Solid State Phenomena Vols. 124-126

Abstract: In modern thermal analysis and design involving thermal transport in solid components it is necessary to apply different modeling of the thermal heat flow in bulk material and across solid surface interfaces either in shape of a layer or a solid-solid interface. Similar differences occur when applying different measurement techniques. Some techniques have been developed specifically for the purpose of performing measurements of bulk properties by removing the influence from thermal contact resistance between the measurement probe and the sample material. Thermal conductivity measurements on metal and ceramic objects of various geometries such as thin bars, thin sheets as well as coatings or layers are here described when using the Transient Plane Source technique. A summary overview of the recent developments of this technique, including its ability to be applied in measurement situations covering a wide range of length and time scales, is also presented. Structural changes in anisotropy can be recorded with high sensitivity by comparative measurements. The technique may be applied in situations requiring non-destructive testing, e.g. samples of particular geometry used for mechanical or tensile testing.

Abstract: Experiments under a cold rotary swaging process have been conducted to investigate the dimensional characteristics of the swaged tube and solid bar for obtaining proper product of desirable quality. Dimensional characteristics are expressed in terms of dimensional deviation and surface roughness of swaged product through the rotary swaging process. The process variables such as forming speed and percent reduction of outer diameter of the product are considered and selected because of playing a key role in the rotary swaging process. Furthermore the developed rotary swaging machine with four-split dies, named as KRSM25, is used in the swaged experiment. Based on the experimental results, it is observed that the process variables affect the quality of swaged product such as dimensional precision, surface roughness of the product. Defect could be found to occur at a value of more than 2.0 mm/rev in forming speed. The dimensional precision of swaged product depends on the percentage reduction of outer diameter and forming speed. The work presented in this paper might be used for available information in the design of the optimum rotary swaging process.

Abstract: Ti-51Ni(at%) and Ti-40Ni-10Cu(at%) alloy wires with diameters of 0.3mm, 0.5mm and 0.7mm were prepared by drawing the alloy ingots fabricated by vacuum induction melting. Heating rates of the wires were investigated by measuring changes in temperatures of them while applying currents in the range of 1 A and 6 A to them and cooling rates were investigated by measuring changes in temperatures of them after cutting currents. Heating rate increased with increasing the amount of current, while cooling rate was kept constant. Both heating rate and cooling rate increased with decreasing diameter of wire. This suggested that high amount of current and small wire diameter were required for high heating and cooling rate. Comparing Ti-50Ni alloy wires with Ti-40Ni-10Cu alloy wires, heating rates of the latter was faster than that of the former, although cooling rates were almost same. This suggested that Ti-40Ni-10Cu alloy wires is better than Ti-50Ni alloy wires for the applications requiring high actuating rates.

Abstract: In order to investigate the atomic structure of sputtered-deposited Fe76Tb24 amorphous film, we performed X-ray anomalous scattering (XAS) measurements at two energies near the Tb K-absorption edge using the synchrotron-radiations (SR). The total, Tb and Fe environmental pair distribution functions (PDF's) of the amorphous film were obtained from the normalized scattering intensities after the corrections for the structural analysis. The coordination numbers were calculated from the area under the fitted PDF profiles multiplied by 4πr 2 and near-neighbor distances were estimated from the positions of the peaks of the fitted profiles.

Abstract: A theoretical method to study the encapsulation of H2 molecules in the cavities of Cs3Na9-A zeolite has been proposed. To study the properties of encapsulated H2 molecules, a Fermi-Dirac like statistics has been introduced. The average binding energy per H2 is obtained as a function of the number of molecules and temperature. The average activation energy is also calculated from the minimum energy path for the α- to α-cage transmission and the average binding energy. The fraction with higher energy than its activation energy has been calculated and revealed that the activation energy for the en- and decapsulation of H2 molecules depends not only on the temperature but also on the number of the encapsulated molecules.

