T. Masumoto

Highly ordered structure of icosahedral quasicrystals in Zn-Mg-RE (RE ≡ rare earth metals) systems

Abstract A new group of stable icosahedral phases (i-phases) in the Zn-Mg-RE system were found to have an ideal composition close to Zn50 Mg42RE8 (RE ≡ Y, Gd, Tb, Dy, Ho or Er). The new i-phases exhibit a highly ordered and nearly perfect face-centred icosahedral lattice as revealed by electron and X-ray diffraction and high-resolution electron microscopy. Powder X-ray diffraction indicates that the i-phase has long-range structural order with a correlation length over 1000 A, which is the largest found in the Frank-Kasper group. These new i-phases have the common valence concentration (about 2.08) and could be regarded as a new class of Hume-Rothery alloys.

Mechanical strength and thermal stability of Ti-based amorphous alloys with large glass-forming ability

Abstract Ti-based alloy powders produced by the high pressure gas atomization technique were found to consist of an amorphous single phase in the particle size range below 32 μm for Ti 50 Zr 10 Cu 40 and below 25 μm for Ti 50 Zr 10 Ni 20 Cu 20 , though the cooling rate of their molten alloys for gas atomization is considerably lower than that for melt spinning. In addition, the TiZrCu amorphous powders exhibit a rather wide supercooled liquid region before crystallization. This is believed to be the first evidence for the appearance of the supercooled liquid region for atomized Ti-based amorphous powders. The significant increase in the glass-forming ability and the wide temperature range of the supercooled liquid region for the TiZrCu ternary alloys are presumably due to the simultaneous satisfaction of the two criteria of the significantly different atomic size ratios among the constituent elements and the difficulty of long-range redistribution of the constituent elements for the growth of crystalline phases.

Workability of the supercooled liquid in the Zr65Al10Ni10Cu15 bulk metallic glass

The workability of the supercooled liquid in metallic glass has been examined through the extrusion of a Zr65Al10Ni10Cu15 at.% bulk glassy alloy with a wide supercooled liquid region. The metallic glass exhibited superplastic-like deformation behavior at high strain rates, resulting in an excellent workability. The working throughout a wide range of extrusion conditions was compatible with retaining the glass phase and the original strength. The extrusion maps and the expression between extrusion temperature, pressure and ram-speed have been established. Moreover, the features of working such as the Barus effect and the advantage of a small stepwise increase in strain rate have been revealed.

Mechanical properties of Fe-Si-B amorphous wires produced by in-rotating-water spinning method

Amorphous wires with high strength and good ductility have been produced in Fe-Si-B alloy system by the modified melt-spinning technique in which a melt stream is ejected into a rotating water layer. These wires have a circular cross section and smooth peripheral surface. The diameter is in the range of about 0.07 to 0.27 mm. Their Vickers hardness (Hv) and tensile strength (σf) increase with silicon and boron content and reach 1100 DPN and 3920 MPa, respectively, for Fe70Si10B20, exceeding the values of heavily cold-drawn steel wires. Fracture elongation(εf), including elastic elongation, is about 2.1 to 2.8 pct. An appropriate cold drawing results in the increase of σf and εf by about eight and 65 pct, respectively. This increase is interpreted to result from an interaction among crossing deformation bands introduced by cold drawing. The undrawn and drawn amorphous wires are so ductile that no cracks are observed, even after closely contacted bending. Further, it is demonstrated that the σf of the Fe75Si10Bl5 amorphous wire increases by the replacement of iron with a small amount of tantalum, niobium, tungsten, molybdenum, or chromium without detriment to the formation tendency of an amorphous wire. Such iron-based amorphous wires are attractive as fine gauge, high strength materials because of their uniform shape and superior mechanical qualities.

Nanocrystalline soft magnetic Fe-M-B (M = Zr, Hf, Nb) alloys and their applications

Abstract This paper reviews our results on the development of a new type of soft magnetic material with high saturation magnetic flux density (Bs) above 1.5 T as well as excellent soft magnetic properties. A mostly single bcc structure composed of α-Fe grains with about 10–20 nm in size surrounded by a small amount of an intergranular amorphous layer was obtained by crystallization of amorphous alloys prepared by melt-spinning technique. The typical nanocrystalline bcc Fe 90 Zr 7 B 3 , Fe 89 Hf 7 B 4 and Fe 84 Nb 7 B 9 ternary alloys subjected to the optimum annealing exhibit high Bs above 1.5 T as well as high effective permeability (μe) at 1 kHz above 20000. Excellent soft magnetic properties of the nanocrystalline Fe-M-B based alloys can be obtained by the decrease in the bcc grain size, magnetostriction (λ) and the increase in Tc of the intergranular amorphous phase by optimizing the crystallization process, chemical composition and adding small amounts of elements. For example, the improved FeZrNbBCu alloy shows the high ue of 160000 combined with the high Bs of 1,57 T. This excellent μe is comparable to those of nanocrystalline Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 and the zero-magnetostrictive Co based amorphous alloys, and the high Bs is comparable to those of the Fe based amorphous alloys with rather good soft magnetic properties. The excellent characteristics of a power transformer, a common mode choke coil, a pulse-transformer and a flux gate magnetic detector made of ‘NANOPERM ™ ’ were found in agreement with its very low core losses, sufficient thermal stability and low stress-sensibility of magnetic properties. The nanocrystalline Fe-M-B based alloys ‘NANOPERM ™ ’ is therefore expected to be used for many kinds of magnetic parts and devices.

