Search

The local atomic structure near an Nb atom in a Ti–Nb binary β –Ti alloy single crystal was examined by means of X-ray fluorescence holography. In the single crystal, high density of the fine ω –Ti phase was homogeneously formed and was distributed in the β –Ti matrix phase by heat treatment. In the ω phase, the atomic displacement accompanying the ω phase formation is suppressed near Nb atoms. Thus, the atoms near an Nb atom tend to maintain the body centered cubic structure even in the ω phase, as Nb is a typical β –stabilizing element. The structural model near an Nb atom in the ω phase is similar to that of a collapsed ω structure. However, the degree of collapse is higher near an Nb atom than that far from it. This inhomogeneous displacement produces diffuse diffraction spots in selected area electron diffraction patterns of the ω phase.

In this study, a Pd40Cu20Ge40 metallic glass has been introduced as a novel prototype of Pd-based metallic glasses. The Pd40Cu20Ge40 glass exhibits glass transition at 52 °C. The glass transition temperature reduced by the melting point of most glasses is roughly 0.5 or 0.6 but that of the Pd40Cu20Ge40 glass is only 0.36, which is considerably lower than those of other metallic glasses. Specific temperature measurement, microstructural observation, viscosity measurement and demonstration of viscous flow forming were performed to confirm that the novel material presented is a glass. From viewpoint of the constraint on the motion of molecules or clusters in glasses, new categorization of glasses has been proposed.

We measured the temperature dependence of the apparent specific heat of Cu55Hf25Ti15Pd5 glassy alloy (metallic glass) by a differential scanning calorimetry method during continuous heating, and investigated the structural relaxation and crystallization processes. The results of structural evolution obtained by transmission electron microscopy are discussed in line with the differential scanning calorimetry data. Kinetics of crystallization process of the supercooled liquid above the glass-transition temperature is also studied. This alloy shows a complex relaxation and crystallization processes which are discussed in the paper.

Radial and longitudinal variations in the Young's modulus of a Zr55Al10Ni5Cu30 metallic glass cylindrical rod were examined by means of nanoindentation. The metallic glass rod, 2.4 mm in diameter, was prepared using a novel mold-casting method designed to suppress crystallization resulting from the heterogeneous nucleation originating from slag covering a molten alloy. In this study, Young's modulus was measured using a multiple partial unloading technique with a spherical indenter. In general, it is assumed that the cooling rate of a metallic glass rod depends on the radius of its cross section. However, no significant difference was found in the measured Young's modulus.

Effect of ball-milling and shot-peening on a metallic glass Zr 55 Al 10 Ni 5 Cu 30 , which possesses a large supercooled liquid region, has been investigated by means of differential scanning calorimetry, x-ray diffractometry and transmission electron microscopy. Metallic glassy ribbons, powders and plates were prepared by melt-spinning, gas-atomizing and mold-clamp casting techniques, respectively. No structural changes were observed in both the ribbon and powder specimens by ball-milling for around 100 h; however, the powder specimens were crystallized by Fe contamination when they were ball-milled for 540 h. No structural evolution was also observed when the plate specimens were subjected to shot-peening, while crystallized plate specimens were easily amorphized by mild and short period shot-peening. These results imply high phase stability of the Zr 55 Al 10 Ni 5 Cu 30 metallic glass against deformation.

Variant rearrangements induced by external magnetic field in Fe–Pd FCT martensite transformed from FCC austenite single crystals have been investigated by means of optical microscopy. Fe–Pd single crystals in fully martensite state contain two large correspondence variants, and a kink due to {1 0 1} twinning is observed at the twinning boundary of the variants. The twinning boundary exhibits both large reversible and small irreversible movement by applying magnetic field as a result of variant rearrangement, and 0.49% of reversible strain is obtained. The variant rearrangement is not completed even though magnetic flux density is increased to maximum of an electromagnet used. The boundary also moves reversibly by application of external compression stress, however, the direction of the boundary movement is opposite with respect to the movement induced by magnetic field and the variant rearrangment is not completed. The reversible strain of 2.8% was also observed when the specimen was compressed.

Tracer diffusion coefficient of 99Mo in α-iron has been determined in the temperature range between 833 and 1163 K by use of a serial sputter-microsectioning technique. The temperature dependence of the diffusion coefficient, D, in the whole temperature range of α-iron across the Curie temperature can be expressed by D= 1.48 +1.51 −0.75 ×10 −2 exp − 282.6±6.4 kJ mol −1 1+ 0.074±0.005 s 2 RT m 2 s − 1 where s is the ratio of spontaneous magnetization at T K to that at 0 K. The factor 0.074 in the above equation is smaller than 0.156 for self-diffusion in α-iron, showing that the influence of the magnetic transformation on the diffusion of molybdenum in α-iron is smaller than that on the self-diffusion as expected from the negative magnetic moment of molybdenum in the lattice of the ferromagnetic iron.

The relationship between microstructures and hydrogen absorption-desorption properties described in terms of pressure-composition (P–C) isotherms has been investigated as a function of the number of hydrogen sorption cycles. While the desorption pressure does not significantly depend on the number of cycles, the absorption pressure decreases as the number of cycles increases with the most significant decrease occurring between the first and second cycles. TEM observations reveal that numerous a -type edge dislocations are introduced during the first absorption cycles. Severe cracking occurs also during the first absorption cycle in such a way that the size of sub-particles delineated by cracks is comparable to that of particles observed after five cycles. The introduction of numerous lattice defects, such as a -type edge dislocations as well as the formation of severe cracks, is responsible for the significant decrease in absorption pressure between the first and second cycles, indicating that reproducible P–C characteristics of LaNi 5 can be achieved only when such numerous dislocations and cracks are formed in the bulk of LaNi 5 particles.

