糸井 貴臣

Numerous thermal vacancies are frozen into FeAl B2-ordered alloy ribbons by a conventional rapid-solidification technique. Through heat treatment at 723 K, clustering of the supersaturated vacancies generates a large number of nanopores, particulary near surfaces, thus creating nanoporous surfaces. The nanoporous surface structure was confirmed by scanning electron microscopy and atomic force microscopy. The behavior of this vacancy clustering was examined by differential scanning calorimetry. An exothermic, irreversible peak, probably due to vacancy clustering, was observed around 800 K, giving an activation energy of about 1.17 eV. The nanopore formation was also observed by in-situ heating experiments in a transmission electron microscope. The pores have specific morphology and crystallography with pore surfaces faceting toward {100} planes. These results suggest that the vacancy clustering is a unique process which enables us to efficiently make nanoporous surfaces.

A thermally stable thin diffusion barrier in Cu/Si contacts was developed using a thin nano-crystalline ZrN film. The Cu/ZrN/Si contact system using a reactively sputtered ZrN barrier with 20 nm in thickness consisting of several to 10 nm grains tolerated annealing at 600 degreesC for 1 h without any Cu. penetration through the barrier. This was interpreted that the scarce structural change in the prepared nano-crystalline ZrN film due to annealing was favorite for the thermal stability of thin barrier application. (C) 2002 Elsevier Science B.V. All rights reserved.

A glassy Al85Ni10La5 alloy has a supercooled-liquid region of 16 K between a glass transition temperature at 526 K and a crystallization temperature at 542 K, while Al85Ni10Eu5 has no supercooled-liquid region and crystallizes at 514 K. Eu-151 Mossbauer spectroscopic study reveals that the Eu ions in Al85Ni10Eu5 are divalent, although the charge state of La ions is naturally considered to be trivalent in Al85Ni10La5. It is supposed that the thermal stability of this glassy alloy system strongly depends on not only the ionic radius of rare earth element but also the electronic state.

Ferromagnetic Co40Fe22Nb8B30 bulk glassy compacts having a high relative density about 99.6% and good soft magnetic properties were synthesized by consolidation of gas-atomized glassy powders. The high density was achieved by hot pressing under a pressure of 70 MPa using a decrease of viscosity in a supercooled liquid region. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

We have investigated the deformation behavior and the influence of deformation on the soft-magnetic properties for a ferromagnetic Fe72Hf8Nb2B18 (at.%) metallic glass that has a wide supercooled liquid region of 76 K before crystallization and good soft-magnetic properties. The metallic glass was found to exhibit superplasticity at the supercooled liquid state. The maximum elongation to failure was 240% that was obtained at 873 K (T-g + 17 K) and at 1.7 x 10(-3) s(-1) under a flow stress of about 100 MPa. In this condition, crystallization occurred at elongation above 100%, resulting from the lack of thermal stability. The metallic glass was, however, deformed up to an elongation of 100% with retaining the good soft-magnetic properties and glassy phase. We succeeded in establishing the constitutive formulation of the flow stress in the supercooled liquid region. Its formulation was expressed well by a stretched exponential function sigma (flow) = 3C epsilon exp(H/RT)[1 - exp(A/{B epsilon exp(H*/RT)}(0.85))]. (C) 2001 Elsevier Science B.V. All rights reserved.

A ferromagnetic amorphous phase with a large supercooled liquid region prior to crystallization and good soft magnetic properties was formed in melt-spun Co40Fe22Nb8-xZrxB30 (x = 0, 2. 4, 6. and 8 at%) alloys. The glass transition temperature (T-g) increases monotonously with increasing Zr content. The crystallization temperature (T-x) also increases by the dissolution of Zr up to 2% and then decreases with further increasing Zr content. The increases is more significant for T-x, resulting in a maximum DeltaT(x)(=T-x - T-g) of 98 K at 2% Zr. The Co-based amorphous alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.41 T-0.42 T, low saturated magnetostriction of 2.4 x 10(-6)-2.9 x 10(-6), low coercivity of 1.2-2.0 A/m, and high permeability of 29000-33000 at 1 kHz over the whole Zr content range. In addition, the cylindrical Co40Fe22Nb6Zr2B30 glassy alloy with a diameter of 1.0mm was prepared by the copper mold casting method. With increasing the cylindrical diameter up to 1.5 mm, the structure changes to coexistent amorphous, Co21Nb2B6, Co3ZrB2 and Co2B phases. It is noticed that the maximum thickness for glass formation is about 6 times larger than that for Co-based amorphous alloys reported up to date. The success of forming Go-based bulk amorphous alloys with high stability of supercooled liquid and good soft magnetic properties is encouraging further development of bulk amorphous soft magnetic materials.

