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  • 11
    Publication Date: 1998-09-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 12
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 676-680 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Solidification of selected Mn-Al-C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable τ (L10) phase formed directly from the melt. Complete solidification to τ phase was interrupted by the competitive evolution of an equilibrium ε phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic τ phase in a Mn0.55Al0.433C0.017 alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at. % (i.e., Mn0.55Al0.416Co0.034 alloy), a transition in structure development occurred so that the samples exhibited γ2 phase formation as well as τ and ε phases. Both microstructural observations and x-ray diffraction examination were used to guide the interpretation and the analysis of solidification pathways. The attainment of the high liquid undercooling required to nucleate the metastable τ phase from the melt may be facilitated by containerless processing.
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  • 13
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4039-4043 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Differential scanning calorimetry (DSC) was used to determine the thermodynamic functions of the undercooled liquid and the amorphous phase with respect to the crystalline state of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy. The specific heat capacities of this alloy in the undercooled liquid, the amorphous state and the crystal were determined. The differences in enthalpy, ΔH, entropy, ΔS, and Gibbs free energy, ΔG, between crystal and the undercooled liquid were calculated using the measured specific heat capacity data as well as the heat of fusion. The results indicate that the Gibbs free energy difference between metastable undercooled liquid and crystalline solid, ΔG, stays small compared to conventional metallic glass forming alloys even for large undercoolings. Furthermore, the Kauzmann temperature, TK, where the entropy of the undercooled liquid equals to that of the crystal, was determined to be 560 K. The Kauzmann temperature is compared with the experimentally observed rate-dependent glass transition temperature, Tg. Both onset and end temperatures of the glass transition depend linearly on the logarithm of the heating rate based on the DSC experiments. Those characteristic temperatures for the kinetically observed glass transition become equal close to the Kauzmann temperature in this alloy, which suggests an underlying thermodynamic glass transition as a lower bound for the kinetically observed freezing process. © 1995 American Institute of Physics.
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  • 14
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4115-4115 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To match the requirements for development of transformer cores with lower iron losses, many new materials are under development including amorphous materials, 6.5% Si–Fe sheets and thin gauged 3% Si–Fe sheets. Among these materials, the thin gauged 3% Si–Fe sheets are attracting attention due to their good magnetic properties and scientific interest. Arai et al. reported that the magnetic properties of the sheets were comparable to those of the amorphous materials and (110)[001] preferred orientation of the sheets are developed by tertiary recrystallization.1 The 100 μm thick 3% Si–Fe sheets were prepared via conventional metallurgical processes including melting and casting, hot rolling to 25 mmT at 1200 °C, first cold rolling to 0.5 mmT, intermediate annealing at 800 °C for 30 min, second cold rolling to 0.25 mmT, intermediate annealing at 800 °C for 30 min, final cold rolling to 100 μm and final annealing at 1200 °C for 1 h in a vacuum of 5×10−6 Torr. Among these processes, the cold rolling process is an important one because preferred orientation of the sheets was developed in the process. Nakano et al. reported that there was an optimum cold rolling ratio to get required magnetic properties of the sheets.2 Recently, we found that the reduction rate, i.e., number of passes, as well as reduction ratio affected the preferred orientation and magnetic properties of the sheets. The number of passes in the first cold rolling process was changed from 7 to 60 and B10 values of the final sheets were changed from 1.30 to 1.84 T according to the number of passes. From x-ray experiments, it was found that intensity of (110) peak in the cold rolled and annealed sheets strongly affected the magnetic properties of the final sheets. We will discuss the relationship between the reduction rate and preferred orientation, and magnetic properties of the thin gauged 3% Si–Fe sheets. © 1997 American Institute of Physics.
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  • 15
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3253-3256 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-crystal epitaxial thin films of γ-Fe2O3(001) have been grown on MgO(001) using oxygen-plasma-assisted molecular beam epitaxy. The structure and magnetic properties of these films have been characterized by a variety of techniques, including reflection high-energy electron diffraction (RHEED), low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy and x-ray photoelectron/Auger electron diffraction (XPD/AED), vibrating sample magnetometry, and ferromagnetic resonance. Real-time RHEED reveals that the film growth occurs in a layer-by-layer fashion. The γ-Fe2O3(001) film surface exhibits a (1×1) LEED pattern. The growth of γ-Fe2O3 films at 450 °C is accompanied by significant Mg outdiffusion. AED of Mg KLL Auger emission reveals that Mg substitutionally incorporates in the γ-Fe2O3 lattice, occupying the octahedral sites. Magnetic moments are ∼2300 G and ∼4500 G for γ-Fe2O3 films grown at 250 °C and 450 °C, respectively. The high magnetic moment for the films grown at 450 °C could be attributed to the high degree of structural order of the films and Mg substitution at octahedral sites. © 1997 American Institute of Physics.
