永瀬 丈嗣

MeV electron irradiation induced crystallization of supercooled liquid and amorphous phases in Zr66.7Cu33.3 Metallic Glass

A macroscopically phase-separated dual-layer ribbon can be obtained from (Co(75)Si(10)B(15))(70)Cu(30) alloy by using a conventional single-roller melt-spinning method, whereas such a structure cannot be obtained from (Fe(75)Si(10)B(15))(70)Cu(30) alloy. Liquid phase separation and amorphous phase formation take place simultaneously in Co-Si-B-Cu alloy, which leads to the formation of a unique structure during rapid solidification. (C) 2010 Elsevier B.V. All rights reserved.

Beta-Ti-type Ti-30Nb-10Ta-5Zr (TNTZ) wires with high bending ductility were developed using the arc-melt-type melt-extraction method. The continuous melt-extracted wire with very smooth surface and small fluctuations in the diameter realizes the high tensile strength and superior bending ductility of TNTZ alloy. The melt-extracted Beta-Ti wire shows the possibility for the use in biomedical applications. The arc-melt-type melt-extraction method is very effective for developing new Beta-Ti-based biomaterials.

MeV electron irradiation can introduce Frenkel pairs, i.e., a vacancy-interstitial pair, in crystals. In metallic glass, density fluctuation, namely, a pair of free volume and anti-free volume, is introduced, resulting in the devitrification of the amorphous phase in some metallic glasses. In this study, we investigated the temperature dependence of MeV-irradiation-induced crystallization of metallic glasses. Phase selection in crystallization shows a significant temperature dependence in various metallic glasses at and under 298 K. The size of the crystalline precipitates changes with irradiation temperature in some metallic glasses.

Beta-Ti-type Ti-30Nb-10Ta-5Zr (TNTZ) wires with high bending ductility were developed using the arc-melt-type melt-extraction method. The continuous melt-extracted wire with very smooth surface and small fluctuations in the diameter realizes the high tensile strength and superior bending ductility of TNTZ alloy. The melt-extracted Beta-Ti wire shows the possibility for the use in biomedical applications. The arc-melt-type melt-extraction method is very effective for developing new Beta-Ti-based biomaterials.

アモルファスFe-Nd-B合金の電子照射誘起結晶化によるナノ組織制御

MeV electron irradiation introduces density fluctuations in metallic glass, which lead to nano-crystallization at temperatures of 298 K and below in Zr(80)Pt(20) metallic glass. This density fluctuation corresponds to the formation of a Frenkel pair, i.e., a vacancy interstitial pair in the metallic crystal. Phase selection in MeV-electron-irradiation-induced crystallization exhibits temperature dependence. Two f.c.c. crystalline phases were reduced to one f.c.c. phase when the temperature was reduced from 298 K to 20 K. The formation of the quasicrystal (QC) phase during thermal crystallization affects MeV-electron-irradiation-induced crystallization. (C) 2009 Elsevier Ltd. All rights reserved.

Cu crystalline globule dispersed Fe-based metallic glass was formed in Fe(60)Cu(10)Zr(10)B(20) and Fe(50)Cu(20)Zr(10)B(20) alloys. The size of Cu crystalline globules was in the range of 10 nanometer order to micrometer order, and these globules were formed by multi-step liquid phase separation. The combination of liquid phase separation to Fe-based and Cu-based liquids and metallic glass formation in Fe-Zr-B liquid led to the formation of a unique solidified structure that could not be formed through conventional solidification modes such as dendrite formation and eutectic and peritectic reactions. The size of the nanoglobules was controlled by the alloy composition. (C) 2010 Elsevier B.V. All rights reserved.

A rapidly solidified wire of Fe-Cu-Si-B alloy with a macroscopically separated structure was formed by the arc-melt-type melt-extraction method. A unique core-wire/surface-cover-layer structure composed of core Fe-Si-B-based amorphous alloy and cover Cu crystal was formed by liquid phase separation during rapid quenching of thermal melt. (C) 2010 Elsevier B.V. All rights reserved.

