Papers by Author: Yasuyuki Kaneno

Abstract: High temperature compression properties of Al-, Cr-or Nb-added Ni₃(Si,Ti) based intermetallic compounds were investigated by uni-axial compression test and microstructural observation. The Al-or Cr-added Ni₃(Si,Ti) alloys after homogenization heat treatment exhibited a two-phase microstructure consisting of L1₂ and Ni-solid solution phases. The Nb-added Ni₃(Si,Ti) alloy after homogenization heat treatment exhibited a triple-phase microstructure consisting of G-phase with D8a structure and Ni-solid solution phase in the L1₂ matrix. The volume fraction of Ni-solid solution phase increased in order of Cr-, Nb-and Al-added Ni₃(Si,Ti) alloys. The Cr-added Ni₃(Si,Ti) alloy was deformable at high strain rate, while the Nb-added one was deformable at low strain rate. It can be considered that the deformability of Ni₃(Si,Ti) at high temperature is closely correlated with volume fraction of Ni-solid solution phase and recrystallization behavior.

Abstract: Two-phase single-crystal intermetallic alloys composed of Ni₃Al (L1₂) and Ni₃V (D0₂₂) with some orientations were compressed at various temperatures, and their deformation microstructures were observed by transmission electron microscopy (TEM). The deformation at room temperature was governed by the glide motion of dislocations in the primary Ni₃Al precipitates and the activation of the microtwins in the Ni₃V variant structures in the channel regions. The interfaces between the primary Ni₃Al precipitates and the Ni₃V variant structures are suggested to work as the barriers to the dislocation motion. While, at temperature above the peak temperature (873 K), the deformation microstructures of the two-phase intermetallic alloy exhibited the ribbon-like deformation microstructures penetrating the constituent phases i.e. through the interfaces between primary Ni₃Al precipitates and the Ni₃V variant structures in the channel regions. It was also suggested that the superior strength in the two-phase intermetallic alloys is due to the high flow strength of the Ni₃V phases and to the interfacial hardening receiving when the dislocations activated in the primary Ni₃Al precipitates propagate to the channel regions.

Abstract: The objective of this study is to investigate the catalytic properties of intermetallic Ni₃Fe foil. We fabricated Ni₃Fe foil of 30 µm in thickness by a metallurgical process, and examined the catalytic activity of the Ni₃Fe foil for methanol decomposition from 513 to 973 K. The Ni₃Fe foil showed activity for methanol decomposition above 623 K. The activity increased with the increase of reaction temperature. Surface analysis revealed that a surface structure of fine Ni-Fe particles dispersed on carbon nanofibers was formed on the foil during the reaction. The activity is attributed to the formation of this fine structure.

Abstract: The effect of a concomitant doping of interstitial type elements boron (B) and carbon (C), and boron (B) and nitrogen (N) on tensile properties of a Ni₃(Si,Ti) intermetallic alloy was investigated in the temperature range between room temperature and 973 K. It was found that the concomitant doping of (C/B) and (N/B) remarkably improved the intermediate-temperature tensile elongation of the Ni₃(Si,Ti) alloy compared with the simple doping of B or C. It was also shown that the fracture surface of the alloy doped with (C/B) and (N/B) exhibited the ductile transgranular fracture mode while that of the alloy doped with only B showed a brittle intergranular fracture mode at 773 K. These results clearly indicate that the concomitant doping of the interstitial type elements are useful for improving the intermediate-temperature tensile ductility of the Ni₃(Si,Ti) alloy.

Abstract: Two atomic percent of refractory elements Ta and Re were added to an L1₂-type Ni₃(Si,Ti) intermetallic alloy in two methods of substituting for Ni or Ti. Alloying effect and substitutional behavior of the refractory elements on microstructure and mechanical properties were investigated. All the alloys were doped with 50 wt.ppm boron to suppress intergranular fracture. The Ta-added Ni₃(Si,Ti) alloys showed an entire or almost L1₂ single-phase microstructure. Their hardness was enhanced due to solid solution hardening which was primarily caused by the atomic size misfit. Also, the yield stress and tensile strength of the alloy where Ta was added by substituting for Ti, increased keeping a high level of tensile elongation. The Re-added Ni₃(Si,Ti) alloys showed a two-or three-phase microstructure containing fine Re-rich dispersions. The Re-added alloys exhibited relatively small grain size, and showed significantly high yield stress and ultimate tensile strength with a high level of tensile elongation.

Abstract: The microstructures and hardness property of dual two-phase intermetallic alloys that arecomposed of various kind of volume fractions of geometrically closed packed (GCP) Ni3Al(L12) and Ni3V(D022) phases were studied. The hardness of dual two-phase intermetallic alloys basically was explained by mixture rule in hardness between primary Ni3Al precipitates and eutectoid region.Nb and Ti addition raised the hardness of dual two-phase intermetallic alloys by solid solute hardening in the constituent phases.The additional hardening arising from interfacial area between primary Ni3Al precipitates and eutectoid region was also found. As temperature increases, theadditional hardening decreased for the base and Nb added alloys but decreased little for the Ti added alloys.