Abstract: Ferritic steels have been candidate structural materials for first wall and blanket structures of fusion power plant since the late 1970’s, when the fast-reactor irradiation showed them to be more swelling resistant than austenitic stainless steels. In this investigation, the coarsening of MX nitrides during aging was studied for Cr-Mo-N-X(X=V, Nb, Ti) ferritic steels. During the aging, (V, Nb, Ti)nitrides were precipitated out. From TEM observation, particle size distribution was confirmed and size distribution follows a typical log-normal distribution. The coarsening rate of MX nitrides was correlated with the Oswald ripening equation.

Abstract: Ga K-edge EXAFS spectra have been analyzed to elucidate the local coordination structure of Ga in two representative selenide Ge-As-Se and Ge-Sb-Se glasses all doped with Pr. Gallium turned out to be coordinated with 4 Se atoms in its first neighboring shell. This implies that Ga does not follow the 8-N rule associated with the short-range order structures of typical covalent glasses, further indicating there being more ionic-bond nature in the Ga-Se bonds compared to other heteropolar chemical bonds in the selenide glasses. This is decisive for the Pr3+ ions to be incorporated in the selenide glasses. In this case, the GaSe4 units can be electrically neutralized by the doped Pr3+ ions that act as a charge compensator. As such, inside the selenide glasses, distributions of Pr3+ ions and the Ga tetrahedral units are closely correlated. Spectroscopic properties of rare earths embedded in these Ga-containing selenide glasses thus can be explained in connection with the proposed role of Ga.

Abstract: The titanium alloys containing the Nb transition elements have been investigated as the Ni-free shape memory and the biomedical alloys with a low elastic modulus. The mechanical properties of the alloys depended upon the meta-stable phases like the α`, α``, ω. To study the martensitic transformations from the β to α`` or α` the Ti-xNb (x=0 to 40 wt%) alloys were melted into the button type ingots using a VAR, and followed by the water-quenching after the soaking at 1000oC for 2hrs. The crystallography of the martensitic phases in the water-quenched alloys was analyzed using a XRD. The diffraction peaks of the orthorhombic martensites were identified by the crystallographic relationship with the bcc matrix. The lattice parameters of the orthorhombic martensites were varied continuously with the contents of the Nb elements. The martensitic transformations of the alloys were studied using the phenomenological theory of Bowles and Mackenzie.

Abstract: The formation of intermetallic compounds in brazed joints between SUS304 and nickel-based filler metal is a major concern, since they considerably degrade the mechanical properties of joints. In this study, the SUS304, which is used widespread, as a general material was vacuum brazed with BNi-2 filler metal, and discussed to determine the influence of different brazing temperature and time on the strength of brazed joints. The results showed that, the mechanical properties of brazing layer could be stabilized through increasing the brazing temperature over 100° C more than melting temperature of filler metal, and increasing the brazing time over 120min. long, and diffusing enough the intermetallic compounds formed in the brazing layer to the base metal.

Abstract: Amorphous selenium (a-Se) film has the potential to fulfill the requirements of a novel x-ray image detector because of its good photo-to-dark impedance ratio, large area coverage, and low temperature deposition. In this work were studied the structural, optical and electrical properties of thermally- evaporated a-Se film for the phosphor-light modulator (PLM). From the x-ray diffraction and electron microscopy experimental results, the deposited film had an amorphous phase without any re-crystallization or defects. Also, the light absorption in widely visible range of 400 ~ 630 nm was over 95 %. From the electrical measurements, the low dark current density of 2.8 nA/cm2 was obtained at 10 V/㎛. The x-ray sensitivity of the 270㎛-Gd2O3:Eu phosphor coupled 20㎛-Se film was 7.31 nC/cm2-mR. From such experimental results, the novel x-ray detector which incorporates phosphor coupled x-ray light modulator, makes an operation at low x-ray exposure possible, therefore, the applications as a medical imaging detector are shown below.