength. This novel ceramic possesses both a Fine Microstructure and densification and is expected to be the foundation of many non-cubic laser ceramics.
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transparent non cubic laser ceramics with Fine Microstructure
Scientific Reports, 2019Co-Authors: Hiroaki Furuse, Naohiro Horiuchi, Byungnam KimAbstract:Transparent polycrystalline ceramics with cubic crystal structure have played important roles in a wide variety of solid-state laser applications, whereas for non-cubic structures, single crystal only has been used. For further progress in optical technologies, effective materials beyond the current limitations are necessary. Here we report a new type of non-cubic ceramic laser material that overturns conventional common sense. It is hexagonal Nd-doped fluorapatite (Nd:FAP) ceramics with an optical quality comparable to single crystal while having random crystal orientation. It is composed of ultraFine grains with a loss coefficient of 0.18 cm−1 at a lasing wavelength of 1063 nm, and its laser oscillation was demonstrated. This is the first verification of lasing in randomly oriented non-cubic ceramics. Laser oscillation in the non-cubic ceramics was realized through both advanced liquid-phase nano-powder synthesis technology and highly controlled pulsed-current sintering techniques. Our findings should open new avenues for future solid-state laser and optical applications.
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effects of heating rate on Microstructure and transparency of spark plasma sintered alumina
Journal of The European Ceramic Society, 2009Co-Authors: Byungnam Kim, Keijiro Hiraga, Koji Morita, Hidehiro YoshidaAbstract:Abstract Commercial alumina powder was densified by spark plasma sintering (SPS) at 1150 °C. During SPS processing, the effects of the heating rate were examined on Microstructure and transparency. With decreasing heating rate, the grain size and the residual porosity decreased, while the transparency increased. At a heating rate of 2 °C/min, the grain size was 0.29 μm, and the in-line transmission was 46% for a wavelength of 640 nm. The mechanisms for the Fine Microstructure and low porosity at slow heating, which are conflicting with some existing results, were explained by considering the role of defect concentration and grain-boundary diffusion during densification.
L Y Sheng - One of the best experts on this subject based on the ideXlab platform.
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investigation on nial tic al2o3 composite prepared by self propagation high temperature synthesis with hot extrusion
Composites Part B-engineering, 2013Co-Authors: L Y Sheng, F Yang, J T GuoAbstract:The NiAl-TiC-Al2O3 in situ composite was fabricated by self-propagation high temperature synthesis and hot extrusion (SHS/HE) technique using element powders. Its Microstructure and mechanical properties were investigated by OM, SEM, TEM and compression test. The results revealed that the NiAl-TiC-Al2O3 composite was densified by the SHS/HE process and had Fine Microstructure. In the composite, TiC particles along NiAl grain boundary agglomerated and grew, but the TiC particles in NiAl grain were Fine. The TiC and Al2O3 particles exhibited an obvious trend to distribute along extrusion direction. Moreover, stacking fault and microtwins in TiC particles and thin amorphous layer along NiAl/TiC phase interface were also observed. In addition, Ti2AlC particle with intergrowth TiC plate inside formed along the NiAl grain boundary. Generally the SHS/HE synthesized NiAl-TiC-Al2O3 composite possessed better mechanical properties, especially at room temperature, which should be ascribed to the Fine Microstructure and predeformation caused by hot extrusion. (c) 2012 Elsevier Ltd. All rights reserved.
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effect of extrusion process on Microstructure and mechanical properties of ni3al b cr alloy during self propagation high temperature synthesis
Transactions of Nonferrous Metals Society of China, 2012Co-Authors: L Y Sheng, X I Tingfei, Chen Lai, Jianting Guo, Yufeng ZhengAbstract:The well-densified Ni3Al-0.5B-5Cr alloy was fabricated by self-propagation high-temperature synthesis and extrusion technique. Microstructure examination shows that the synthesized alloy has Fine Microstructure and contains Ni3Al, Al2O3, Ni3B and Cr3Ni2 phases. Moreover, the self-propagation high-temperature synthesis and extrusion lead to great deformation and recrystallization in the alloy, which helps to reFine the Microstructure and weaken the misorientation. In addition, the subsequent extrusion procedure redistributes the Al2O3 particles and eliminates the γ-Ni phase. Compared with the alloy synthesized without extrusion, the Ni3Al-0.5B-5Cr alloy fabricated by self-propagation high-temperature synthesis and extrusion has better room temperature mechanical properties, which should be ascribed to the Microstructure evolution.
