Kenzo Fukaura

Cast structure and mechanical properties of Zr–Cu–Ni–Al bulk glassy alloys

Abstract Homogeneous melting without any nuclei was performed using the cold copper nozzle arc casting furnace and ladle arc-melt type furnace. Casting of a bulk glassy alloy can be achieved by using a copper nozzle arc casting furnace, which eliminates nucleation site (cold spot) for crystallization. Besides, the pouring molten alloy was melted homogeneously by arc heating before casting into the mold, similar to a pseudo float melting state. To produce a bulk glassy alloy sheet, a combination of the ladle arc-melt type furnace and squeeze cast method was used. Using this method, we succeeded in producing Zr 50 Cu 30 Ni 10 Al 10 bulk glassy alloys in a rod shape by the former method and in a sheet form by the later method. Tensile strength of the Zr 50 Cu 30 Ni 10 Al 10 bulk glassy alloy sheet is about 1900 MPa and the plasticity of the alloy at room temperature is significantly improved by cold rolling.

Stable decagonal quasicrystal in an Al-Mn-Fe-Ge system

A thermodynamically stable quasicrystalline phase with a decagonal structure was found to be formed in an Al40Mn25Fe15Ge20. The single phase was prepared by conventional solidification, followed by annealing for 100 h at 1050 K and then water quenching. The decagonal phase was identified to be the 6 layer (1.2 nm) Al4Mn-type decagonal structure. This alloy exhibits magnetization of 6.3 emu/g in an applied field of 10 kOe at 40 K.

Anisotropic Diamagnetic Susceptibility of AlNiCo Quasi-crystal

We have carried out magnetization measurements of a single decagonal Al72Ni12Co16 quasi-crystal for the cases of the magnetic field parallel and perpendicular to the periodic axis with a torsion-type magnetic balance in various magnetic fields up to 10 kOe from 4.2 K to room temperature. Anisotropic diamagnetic susceptibility was observed, which is closely correlated to the electron motions in the quasi-crystal.

Influence of Microshot Peening on Surface Layer Characteristics of Cold Tool Steel

Shot peening is a surface treatment and improves the performance of engineering components. More recently, a new type of microshot has been developed to enhance peening effect. In the present study, the influence of microshot peening on the surface layer characteristics of cold tool steel was investigated. In the experiment, the microshot peening apparatus with a heating furnace was produced experimentally. The projective method of the microshot was a compressed air type. The peening microshots of 0.1mm diameter were cemented carbide and the workpiece was commercially cold tool steel SKD11. Surface roughness, compressive residual stress, and hardness in the peened workpiece were measured. The effect of microshot peening on the fatigue strength of cold tool steel was also examined. The use of hard microshot such as cemented carbide was found to cause a significantly enhanced peening effect for cold tool steel.

INFLUENCE OF SHOT PEENING ON SURFACE CHARACTERISTICS OF HIGH-SPEED STEELS

High-speed steels are generally used for the cutting of other hard materials. These are hard materials, and can be used at high temperatures. Therefore, some of them are used for warm metal forming such as forging. However, in the tools used in hot working, an excellent hot hardness and long-life fatigue are strongly required. In the present study, the influence of shot peening on the surface characteristics of high-speed steels was investigated. Shot peening imparts compressive residual stresses on the metal surface, thus improving the fatigue life of the machine parts. In the experiment, the shot peening treatment was performed using an air-type shot peening machine. The shots made of cemented carbide were used. The workpieces were two types, W-type and Mo-type alloys. Surface roughness, compressive residual stress, and hardness of the peened workpieces were measured. It was found that shot peening using the hard shot media was effective in improving the surface characteristics of high-speed steels.

Butt Joining of Dissimilar Sheets by Shot Peening

The butt joining of dissimilar sheets using a shot peening process was investigated. Shot peening is a surface treatment and improves the performance of engineering components. In shot peening, the substrate undergoes a large plastic deformation near its surface due to a hit with many shots. Thus, plastic flow characterized by a shear droop occurs at the edge of the substrate due to shot peening. When the dissimilar sheets with the edge of the notch geometry are connected without level difference and shot-peened the connection, the sheets can be joined due to the plastic flow generated by the large plastic deformation during shot peening. In the experiment, a compressed-air-type shot peening machine was employed. The influences of processing conditions on the joining of the dissimilar sheets were examined. The joint strength increased with the kinetic energy of shots. It was found that the present method using shot peening process was effective in joining dissimilar sheets.

Lining of Carbon Steel with Metal Foils by Shot Peening

A lining process for carbon steel using shot peening was investigated. In the shot peening experiment, the dissimilar foil set on the carbon steel substrate is pelted with many shots at a high velocity. The foil is bonded to the surface of the substrate due to plastic deformation induced by the collision of the shots. In the experiment, an air-type shot peening machine with an electrical heater was employed. The substrates are commercially carbon steel S45C, and the foils are commercially pure aluminum, pure copper, and pure nickel. The effects of shot conditions and the heating temperature on the joinability were examined. To improve surface characteristics such as wear resistance and corrosion resistance, the surface alloying of the lined workpiece was also attempted. The metal foils were successfully joined to the surface of the substrate. It was found that surface properties of carbon steel could be improved by the shot lining process.

Strain Affected Properties of Icosahedral Al–Pd–Mn Single Ingot

Some physical properties of the Al–Pd–Mn icosahedral quasicrystal are drastically changed by inhomogeneous strain distribution, as exemplified for the electrical resistivity and the Vickers hardness. In order to reveal the intrinsic properties of the Al–Pd–Mn icosahedral alloy, the study on the relation between the strain and the properties was investigated. By the full anneal treatment (1000 K, 50 h), the anisotropies of the electrical resistivity and the Vickers hardness are found to annihilate significantly with decreasing anisotropic strain distribution. And the intrinsic properties are estimated by the extrapolation from the relation between the strain and the physical property to the no strain state.

Tensile Deformation Behaviors of Metastable Austenitic Stainless Steels Studied by Neutron Diffraction

Tensile deformation behaviors of three austenitic stainless steels, JIS-SUS310S, 304 and 301L, were studied by static tensile tests and in situ neutron diffraction. In the mechanical properties obtained by the static tensile tests, the 304 and 301L steels showed better balance of tensile strength and uniform elongation than the 310S one because of TRIP effect. The angular dispersion neutron diffractions with a wavelength of 0.16 or 0.182 nm were performed during stepwise tensile testing by using a neutron diffractometer for residual stress analysis (RESA) at the Japan Atomic Energy Agency. The lattice plane strain, stress-induced martensite volume fraction, dislocation density and so on were estimated by the profile analysis as a function of applied stress. The change in lattice plane spacing for austenite indicated four deformation stages. In the comparison of lattice plane strain among the tested steels, a phase stress caused by the stress-induced martensite seems to overlap the intergranular stress of austenite phase. Judging from the results of profile analysis, the strain partitioning of austenite phase in metastable austenitic steels became larger with increasing of the volume fraction of stress-induced martensite during tensile deformation.

Grain Refinement of Metal Surface Using Hot Shot Peening

In this study, the grain refinement near the surface of metal workpiece using hot shot peening was investigated to improve the surface properties of the workpiece. In this process, the grains were refined due to plastic deformation generated by the collision of a lot of shots under hot working conditions. A model experiment using two shots was carried out to examine the effects of the amount of deformation, the processing temperature and the time interval of the collision on grain size. In the experiment, the workpieces were stainless steel SUS304 and commercially pure copper. It was found that the global surface layer successfully attained to the fine grains by means of hot shot peening.