Electron-irradiation-induced solid-state amorphization (SSA) in C16-Zr(2)Ni was investigated by molecular dynamics (MD) simulations by focusing on the atomic-scale mechanism. C16-Zr(2)Ni is a typical intermetallic compound that undergoes SSA under MeV electron irradiation. Electron-irradiation-induced SSA was achieved through the accumulation of lattice defects by MD calculations using an embedded-atom (EAM) potential. The Frenkel pairs introduced in the intermetallic compounds could not be removed because of the difficulties in converting the defective crystal back into the original crystal through thermal recovery of the lattice defects; this caused chemical and topological disorder in the crystal. Thermal relaxation (thermal recovery of lattice defects) increased topological and chemical disorder in the local areas of the crystal. The increase in the disordered local area in turn induced SSA. Changes caused by thermal relaxation of the lattice defects in the atomic configuration induced SSA in intermetallic compounds. (C) 2009 Published by Elsevier Ltd.

A rapidly solidified wire of Fe-Cu-Si-B alloy with a macroscopically separated structure was formed by the arc-melt-type melt-extraction method. A unique core-wire/surface-cover-layer structure composed of core Fe-Si-B-based amorphous alloy and cover Cu crystal was formed by liquid phase separation during rapid quenching of thermal melt. (C) 2010 Elsevier B.V. All rights reserved.

Electron-irradiation-induced solid-state amorphization (SSA) in C16-Zr(2)Ni was investigated by molecular dynamics (MD) simulations by focusing on the atomic-scale mechanism. C16-Zr(2)Ni is a typical intermetallic compound that undergoes SSA under MeV electron irradiation. Electron-irradiation-induced SSA was achieved through the accumulation of lattice defects by MD calculations using an embedded-atom (EAM) potential. The Frenkel pairs introduced in the intermetallic compounds could not be removed because of the difficulties in converting the defective crystal back into the original crystal through thermal recovery of the lattice defects; this caused chemical and topological disorder in the crystal. Thermal relaxation (thermal recovery of lattice defects) increased topological and chemical disorder in the local areas of the crystal. The increase in the disordered local area in turn induced SSA. Changes caused by thermal relaxation of the lattice defects in the atomic configuration induced SSA in intermetallic compounds. (C) 2009 Published by Elsevier Ltd.

Beta-Ti-type Ti-30Nb-10Ta-5Zr (TNTZ) wires with high-ductility were developed using the arc-melt-type melt-extraction method. The continuous melt-extracted wire with very smooth surface and small fluctuations in the diameter realizes the high tensile strength and superior. bending ductility of TNTZ alloy. The melt-extracted Beta-Ti wire shows the possibility for the use in biomedical applications. The arc-melt-type melt-extraction method is very effective for developing new Beta-Ti-based biomaterials. [doi:10.2320/matertrans.M2009163]

A dual-layer ribbon of Co-Si-B-Cu alloy was prepared by the single-roller melt-spinning method. The substrate surface comprised Co-Si-B-based amorphous phase with Cu crystalline nanoscale globules, while the free surface showed a thin crystalline Cu layer. A macroscopically separated unique structure was obtained by the simultaneous occurrence of liquid phase separation of the Co-Cu-based alloy system and amorphous phase formation in the Co-Si-B alloy layer. © 2010 Elsevier Ltd. All rights reserved.

MeV electron irradiation can introduce a single atom displacement through electron knock-on effect in metallic materials. In a crystal, a pair of vacancy and interstitial, namely, a Frenkel pair is formed by MeV electron irradiation. In contrast, a pair of free volume and counterpart (anti free volume), namely, density fluctuation is formed by a single atom displacement in an amorphous. Density fluctuation introduction by the irradiation sometimes leads the devitrification of an amorphous phase in some metallic glasses. High voltage electron microscope (HVEM) offers an unique opportunity to understand density fluctuation in metallic glasses through the irradiation induced structure change. In this study, MeV electron irradiation induced crystallization of melt-spun amorphous phase in Fe-M-B (M=Nd and Zr) ternary metallic glass was investigated focusing on the phase stability of an amorphous phase against the irradiation. The irradiation induced crystallization of melt-spun amorphous phase by 2.0MV electron irradiation at 298K was observed in both Fe-Nd-B and Fe-Zr-B metallic glasses.