This paper aims to with the review the formation, thermal stability and magnetic properties of Fe-based glassy alloys in as-cast bulk and melt-spun ribbon forms. The glassy alloys with a supercooled liquid region over 50 K before crystallization were formed in Fe-(Al,Oa)-P-C-B-Si, Fe-(Cr,Mo,Nb)-(Al,Ga)-(P,C,B), Fe-(Zr,Hf,Nb)-B, Fe-Co-(Zr,Nb,Ta)-(Mo,W)-B and Co-Fe-(Zr:Nb,Ta)-B systems and bulk glassy alloys were produced in a thickness range below 2 mm for the Fe-(Al,Ga)-(P,C,B,Si) system and 6 mm for the Fe-Co-(Zr,Nb,Ta)-(Mo,W)-B system by copper mold casting. The ring-shape glassy Fe-(Al,Ga)-(P,C,B,SI) alloys exhibit better soft magnetic properties as compared with the ring-shape alloy made from the ribbon because of their unique domain structure. The 30%B-containing glassy alloys in the Fe-Co-(Zr,Nb,Ta)-B system also exhibit a high-frequency permeability of 8000 at 1MHz The combination of high glass-forming ability and good soft magnetic properties indicates the possibility of future development as a new bulk glassy magnetic material.

New Fe-based and Go-based amorphous alloys with a high B concentration of 30at% were formed in (Fe,Co,Ni)(62)Nb8B30 system. The amorphous alloys exhibit a wide supercooled liquid region (Delta T-x) above 80K before crystallization in the range of 5 to 40%Co and 0 to 10%Ni and the largest Delta T-x is 87K for Fe52Co10Nb8B30. The Fe62-xCoxNb8B30 alloys exhibit good soft magnetic properties i.e., low coercive force (H-c) of 2-3 Am high effective permeability (mu(c)) of 20000-30000 at 1kHz and low saturated magnetostriction (lambda(s)) of 2-8 x 10(-6), The high Il characteristics are maintained in a higher frequency range and the highest mu(e) at 1kHz is 7500 for Co40Fe22Nb8B30 with a high resistivity of 237 mu Omega cm. The finding of the (Fe,Co)(62)Nb8B30 amorphous alloys exhibiting large Delta T-x, good high-frequency permeability and high resistivity is encouraging the future development as a new soft magnetic materials.

Ferromagnetic amorphous Fe-Nb-B alloys containing 30 at%B were found to exhibit a large supercooled liquid region with a temperature interval over 50 K before crystallization and the largest Delta T-x(=T-x-T-g) reaches 71 K for Fe62Nb8B30. The Delta T-x is strongly dependent on B content, while the soft magnetic properties of saturated magnetization (I-s), permeability (mu(e)) and saturated magnetostriction (lambda(s)) are dependent on Nb content. The Fe62Nb8B30 amorphous alloy exhibits good soft magnetic properties of 0.68 T for I-s, 2.6 A/m for coercive force (H-c), 19300 for mu(e) at 1 kHz and 7.7 x 10(-6) for lambda(s). The crystallization takes place through a single exothermic reaction, accompanying the simultaneous precipitation of the three crystalline phases of alpha-Fe, Fe2B and FeNb2B2. The crystallization mode which requires long-range atomic rearrangements plays a dominant role in achieving the high stability of the supercooled liquid against crystallization.

The increase in B content to 30 at. % for Fe-Co-Ni-Nb-B amorphous alloys caused an extension of a supercooled liquid region before crystallization, and a wide supercooled liquid region greater than 80 K was obtained in a wide composition range of 5-42 at. % Co and 0-10 at. % Ni for Fe62-x-yCoxNiyNb8B30 amorphous alloys. High B-containing amorphous alloys with low Ni content below 10 at. % have high electrical resistivity above 230 mu Omega cm and exhibit good soft magnetic properties, i.e., a low coercive force of 2 A/m, low saturated magnetostriction of 2-7 X 10(-6), and high permeability of 21 000-29 300 at 1 kHz and 5000-7500 at 1 MHz. The high-frequency permeability characteristics at 1 MHz are much better than those for any kind of soft magnetic materials, and have been presumed to result from the decrease in eddy current loss caused by the increase in electrical resistivity. The synthesis of the Fe-Co-Nb-B amorphous alloys exhibiting a wide supercooled liquid region greater than 80 K and high-frequency permeability of 7500 at 1 MHz is promising for future development as a type of soft magnetic material. (C) 1999 American Institute of Physics. [S0003-6951(99)01417-5].