Artem Arlazarov - One of the best experts on this subject based on the ideXlab platform.
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mechanism of ultra Fine Microstructure formation during art annealing of a medium mn steel
PTM 2015 - International conference on solid-solid phase transformations in inorganic materials, 2015Co-Authors: Artem Arlazarov, Mohamed Goune, Alain Hazotte, Olivier Bouaziz, Frederic KegelAbstract:The medium Mn steels are a topic of interest from both practical and scientific point of view. Many studies were focused on the Microstructure characterization, but only some of them addressed the mechanisms of austenite formation and stabilization. Hence, there are still remaining questions regarding the link between the optimum retained austenite fraction and stability and the austenite formation including both the morphological and kinetics aspects. In this work, different ART annealing treatments were performed on a cold rolled 0.1C – 4.7Mn (wt.%) steel. SEM and TEM observations as well as XRD and magnetic measurements were done to characterize the resulting Microstructures. Microstructure evolution was analyzed as a function of soaking time: precipitation and dissolution of cementite; austenite nucleation, growth and stabilization. The experimental observations were compared with the predictions from thermodynamic calculations. Based on the obtained results, a mechanism of austenite formation and stabilization during ART annealing is proposed.
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evolution of Microstructure and mechanical properties of medium mn steels during double annealing
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: Artem Arlazarov, Mohamed Goune, Alain Hazotte, Olivier Bouaziz, Gerard Petitgand, Patrick BargesAbstract:A double annealing process was applied to cold rolled medium Mn steel. The evolution of both Microstructure and mechanical properties during the second annealing were analysed. Austenite reverted transformation (ART) was observed during intercritical annealing. It was shown that a complex ultra-Fine Microstructure composed of three phases (retained austenite/martensite/ferrite) was formed and two types of morphologies were detected (lath-like and polygonal). Furthermore, a high volume fraction of retained austenite (22%), which was stabilized at room temperature, was the origin of a TRIP effect. A good balance between strength and ductility can be achieved by optimizing the heat treatment. The various results are discussed and some mechanisms are proposed to explain the observations.
Yufeng Zheng - One of the best experts on this subject based on the ideXlab platform.
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additive manufacturing of ultraFine grained high strength titanium alloys
Nature, 2019Co-Authors: Duyao Zhang, Yufeng Zheng, Mark A Gibson, H L Fraser, D H Stjohn, Mark Alan EastonAbstract:Additive manufacturing, often known as three-dimensional (3D) printing, is a process in which a part is built layer-by-layer and is a promising approach for creating components close to their final (net) shape. This process is challenging the dominance of conventional manufacturing processes for products with high complexity and low material waste1. Titanium alloys made by additive manufacturing have been used in applications in various industries. However, the intrinsic high cooling rates and high thermal gradient of the fusion-based metal additive manufacturing process often leads to a very Fine Microstructure and a tendency towards almost exclusively columnar grains, particularly in titanium-based alloys1. (Columnar grains in additively manufactured titanium components can result in anisotropic mechanical properties and are therefore undesirable2.) Attempts to optimize the processing parameters of additive manufacturing have shown that it is difficult to alter the conditions to promote equiaxed growth of titanium grains3. In contrast with other common engineering alloys such as aluminium, there is no commercial grain reFiner for titanium that is able to effectively reFine the Microstructure. To address this challenge, here we report on the development of titanium–copper alloys that have a high constitutional supercooling capacity as a result of partitioning of the alloying element during solidification, which can override the negative effect of a high thermal gradient in the laser-melted region during additive manufacturing. Without any special process control or additional treatment, our as-printed titanium–copper alloy specimens have a fully equiaxed Fine-grained Microstructure. They also display promising mechanical properties, such as high yield strength and uniform elongation, compared to conventional alloys under similar processing conditions, owing to the formation of an ultraFine eutectoid Microstructure that appears as a result of exploiting the high cooling rates and multiple thermal cycles of the manufacturing process. We anticipate that this approach will be applicable to other eutectoid-forming alloy systems, and that it will have applications in the aerospace and biomedical industries. Titanium–copper alloys with fully equiaxed grains and a Fine Microstructure are realized via an additive manufacturing process that exploits high cooling rates and multiple thermal cycles.