MeV electron irradiation can introduce a single atom displacement through electron knock-on effect in metallic materials. In a crystal, a pair of vacancy and interstitial, namely, a Frenkel pair is formed by MeV electron irradiation. In contrast, a pair of free volume and counterpart (anti free volume), namely, density fluctuation is formed by a single atom displacement in an amorphous. Density fluctuation introduction by the irradiation sometimes leads the devitrification of an amorphous phase in some metallic glasses. High voltage electron microscope (HVEM) offers an unique opportunity to understand density fluctuation in metallic glasses through the irradiation induced structure change. In this study, MeV electron irradiation induced crystallization of melt-spun amorphous phase in Fe-M-B (M=Nd and Zr) ternary metallic glass was investigated focusing on the phase stability of an amorphous phase against the irradiation. The irradiation induced crystallization of melt-spun amorphous phase by 2.0MV electron irradiation at 298K was observed in both Fe-Nd-B and Fe-Zr-B metallic glasses.

Phase selection in electron-irradiation-induced crystallization and crystal-to-amorphous-to-crystal (C-A-C) transition at 298 K in quasicrystal-forming Zr-Pt metallic glass alloys were investigated. Two types of f.c.c. nano-crystalline precipitates were formed in amorphous Zr(80)Pt(20) and Zr(66.7)Pt(33.3) alloys under electron irradiation; such unique nano-crystalline structures were not observed during thermal annealing. It was inferred that unique phase selection in electron-irradiation-induced crystallization and thermal crystallization can be explained by the large negative chemical mixing enthalpy (Delta H(chem)) in Zr-Pd and Zr-Pt alloys. (C) 2009 Elsevier Ltd. All rights reserved.

Nanocrystallization of amorphous alloys induced by electronic energy deposition has been frequently reported in recent years. In this paper, the crystallization of amorphous Fe85B15 alloy was performed by electron irradiation with 2 MeV electrons LIP to a flux of 4.0 x 10(24) m(-2) s(-1). It was found that at 298 K, nanocrystalline Fe-B intermetallic phases formed prior to alpha-Fe phase, while at 463 K. only the alpha-Fe phase was observed. This phenomenon cannot be interpreted in terms of the electron-beam heating, but may be attributed to the irradiation-induced increases in the short-range order and atomic diffusivity. Theoretical analysis also showed that the maximum-temperature rise driven by beam heating is Much lower than that required for thermal crystallization. Our work offers strong evidence that the irradiation-induced crystallization in amorphous alloys is not a thermal activation process. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Mechanical atomic displacement in intermetallic compounds can be introduced by various processes such as severe plastic deformation, mechanical milling and electron irradiation, resulting in the crystal-to-amorphous (C-A) transition and amorphous-to-crystal (A-C) transition in some alloy systems. Recently, unique atomic displacement-induced-phase transitions containing both amorphization and crystallization was found: a crystal-to-amorphous-to-crystal (C-A-C) transition under electron irradiation and a cyclic C-A transition during mechanical milling. The features and predicting factors of alloy systems which undergo C-A-C transition under MeV electron irradiation are discussed based upon the analysis of experimental data reported to date in intermetallic compounds irradiated by high voltage electron microscope (HVEM).

New Zr-based metallic glass wires with and without bio-toxic elements of Ni and Al for the application to biomaterials were prepared by arc-melting type melt-extraction method and their characteristics were tested. The continuous metallic glass wires with a good white luster and smooth surface were obtained in various alloys such as conventional Zr-Al-Ni-Cu, Ni-free Zr-Al-Co-Cu, and Ni and Al free Zr-Ti-Co alloys. The Zr-based metallic glass wires exhibit high tensile strength reaching 1 GPa. Furthermore, the metallic glass wires showed good bending ductility and could be bent through 180 degrees without fracture. The Zr-based metallic glass wires achieve simultaneously high tensile strength, good bending ductility and high thermal stability.

