Papers by Author: Tadachika Nakayama

Paper TitlePage

Authors: Kouichi Yasuda, Tadachika Nakayama, Satoshi Tanaka
Abstract: A mechanical model is proposed to estimate internal stress during sintering of ceramic multiphase laminates. A symmetrical multi-layered laminate is assumed, and one-dimensional elastic analysis is carried out on the change in stress of each layer during sintering, based on the differences in sintering strain, thermal expansion strain and phase transformation strain between the layers. By taking a limit such that the thickness of each layer approaches infinitesimally small, the internal stress expression can be extended into the case of the materials with continuous compositional change (viz. functionally gradient materials).
14
Authors: Jun Inoue, Tadachika Nakayama, Tsuneo Suzuki, Hisayuki Suematsu, Wei Hua Jiang, Koichi Niihara
Abstract: Chromium oxynitride (Cr(N,O)) thin film have been successfully prepared by using pulsed laser deposition. The composition of the thin film was determined to be Cr0.50N0.23O0.28 by Ruthreford backscattering spectroscopy (RBS). The structural analysis was carried out by using X-ray diffraction (XRD), and out-of-plane and in-plane measurements were used to clarify the axial ratio (c/a) of the Cr(N,O) phase. The lattice constants of a and c axes in the Cr(N,O) phase were found to be 0.414 and 0.419 nm, respectively. From these results, the cubic to tetragonal phase change by substitution of the oxygen atoms for nitrogen atoms was confirmed for the crystal Cr(N,O) compounds.
1006
Authors: Y. Tokoi, Tadachika Nakayama, Hisayuki Suematsu, Wei Hua Jiang, K. Yatsui, Koichi Niihara
Abstract: Copper nanosized powders were prepared by pulsed wire discharge (PWD) in N2 gas at low pressure (130 Pa) with high-speed gas puff. The pressure around one of the electrodes was changed to investigate the effect of electrical discharge prevention by gas puff. The peak pressure was changed from 22 kPa to 10 kPa in the gas puff apparatus by changing the distance from an acrylic resin tube and a bottom plate. The energy deposition in the copper wire at 22, 15 and 10 kPa was about 40, 37 and 33 J, respectively. The energy deposition in the wire increased with the increase in pressure around the electrode.
1010
Authors: Tadachika Nakayama, Y. Ushigami, T. Nagashima, Yozo Suga, N. Takahashi
611
Authors: Y. Ushigami, Kenji Kawasaki, Tadachika Nakayama, Yozo Suga, J. Harase
1081
Authors: Yoon Ho Kim, Tohru Sekino, Hirokazu Kawaoka, Rak Joo Sung, Takafumi Kusunose, Tadachika Nakayama, Koichi Niihara
Abstract: Si3N4 ceramics with V2O5 based glasses as sintering additives were successfully fabricated by a powder mixing process and rapid sintering by the PECS method. The fabricated materials by Pulsed Electric Current Sintering (PECS) exhibited very fine microstructure with α and β grains. Electric conductivity for the Si3N4/(V2O5-B2O3) and the Si3N4/(V2O5-B2O3-Al2O3) at room temperature were four and six orders of magnitude higher at room temperature, and two and three orders of magnitude higher at 1000 oC than the conventional Si3N4, respectively
645
Authors: M. Nagashima, Tadachika Nakayama, S. Yamanaka, M. Fujikane, T. Sawada, Yamato Hayashi, Tohru Sekino, Takafumi Kusunose, Koichi Niihara
254
Authors: Yoon Ho Kim, Tohru Sekino, Hirokazu Kawaoka, Takafumi Kusunose, Tadachika Nakayama, Koichi Niihara
Abstract: The electrical conductivity was provided to structural ceramics by controlling the grain boundary phase. We focused on the grain boundary phase of Si3N4 ceramics, which can be considered as an infinite network for conducting paths. In this study, we investigated the correlationship of the microstructure, mechanical properties, and electrical conductivity of Si3N4 ceramics with V2O5 based glasses. The Si3N4 ceramic with V2O5 based glasses were successfully fabricated by controlling the composition of grain boundary phase. Fabricated materials by a PECS method indicated a very fine microstructure. The mechanical properties of Si3N4 ceramics with V2O5 based glasses were not good compared to those of conventional Si3N4. However, the values for the SNVB and the SNVBA were four or six orders of magnitude higher at room temperature and had excellent mechanical properties compared to pure V2O5 based glasses.
501
Authors: Norihito Tanaka, Tohru Sekino, Takafumi Kusunose, Hao Wang, Tadachika Nakayama, Koichi Niihara
Abstract: 3Y-TZP/TiNiCo composites have been successfully fabricated by three step heating (dehydrogenation, hydrogen reduction, hot-pressing) of 3Y-TZP /NiO/TiH2/CoO powder mixtures. XRD analysis revealed that TiNi-base intermetallic compounds such as Ni4Ti3, NiTi, Ni3Ti had formed. The bending strength of 3Y-TZP/TiNiCo composites (~650 MPa) were much higher than those of 3Y-TZP monolith (350 MPa) sintered at the same condition. The electrical resistivity characteristics indicated that 3Y-TZP/30 vol%TiNiCo composites were good electrical conductors. Cobalt addition to TiNi phase influenced on electrical properties of final composites, while their fracture strength was unchanged by the Co addition.
673
Authors: Hiroki Asami, Jun Inoue, M. Hirai, Tsuneo Suzuki, Tadachika Nakayama, Hisayuki Suematsu, Wei Hua Jiang, Koichi Niihara
Abstract: Chromium magnesium oxynitride ((Cr,Mg)(N,O)) thin films have been prepared by pulsed laser deposition (PLD) method with changing the surface area ratio of Mg target (SR) from 0 to 100 %. As a result of the analysis by energy dispersive X-ray spectroscopy (EDX), it was found that magnesium content in the total metallic elements (Cr1-x, Mgx) are controlled by changing SR from 0 to 100 % to be the x ranging from 0 to 1.0. Since the crystal structure of main phase in all thin films was found to be NaCl type, the XRD results showed that the thin films were mainly consisted of (Cr,Mg)(N,O). The hardness of (Cr,Mg)(N,O) thin films were increased almost linearly up to SR = 50 %, above which it decreases rapidly. The maximum Vickers hardness (HV) of 3600 was obtained for the thin film which was prepared by SR = 50 %, and the minimum HV of 1650 was obtained for the thin film which was prepared by SR = 100 %.
311
Showing 1 to 10 of 25 Paper Titles