日本金属学会誌
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
80 巻 , 9 号
選択された号の論文の7件中1~7を表示しています
論文
  • 井尻 政孝, 富田 悠希, 石川 高史, 竹元 嘉利
    2016 年 80 巻 9 号 p. 547-552
    発行日: 2016年
    公開日: 2016/08/25
    ジャーナル フリー
     Certain β-Ti alloys, Ti-4Fe-7Al and Ti-10Mo-7Al, the compositions of which are characterized by a 7% aluminum addition to the β lower-limit compositions, exhibit an interesting phenomenon upon tempering. For example, these alloys drastically harden upon tempering at 450℃ for several seconds, and the sample surface becomes severely uneven. When a strip specimen is bent plastically or elastically into a U-shape and heated to 450℃, the shape spontaneously deforms towards the inside, which is different from the behavior of shape-memory alloys. In this study, Ti-35Nb-7Al alloy was selected as a candidate novel alloy, and the microstructure, the characteristics of age hardening and the shape evolution of a U-shaped specimen upon heating were investigated. The quenched alloy was a single β-phase, and its hardness was considerably higher than that of binary Ti-35Nb alloy. The smooth surface of the quenched specimen became uneven at around 300℃ upon heating. Either case of U-shaped specimen, which was plastically or elastically bent, exhibited spontaneous bending towards the inside by heating up. It was found that, with tempering, Ti-35Nb-7Al also exhibits the novel phenomenon, similarly to Ti-4Fe-7Al and Ti-10Mo-7Al. Fine needle-α″ and ω-particles were formed in the β matrix after isothermal aging at 450℃ for 3 min and gave rise to a remarkable hardening. STEM-EDS analysis revealed that the Nb content decreased in the α″ products formed by tempering. Consequently, the β→α″ transformation upon tempering on this alloy is accompanied with atomic diffusion. Extra spots at 〈100〉*, such as those of the B2 structure, were observed in the selected-area diffraction patterns of the TEM foils prepared by common electropolishing techniques. However, a TEM foil prepared with an FIB (focused ion beam) did not exhibit the extra spots. These results suggested that the extra spots were caused by hydrogen absorption in the specimen during electropolishing.
  • 鯵坂 祐介, 宮嶋 陽司, 尾中 晋
    2016 年 80 巻 9 号 p. 553-561
    発行日: 2016年
    公開日: 2016/08/25
    [早期公開] 公開日: 2016/07/08
    ジャーナル フリー
     Orientation changes of a Cu single crystal with an initial orientation of {111}〈112〉 caused by cold-rolling were analyzed using electron back-scatter diffraction patterns obtained by scanning electron microscopy. The orientation changes were understood as the rotation around TD and the formation of band-like structures parallel to RD was observed after the cold-rolling.
      Multiple-slip systems of the {111}〈112〉 single crystal operated by the cold-rolling were discussed. Orientation changes after the cold-rolling were explained reasonably by the operations of two different multiple-slip systems. High-angle grain boundaries were formed between the band-like structures in the single crystals rolled to 30% and 50% reduction. Striped patterns observed on the TD plane in the region where one of the multiple slip systems operated were also discussed. The striped patterns were explained by small-angle tilt boundaries consisting of arrays of edge dislocations on the slip planes.
  • 齋藤 周也, 鈴木 広野, 小茂鳥 潤, 深沢 剣吾, 三阪 佳孝, 川嵜 一博
    2016 年 80 巻 9 号 p. 562-569
    発行日: 2016年
    公開日: 2016/08/25
    [早期公開] 公開日: 2016/07/08
    ジャーナル フリー
     In order to form a Ni-Al intermetallic compound layer on a carbon steel surface, Atmospheric-controlled Induction Heating Fine Particle Peening (AIH-FPP) was carried out at 900℃ in argon atmosphere with nickel and aluminum particles mechanically milled by planetary ball mills. The treated surface was analyzed using a scanning electron microscope (SEM), an energy dispersive X-ray spectrometer (EDX), and an X-ray diffraction (XRD). Oxidation tests were carried out at 900℃ for 100 hours. Results showed that the Ni-Al intermetallic compound layer with a thickness of 200 μm was formed in the case of the specimen treated by the aluminum rich shot particles; the ratio of Ni to Al was 1 to 4 (mol). This was because (i) melted aluminum particles decreased the melting point of nickel particles and the steel substrate, and (ii) partially melted area promoted a combustion synthesis reaction between nickel and aluminum, resulting in forming the Ni-Al intermetallic compound layer. The AIH-FPP treated surface showed a higher oxidation resistance than that of the un-treated specimen. This was because Al2O3 continually created from the Ni-Al intermetallic compound layer protected the steel substrate.
  • 國貞 雄治, 坂口 紀史
    2016 年 80 巻 9 号 p. 570-574
    発行日: 2016年
    公開日: 2016/08/25
    [早期公開] 公開日: 2016/07/08
    ジャーナル フリー
     We have investigated trapping effects of monoatomic vacancies Vmono and alloy atoms on hydrogen diffusion at Al(111) surfaces. We performed first-principles calculations based on density functional theory with generalized gradient approximation in order to obtain the hydrogen adsorption energies in the vicinity of monoatomic vacancies and alloy atoms in Al(111) subsurfaces. We considered Si, Cr, Mn, Fe, Cu, Ge, and Zn as alloy atoms. We substituted one Al atom with one monoatomic vacancy or alloy atom, which corresponds to Al0.95X0.05(111) (X=Si, Cr, Mn, Fe, Cu, Ge, Zn, Vmono) surfaces. We found that all of monoatomic vacancies and alloy atoms increase adsorption energies. We also clarified that hydrogen atoms make strong covalent bonds in Cr, Mn, Fe-alloyed Al(111) subsurfaces, while they make only weak ionic bonds in pure and Si, Cu, Ge, Zn-alloyed Al(111) subsurfaces.