Ductile aluminium-base amorphous alloys with two separate phases

Caracterisation de la resistance a la rupture par traction, de la ductilite de flexion, de la durete, de la temperature de cristallisation, de la chaleur de cristallisation et de la conductivite electrique des alliages amorphes Al-5 a 30% at. Si-5 a 30% at. X et Al-15 a 40% at. Ge-5 a 30% at. X ou X represente Ti, Zr, V, Nb, Cr, Co, Ni, Cu

Stability and transformation to crystalline phases of amorphous ZrAlCu alloys with significant supercooled liquid region

Abstract Crystallization from the supercooled liquid region was examined for an amorphous Zr65Al7.5Cu27.5 alloy with a significant supercooled liquid region before crystallization, with the aim of investigating the reason for the appearance of the wide supercooled liquid region. The crystallization takes place through the precipitation of a b.c.t. Zr2(Cu, Al) single phase which grows with a dendritic mode. The Avrami exponent (n value) and the activation energies for the nucleation and crystallization are 3.7, 260 and 230 kJ mol−1 respectively. Based on existing structural data as well as the present results, it is presumed that the appearance of the supercooled liquid region is due to the difficulty of growth resulting from the necessity of long-range redistribution of Al at the solid-liquid interface and to the difficulty of precipitation of Zr2(Cu, Al) caused by the large solid-liquid interfacial energy resulting from the highly dense random packed structure consisting of elements with significantly different atomic sizes and attractive bonding nature.

Stable Zn[sbnd]Mg[sbnd]rare[sbnd]earth face-centred icosahedral alloys with pentagonal dodecahedral solidification morphology

Abstract A thermodynamically stable face-centred icosahedral phase with a pentagonal dodecahedral solidification morphology has been found in Zn[sbnd]Mg[sbnd]RE (RE [tbnd] Y, Tb, Dy, Ho or Er) alloys. We report here the structure, stability and morphology in this new group of icosahedral alloys on the basis of results for the Zn[sbnd]Mg[sbnd]Y system.

Microstructures of FePt–Al–O and FePt–Ag nanogranular thin films and their magnetic properties

The microstructure and magnetic property relationship in L10 ordered FePt–Al–O and FePt–Ag granular thin films have been studied. As-sputtered FePt–Al–O films, composed of isolated fine spherical FePt particles of ∼2 nm diameter with a disordered face-centered-cubic (fcc) structure, exhibit superparamagnetism. Annealing above 650 °C induces a transformation from a disordered fcc structure to ordered L10 phase and the films become magnetically hard. The microstructures of these films change greatly depending on the film compositions and annealing conditions, which are correlated with the magnetic properties. It was found that FePt particles smaller than 5 nm do not order at 500 °C, while the continuous FePt film orders perfectly at the same temperature, suggesting that the ordering temperature, Tc, decreases significantly when the particle size becomes less than 5 nm. In the FePt–Ag granular thin film, when the Ag composition is around 50 at. %, high coercivity (∼10 kOe) and fine uniform microstructure are...

Application of the selected area channeling pattern method to the study of intergranular fracture in Ni3Al

Abstract The selected area channeling pattern method was applied to the characterization of grain boundaries on the basis of the coincidence lattice site model and to the detection of plastic strain accompanying intergranular fracture in cast or recrystallized Ll 2 type Ni 3 Al and Ni 3 (Al, Ti) polycrystals. The sum of the numbers of low angle and twin (Σ3) boundaries observed was less than 20% of the number of all boundaries studied. An evident resistivity of low angle and Σ3 boundaries against intergranular cracking was found. The boundaries of grains having the coincidence orientation relation (Σ5-Σ29) and random boundaries were preferentially broken under tensile stress. The amount of plastic strain accompanying intergranular fracture of Ni 3 Al was found to depend upon processing conditions (as-cast or as-recrystallized state), deformation temperature, and substitution of titanium for aluminum. It is pointed out that the amount of plastic strain is consistently larger in materials having higher resistivity against intergranular cracking.