Papers by Author: Hidemi Kato

Abstract: This paper describes investigation of the mechanical properties and biocompatibility of the Ti-based low-alloys minor alloying by the noble metal. It was found that almost all of the investigated Ti-based low-alloys, minor alloying by the noble metal, have relatively high biocompatibility, but found to be very brittle during tensile tests. The Ti₉₄Au₃Nb₃ alloy exhibited relatively good tensile mechanical properties, having very good plasticity.

Abstract: In recent years, bulk metallic glasses (BMGs) have received considerable attention due to their unique mechanical properties. However, the deformation of BMGs is highly localized in a few shear bands so that many of them exhibit poor plasticity. As such, more and more researchers have focused on improving the plasticity by in-situ or ex-situ introducing of nanoor micro-scale crystalline phases into the metallic glassy matrix in order to formation of multiple shear bands.

Abstract: Amorphous Cu–Zr metallic alloys were studied as precursors to catalysts for methanol steam reforming to produce hydrogen. The alloy ribbons were prepared by single-roll rapid solidification, and the optimum pretreatment method and conditions were determined. The activity of the catalysts prepared by the improved pretreatment method was greater than that of previously prepared catalysts by two degrees of magnitude. The addition of a very small amount of Pt enhanced the activity without increasing CO formation.

Abstract: We Successfully Prepared the Rod Glassy Samples of (Fe_1-xCo_x)₇₆Si₉B₁₀P₅ (x = 0~0.4) Bulk Metallic Glass (BMG) with the Diameters up to 3.0 mm by Substituting Fe for a Small Amount of Co Element. A Certain Amount of Co Substitution for Fe Contributes to the Increase of the Glass-Forming Ability (GFA) while Maintaining Good Mechanical Properties (the Fracture Strength up to 3700 MPa). This Co-Added Ferromagnetic Bulk Glassy Alloy System Also Exhibits a Higher Saturation Magnetization of 1.49 T and Lower Coercive Force (H_c, 1.2 A/m). The Fe-Based BMGs with Alloying a Small Amount of Co Element Demonstrate Excellent Combination of High GFA, Good Soft-Magnetic Properties as Well as High Strength.

Abstract: In this study, rapidly solidified Co-Sn-Ti and Co-Sn-Si alloys were investigated as candidate cathodic materials for lithium-ion batteries. (Co0.5Sn0.5)1-xTix (x=0.1, 0.2, 0.3, 0.4) and (Co0.5Sn0.5)0.9Si0.1 alloys were produced by Ar arc-melting. These alloys were further rapidly solidified into ribbons by the single-roll melt-spinning method. Constituent phases in the ribbons were identified by XRD, indicating that all of the alloys were composed of crystalline multi-phases with no amorphous phase. The microstructure of the ribbons was observed by SEM and TEM, and the chemical composition of constituent phases was analyzed by TEM-EDS. It is found from the SEM and TEM observations that the grain size of the constituent phases ranged from tens to hundreds nanometers due to the rapid solidification effect.

Abstract: A Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5 at. %) alloy system is found to exhibit a different dependence of glass-forming ability (GFA) on atmosphere-pressure during mold casting process. High-Pd alloys (x=7.5-17.5) show a remarkable increase of critical size for glass formation (dc) as casting-atmosphere (Ar) pressure varies from vacuum to ambient. No significant change of dc, however, is observed in low-Pd alloys (x=0-5) despite the variation in atmosphere pressure. The origin of the phenomenon is unveiled by correlating the cooling characteristic during mold casting and on-cooling phase transformation characteristic of the alloy system.

Abstract: Monolithic Zr65Al7.5Ni10Pd17.5 and Zr65Al7.5Ni10Cu17.5 hardly had plastic deformability in tension at room temperature, although Zr65Al7.5Ni10Pd17.5 showed a large plastic strain in compression. A depressed zone that is the evidence of viscous flow deformation (so-called viscous flow depression zone; VFD-zone) was observed for Zr65Al7.5Ni10Pd17.5 around the edge at the point of failure on its specimen surfaces. However, no VFD-zone was seen for Zr65Al7.5Ni10Cu17.5. Thus, a clear difference in tensile plastic behavior was found between Zr65Al7.5Ni10Pd17.5 and Zr65Al7.5Ni10Cu17.5. A structural change in the vicinity of the fracture surface of Zr65Al7.5Ni10Pd17.5 was measured by micro-beam X-ray diffractometry (MB-XRD). We may be able to discuss the room temperature plasticity of Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses correlating with the phase stability of the amorphous and icosahedral quasi-crystalline phases.

Abstract: Crystalline precipitates in a bulk-metallic-glass (BMG) braze were investigated with an intense x-ray microbeam. The precipitates were found in the Pd40Cu30P20Ni10 BMG braze matrix after joining crystalline Ti-6Al-7Nb. However, the role (if any) played by the precipitates in improving the mechanical bond of the BMG/crystalline joint is unknown. X-ray microdiffraction and microfluorescence measurements from small sample volumes were made with an ~ 0.5 x 0.5 μm2 beam. Spatially-resolved Laue diffraction and x-ray fluorescence measurements were made on several second-phase crystals within the BMG matrix. Although precipitate crystals with the observed compositions were anticipated to be predominantly hexagonal, one of the crystals was found to be cubic or tetragonal. The instrumentation includes capabilities for 3D depth-resolved measurements of crystal structure and for fluorescence analysis of elemental composition. Depth profiling gave information about the grain distribution and morphology in the BMG matrix.

Abstract: The hydrogen-induced internal friction and mechanical strength of the Ti-rich Ti34Zr11Cu47Ni8 and (Ti34Zr11Cu47Ni8)98Si2 hydrogenated glassy alloys have been investigated. It is found that the tensile strength is more than 0.8 GPa at room temperature when the hydrogen content is below about 20 at% for both alloys. The frequency dependence of peak temperature of the hydrogen-induced internal friction of (Ti34Zr11Cu47Ni8)98Si2-17.3 at%H hydrogenated glassy alloys has been clarified. Activation energy and pre-exponential factor are estimated to be 0.35 eV and 1.3x10-12, respectively. Compared with these values with those of Zr40Cu49Al10Si1 hydrogenated glassy alloys which show an internal friction peak around 300 K at about 300 Hz, it is found that the activation energy is much smaller than that of the latter although the pre-exponential factor is almost the same. Considering their similar composition and different component (Al), it is suggested that the component Al of the latter glassy alloys is effective for the higher activation energy which results in the increase of the peak temperature.