Experimental and modelling studies for solidification of undercooled Ni–Fe–Si alloys

2019 ◽  
Vol 377 (2143) ◽  
pp. 20180208 ◽  
Author(s):  
Dasari Mohan ◽  
Gandham Phanikumar
Keyword(s):  
Phase Field ◽  
High Speed ◽  
Phase Field Model ◽  
High Growth ◽  
Microstructural Characterization ◽  
Alloy System ◽  
Internal Structures ◽  
Modelling Studies ◽  
Kinetic Undercooling

We present experimental results, analytical calculations and phase-field simulations for undercooled Ni–Fe–Si alloy system. Undercooling experiments are performed using flux encapsulation along with in situ measurement of recalescence speed using a high-speed camera followed by microstructural characterization. Dendrite growth calculations are performed using a modified Boettinger, Coriell and Trivedi theory to incorporate constitutional undercooling due to multiple segregating elements and a modified kinetic undercooling term. Phase-field simulations are performed using a multi-component phase-field model to generate dendrites in this alloy. High growth velocities are observed and the analytical calculations are in good agreement with experiments. The microstructure evolution from the phase-field simulations indicates that there is a difference in solute segregation during growth of dendrites. This article is part of the theme issue ‘Heterogeneous materials: metastable and non-ergodic internal structures’.

Phase-Field Simulation of Solidification With Density Change

2004 ◽  
Author(s):  
Ying Sun ◽  
Christoph Beckermann
Keyword(s):  
Phase Field ◽  
Density Ratio ◽  
Phase Field Model ◽  
Sharp Interface ◽  
Interface Condition ◽  
Diffuse Interface ◽  
Two Phase ◽  
Kinetic Undercooling ◽  
Two Phases ◽  
Mixture Velocity

Phase-field models of solidification with convection often assume the existence of a single (mixture) velocity at any location inside the diffuse interface, and the phase-field, φ, is advected by this mixture velocity. In this paper, the advection of the phase-field is examined for a one-dimensional normal flow to a solidification front induced by a density difference between the solid and liquid. It is found that the results from a phase-field model that assumes a single velocity inside the diffuse interface are generally not in agreement with the sharp interface condition for the kinetic undercooling of the front in the presence of unequal densities, regardless of the interface width. By introducing a two-phase approach, where the solid and liquid are assumed to coexist inside the diffuse interface with different velocities, good agreement with the sharp interface condition is obtained irrespective of the density ratio between the two phases.

scholarly journals Dendrite fragmentation: an experiment-driven simulation

2018 ◽  
Vol 376 (2113) ◽  
pp. 20170213 ◽  
Author(s):  
T. Cool ◽  
P. W. Voorhees
Keyword(s):  
Phase Field ◽  
Contact Region ◽  
Three Dimensional ◽  
Dendritic Structure ◽  
Phase Field Model ◽  
Alloy System ◽  
Growth Conditions ◽  
Dendrite Fragmentation ◽  
Kinetics Of ◽  
Small Spacing

The processes leading to the fragmentation of secondary dendrite arms are studied using a three-dimensional Sn dendritic structure that was measured experimentally as an initial condition in a phase-field simulation. The phase-field model replicates the kinetics of the coarsening process seen experimentally. Consistent with the experiment, the simulations of the Sn-rich dendrite show that secondary dendrite arm coalescence is prevalent and that fragmentation is not. The lack of fragmentation is due to the non-axisymmetric morphology and comparatively small spacing of the dendrite arms. A model for the coalescence process is proposed, and, consistent with the model, the radius of the contact region following coalescence increases as t 1/3 . We find that small changes in the width and spacing of the dendrite arms can lead to a very different fragmentation-dominated coarsening process. Thus, the alloy system and growth conditions of the dendrite can have a major impact on the fragmentation process. This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’.

A Phase Field Model for Grain Refinement in Deeply Undercooled Metallic Melts

2001 ◽  
Vol 677 ◽  
Author(s):  
A.M. Mullis ◽  
R.F. Cochrane
Keyword(s):  
Grain Refinement ◽  
Phase Field ◽  
Growth Velocity ◽  
Morphological Changes ◽  
Phase Field Model ◽  
Side Branch ◽  
Kinetic Undercooling ◽  
Self Similar ◽  
Metallic Melts ◽  
Undercooled Melts

ABSTRACTWe present the results of phase field simulations of dendritic growth into pure undercooled melts, at growth velocities up to 35 m s−1. We find that, at low growth velocities, dendrite morphologies are broadly self-similar with increasing growth velocity. However, above ≈ 15 m s−1 the initiation of side-branching moves closer to the dendrite tip with increasing growth velocity. This appears to be related to the level of kinetic undercooling at the tip. Once side- branch initiation begins to occur within 1-2 radii of the tip, profound morphological changes occur, leading to severe thinning of the dendrite trunk and ultimately repeated multiple tip- splitting. This process can be invoked to explain many of the observed features of spontaneous grain refinement in deeply undercooled metallic melts.

An atomic-resolution microscope study of Al contracts on GaAs

1986 ◽  
Vol 44 ◽  
pp. 726-727
Author(s):  
Z. Liliental-Weber ◽  
C. Nelson ◽  
R. Ludeke ◽  
R. Gronsky ◽  
J. Washburn
Keyword(s):  
High Speed ◽  
Schottky Contacts ◽  
Detailed Knowledge ◽  
The Past ◽  
Semiconductor Interfaces ◽  
Deposited Metal ◽  
Microwave Applications ◽  
Free Interfaces ◽  
Potential Use

The properties of metal/semiconductor interfaces have received considerable attention over the past few years, and the Al/GaAs system is of special interest because of its potential use in high-speed logic integrated optics, and microwave applications. For such materials a detailed knowledge of the geometric and electronic structure of the interface is fundamental to an understanding of the electrical properties of the contact. It is well known that the properties of Schottky contacts are established within a few atomic layers of the deposited metal. Therefore surface contamination can play a significant role. A method for fabricating contamination-free interfaces is absolutely necessary for reproducible properties, and molecularbeam epitaxy (MBE) offers such advantages for in-situ metal deposition under UHV conditions

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