A Co-based amorphous phase with glass transition and supercooled liquid region before crystallization was formed in Co70-xFexZr10B20 and Co72-xFexZr8B20 alloys containing more than 14 at % Fe. The crystallization temperature (T-x) is 899 K for the Co-Zr-B alloys and remains unchanged in the Fe concentration range up to 20%. The glass transition temperature (T-g) decreases with increasing Fe content, and the Delta T-x(= T-x-T-g) increases from 25 K at 14% Fe to 34 K at 21% Fe. The amorphous alloys with glass transition crystallize with a single stage precipitation of bcc Fe(Co) and Co3ZrB2 phases. The Go-rich amorphous alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.58-0.83 T, low coercivity of 4.7-8.3 A/m, and high permeability of 5500-18 300 in the frequency range of 1-10(3) kHz and low magnetostriction between - 1.5 x 10(-6) and + 10 x 10(-6) including zero. The success in synthesizing the soft magnetic amorphous alloys with high stability of supercooled liquid is promising for the future development of ferromagnetic Co-based bulk amorphous alloys. (C) 1998 American Institute of Physics.

New Co-based amorphous alloys with a wide supercooled liquid region above 40 K before crystallization and good soft magnetic properties were synthesized in the Co72-xFexZr8B20 and Co63Fe7Zr10-xMxB20 (M=Nb, Ta or W) systems. The supercooled liquid region defined by the difference between crystallization temperature (T-x) and glass transition temperature (T-g), Delta T-x(= T-x - T-g), is 39 K for Co56Fe16Zr8B20, 45 K for Co63Fe7Zr6Nb4B20, 40 K for Co63Fe7Zr4Ta6B20 and 44 K for Co63Fe7Zr6W4B20. The glass transition is also observed for the Co63F7M10B20 (M = Ta or W) alloys. The Co-based amorphous alloys with Delta T-x above 40 K exhibit low coercivity of 2.5 to 5.6 A/m, low magnetostriction of 1.7 x 10(-6) to 3.0 x 10(-6) and high permeability (mu(e)) of 10000 to 23000 at 1 kHz. The good mu(e) characteristics are maintained in a high frequency range and the mu(e) at 1 MHz is 5700 for Co56Fe16Zr8B20 and 6800 for Co63F7Zr6Ta4B20. The high frequency permeability is superior to those for conventional Co- and Fe-based amorphous alloys. The electrical resistivity (rho(n)) is as high as 1.7 to 2.0 mu Ohm m and hence the reduction of eddy current loss caused by the high rho(n) is presumed to be the origin of the better high-frequency permeability. The simultaneous achievements of good soft magnetic properties and high rho(n) are presumably due to the formation of a unique amorphous structure in which two kinds of atomic pairs of metal-metal (Co-Fe-Zr-M) and metal-metalloid (Co-Fe-Zr-M-B) types are homogeneously mixed on a subnanoscale, because the former type pair has good soft magnetic properties and the latter type pair has high rho(n). The good combination of high stability of the supercooled liquid and good soft magnetic properties is expected to induce future development as a new type of soft magnetic bulk amorphous alloy.

New Fe-based amorphous alloys in Fe-Co-Ni-Zr-B system exhibiting a wide supercooled liquid region before crystallization and good soft magnetic properties were found to be formed by melt spinning. The composition range of the amorphous (Fe1-x-yCoxNiy)(70)Zr10B20 alloys with the wide supercooled liquid region above 50 K extends from 0 to 36 at%Co and 0 to 30%Ni and the largest value of the supercooled liquid region defined by the difference between the glass transition temperature (T-g) and crystallization temperature (T-x), Delta T-x(= T-x - T-g) is 68 K for Fe56Co7Ni7Zr10B20. The crystallization from the supercooled liquid of the Fe56Co7Ni7Zr10B20 alloy upon continuous healing occurs through a single stage and the resulting crystallized structure consists of alpha-Fe, Fe2Zr and Fe3B phases containing Co and Ni elements. These Fe-based amorphous alloys exhibit good soft magnetic properties and the saturation magnetization, coercive force, permeability at 1 kHz and Curie temperature are respectively 0.96 T, 2.41 A/m, 17700 and 567 K for the amorphous Fe56Co7Ni7Zr10B20 alloy annealed for 600 s at 750 K. The finding of the Fe-based amorphous alloys with good soft magnetic properties and high thermal stability of the supercooled liquid is important for future development of ferromagnetic bulk amorphous alloys.