Formation of nano-structure in melt-spun ternary Fe-Nd-B alloys was examined focusing on electron irradiation induced crystallization. In Fe82.2Nd7.1B10.7 (Fe/Nd/B = 23/2/3), Fe77Nd4.5B18.5 and Fe71Nd9B20 alloys, melt-spun amorphous phase changed to a crystalline phase during electron irradiation and nano-structure was formed. The crystalline phase in melt-spun Fe86Nd9B5 and Fe82.4Nd11.8B5.8 (Fe/Nd/B = 14/2/1) alloys was unstable under electron irradiation and electron irradiation induced amorphization occurred. With the further irradiation,crystallization from the amorphous phase was induced resulting in forming nano-crystalline structure. The onset total dose for the irradiation induced crystallization, namely, stability of the amorphous phase against electron irradiation depends strongly on the Fe-ratio, crystallization temperature, mismatch entropy and mixing enthalpy of the alloys.

Formation of nano-structure in melt-spun ternary Fe-Nd-B alloys was examined focusing on electron irradiation induced crystallization. In Fe82.2Nd7.1B10.7 (Fe/Nd/B = 23/2/3), Fe77Nd4.5B18.5 and Fe71Nd9B20 alloys, melt-spun amorphous phase changed to a crystalline phase during electron irradiation and nano-structure was formed. The crystalline phase in melt-spun Fe86Nd9B5 and Fe82.4Nd11.8B5.8 (Fe/Nd/B = 14/2/1) alloys was unstable under electron irradiation and electron irradiation induced amorphization occurred. With the further irradiation,crystallization from the amorphous phase was induced resulting in forming nano-crystalline structure. The onset total dose for the irradiation induced crystallization, namely, stability of the amorphous phase against electron irradiation depends strongly on the Fe-ratio, crystallization temperature, mismatch entropy and mixing enthalpy of the alloys.

The difference in electron irradiation induced crystallization behavior of melt-spun amorphous phase among Zr66.7M33.3 (M = Cu, Ni and Pd) alloys was investigated. An amorphous phase was unstable under electron irradiation and the irradiation induced crystallization of the amorphous phase occurred in the three alloys. The phase selection of electron irradiation induced crystallization in Zr66.7Pd33.3 was obviously different from that in Zr66.7Cu33.3 and Zr66.7Ni33.3, while there was no significant difference between the latter two. The origin of the unique phase selection in Zr66.7Pd33.3 alloy was discussed based on the database of electron irradiation induced crystallization in Zr-based alloys.

Electron irradiation induced crystal-to-amorphous-to-crystat (C-A-C) transition in metallic glasses was investigated in various metallic glasses among binary Zr-based. ternary Fe-Nd-B and Fe-Zr-B alloys. In situ observation of the TEM miciostructures and corresponding SAD patients was performed by ultra high-voltage electron microscope (UHVEM). The origin of amorphization, crystallization and C-A-C transition was discussed based on the temperature-Gibbs free energy diagram.

The effect of electron irradiation on the phase transformation in binary Fe-Nd and ternary Fe-Nd-B alloys was investigated. Electron irradiation induced nano-crystallization of amorphous-to-crystal (A-C) transition was observed in several Fe-Nd-B metallic glasses. In Nd2Fe14B compound. solid-state amorphization (SSA) of crystal-to-amorphous (C-A) transition Occurred under electron irradiation. With further irradiation. the amorphous phase obtained by SSA transformed to the nano-crystalline phase through irradiation induced crystallization. resulting in crystal-to-amorphous-to-crystal (C-A-C) transition. A-C, C-A and C-A-C transition were also observed in some ternary Fe-Nd-B and binary Fe-Nd alloys. The electron irradiation technique is effective for the formation and control of nano-crystalline structure through A-C transition of amorphous phase and/or C-A-C transition of metallic compounds.

Electron irradiation induced nano-crystallization of melt-spun amorphous phase in Fe-Zr-B ternary alloys was investigated focusing on the difference in phase stability of amorphous phase during thermal annealing and electron irradiation. Nano-composite structure composed of nano-crystalline alpha-Fe precipitates with b.c.c.-structure, metallic Compounds and a residual amorphous matrix was formed under 2.0 MeV electron irradiation at 298 K, while such nano-structure was hardly realized by thermal annealing. The phase stability of an amorphous phase against electron irradiation was discussed based on the relationship between thermal properties and critical onset total dose of electron irradiation induced crystallization at 298 K.

