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  • 1990-1994  (6)
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Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Laser processing of Nb3Al(Ge, Si) high-field superconductors (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2686-2691 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The laser irradiation process is a promising method for the fabrication of metastable Al5–Nb3Al(Ge,Si) compounds. Thereby Nb-sheathed Nb-25 at. % Al(Ge,Si) microcomposite tapes are prepared by a conventional powder metallurgical method and heat treated by a high-intensity CO2-laser beam. The parameters selected during laser beam irradiation of the composite determine the relative amounts of molten, heat-affected or unreacted material. In order to obtain large overall superconducting currents, it is favorable to melt a large fraction of the microcomposite without melting the surrounding Nb sheath. The cooling rate after laser beam irradiation determines the structure and the formation of metastable phases in the resolidifying material. The sequences of the process are simulated by heat flow calculations, which consider laser power, beam diameter, tape velocity, thickness, and microstructure, as well as heat transfer coefficients. From these calculations we could deduce optimum conditions for the laser treatment, leading to Jc values of 105 A cm−2 at 10 T and 104 A cm−2 at 16 T.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354662
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Amorphization of Ti/Cr multilayer films by solid-state reaction (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2249-2253 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The solid-state reaction in Ti/Cr multilayered diffusion couples at temperatures between 450 and 650 °C was investigated by x-ray diffraction. It was found that an amorphous phase is formed at a concentration around 55 at. % Cr. The results are in excellent agreement with those obtained from mechanically alloyed powders, and with the corresponding metastable phase diagram calculated by the calculation of phase diagrams method. The observations strongly suggest that inverse melting is possible in the Ti-Cr system at around 55 at. % Cr.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353129
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Metastable phase formation in mechanically alloyed and ball milled Ti–Si (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2478-2487 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Ti–Si system is chosen as a model system to study the mechanical alloying of elemental powder blends in which one of the components is brittle. In addition, the stability of intermetallic compounds upon milling is investigated, in order to interpret the metastable phase formation during the milling process. Detailed x-ray investigations show that during mechanical alloying, a solution of Si in Ti preceeds the formation of amorphous or intermetallic phases. The selection of phases formed, as well as the final state, are influenced by the overall composition of the powder blends, and by the milling procedure applied. However, predictions can be made by considering the free energy curves of the stable and metastable phases in the Ti–Si system, which have been calculated by the CALPHAD method. Milling of the intermetallic compounds generally leads to the same final state as the mechanical alloying of elemental powder blends with corresponding compositions. These results demonstrate that the intermetallic compounds are energetically destabilized upon milling, allowing for phase transformations into metastable phases, such as amorphous or metastable crystalline alloys. The energetic destabilization of intermetallic compounds mainly originates from the chemical disorder caused by the milling process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351594
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal stability of the unstable fcc-Fe50Cu50 phase prepared by mechanical alloying (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1056-1058 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An unstable fcc-Fe50Cu50 alloy has been prepared by milling of elemental powder blends. The structure and the decomposition behavior of the alloy were studied by x-ray diffraction and Mössbauer spectroscopy. A broad distribution of different local environments of the iron atoms was observed in the fcc-FeCu phase. This indicates that Fe and Cu are mixed on an atomic level. In the initial state of decomposition, iron atoms precipitated coherently in the fcc-FeCu matrix as fcc-Fe particles. At higher annealing temperatures the particle size increased during the thermal treatment, and the fcc-Fe precipitates transformed into the bcc-Fe structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109832
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Mössbauer investigations of mechanical alloying in the Fe-Cu system (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2768-2770 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fcc-Fe50Cu50 solid solution was prepared by mechanical alloying of elemental Fe and Cu powder blends. The alloying process was studied by using x-ray diffraction and Mössbauer spectroscopy. Initially, the milling process reduced the crystallite sizes of both elemental powders. After 20 h milling, some Fe particles transformed into the fcc structure. Due to the structural similarity of the fcc-Fe and fcc-Cu phases, composites consisting of coherent Cu and Fe regions were formed. The increasing density of interfaces during further milling resulted in an interdiffusion of Cu and Fe. The alloying process was monitored by Mössbauer investigations which showed an increasing Fe concentration in fcc Cu. After 50 h of milling, the Mössbauer spectra consisted of a broadened sextet caused by a hyperfine field distribution, which demonstrates that the Fe and Cu were alloyed on an atomic level. These observations are in agreement with a model proposed by C. Gente, M. Oehring, and R. Bormann [Phys. Rev. B 48, 13244 (1993)] describing the formation of unstable alloys by mechanical alloying.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110329
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Inverse melting of a metastable Nb45Cr55 solid solution (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 318-320 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An Nb45Cr55 solid solution was prepared by mechanical alloying in a planetary ball mill and investigated by x-ray diffraction and calorimetry. It was found that the structure evolution upon heating exhibited three distinct stages, the first resulting in complete amorphization, whereas the second and third are related to the subsequent crystallization of the amorphous phase. These results are in agreement with the free-energy functions calculated from the thermochemical data of the system. They show that for a composition of Nb45Cr55 a second melting point (often termed "inverse melting point'') exists at about 900 °C, below which the undercooled liquid has a lower free energy than the crystalline body-centered-cubic phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112358
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    Paper (German National Licenses)
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