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  • 16
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1545-1547 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: HgTe-CdTe superlattices and other microstructures such as single and double barrier tunneling structures are commonly grown by molecular beam epitaxy with the mercury flux continuously on the sample during the growth. This means that some mercury will be incorporated in the CdTe layers. We present here, for the first time, a measurement of the amount of mercury incorporated in thin layers of CdTe. X-ray photoelectron spectroscopy was used to measure the amount of mercury. The amount of mercury was found to be between 3 and 9% for CdTe (111)B, depending on the growth conditions. The amount of mercury was found to increase with mercury flux and to decrease as the substrate temperature was increased. Under the same conditions, it was found that much more mercury was incorporated in the (100) orientation. The type of substrate (CdTe or GaAs) was not found to influence the results. These results indicate that the amount of mercury in the CdTe layers of HgTe-CdTe superlattices is not quite as low as expected from measurements of thick CdTe layers, but it can be low enough that it does not influence significantly the results on the superlattice system in the (111) orientation.
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  • 17
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 2025-2027 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: p-type doping of HgCdTe(100) layers with lithium during growth by molecular beam epitaxy is reported. Hall measurements have been performed on these layers between 300 and 30 K. The Li concentration is found to increase with the Li cell temperature. Li-doped HgCdTe layers are estimated to have very shallow acceptor levels. Acceptor concentrations as high as 8×1018 cm−3 have been achieved. At low doping levels, due to residual donors, layers show compensation. Incorporation coefficient of Li close to 1 and almost 100% electrical efficiency for Li in molecular beam epitaxy HgCdTe layers were observed. However, Li is found to diffuse rapidly in HgCdTe layers grown by molecular beam epitaxy.
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  • 18
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3111-3113 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-temperature high-vacuum electrostatic levitation (HTHVESL) and differential scanning calorimetry (DSC) were combined to determine the hemispherical total emissivity εT, and the specific heat capacity cp, of the undercooled liquid and throughout the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy. The ratio of cp/εT as a function of undercooling was determining from radiative cooling curves measured in the HTHVESL. Using specific heat capacity data obtained by DSC investigations close to the glass transition and above the melting point, εT and cp were separated and the specific heat capacity of the whole undercooled liquid region was determined. Furthermore, the hemispherical total emissivity of the liquid was found to be about 0.22 at 980 K. On undercooling the liquid, the emissivity decreases to approximately 0.18 at about 670 K, where the undercooled liquid starts to freeze to a glass. No significant changes of the emissivity are observed as the alloy undergoes the glass transition. © 1995 American Institute of Physics.
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  • 19
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2136-2138 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Various sample sizes of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 with masses up to 80 mg were undercooled below Tg (the glass transition temperature) while electrostatically levitated. The final solidification product of the sample was determined by x-ray diffraction to have an amorphous phase. Differential scanning calorimetry was used to confirm the absence of crystallinity in the processes sample. The amorphous phase could be formed only after heating the samples above the melting temperature for extended periods of time in order to break down and dissolve oxides or other contaminants which would otherwise initiate heterogeneous nucleation of crystals. Noncontact pyrometry was used to monitor the sample temperature throughout processing. The critical cooling rate required to avoid crystallization during solidification of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy fell between 0.9 and 1.2 K/s. © 1994 American Institute of Physics.
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  • 20
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High temperature high vacuum electrostatic levitation was used to determine the complete time–temperature–transformation (TTT) diagram of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy in the undercooled liquid state. This is the first report of experimental data on the crystallization kinetics of a metallic system covering the entire temperature range of the undercooled melt down to the glass transition temperature. The measured TTT diagram exhibits the expected "C'' shape. Existing models that assume polymorphic crystallization cannot satisfactorily explain the experimentally obtained TTT diagram. This originates from the complex crystallization mechanisms that occur in this bulk glass-forming system, involving large composition fluctuations prior to crystallization as well as phase separation in the undercooled liquid state below 800 K. © 1996 American Institute of Physics.
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