Electron-irradiation-induced phase transformations in supercooled liquid, amorphous and crystalline phases were investigated in Zr66.7Cu33.3 (numbers indicate at.%) metallic glass. The supercooled liquid and amorphous phases were unstable under electron irradiation at and above 552K: C11(b)-Zr2CU crystalline phase was formed through electron irradiation induced crystallization. Electron-irradiation-induced crystal-to-supercooled liquid transition and crystal-to-amorphous transition in C11(b)-Zr2Cu crystalline phase did not occur at and above 552 K. Phase selection in electron irradiation induced crystallization was sensitive to the phase stability of crystalline phases against electron irradiation. (c) 2006 Elsevier B.V. All rights reserved.

Electron irradiation induced phase transformation behavior in Fe77Nd4.5B19.5 (number indicate at.%) metallic glass was investigated. The melt-spun amorphous phase could not keep the original structure under electron irradiation at 298 K. alpha-Fe, Nd2Fe14B and Fe17Nd2 phases precipitated from the amorphous phase. There was a great difference in phase selection in a crystallization process between thermal annealing and electron irradiation. The Nd2Fe14B and Fe17Nd2 intermetallic compounds transformed to an amorphous phase under electron irradiation at 121 K, while the amorphization of alpha-Fe solid solution did not occur. A unique nanocrystalline structure which cannot be realized by thermal crystallization was formed through electron irradiation induced crystallization and amorphization. (c) 2006 Elsevier B.V. All rights reserved.

In situ observation of solid-state amorphization in Nd2Fe14B compound was achieved by electron irradiation method. Under 2.0 MeV electron irradiation, crystalline contrast corresponding to Nd2Fe14B crystalline phase in a bright-field image disappeared suddenly when the total dose reached a critical value. The amorphous phase was rapidly formed tinder electron irradiation. Solid-state amorphization process at the critical total dose seems to be analogous to thermal melting process of crystal at the melting temperature. (c) 2006 Elsevier B.V. All rights reserved.

Effect of electron irradiation on supercooled liquid ill Zr66.7Cu33.3. Zr65Al7.5Cu27.5 and Zr60Al15Ni25 metallic glasses was investigated by in situ TEM observation. The electron irradiation induced crystallization Occurred in the supercooled liquid with nucleation and growth mode similar to that by thermal annealing. The electron irradiation accelerated crystallization resulting in different size and morphology of precipitates from those by thermal annealing. There was no significant difference in phase selection and crystallization mode Of Supercooled liquid between thermal annealing and electron irradiation, while electron irradiation induced crystallization behavior of an amorphous phase was different from that of thermal crystallization.

Both amorphization and crystallization were observed in Zr66.7Pd33.3 metallic glass under electron irradiation. The melt-spun amorphous phase was not stable under 2.0 MV electron irradiation and two kinds of fcc-solid solution were precipitated through electron irradiation-induced crystallization at 103 and 298 K. The fcc-solid Solution obtained by electron irradiation-induced crystallization at 298 K transformed to an amorphous phase during irradiation at 103 K. Electron irradiation-induced phase transformation behavior in Zr66.7Pd33.3 metallic glass can be explained by phase stability of an amorphous phase and crystalline phases against electron irradiation.

Electron irradiation induced phase transformation behavior of an amorphous phase in Zr66.7Ni33.3 alloy, and an amorphous phase or supercooled liquid in Zr60Al15Ni25 alloy was investigated. The amorphous phase could not maintain the original glassy structure under electron irradiation at 298 K, and f.c.c.-solid solution precipitated under electron irradiation in both alloys. The precipitation of C16-Zr2Ni, big-cube (metastable f.c.c.-based Zr2Ni intermetallic compound), Zr6Al2Ni and Zr5AlNi4 crystalline phases from an amorphous phase was not observed during electron irradiation induced crystallization. The amorphous phase in Zr60Al15Ni25 metallic glass shows the highest phase stability against electron irradiation induced crystallization among Zr66.7Cu33.3, Zr66.7Ni33.3, Zr(65)A(17.5)Ni(27.5), Zr65Al15Ni25 and Zr65Al7.5Ni10Cu17.5 alloys. In Zr(60)AI(15)Ni(25) metallic glass, electron irradiation promoted the precipitation of f.c.c.-solid solution and Zr6Al2Ni crystalline phases from the supercooled liquid. (c) 2006 Elsevier Ltd. All rights reserved.

