Natalia Shevchenko
Helmholtz-Zentrum Dresden-Rossendorf
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Featured researches published by Natalia Shevchenko.
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science | 2013
Natalia Shevchenko; Stephan Boden; Gunter Gerbeth; Sven Eckert
The directional solidification of Ga-25wt pct In alloys within a Hele-Shaw cell under the influence of thermosolutal convection was observed by means of X-ray radioscopy. The unstable density stratification at the solidification front causes the formation of rising plumes containing solute-rich liquids. The development of the chimneys and the probability of their surviving depend sensitively on the spatial and temporal properties of the flow field. Variations of the vertical temperature gradient along the solidification cell lead to the observation of different mechanisms for chimney formation. Perturbations of the dendritic structure are the origin of development of segregation freckles in case of low temperature gradients. The long-term stabilities of these segregation channels are strongly influenced by the transient nature of the melt convection. The situation at higher temperature gradients is characterized by two dominating convection rolls in the liquid phase which are driven by a lateral temperature gradient and the convex shape of the solidification front. The penetration of this flow pattern into the mushy zone results in continuous accumulation of solute in the central part of the mushy zone followed by a remelting of the solid fraction and the occurrence of a stable chimney.
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science | 2015
Klaus Timmel; Natalia Shevchenko; Michael Röder; Marc Anderhuber; P. Gardin; Sven Eckert; Gunter Gerbeth
We present an experimental study concerned with investigations of the two-phase flow in a mock-up of the continuous casting process of steel. A specific experimental facility was designed and constructed at HZDR for visualizing liquid metal two-phase flows in the mold and the submerged entry nozzle (SEN) by means of X-ray radioscopy. This setup operates with the low melting, eutectic alloy GaInSn as model liquid. The argon gas is injected through the tip of the stopper rod into the liquid metal flow. The system operates continuously under isothermal conditions. First results will be presented here revealing complex flow structures in the SEN widely differing from a homogeneously dispersed bubbly flow. The patterns are mainly dominated by large bubbles and large-area detachments of the liquid metal flow from the inner nozzle wall. Various flow regimes can be distinguished depending on the ratio between the liquid and the gas flow rate. Smaller gas bubbles are produced by strong shear flows near the nozzle ports. The small bubbles are entrained by the submerged jet and mainly entrapped by the lower circulation roll in the mold. Larger bubbles develop by coalescence and ascend toward the free surface.
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science | 2015
Ali Saad; Charles-André Gandin; Michel Bellet; Natalia Shevchenko; Sven Eckert
Freckles are common defects in industrial casting. They result from thermosolutal convection due to buoyancy forces generated from density variations in the liquid. The present paper proposes a numerical analysis for the formation of channel segregation using the three-dimensional (3D) cellular automaton (CA)—finite element (FE) model. The model integrates kinetics laws for the nucleation and growth of a microstructure with the solution of the conservation equations for the casting, while introducing an intermediate modeling scale for a direct representation of the envelope of the dendritic grains. Directional solidification of a cuboid cell is studied. Its geometry, the alloy chosen as well as the process parameters are inspired from experimental observations recently reported in the literature. Snapshots of the convective pattern, the solute distribution, and the morphology of the growth front are qualitatively compared. Similitudes are found when considering the coupled 3D CAFE simulations. Limitations of the model to reach direct simulation of the experiments are discussed.
International Journal of Materials Research | 2015
Yuriy Plevachuk; V. Sklyarchuk; Natalia Shevchenko; Sven Eckert
Abstract The broad interest in the thermophysical properties of gallium-based melts is stimulated by their extensive use in various applications, such as sliding contacts, heat-sensitive elements of liquid-metal thermometers and thermocouples, carrier liquid for conducting magnetic fluids and the working medium for physical modeling in solidification and magnetohydrodynamic studies. The electrical conductivity, thermal conductivity, viscosity, density and thermoelectric power were determined for different alloy compositions in a wide temperature range below and above the liquidus. Respective scaling relations are proposed. A comparison with data available in literature is given.
IOP Conference Series: Materials Science and Engineering | 2017
B. Krull; E Strumpf; O Keplinger; Natalia Shevchenko; Jochen Fröhlich; Sven Eckert; G Gerbeth
The paper proposes a combined experimental and numerical procedure for the investigation of bubbly liquid-metal flows. It describes the application to a model configuration consisting of a recirculating GaInSn flow driven by an argon bubble chain. The experimental methods involve X-ray measurements to detect the bubbles and UDV measurements to gain velocity information about the liquid metal. The chosen numerical method is an immersed boundary method extended to deformable bubbles. The model configuration includes typical phenomena occurring in industrial applications and allows insight into the physics of bubbly liquid-metal flows. It constitutes an attractive test case for assessing further experimental and numerical methods.
IOP Conference Series: Materials Science and Engineering | 2017
Natalia Shevchenko; H. Neumann-Heyme; C Pickmann; Elke Schaberger-Zimmermann; G Zimmermann; K Eckert; Sven Eckert
Solidification experiments and numerical simulations have been performed to improve the understanding of the complex interrelation between melt flow and the formation of dendritic structures during solidification of Al-Cu and Ga-In alloys. Melt flow induces various effects on grain morphology primarily caused by convective transport of solute, such as a facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Within this project special interest was focused on fragmentation and segregation phenomena. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. X-ray radioscopy was applied as a powerful tool for the visualization of dendritic growth and coarsening.
Archive | 2016
Klaus Timmel; Bernd Willers; Thomas Wondrak; Michael Röder; Natalia Shevchenko; Gunter Gerbeth; Sven Eckert
The quality of the produced steel in the continuous casting process is significantly governed by the melt flow in the mold. However, direct flow measurements in liquid metals are still rather scarce. In order to investigate these flow phenomena, three experimental facilities operating with low melting liquid metals were installed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The melt flow in the models is measured by the Ultrasonic Doppler Velocimetry (UDV) or the Contactless Inductive How Tomography (CIFT), multi-phase flows can be visualized by X-ray imaging. The obtained measurement results are primarily used for validation of numerical models.
Advances in the Science and Engineering of Casting Solidification: An MPMD Symposium Honoring Doru Michael Stefanescu | 2015
Natalia Shevchenko; Olga Roshchupkina; Sven Eckert
The directional solidification of Ga-25wt%In alloys within a Hele-Shaw cell has been studied by X-ray radioscopy. The investigations were focused on the influence of melt convection on the dendritic growth. Natural convection occurs during a bottom up solidification because a lighter solute is rejected during crystallization. Forced convection has been produced by a specific electromagnetic pump. The direction of forced melt flow is almost horizontal at the solidification front. Melt flow induces various effects on grain morphology caused primarily by convective transport of solute, such as facilitation of the growth of primary trunks or lateral branches, dendrite remelting, fragmentation or freckle formation depending on the dendrite orientation, the flow direction and intensity. Forced flow eliminates solutal plumes and damps local fluctuations of solute. A preferential growth of the secondary arms occurs at the upstream side of the dendrites, whereas high solute concentration at the downstream side inhibits the formation of secondary branches.
European Physical Journal-special Topics | 2013
Sven Eckert; Petr A. Nikrityuk; Bernd Willers; Dirk Räbiger; Natalia Shevchenko; Hieram Neumann-Heyme; Vadim Travnikov; Stefan Odenbach; Axel Voigt; Kerstin Eckert
European Physical Journal-special Topics | 2013
Natalia Shevchenko; Stefan Boden; Sven Eckert; Dmitry Borin; Michael Heinze; Stefan Odenbach