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Subject: Amorphous metals ×

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Now showing 1 - 4 of 4
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    Roles of hydrogenation, annealing and field in the structure and magnetic entropy change of Tb-based bulk metallic glasses
    (New York : American Institute of Physics, 2013) Luo, Qiang; Schwarz, Björn; Mattern, Norbert; Shen, Jun; Eckert, Jürgen
    The reduction of open-volume regions in Tb-based metallic glass (MG) by annealing and hydrogen charging was found to rearrange the atomic structure and tune the magnetic behaviors. After crystallization, the magnetic structure and magnetic entropy change (MEC) alters due to the structural transformation, and a plateau-like-MEC behavior can be obtained. The hydrogen concentration after charging at 1mA/cm2 for 576 h reaches as high as 3290 w-ppm. The magnetization behavior and the MEC change due to the modification of the exchange interaction and the random magnetic anisotropy (RMA) upon hydrogenation. At low temperatures, irreversible positive MEC was obtained, which is related to the internal entropy production. The RMA-to-exchange ratio acts as a switch to control the irreversible entropy production channel and the reversible entropy transfer channel. The field dependence of the MEC is discussed in term of the competition among Zeeman energy, exchange interaction and RMA.
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    Thermal annealing studies of GeTe-Sb2Te3 alloys with multiple interfaces
    (New York : American Institute of Physics, 2017) Bragaglia, Valeria; Mio, Antonio M.; Calarco, Raffaella
    A high degree of vacancy ordering is obtained by annealing amorphous GeTe-Sb2Te3 (GST) alloys deposited on a crystalline substrate, which acts as a template for the crystallization. Under annealing the material evolves from amorphous to disordered rocksalt, to ordered rocksalt with vacancies arranged into (111) oriented layers, and finally converts into the stable trigonal phase. The role of the interface in respect to the formation of an ordered crystalline phase is studied by comparing the transformation stages of crystalline GST with and without a capping layer. The capping layer offers another crystallization interface, which harms the overall crystalline quality.
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    Dynamics of serrated flow in a bulk metallic glass
    (New York : American Institute of Physics, 2011) Ren, J.L.; Chen, C.; Wang, G.; Mattern, N.; Eckert, J.
    Under compression loading, bulk metallic glasses (BMGs) irreversibly deform through shear banding manifested as a serrated flow behavior. By using a statistical analysis together with a complementary dynamical analysis of the stress-time curves during serrated flow, we characterize the distinct spatiotemporal dynamical regimes and find that the plastic dynamic behavior of a Cu50Zr45Ti5 BMG changes from chaotic to self-organized critical behavior with increasing strain rate. This plastic dynamics transition with the strain rate is interpreted in the frame of the competence between the neighboring elastic strain field forming and relaxation processes.
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    Structural evolution in Ti-Cu-Ni metallic glasses during heating
    (New York : American Institute of Physics, 2015) Gargarella, P.; Pauly, S.; Stoica, M.; Vaughan, G.; Afonso, C.R.M.; Kühn, U.; Eckert, J.
    The structural evolution of Ti50Cu43Ni7 and Ti55Cu35Ni10 metallic glasses during heating was investigated by in-situ synchrotron X-ray diffraction. The width of the most intense diffraction maximum of the glassy phase decreases slightly during relaxation below the glass transition temperature. Significant structural changes only occur above the glass transition manifesting in a change in the respective peak positions. At even higher temperatures, nanocrystals of the shape memory B2-Ti(Cu,Ni) phase precipitate, and their small size hampers the occurrence of a martensitic transformation.