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effect of extrusion process on Microstructure and mechanical properties of ni3al b cr alloy during self propagation high temperature synthesis
Transactions of Nonferrous Metals Society of China, 2012Co-Authors: L Y Sheng, X I Tingfei, Chen Lai, Jianting Guo, Yufeng ZhengAbstract:The well-densified Ni3Al-0.5B-5Cr alloy was fabricated by self-propagation high-temperature synthesis and extrusion technique. Microstructure examination shows that the synthesized alloy has Fine Microstructure and contains Ni3Al, Al2O3, Ni3B and Cr3Ni2 phases. Moreover, the self-propagation high-temperature synthesis and extrusion lead to great deformation and recrystallization in the alloy, which helps to reFine the Microstructure and weaken the misorientation. In addition, the subsequent extrusion procedure redistributes the Al2O3 particles and eliminates the γ-Ni phase. Compared with the alloy synthesized without extrusion, the Ni3Al-0.5B-5Cr alloy fabricated by self-propagation high-temperature synthesis and extrusion has better room temperature mechanical properties, which should be ascribed to the Microstructure evolution.
Xing Zhang - One of the best experts on this subject based on the ideXlab platform.
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fabrication of y2o3 transparent ceramics by hot isostatic pressing from precipitated nanopowders
Optical Materials, 2019Co-Authors: Xinyou Huang, Xing Zhang, Zewang Hu, Yagang Feng, Xiaoying Li, Haohong Chen, Lexiang Wu, Jiang LiAbstract:Abstract Yttrium (Y2O3) nanopowders were synthesized via the precipitation method using ammonium hydrogen carbonate (AHC) as the precipitant. The influences of calcination temperature on the composition and morphology of the powders were investigated. Fine Y2O3 powders with low-agglomeration were obtained by calcining the precursor at 1100 °C for 4 h. The primary crystallites were calculated to be ∼47 nm in size and weakly agglomerated to particles with size of ∼79 nm. Using the synthesized powders as the starting materials, Y2O3 ceramics were fabricated by vacuum sintering at different temperatures combined with HIP post-treatment. The densification and micro-structure evolution of the Y2O3 ceramics were systematically investigated. The ceramic sample vacuum sintered at 1500 °C for 2 h and post-HIPed at 1550 °C for 3 h exhibited a uniform and Fine Microstructure with the average grain of about 1.0 μm. The in-line transmittance of the ceramic sample reached 80.1% at 1100 nm.
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effects of ce substitution on magnetic properties and Microstructure of nd pr fe b melt spun powders
Journal of Magnetism and Magnetic Materials, 2016Co-Authors: Xing ZhangAbstract:Abstract The effects of Ce-substitution on the magnetic properties and Microstructure of [(Nd 4 Pr) 1− x Ce x ] 27 Fe 72 B ( x =0, 0.1, 0.24, 0.5, 0.8 wt%) melt-spun powders have been investigated. The magnetic properties B r and (BH) max of Nd–Pr–Fe–B melt-spun powders decrease with the increase of Ce proportion except the [(Nd 4 Pr) 0.76 Ce 0.24 ] 27 Fe 72 B ( x =0.24) sample, in which coercivity is relatively high ( H cj =8.49 kOe). It may result from the mixed valence, the Fine Microstructure and higher volume fraction of grain boundary phase. The α-Fe and Fe 2 B phases tend to increase with higher content of the Ce. Both the Curie temperature and the crystallization temperature decrease with the Ce content increasing.