Journal of the Japan Institute of Metals and Materials

Regular Article

Relationship of Rolling Reduction with Microstructure and Mechanical Properties of Cold-Rolled Ti-20V-4Al-1Sn Alloy

Naofumi Ide, Tatsuro Morita, Takashi Maeda, Hideto Seto

2014 Volume 78 Issue 3 Pages 103-108
Published: 2014
Released on J-STAGE: March 01, 2014

DOIhttps://doi.org/10.2320/jinstmet.JBW201306

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This study was conducted to investigate the relationship of rolling reduction with the microstructure and mechanical properties of cold-rolled Ti-20V-4Al-1Sn alloy. Cold rolling was performed under the rolling reduction between 10-50%. The microstructure was compressed by cold rolling, and became finer. Plastic deformation was partially inhomogeneous in the thickness direction of the cold-rolled material. The preferred orientation of the formed crystallographic texture was {112}〈110〉~{001}〈110〉 which is typical in metals possessing the bcc structure. The texture evolved with increasing rolling reduction. Hardness and static strength were increased by increase in rolling reduction because of work hardening and microstructural refinement. Anisotropy was induced in yield strength and work hardening exponent by cold rolling; however, it was not marked in hardness and tensile strength.

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Fabrication of Ti_1−xCr_xO_z and Analysis of Its Microstructure and Thermoelectric Properties

Katsuhiro Sagara, Yun Lu, Yuta Kikuchi, Takahiro Nozue, Satoshi Ogura, ...

2014 Volume 78 Issue 3 Pages 109-116
Published: 2014
Released on J-STAGE: March 01, 2014

DOIhttps://doi.org/10.2320/jinstmet.J2013071

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To obtain Ti_1−xCr_xO_z, mixed powder of TiO₂ and Cr powders was sintered in a graphite die by spark plasma sintering (SPS). The composition and the microstructure of the sintered compacts were examined by XRD and SEM. In addition, the thermoelectric properties of the sintered compacts were measured, the relationship of the thermoelectric properties and phases was also discussed. The results showed that the multiphase with compositions of Ti_nO_2n−1, TiCrO₃ and Cr was obtained. The phases formed in a transformation from the rutile type TiO₂ to TiCrO₃ with the reduction during SPS and an increase in Cr additive fraction. The electrical resistivity of the sintered compacts greatly decreased due to an increase in Cr additive fraction. The thermoelectric performance of the sintered compacts was enhanced obviously, and the largest power factor of Ti_1−xCr_xO_z with x=0.25 reached 0.57 mW/K²m at 973 K.

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Thermodynamic Analysis on a Segregation Behavior of Alloying Elements to Stacking Faults in Mg-Y-Zn Based LPSO Structures

Tatsuki Umebayashi, Satoshi Iikubo, Hiroshi Ohtani

2014 Volume 78 Issue 3 Pages 117-125
Published: 2014
Released on J-STAGE: March 01, 2014

DOIhttps://doi.org/10.2320/jinstmet.JBW201307

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A long period stacking ordered (LPSO) structure in Mg-based alloys is characterized by the periodical arrangement of stacking faults introduced to hcp matrix lattice. Alloying elements of rare earth atoms and transition metal atoms segregate to the stacking faults (SFs) and form chemically ordered structures in the layers. The atomic arrangement of matrix phase and SF layer in the LPSO structures corresponds to those in hcp and fcc structures, respectively. Thus in the present work, the free energies for the hcp and fcc phases in the Mg-Y-Zn ternary system obtained from the first-principles calculations combined with the cluster variation method were introduced to the CALPHAD method. Segregation coefficients between hcp matrix and fcc SF were calculated applying the parallel tangent law. The calculated results showed that the Y and Zn atoms segregate to the SFs, mainly because of the difference in chemical potentials for each element between fcc and hcp.

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Recovery and Recrystallization Processes in Oxygen-Free Copper after Cold-Rolling

Takuya Kajiura, Masaaki Tsukamoto, Atsushi Yamamoto

2014 Volume 78 Issue 3 Pages 126-131
Published: 2014
Released on J-STAGE: March 01, 2014

DOIhttps://doi.org/10.2320/jinstmet.J2013067

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The processes of recovery and recrystallization in oxygen-free copper were observed in detail in the same area of a specimen using an SEM(scanning electron microscopy)-EBSD(electron back scatter diffraction) system. Specimens were solution heat-treated at 823 K for 3.6 ks. Then, the specimens were cold-rolled at a reduction rate of 75%, and subsequently, annealed at 523 K. Intermittent annealing using a salt bath, Ar⁺ ion-polishing and EBSD measurement were repeated. High and low angle boundaries were induced by cold-rolling. Prior grain boundaries were observed with a relatively high contrast, which allows one to observe the strain-induced grain boundary migration(SIBM). Dislocation cells surrounded by high-angle boundaries grew into recrystallized grains without any change in their orientations. In addition, recovery structures grew owing to the migration of high-angle boundaries. The migration of high-angle boundaries did not always lead to the formation of recrystallized grains but resulted in the growth of the recovered region. These behaviors were similar to those observed during recrystallization on an Al-Mg-Si alloy and commercial pure aluminum. Such recrystallization generally occur in metals and alloys in which dislocation cells are formed upon deformation by cold-rolling.

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Ion Bombardment Effects on Internal Stress of Ni Thin Film during Sputter Deposition Process

Ryoichi Toyoda, Soichiro Toya, Maki Hashimoto, Ami Kohri, Yoshihito Ma ...

2014 Volume 78 Issue 3 Pages 132-136
Published: 2014
Released on J-STAGE: March 01, 2014

DOIhttps://doi.org/10.2320/jinstmet.JBW201302

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In this study, the effects of an ion bombardment parameter P_i of argon (Ar), krypton (Kr) and xenon (Xe) on the internal stress and crystal structure of a nickel (Ni) thin film were discussed. Ni thin films were prepared by a DC magnetron sputtering process. Ar, Kr and Xe were used as sputtering gases. As a means of expressing the effect of ion bombardment, the ion bombardment parameter P_i based on the magnitude of ion momentum P_G⁺ (G: Ar, Kr or Xe) and an impingement ratio of sputtering gas ions i_G⁺ to that for Ni particles a_Ni was proposed. Plasma diagnostics were carried out with a single Langmuir probe during the sputter deposition. The magnitude of the ion momentum estimated from the plasma potential was independent of the cathode discharge power. With an increase in cathode discharge power, the increase in a_Ni onto the substrate was greater than the increase in i_G⁺. It has become evident that the ratio of impingement i_G⁺ to a_Ni onto the substrate mainly affects the variation in P_i in relation to the cathode discharge power. The FWHM (full width at half maximum) of X-ray diffraction peaks and the internal stress of the films varied linearly with the ion bombardment parameter P_i regardless of the sputtering gas species. The internal stress of Ni thin films could be controlled by adjusting the ion bombardment parameter P_i.

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