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  • 1
    Electronic Resource
    Electronic Resource
    Grain refinement induced by a critical crystal growth velocity in undercooled melts (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 324-326 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Containerless undercooling by electromagnetic levitation has been used to measure both growth velocity and grain size as a function of undercooling in Cu70Ni30 and Cu69Ni30B1 alloys. At a critical undercooling ΔT* the temperature dependence of the growth velocity changes discontinuously. This is accompanied by a sudden drop of grain size in the solidified product by more than two orders of magnitude. The comparative investigations show that it is not a critical undercooling that initiates the grain refinement process, but rather a critical crystal growth velocity, which approximately equals the diffusive speed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103289
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  • 2
    Electronic Resource
    Electronic Resource
    Growth of lamellar eutectic dendrites in undercooled melts (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 1643-1649 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electromagnetic levitation is used to undercool bulk samples of eutectic Ni 21.4 at % Si alloys. Large undercoolings ΔT up to ΔT=220 K are achieved by containerless processing of the melts. Crystal growth velocities are measured as a function of undercooling. The growth kinetics during solidification of the eutectic alloys is controlled by atomic diffusion. A maximum in the relation of the growth velocity on undercooling is observed which is due to the progressively decreasing diffusion coefficient counteracting the enhancement of the driving force of crystallization with increasing undercooling. Microstructure analysis of as-solidified samples reveals colonies of eutectic lamellae enveloped by a nonplanar growth front of a dendritelike morphology. The experimental data are analyzed within current models of crystal growth taking into account a negative temperature gradient in front of the solidification front. While the thermal undercooling causes a dendriticlike morphology of the solidification front, constitutional and curvature undercooling control the formation of the eutectic colonies behind it. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368233
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  • 3
    Electronic Resource
    Electronic Resource
    Nonequilibrium solidification of hypercooled Co–Pd melts (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 3028-3034 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Co–Pd alloy melts are characterized by a low heat of fusion and, as a consequence, by a comparably small critical undercooling for the hypercooling limit ΔThyp of the order of 300 K. It is shown that containerless processing of bulk melts by electromagnetic levitation offers undercooling levels of ΔT(approximate)350 K thus exceeding the hypercooling limit considerably. Solidification of undercooled melts from the hypercooling regime leads to rapid crystallization of the entire sample under nonequilibrium conditions. The electromagnetic levitation technique in combination with time-resolved recalescence detection was used to measure the growth velocity of Co–Pd alloy melts as a function of undercooling prior to solidification. The growth velocities of undercooled metallic melts were measured in an undercooling range exceeding the hypercooling limit. The experimental results are discussed within current theory of dendritic growth. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367057
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  • 4
    Electronic Resource
    Electronic Resource
    Liquid metal undercooled below its Curie temperature (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1723-1724 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electromagnetic levitation has been used to undercool an alloy of Co80Pd20 below the Curie temperature of the solid α phase. If the temperature of the undercooled liquid decreases below the Curie temperature an attractive force between the sample and an external permanent magnet was observed. This may indicate the existence of a metallic liquid showing magnetic ordering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112898
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  • 5
    Electronic Resource
    Electronic Resource
    Containerless Undercooling and Solidification of Pure Metals (1991)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 21 (1991), S. 23-44 
    Details
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ms.21.080191.000323
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  • 6
    Electronic Resource
    Electronic Resource
    Verification of metastable phase diagrams byin situ measurements on undercooled melts (1996)
    Springer
    International journal of thermophysics 17 (1996), S. 1217-1226 
    Details
    ISSN: 1572-9567
