Muneyuki Imafuku

Structural study of amorphous Fe70M10B20(M = Zr, Nb and Cr) alloys by X-ray diffraction

The local atomic structures in the amorphous Fe70Zr10B20 ,F e 70Nb10B20 and Fe70Cr10B20 alloys with different Tx were studied by the ordinary X-ray diffraction, anomalous X-ray scattering (AXS) measurements and EXAFS analyses. The essential features of the atomic structures resemble in these amorphous alloys. Only the difference in the local atomic structure is a distorted shape of the triangular prism due to the size difference between Fe and M. From the correspondence of the size difference with Tx and the study of the crystallization process by the DSC measurements and the X-ray diffraction method, we conclude that the difference of their thermal stability is closely related with the difficulty of rearrangements of the prisms during crystallization.

Formation of τ-Phase in Fe60Nb10B30Amorphous Alloy with a Large Supercooled Liquid Region

A metastable nanocrystalline τ-phase with a complex fcc structure was confirmed as a primary precipitation phase in the melt-spun Fe60Nb10B30 amorphous alloy with a two-stage crystallization process. The phase transformation from the amorphous phase to the τ-phase takes place at 1001 K at a heating rate of 0.67 K/s. The microstructure of this phase is composed of homogeneously distributed fine grains in the diameter range below 10 nm. The composition of this phase is almost the same as that of the starting amorphous phase. The τ-phase decomposes into α-Fe, Fe3B and Fe2B phases in the second-stage reaction.

Structural study of Fe90−xNb10Bx (x=10, 20 and 30) glassy alloys

Abstract The local atomic structures of Fe90−xNb10Bx (x=10, 20 and 30) glassy alloys have been investigated by anomalous X-ray scattering measurements. A trigonal prism-like chemical short range ordered (CSRO) structure of (Fe,Nb)6B was found in Fe60Nb10B30 and Fe70Nb10B20 alloys exhibiting a large supercooled liquid region defined by the temperature interval, ΔTx between the glass transition temperature, Tg and the crystallization temperature, Tx, (ΔTx=67 and 53 K, respectively), whereas this kind of local structure was not identified for Fe80Nb10B10 having no glass transition. The variation in thermal stability of the Fe–Nb–B alloys originates in a difference in the stability of the local atomic structures with particular compositions.

Investigation of short-range order in nanocrystal-forming Zr60Cu20Pd10Al10 metallic glass and the mechanism of nanocrystal formation

Rapidly solidified ribbons from the nanocrystal-forming Zr60Cu20Pd10Al10 alloy prepared at various melting liquid temperatures were used to study the influence of the liquid state upon quenched-in nuclei. With lowering quenching liquid temperatures, the small-angle x-ray scattering shows increased related periodic composition fluctuations and the radial distribution function analysis from x-ray diffraction method reveals that the coordination number of Pd around Zr increases. These results provide evidence for the stronger attractive interaction in Zr–Pd, which exhibits large negative mixing enthalpy, leads to the formation of (Zr, Pd)-rich domains of short-range order in the liquid. They remain in the amorphous phase as quenched-in nuclei and therefore contribute to nanocrystalline formation.

Structural study of quasicrystallization in Zr–NM (NM=Pd or Pt) metallic glasses

Abstract Glassy Zr 70 Pd 30 and Zr 80 Pt 20 alloys were prepared by melt spinning. Icosahedral-like local atomic configurations were identified in these alloys by ordinary and anomalous X-ray scattering measurements. In the case of Zr 70 Pd 30 alloy, the total coordination numbers ( N ) around Zr and Pd in the nearest neighboring region were 11.3 and 8.9, respectively, which implies the existence of an icosahedral-like local atomic structure around Zr. On the other hand, the glassy Zr 80 Pt 20 alloy shows a pronounced pre-peak in its X-ray scattering intensity profile, indicating strong chemical short-range-ordered clusters. The N values around Zr and Pt are both 11.1, and close to 12.0. Furthermore, the atomic distances of Zr–Zr and Pt–Pt are almost the same. Thus, icosahedral-like local atomic structures with strong correlations are already formed both around Zr and Pt. The stronger chemical affinity of the Zr–Pt pair over the Zr–Pd pair seems to contribute to the stabilization of the quasicrystalline phase through the rigid icosahedral clusters.