The generation of lattice defects and their effects on hydrogen sorption properties described in terms of pressure–composition ( P–C ) isotherms have been investigated as a function of the number of hydrogen sorption cycles for LaNi 5 and FeTi. For LaNi 5 , while the desorption pressure does not significantly depend on the number of cycles, the absorption pressure drastically decreases between the first and second cycles. Numerous dislocations of edge character with Burgers vectors of the 1/3〈1 2 10〉-type as well as numerous cracks are introduced during the first absorption cycle. The introduction of numerous lattice defects such as a -type edge dislocations and the formation of severe cracks seems to be completed during the first cycle, resulting in the reproducible P–C characteristics for the subsequent cycles. In contrast, FeTi exhibits ever-changing P–C characteristics with cycle number. The introduction of dislocations and cracks occurs during each of the absorption cycles. However, the extent to which this occurs is considerably smaller in each absorption cycle of FeTi than in the first absorption cycle of LaNi 5 . The difference in material response to hydrogenation seems to be closely related to the difference in ductility of these two intermetallics.

Microstructures and defect structures in intermetallic compounds in the La–Ni alloy system have been investigated by transmission electron microscopy in the composition range of La–77.8∼83.2 at.%Ni, which corresponds to compositions between two intermetallic phases, La 2 Ni 7 and LaNi 5. The intermetallic phase, La 5 Ni 19 of the Ce 5 Co 19 -type is found for the first time to exist as an equilibrium phase at a composition between La 2 Ni 7 and LaNi 5 . This phase is stable at high temperatures around 1000°C but decomposes into La 2 Ni 7 and LaNi 5 below 900°C. Numerous stacking faults are observed on basal planes in La 5 Ni 19 but the density of these basal stacking faults is greatly reduced in La 2 Ni 7 . Most stacking faults in La 5 Ni 19 are identified to be of the inter-block layer type while most of those in La 2 Ni 7 are identified to be of the intra-block-layer type.

A wavelength dispersive X-ray spectrometer is designed and developed for X-ray fluorescence analysis and spectroscopy using an X-ray microprobe at SPring‐8 BL39XU. The spectrometer uses a flat analyzer crystal, and X-rays from a small beam spot are dispersed by the crystal onto a position sensitive proportional counter. The energy resolution of the spectrometer is determined by the spatial resolution of the position sensitive proportional counter, and the additional use of the slit-scan can improve the energy resolution if necessary. Performance of the spectrometer is evaluated by using a conventional X-ray source, and preliminary experimental results of the X-ray microprobe by using brilliant hard X-rays from an X-ray undulator are reported. q 1999 Elsevier Science B.V. All rights reserved.

Tungsten (W) M III X-ray absorption spectra of a periodic multilayer, (Si/W) 100 /Si, were measured with the change of X-ray grazing angle using sample current method. Under not total reflection condition, the absorbance changed little except at W M III absorption edge. While under the total reflection condition, the absorbance increased with the increase of the X-ray energy and the increment changed from low to high at the W M III absorption edge. This result reflected the variation of the X-ray evanescent wavelength caused by the absorption effect of W.

Sulfur X-ray photoelectron spectra (XPS) and X-ray absorption spectra (XAS) of an aerosol sample collected by an Andersen sampler were measured using a synchrotron beam line. While the XPS was more surface sensitive than XAS, the detection limit of XAS was better than that of XPS. It was concluded that the XAS was more suitable for the chemical state analysis of sulfur in aerosol samples than XPS.

Kα 1,2 ( K - L 3,2 ) X-ray fluorescence spectra of MnF 2 have been measured for excitation X-ray energy at 688.0, 695.0 and 725.0 eV. Monochromatized synchrotron radiation was used for primary excitation. The fluorine K absorption spectrum of MnF 2 has also been measured and the absorption edge found to be at 690.0 eV. The excitation energy was thus 2 eV below, 5 eV above and 35 eV above the threshold. Multiply ionized Kα 3,4 ( KL - L 2 ) satellites, as well as the line broadening, were observed. The relation between the metal-F bond length and the F K absorption spectral shape is discussed.

TiB/Ti composite were produced by SHS (self propagating high temperature synthesis) under conditions of PHIP (pseudo-hot isostatic pressing). The synthesis conditions were optimized to produce highly dense materials conforming a high volume fraction of TiB. Self-propagating reaction of the Ti and B powders occurred above the α- to β-Ti transformation temperature (1155 K). The composites consist of Ti matrices with dispersed TiB reaction products of 2–30 μm size. Near fully dense composites with a TiB/Ti volume ratio of 33–44 vol.% were synthesized for B/Ti atomic ratios of 0.3–0.4 at pseudo isostatic pressures of 100 MPa. The Vickers hardness and fracture stress of the composites are 5.6–7.1 and 2.1–2.3 GPa, respectively, and the wear of the composite is approximately 7–9% of the Ti and Ti–6Al–4V.