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79 巻, 6 号
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三浦 博己, 松本 洸太, 小林 正和2015 年 79 巻 6 号 p. 295-302
発行日: 2015年
公開日: 2015/06/01
ジャーナル フリーA hot extruded AZ61Mg alloy was multi-directionally forged (MDFed) under decreasing temperature conditions using a die. MDFing was successfully carried out, and the coarse initial grains with an average grain size of 21.6 μm were gradually fragmented to 0.3 μm in average at cumulative strain of ∑Δε=7.2. It showed quite high hardness of 958 MPa and tensile strength of 465 MPa with ductility of 15%. The tensile behavior of the ultrafine grained AZ61 Mg alloy exhibited large temperature and strain rate dependency irrespective of temperature. Superplasticity of 680% elongation to fracture could be achieved at 423 K and at strain rate of 1.0×10−4 s−1. Such mechanical properties depending on temperature and strain rate were reasonably understood by considering the effect of grain boundary sliding. The tensile strength of the MDFed AZ61Mg alloy was further raised to 490 MPa by additional cold rolling.
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土井 康太郎, 宮部 さやか, 藤本 慎司2015 年 79 巻 6 号 p. 303-307
発行日: 2015年
公開日: 2015/06/01
ジャーナル フリーDissolution and repassivation of type 316L stainless steel during cyclic deformation were examined in a simulated body environment. Samples were exposed to simulated body fluid (SBF) with or without cells, and then subjected to cyclical deformation in the SBF kept at cell culturing condition. The cyclic stress ratio and maximum stress were 0.1 and 300 MPa, respectively. Transients of stress, strain and corrosion potential were recorded during the test.
The corrosion potential became less noble immediately after the start of the test, but started to increase again after about 10-1000 cycles, The minimum corrosion potential depends on the treatment prior to the deformation: the lowest value was observed for the specimen previously immersed in SBF for 1 day without cells, whereas the highest one was shown by the specimen immersed for 1 week in the presence of cultured cells. This reveals that proteins and cells inhibit metal dissolution during deformation. On the other hand, the time needed for the potential revert to noble was the longest for the sample containing cells, and shortest for the cell-free sample immersed for 1 day. This denotes that proteins and cells also suppress repassivation.
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岩田 博之, 沓名 宗春, 坂 公恭2015 年 79 巻 6 号 p. 308-314
発行日: 2015年
公開日: 2015/06/01
ジャーナル フリーSurfaces of {100} Si wafers were laser-peened in water by a Q-switch YAG laser with an energy density ψo ranging from 1 to 10 GW/cm2. To start with, morphology of the ablated surfaces was analyzed by a 3-dimensional optical microscope. When the energy density ψo is higher than 5 GW/cm2, macroscopic cracking did not take place. Therefore, on three samples irradiated with ψo=2, 3 and 5 GW/cm2, defect structures in the sub-surface layers were examined by transmission electron microscopy comprehensively. When ψo=2 GW/cm2, the ablated surface was quite smooth and no extensive damage was introduced in the sub-surface region. However, close inspection showed that a subsurface layer about 200 nm thick contained a considerable density of small bubbles and a small number of dislocations running vertically towards the ablated surface. When ψo=3 GW/cm2, the sub-surface damaged layer became more profound with a much higher density of small bubbles and dislocations. On top of this, a considerable density of much larger bubbles were formed, on the inside-wall of which quite a high density of fine crystalline particles were attached. It is concluded that these bubble-containing layer must have been melted on laser irradiation. The bubbles must have been vapor Si formed in the liquid Si, which condensed on the inner wall on cooling. The vertical dislocations are misfit dislocation formed on solidification of the molten Si. However, in the matrix of Si underneath dislocations were rarely observed. This indicates that that region of Si that remained crystalline during the laser irradiation did not receive a stress strong enough to induce dislocations even at a high temperature just below the melting point. When ψo=5 GW/cm2, underneath the bubble-containing layer a high density of dislocations were introduced. However, most of these dislocations appeared different from the ordinary 1/2〈110〉{111} dislocations. Electron diffraction showed no evidence of the high-pressure phases.
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高下 拓也, 中村 尚道, 尾﨑 由紀子2015 年 79 巻 6 号 p. 315-323
発行日: 2015年
公開日: 2015/06/01
ジャーナル フリーThe coercive force of an iron powder core decreases with an increase in the circularity of raw iron powder. Microstructural observation reveals that the crystal grain size of the iron powder core is reduced through recrystallization during the stress relief annealing after the powder compaction. An analysis of the work hardening behavior through the compaction process shows that a rounder particle shape leads to a smaller particle deformation, resulting in a reduction of the crystal grain refinement through recrystallization. A grain boundary pinning model well describes the reduction of coercive force with the increase in the eventual grain size.
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中井 創一朗, 宮田 昌悟, 小茂鳥 潤2015 年 79 巻 6 号 p. 324-329
発行日: 2015年
公開日: 2015/06/01
ジャーナル フリーArticular cartilage has a poor ability to regenerate and repair itself. To restore cartilage defects, a method has been developed by culturing autologous chondrocytes to create a three dimensional tissue and then implanting the cultured tissue. However, articular chondrocytes easily leads to de-differentiation state and loses their ability to synthesize the functional cartilaginous matrixes during in vitro culture. Therefore, it is important to maintain their differentiated phenotype during the expansion culture of chondrocytes. The objective of this study is to develop a novel culturing methodology combined surface modification and mechanical stimuli on articular cartilage. To develop a surface-modified substrate, a SUS316L stainless plate was treated by Fine Particle Peening (FPP) technique using alumina particles. The chondrocytes were cultured on the modified stainless plate and stimulated by fluid-induced shear stress using a custom-made flow culture system. As a result, proliferation rate was increased and phenotypic-change of chondrocytes was also observed by culturing the chondrocytes on physically modified surface combined with fluid-induced shear stress. In addition, the synergetic effect on proliferation rate was observed by applying the surface modification and flow shear stress simultaneously.
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大塚 治, 簗場 豊, 吉川 健, 山下 光雄2015 年 79 巻 6 号 p. 330-337
発行日: 2015年
公開日: 2015/06/01
ジャーナル フリーWe have developed a method for recycling selenium from Se-containing wastewater using the selenium-oxyanion-reducing aerobic bacterium Pseudomonas stutzeri NT-I. The treatment of Se-containing wastewater with the NT-I strain provided bio-selenium, which is mainly composed of organic matter and 11-14 mass% of Se. In the present study, we investigated the recovery of Se from bio-selenium by oxidizing roasting and chemical reduction. After thermodynamic calculations were performed to estimate the oxidation behavior during the roasting process, roasting experiments were conducted on bio-selenium under varying roasting conditions. The selenium in bio-selenium was recovered in the form of solid SeO2 with a purity of 99% in a maximum yield of 97% after roasting at 700℃. Furthermore, the chemical reduction of SeO2 to Se was carried out, and metallic Se with a purity of 99% (based on metal) was obtained.
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