Pinpoint nano-crystallization in Fe-based metallic glass was achieved by 2.0MV electron irradiation. Circular nano-crystalline structure regions with about 1 mu m in diameter were formed in the metallic glass and they were well dispersed in the amorphous matrix. In Fe77.5Nd4B18.5 alloy, micrometer order hard magnetic nano-composite region was formed in non-magnetic metallic glass matrix by electron irradiation. Electron irradiation induced crystallization is very effective for obtaining superior functional metallic materials with fine magnetic domains.

Electron irradiation induced crystallization is effective for producing a nano-crystalline phase at the localized region in metallic glass matrix. In Zr66.7Pd33.3 metallic glass, two kinds of f.c.c. super-saturated solid solution which were confirmed by high resolution electron microscopy observation and diffraction analysis precipitated from an amorphous phase at 298K irradiation. Temperature dependence of phase selection in electron irradiation induced crystallization was also examined.

The crystallization behavior of Zr65.0Al7.5Cu27.5 (at.%) metallic glass with 753 and 1053 K annealing treatment and its effect on oxidation resistance around the supercooled liquid region at 623 and 663 K was studied. The crystalline phase of bct-Zr2Cu precipitates for the specimen annealed at 753 K was observed, while duplex structures of bct-Zr2Cu and Zr2Al formed in the specimen annealed at 1053 K. The oxidation resistance of the specimen depended on the amount of crystalline precipitates. Regardless of the exposure temperature, the annealed specimens showed higher oxidation resistance than the melt-spun one, especially for the specimen annealed at 1053 K. The formation of numerous crystalline phases of bct-Zr2Cu and Zr2Al from the matrix was responsible for improving the oxidation resistance due to their higher oxidation resistance and promotion of the development of Al2O3 and oxides of copper. The oxide constituents of the amorphous alloy after long exposure depended on the temperature. The oxide was composed of a large amount of CuO, some tetragonal and monoclinic-ZrO2 and a minor amount of Cu2O as well as a slight amount of Al2O3 for the melt-spun specimen during exposure at 623 K. Under the 663 K exposure, however, the oxide state of Cu3+ in the scale was also detected. (c) 2006 Elsevier B.V. All rights reserved.

The effect of thermal crystallization on viscous flow of supercooled liquid in Zr60Al15Ni25 metallic glass was investigated. Zr6Al2Ni crystalline precipitates with ellipsoidal morphology appeared during thermal annealing and deformation at high temperatures. No significant difference in phase selection or morphology of crystalline precipitates was observed between non-deformed and deformed specimens. The viscous flow behavior is very sensitive to the strain rate and the stress-strain behavior can be classified into three types depending on the strain rate: stress overshoot mode, stable viscous flow mode with constant flow stress. and strain hardening mode. The strain hardening is caused by the precipitation of Zr6Al2Ni phase from supercooled liquid. The flow stress increased with increase in the crystallization ratio for specimens containing a volume fraction of Zr6Al2Ni phase higher than 10% although the stress showed no significant change with slight crystallization. (c) 2006 Elsevier Ltd. All rights reserved.

Transformation and change in the microstructure of Nd2Fe14B compound under electron irradiation were examined. The Nd2Fe14B compound did not maintain its original structure under electron irradiation and was transformed to an amorphous phase through solid-state amorphization. With further electron irradiation, crystallization of the amorphous phase occurred forming a nano-crystalline structure. The phase selection of electron irradiation induced crystallization depended strongly on the irradiation temperature; nanocrystalline alpha-Fe phase precipitated in the amorphous phase at 104 K, while a nanoduplex structure composed of alpha-Fe, compounds and residual amorphous phase was formed at 298 K. Electron irradiation induced phase transformation is a very effective method to control the nanocrystalline structure in Fe-Nd-B alloy.