    Keywords: metastable phase formation ; rapid solidification ; stainless steel alloys ; temperature measurements ; undercooled melts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electromagnetic levitation technique combined with pyrometric methods have been applied to verify the metastable phase diagram of Fe Cr Ni alloys byin situ observation of phase selection processes in undercooled melts. The temperatures of levitated drops prior to solidification were determined by a two-color pyrometer and the recalescence behavior of the undercooled melt was recorded from a high-speed photosensing device with a sampling rate of 1 MHz. Fe69Cr31 ,Ni, alloy melts with different Cr/Ni ratios were investigated for undercooling levels up to 320 K. The transition from single- to double-recalescence behavior was found beyond a critical undercooling level for primary austenitic alloys with Cr Ni 〈 1.5. For the first time, this gives direct evidence of metastable phase formation in this alloy system fromin situ observations. The dendrite growth velocity displayed a sudden drop at the critical undercooling level, confirming the metastable phase formation. The intermediate arrest temperature of the double-recalescence event fits well with the calculated metastable liquidas line derived from a subregular solution model for the Gibbs free energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01442008
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  • 7
    Electronic Resource
    Electronic Resource
    Rapid eutectic growth of undercooled metallic alloys (1993)
    Springer
    Journal of materials science 12 (1993), S. 1774-1777 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00517607
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  • 8
    Electronic Resource
    Electronic Resource
    Containerless solidification of germanium by electromagnetic levitation and in a drop-tube (1997)
    Springer
    Journal of materials science 32 (1997), S. 1437-1442 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Containerless solidification of germanium has been realized by electromagnetic levitation and drop-tube processing, respectively. The effect of undercooling in the range of 40–426 K on the as-solidified structures of levitation melted Ge drops (∼8.4 mm diameter) was investigated. For undercoolings less than 300 K, the lamellar twins were grown, whereas a microstructural transition to equiaxed grains was observed at undercoolings ≥300 K. Further increasing the undercooling to 400 K, a significant reduction in grain size was achieved. In addition to a similar microstructural development among the particles solidified during free fall in a 8.5 m drop-tube, high-undercooling-induced single crystals were found for some droplets less than 200 μm in diameter. The results on the transition from twins to fine equiaxed grains are accounted for by theories of solidification kinetics and a dendrite break-up model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018593615171
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of ZrO2 and SiO2 on glass forming ability of Zr57Cu20Al10Ni8Ti5 alloy (1999)
    Springer
    Journal of materials science 34 (1999), S. 3795-3800 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Zr57Cu20Al10Ni8Ti5 has very high glass forming ability (GFA) due to its low crystal growth rate which limits development of crystallites arising from container walls or nuclei. Effect of ZrO2 and SiO2 on GFA was studied by investigating the solidification microstructures of alloys containing different amount of the oxides. Amorphous ingots were formed by melting and freezing alloys without addition of the oxides using an arc furnace. Partially amorphous ingots were formed for addition of the oxides up to 0.2 wt %. Amorphous forming conditions of alloys containing greater concentration of the oxides were studied using a drop tube. GFA decreases with increasing concentration of the oxides. However, superheating of melts eliminates some effects of the oxides. Different types of oxides leads to different microstructures due to their different heterogeneous nucleation rates and nucleation temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004648732247
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  • 10
    Electronic Resource
    Electronic Resource
    Thermal conductivity and specific heat of amorphous Zr0.67Ni0.33 after structural relaxation (1986)
    Springer
    The European physical journal 63 (1986), S. 173-178 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Low-temperature measurements of the thermal conductivity κ (0.3K≦T≦5K) and of the specific heatC (0.07K≦T≦3.5K) of splat-cooled amorphous superconducting Zr0.67Ni0.33(T c ≈2.7K) after different annealing stages are reported. κ increases progressively (up to 55%) after annealing. An analysis of κ with the help of normal-state measurements belowT c in an overcritical field shows that the phonon-electron scattering remains unaltered after annealing. Hence the increase in κ must be entirely attributed to structure-induced (“intrinsic”) scattering, i.e. by two-level tunneling states (TLS) at low temperatures (T≦1K). The specific heat shows a small decrease aboveT c (by 8%) which is attributed to a small diminution of the electronic density of states at the Fermi level and to a small increase in the Debye temperature. ForT≪T c where TLS dominate, the specific heatC decreases less upon annealing than expected from the increase of κ in the standard tunneling model. This points to a change in the TLS relaxation time spectrum upon annealing, as observed previously for Zr x Cu1−x glasses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01309235
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