Papers by Keyword: Bulk Metallic Glass (BMG)

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Authors: Masahito Watanabe, Akitoshi Mizuno, Toshihiko Akimoto, Shinji Kohara
Abstract: It is well known that multi-component alloys form bulk metallic glasses (BMGs) from the supercooled liquid state without rapid quenching. However, the mechanism of phase selection between crystal and glass states has not been fully clarified. To obtain an insight into the glass-forming processes, we carried out in-situ observation on the solidification of Zr-based BMG-forming alloys from its supercooled liquids by time-resolved X-ray diffraction combined with the conical nozzle levitation (CNL) technique to achieve a containerless melting. For Zr-based alloys, we succeeded in detecting the X-ray diffraction patterns during glass formation from the supercooled liquid state as well as the crystallization from the liquid state. Furthermore we performed the precise structure analysis of supercooled state of Zr-based binary liquids. Based on the liquid structure and in-situ observation results, we discussed about the phase selection mechanism between crystal and glass states.
Authors: Jean-Louis Uriarte, A. Le Moulec, Alain Reza Yavari
Authors: Mohammad Mezbahul-Islam, Elhachmi Essadiqi, Mamoun Medraj
Abstract: The Mg-Cu-Y system has been experimentally investigated using differential scanning calorimetry (DSC). Vertical sections and phase assemblage diagrams are calculated using thermodynamic modeling. Solidification behavior of the key alloys was discussed in light of the thermodynamic calculation. Melting temperatures of two of the ternary compounds; Mg18CuY and Mg4CuY, are predicted using the modified thermodynamic database of this system. Key words: Mg alloys, Bulk metallic glass, Differential scanning calorimetry, Thermodynamic modeling.
Authors: Pham Huu Loc, Fang Jung Shiou
Abstract: This study investigates the optimal abrasive water jet polishing parameters for Zr-based bulk metallic glass (BMG) material by using the Taguchi method. An abrasive water jet polishing (AWJP) system is newly designed and mounted on a machining center. In order to determine the optimal polishing parameters for the Zr-based BMG sample, six polishing parameters, namely the hydraulic pressure, the impact angle, the standoff distance, the abrasive material, the abrasive concentration, and the polishing time, are chosen as the control factors of experiments. The optimal AWJP parameters are determined after carrying out the experiments based on the Taguchi’s L18 orthogonal array experimental results. These optimal parameters are the combination of the hydraulic pressure of 2 kg/cm2, the impact angle of 30o, the standoff distance of 15 mm, the abrasive material of SiC, the abrasive concentration of 1:5, and the polishing time of 60 minutes. The surface roughness is improved from an initial value of Ra = 0.675μm to a final value of Ra = 0.016μm by using the AWJP optimal parameters.
Authors: Daniel R. East, Michael Kellam, Mark A. Gibson, Aaron Seeber, Daniel Liang, Jian Feng Nie
Abstract: Sheets of a Mg60Cu29Gd11 alloy were produced by twin roll casting with all operational variables, except roll speed, being kept constant. As a function of the roll speed, the structure of the as-cast sheet changed from being crystalline to fully amorphous and then back to crystalline. Through careful selection of the casting speed that is suitable for the selected alloy system and with which the exit temperature of the sheet remains within the supercooled liquid region, a malleable sheet with no surface defects is produced. This work shows that twin roll sheet casting is a viable process for the production of magnesium-based bulk amorphous sheet in a continuous manner and on an industrial scale.
Authors: N.P. Kobelev, E.L. Kolyvanov, V.A. Khonik
Abstract: Irreversible structural relaxation of bulk amorphous Zr52.5Ti5Cu17.9Ni14.6Al10 was studied by means of logarithmic decrement and shear modulus measurements using an inverse torsion pendulum in the frequency range from 5 Hz to 40 Hz. Irreversible contributions to the decrement and shear modulus and their frequency, temperature, and time dependences were investigated. The activation energy spectrum of irreversible structural relaxation has been reconstructed. It has been shown that irreversible structural relaxation can be regenerated by a special heat treatment. The results obtained are discussed within the framework of a phenomenological model, which implies existence of two-well relaxation centers in the glass structure.
Authors: Akira Takeuchi, Akihisa Inoue
Abstract: The relationships of optimal compositions of bulk metallic glasses (BMGs) have been analyzed with a set of thermodynamic quantities of mismatch entropy normalized with respect to Boltzmann's constant (Sσ!/kB) and mixing enthalpy (Hmix) and with assistance of classification result of BMGs. The analysis shows clear dependence of the location of Sσ!/kB and Hmix values for optimal compositions of ternary BMGs in Sσ!/kB-Hmix chart in each alloy system. The ternary BMGs are summarized into four types: (1) Cu-based, (2) La-, Zr- and Ca-based, (3) Pd-based and (4) Fe- and Mg-based BMGs according to their maximum value of Sσ!/kB ((Sσ!/kB)max) and the largest and negative value of Hmix ((Hmix)L.N.) or their half values which are obtained for each system. These types of BMGs are related with the local arrangements of BMGs, which are widely accepted as an icosahedral structure for Metal-Metal type, a transformed tetragonal dodecahedrons and triacontrahedrons structure for Pd-Metalloid type, and a network-like structure for Metal-Metalloid type.
Authors: Kyung Tae Hong, Young Su Ji, Sung Jae Chung, Myoung Ryul Ok, Yun Hoon Ji, Kyung Sub Lee
Authors: Hiroshi Okuda, Isao Murase, Shojiro Ochiai, Yokoyama Yoshihiko, Katsuaki Inoue
Abstract: Anomalous small and wide angle scattering measurements on electron-beam welded joint has been carried out at Zr absorption edge. We preformed an anomalous and simultaneous small- and wide-angle scattering (A-SWAXS) analysis on the welded joint with and without crystallization. For the wide angle measurements, we extend the SAXS measurements up to 13 nm-1, where q is still below the first halo, but is large enough for several Bragg peaks to be observed. In the present analysis, the ASAXS analysis at the HAS/beads interface is interpreted in conjunction with the corresponding AWAXS analysis. The origin of SAXS and WAXS was found to be different.
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