“…Scales are observed in the undercooling range where anomalous growth behavior is observed, i.e., for decreasing growth velocities with increasing undercooling. The scaled front consists of numerous nuclei ahead of the crystal-liquid interface that occurs in the undercooling range featuring the negative slope for the crystal growth velocity at Δ T < 250 K. This unusual behavior is confirmed experimentally and explained theoretically using analytical solutions for the crystal growth front with the polydisperse ensemble of crystals nucleating ahead of the parent front 60 , 61 . Fig.…”
Section: Recent Achievementsmentioning
confidence: 61%
“… Classification is given by the behavior of solidification front velocity V as a function of undercooling ΔT . Note that for the same undercooling, one can find different forms of recalescence and final primary microstructures depending of the content of Nickel, i.e., for different nominal compositions of the Al-rich Al-Ni alloys 61 , 62 . …”
Section: Recent Achievementsmentioning
confidence: 99%
“…The scale distribution was analysed, and the results show that a lower number of larger scales forms with increasing undercooling. The analysis method for determining the front of recalescence (as an envelope of the crystallization front) 58 , 59 remains also appropriate for this front morphology, however, the observed front represents a predominantly nucleation front successfully competing with the growth front of dendrites 61 . This is confirmed by the in situ observation of the recalescence front using the high-speed camera as well as by metallographic evaluations on images of the microstructures shown in Fig.…”
Space levitation processing allows researchers to conduct benchmark tests in an effort to understand the physical phenomena involved in rapid solidification processing, including alloy thermodynamics, nucleation and growth, heat and mass transfer, solid/liquid interface dynamics, macro- and microstructural evolution, and defect formation. Supported by ground-based investigations, a major thrust is to develop and refine robust computational tools based on theoretical and applied approaches. This work is accomplished in conjunction with experiments designed for precise model validation with application to a broad range of industrial processes.
“…Scales are observed in the undercooling range where anomalous growth behavior is observed, i.e., for decreasing growth velocities with increasing undercooling. The scaled front consists of numerous nuclei ahead of the crystal-liquid interface that occurs in the undercooling range featuring the negative slope for the crystal growth velocity at Δ T < 250 K. This unusual behavior is confirmed experimentally and explained theoretically using analytical solutions for the crystal growth front with the polydisperse ensemble of crystals nucleating ahead of the parent front 60 , 61 . Fig.…”
Section: Recent Achievementsmentioning
confidence: 61%
“… Classification is given by the behavior of solidification front velocity V as a function of undercooling ΔT . Note that for the same undercooling, one can find different forms of recalescence and final primary microstructures depending of the content of Nickel, i.e., for different nominal compositions of the Al-rich Al-Ni alloys 61 , 62 . …”
Section: Recent Achievementsmentioning
confidence: 99%
“…The scale distribution was analysed, and the results show that a lower number of larger scales forms with increasing undercooling. The analysis method for determining the front of recalescence (as an envelope of the crystallization front) 58 , 59 remains also appropriate for this front morphology, however, the observed front represents a predominantly nucleation front successfully competing with the growth front of dendrites 61 . This is confirmed by the in situ observation of the recalescence front using the high-speed camera as well as by metallographic evaluations on images of the microstructures shown in Fig.…”
Space levitation processing allows researchers to conduct benchmark tests in an effort to understand the physical phenomena involved in rapid solidification processing, including alloy thermodynamics, nucleation and growth, heat and mass transfer, solid/liquid interface dynamics, macro- and microstructural evolution, and defect formation. Supported by ground-based investigations, a major thrust is to develop and refine robust computational tools based on theoretical and applied approaches. This work is accomplished in conjunction with experiments designed for precise model validation with application to a broad range of industrial processes.
“…The theory under consideration can be extended to a very important case of rapid crystallization frequently met in practice (e.g., when considering the undercooled melt droplets solidifying in EMLs [25]). One of the important phenomena recently observed using the EML facility onboard the International Space Station is the anomalous behavior of crystal growth rate depending on the process driving force-melt undercooling [30]. To describe this phenomenon in detail, we can use a modified CBIE version extended to the case of rapid migration of solid/liquid interfaces [31].…”
The growth of a parabolic/paraboloidal dendrite streamlined by viscous and potential flows in an undercooled one-component melt is analyzed using the boundary integral equation. The total melt undercooling is found as a function of the P\'eclet, Reynolds, and Prandtl numbers in two- and three-dimensional cases. The solution obtained coincides with the modified Ivantsov solution known from previous theories of crystal growth. Varying P\'eclet and Reynolds numbers we show that the melt undercooling practically coincides in cases of viscous and potential flows for a small Prandtl number, which is typical for metals. In cases of water solutions and non-metallic alloys, the Prandtl number is not small enough and the melt undercooling is substantially different for viscous and potential flows. In other words, a simpler potential flow hydrodynamic model can be used instead of a more complicated viscous flow model when studying the solidification of undercooled metals with convection.
“…The theory under consideration could be further developed to describe the anomalous (U-shape) behaviour of the velocity-undercooling relationship found in experiments aboard the International Space Station [53]. To describe these experiments where dendritic growth and crystal nucleation occur simultaneously ahead of the recalescence front, we also need to use nucleation theory at initial and intermediate stages (see, among others, recently published papers [54][55][56][57]).…”
In this paper, we develop a theory of stable dendritic growth in undercooled melts in the presence of conductive and convective heat and mass transfer boundary conditions at the solid/liquid interface of a dendrite. To simplify the matter and construct the analytical theory, conductive and convective mechanisms are considered separately. Namely, the laws for total undercooling and selection criterion defining the stable growth mode (dendrite tip velocity and diameter) are derived for conductive and convective boundary conditions. To describe the case of simultaneous occurrence of these heat and mass transfer mechanisms, we sew together conductive and convective laws using power stitching functions. The generalised selection theory is compared with experimental data for Al24Ge76 and Ti45Al55 undercooled melts.
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