    Isosurfaces of electron density difference of hydrogen atoms at the most stable adsorption sites in (a) pure and (b) Cr-alloyed Al(111) subsurfaces. Electron density increase in darker (red) regions and decrease in lighter (blue) regions. The isosurface value is 0.002e Å−3. Black, gray (green), and white balls are aluminum, chromium and hydrogen atoms, respectively. Black lines show the supercell which we considered.
  • 中上 雄史, 君塚 肇, 尾方 成信
    2016 年 80 巻 9 号 p. 575-584
    発行日: 2016年
    公開日: 2016/08/25
    [早期公開] 公開日: 2016/07/25
    ジャーナル フリー
     Nanosized precipitates of solute atoms, which are often called “Guinier-Preston (GP) zones,” are known to play a significant role in the precipitation-hardening effect on the Al alloys. In this study, the controlling factors for the formation of solute nanoclusters as in GP1 and GP2 zones, which are observed in the early and middle stages, respectively, of aging in the Al-Cu system, were investigated by extracting and examining the intra- and intercluster interaction energies of Cu in Al using density functional theory (DFT). DFT-calculated two- and three-body binding energies for Cu indicated that a Cu-Cu pair tends to bind at the first nearest-neighbor (1NN) positions, and a Cu-Cu-Cu triplet energetically prefers the arrangement of the triangular atomic cluster that contains two Cu-Cu pairs at the 1NN positions on the same {100} plane. Such a characteristic short-range ordering was suggested to be dominated by attractive three-body interactions due to the chemical (charge localization) effect, leading to planar clustering as found in the GP1 zones along the {100} planes. Intercluster interaction energies between two Cu planar clusters in Al were also calculated based on DFT. The results indicated that the energetically preferable configuration was the one in which two planar clusters are aligned at an intercluster distance of 2a (where a is the lattice constant of Al); it is noteworthy that this distance was the same to that in the basic structures of the GP2 zones observed in the experiments. A potential model for a dilute Al-Cu system was constructed on the basis of the extracted intra- and intercluster interactions, and then applied to atomistic Monte Carlo modeling for predicting the planar segregation of Cu atoms at finite temperatures. As a result, the formation of planar Cu clusters and the alignment of two planer clusters separated by 2a were successfully reproduced within a specific temperature range. This demonstrated that these interactions were important controlling factors for the formation of a characteristic pattern of solute clusters in the Al-Cu system.
  • 鈴木 成実, 佐々木 亮祐, 松村 義人, 近藤 正聡
    2016 年 80 巻 9 号 p. 585-592
    発行日: 2016年
    公開日: 2016/08/25
    [早期公開] 公開日: 2016/07/29
    ジャーナル フリー
     The characterization of Zr oxide layer formed in Ar and O2 gas mixture at 973 K on the surface of Zr metal was characterized by electrochemical impedance spectroscopy (EIS). The increase of the layer thickness and the formation of the horizontal crack in the layer were evaluated in-situ using EIS. The thickness of the Zr oxide layer estimated by EIS agreed well with that by EPMA analysis. It was found that the time constant τ of the Zr oxide layer obtained by the EIS increased with the oxidation time. This trend indicated the growth of horizontal crack. The constant phase element (CPE) parameter p was obtained from the results of EIS. The change of p indicated that the Zr oxide layer has the gradient of the chemical composition in its thickness direction. The single horizontal crack and compositionally gradient in the oxide layer was modeled as they electrically functioned in the equivalent circuits. The simulation results indicated that the EIS method can be used as the in-situ monitor the gradient of the chemical composition and the crack formation in the oxide layer.
    (a) Thikness, (b) CPE parameter p and (c) Resistance of oxide layer as function of oxidation time.
  • 増田 高大, 瀧沢 陽一, 湯本 学, 小田切 吉治, 堀田 善治
    2016 年 80 巻 9 号 p. 593-601
    発行日: 2016年
    公開日: 2016/08/25
    [早期公開] 公開日: 2016/07/29
    ジャーナル フリー
     In this study, the method of high-pressure sliding (HPS) was applied for grain refinement of an A2024 alloy. Sheet samples with 10-15 mm width and 100 mm length with 1 mm thickness were processed by HPS under pressures of 2-3 GPa. Microstructural observations revealed that the grain size was refined to ~200 nm. Tensile tests showed that the ultimate tensile strength reached 886 MPa with a total elongation of 7.1% and the anisotropy of samples was less developed in the HPS-processed samples. Extra strengthening was attained by aging at 423 K after HPS processing, leading to an ultimate tensile strength of 967 MPa at the peak aged condition. Superplastic elongation of more than 400% appeared when the A2024 alloy processed by HPS for 20 mm was deformed in tension at a testing temperature of 623 K with an initial strain rate of 1.0×10−3 s−1.
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