Nano quasicrystal formation and local atomic structure in Zr–Pd and Zr–Pt binary metallic glasses

Abstract Formation of the nanoscale icosahedral quasicrystalline phase (I-phase) in the melt-spun Zr70Pd30 and Zr80Pt20 binary metallic glasses were reported. Local atomic structure in the glassy and quasicrystal (QC)-formed states were also analyzed by XRD and EXAFS measurements in order to investigate the formation mechanism of QC phase. The distorted icosahedral-like local structure can be identified around Zr atom in the Zr70Pd30 metallic glass. In the QC formation process, a change of local environment around Zr is detected, in which the approximately one Zr atom substitutes for one Pd atom. In contrast, since the local environment around Pt atom is remaining during the QC precipitation, it is suggested that the stable icosahedral local structure is mainly formed around a center Pt atom in the glassy state in Zr80Pt20. We also found that the local environment around Zr atom significantly changes during the quasicrystallization in the alloy. These results differ from those in the Zr70Pd30 metallic glass.

Local atomic structure of Fe–Co–Ln–B(Ln=Sm,Tb or Dy) amorphous alloys with supercooled liquid region

Abstract The local ordering structures of Fe70Co10B20 and Fe 67 Co 10 Ln 3 B 20 ( Ln = Sm , Tb or Dy ) alloys have been studied by X-ray diffraction. The analyses of interference functions and radial distribution functions revealed that the local atomic ordering becomes weaker and the coordination number of transition metals around Fe decreases while that of transition metals around B remains almost unchanged by the addition of Ln element to Fe–Co–B alloy. These results indicate that the amorphous phase consists of (Fe,Co)–B-based rigid local structure units and the Ln atom is inserted between them. The unique structure may cause the appearance of supercooled liquid region with the difficulty of re-arrangement of atoms during annealing.

Local structure characterization in quasicrystal-forming Zr80Pt20 binary amorphous alloy

The local structure of melt-spun Zr80Pt20 alloy was investigated in the amorphous and icosahedral quasicrystal (QC)-formed states by x-ray diffraction and extended x-ray absorption fine structure measurements. While the local environment around the Zr atom in the amorphous state is considerably different from that in the QC-formed state, it remains during the quasicrystallization around the Pt atom. It is suggested that the stable icosahedral local structure is mainly formed in the center of the Pt atom in the amorphous state.

In situ preparation of YBa2Cu3Oy thin films without post‐oxygenation cooling using opposed‐targets magnetron sputtering

Superconducting YBa2Cu3Oy thin films have been successfully prepared in situ by the opposed‐targets magnetron sputtering method without introducing oxygen into the sputtering chamber after deposition. Although the films were cooled down under 1 atm of nitrogen atmosphere after deposition, they showed zero resistance Tc as high as 88 K with a relatively sharp transition width ΔTc (90%–10%) of 2 K. This suggests that the growing films contain enough oxygen to show superconductivity, in other words, the possibility of forming the orthorhombic structure during growth. Further, the films showed lower Tc at 83.5 K when they were cooled down under oxygen. This unexpected result can be explained by the overdoping of holes in the Cu‐O2 planes.

Advanced x-ray stress analysis method for a single crystal using different diffraction plane families

Generalized formula of the x-ray stress analysis for a single crystal with unknown stress-free lattice parameter was proposed. This method enables us to evaluate the plane stress states with any combination of diffraction planes. We can choose and combine the appropriate x-ray sources and diffraction plane families, depending on the sample orientation and the apparatus, whenever diffraction condition is satisfied. The analysis of plane stress distributions in an iron single crystal was demonstrated combining with the diffraction data for Fe{211} and Fe{310} plane families.Generalized formula of the x-ray stress analysis for a single crystal with unknown stress-free lattice parameter was proposed. This method enables us to evaluate the plane stress states with any combination of diffraction planes. We can choose and combine the appropriate x-ray sources and diffraction plane families, depending on the sample orientation and the apparatus, whenever diffraction condition is satisfied. The analysis of plane stress distributions in an iron single crystal was demonstrated combining with the diffraction data for Fe{211} and Fe{310} plane families.