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Volume 78, Issue 6
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Regular Article
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Toshiyuki Sawada2014 Volume 78 Issue 6 Pages 211-217
Published: 2014
Released on J-STAGE: June 01, 2014
JOURNAL FREE ACCESSThe effect of the hardness of fine media used in shot peening on the surface modification behavior of workpiece with high hardness was investigated. Vacuum carburized JIS-SCM822 with the surface of 810 HV in Vickers hardness was shot peened by fine media with the range from 390 to 1550 HV in Vickers hardness, followed by the examination of their surface modification behavior.
Shot peening was carried out by suction-type air peening machine. Peening conditions were 0.6 MPa in air pressure, 10 s in peening time and 50 mm in peening distance. Various gas atomized powders sieved from 45 to 125 μm in particle diameter were used as fine peening media.
On the peened surface by the fine media with remarkably higher hardness than that of workpiece, deep nanocrystalline layer with more than 2 μm in depth and less than 15 nm in grain size was generated. In these nanocrystalline layers, the thickness increased and grain size decreased with increasing Vickers hardness of used peening media. In addition, Vickers hardness on peened surface also increased with increasing Vickers hardness of used peening media. Especially, the hardening effect on peened surface was outstanding, in the case of using fine peening media with more than 1020 HV in Vickers hardness. It seemed that this hardening effect was caused by grain refinement strengthening in nanocrystalline layer.
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Shota Umezaki, Yoshinori Murata, Kyohei Nomura, Keiji Kubushiro2014 Volume 78 Issue 6 Pages 218-224
Published: 2014
Released on J-STAGE: June 01, 2014
JOURNAL FREE ACCESSGrain size dependence of dislocation density and its character in austenitic stainless steels subjected to plastic strain was evaluated quantitatively by means of X-ray diffraction and Electron Back Scattering Diffraction (EBSD). Various amounts of the plastic strain up to 15% were given by a tensile instrument at 650℃ and three kinds of grain size (17, 46 and 87 μm) were employed. Misorientation in crystal direction in each grain was determined by two parameters, GOS (Grain Orientation Spread) and KAM (Kernel Average Misorientation). GN (Geometrically Necessary) dislocation density was estimated from KAM parameter. GOS parameter increased with a linear relationship to the amount of plastic strain regardless of the grain size, whereas KAM parameter increased with increasing plastic strain but showed the grain size dependence. Change in total dislocation density with plastic strain showed a similar trend in KAM parameter. It is found that the difference in the total dislocation density at a plastic strain was consistent exactly with the difference in GN dislocation density depending on the grain size. These results were confirmed by TEM observations using several kinds of specimens used in X-ray experiments.
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Toshimichi Nakayama, Ken Kurosaki, Yuji Ohishi, Hiroaki Muta, Shinsuke ...2014 Volume 78 Issue 6 Pages 225-229
Published: 2014
Released on J-STAGE: June 01, 2014
JOURNAL FREE ACCESSThe efficiency of thermoelectric (TE) materials is quantified by a dimensionless figure of merit ZT. To enhance ZT, it is important to reduce the lattice thermal conductivity (κlat) with maintaining the high electrical conductivity. Cage-like compounds with phonon-glass and electron-crystal properties such as filled-skutterudites have attracted much attention as high-performance TE materials. In these compounds, the guest atoms in the cages of the host framework lattice rattle and reduce the κlat. Our group has focused on semiconductor RE5X3P (RE=Gd, La, X=Si, Ge). RE5X3P have a cage-like structure composed of RE and X, in which P can be filled in the cages. In the present study, prior to the TE characterization of RE5X3P, polycrystalline bulk samples of RE5X3 were prepared and their high-temperature TE properties were examined. Gd5Si3 and Gd5Ge3 showed a metallic behavior with relatively low κlat. At around 400 K, the κlat values of Gd5Si3 and Gd5Ge3 were 3.3 and 1.7 W m−1 K−1, respectively.
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Hiroyuki Watanabe, Yasuyoshi Sasakura, Toshiji Mukai2014 Volume 78 Issue 6 Pages 230-234
Published: 2014
Released on J-STAGE: June 01, 2014
JOURNAL FREE ACCESSTensile response at low strains and damping capacity were characterized in pure magnesium and Mg-1 mass%Ca alloy with the aim of revealing the effect of extrusion process and Ca addition. The damping capacity of extruded magnesium and solution treated Mg-1 mass%Ca alloy was lower than that of cast magnesium in the strain range examined. The proportional limit in the stress-strain relation of extruded magnesium and solution treated Mg-1 mass%Ca alloy was higher than that of cast magnesium. For all materials examined, the proportional limit corresponded to the critical strain, above which damping capacity begins to increase with strain. This suggests that dislocations breaking away from weak pinning points such as impurity/solute atoms causes the deviation from linearity in the stress-strain relation.
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Chang Liu, M. Asato, N. Fujima, T. Hoshino2014 Volume 78 Issue 6 Pages 235-240
Published: 2014
Released on J-STAGE: June 01, 2014
JOURNAL FREE ACCESSWe present systematically ab-initio calculations for defect energies of 3d and 4sp impurities (Sc~Ge) in Fe. The calculations are based on the Generalized-Gradient-Approximation in the density-functional formalism and the full-potential Korringa-Kohn-Rostoker (FPKKR) Green's function method. We first examine the distance dependence, from the 1st- to 10th-nearest neighbors, of the impurity-impurity (I-I; I=Sc~Ge) interaction energies (Eint) and show that for most cases, the 1st-nearest neighboring I-I interaction energies (Eint1) are dominant. We found that fundamental features of phase diagrams of Fe-based binary alloys, such as segregation, solid solution, and order, known experimentally, may be classified by use of the sign and magnitude of Eint1. Second we discuss the calculated results for the 1st- and 2nd-nearest neighboring interaction energies of perturbed-angular-correlation (PAC)-probe Sn with 3d and 4sp impurities in Fe. The comparison of the calculated results with available experimental results shows that the observed attraction for Sn-Co, Sn-Ni, and Sn-Cu may be understood by the 1st-nearest neighboring interaction energies of these impurity pairs, while the observed repulsion for Sn-Ga, and Sn-Ge by the 2nd-nearest neighboring interaction energies of these impurity pairs. We also discuss the magnetism of single impurities X (=Sc~Cu) in Fe. The anti-parallel coupling to the bulk magnetization of the neighboring Fe atoms is stable for Sc~Mn, while the parallel coupling for Fe~Cu.
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