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Depending on the anisotropy of the interphase boundary energy function, different eutectic grains, and hence microstructures, may grow simultaneously at the same experimental conditions. In order to investigate the surface energy anisotropy space, rotating directional solidification (RDS) experiments are used. It is known that the interphase boundary trace obtained with RDS is homothetic to the Wulff form of the interphase boundary. Hence, when the interphases are circular, as in the video below, the crystal/crystal surface energies are quasi-isotropic. (Angular velocity, ω = 0.013 deg/s. Time difference between images is 10 s, movie is recorded with 10 frames/second, and the total duration of the movie in real time is 44.17 minutes.)
On the other hand, if the interphase boundary energy is anisotropic, the interphases do not adjust themselves to sample rotation but follow the minimum energy orientation. As a result, anisotropic grains, such as locked, nearly-locked, are obtained. A new type of anisotropic three-phase eutectic grain, entitled as "Laminated Matrix with Rods" (LMR) observed in β(In)-In2Bi-γ(Sn) system during real-time rotating directional solidification (RDS) experiments is shown in the next video, below. Top and bottom views of the same region in thin sample (13 μm) is obtained by the unique double-sided microscopy system. In this grain, due to the anisotropy in In2Bi/γ(Sn) interphase boundary, the evolving phases, and hence, the microstructures observed through the two glass plates of the thin sample are completely different, despite the strong confinement effect. During RDS experiments, the morphology or the aspect ratio of all phases change periodically and drastically. Specifically, In2Bi, β(In), and γ(Sn) phases evolve from all being lamellar perpendicular to the sample wall to the matrix, elongated/trapezoidal rods, and a lamella parallel to the sample wall, respectively. The results show that these morphological transitions are due to change in the interphase boundary orientation with respect to the growth direction. (Angular velocity, ω = 0.010 deg/s. Time difference between images is 300 s, movie is recorded with 10 frames/second, and the total duration of the movie in real time is 11.92 hours.) For details, see S. Mohagheghi and M. Serefoglu, On the Effect of Interphase Boundary Energy Anisotropy on Morphologies: A New Type of Eutectic Grain Observed in a Three-Phase Eutectic System, Met. Mater. Trans. A, 2024
For further information, contact Melis Serefoglu, Marmara University, Istanbul
Directional solidification begins from an unmelted as-cast eutectic seed as a single-phase Al2Cu layer. The Al-phase, being present at grain boundaries of Al2Cu, spreads out and covers the Al2Cu-liquid interface in a quasi-2D seaweed pattern (0:02-0:03 in the video). This "invasion" process has been observed before in transparent alloy systems (Akamatsu et al., Metall and Mat Trans A 32, (2001): 2039-48) The seaweed pattern is followed in the early stages of coupled growth by a "maze" or labyrinth pattern, which is a precursor to lamellar growth. The movie was obtained by X-ray tomography on a Phoenix Nanotom system and shows a region of about 450 μm width.
Directional solidification of regular and irregular eutectics. Courtesy John Hunt. (98.5 Mb)
A solitary wave travels from
left to right along a steady lamellar eutectic front
(x10 accelerated). This nonlinear phenomenon is typical
of an out-of-equilibrium pattern forming
system. Thin-sample directional solidification of a
near-eutectic transparent alloy (CBr4-C2Cl6).
Horizontal dimension: 620 microns.(0.3 Mb)
(Movie provided by Silvere Akamtsu)
Thin-sample directional solidification is used here
for observing the initial stages of eutectic growth. The
movie shows a mechanism by which a large eutectic grain
can form. In a slightly hypereutectic alloy (transparent
CBr4-C2Cl6 alloy), a thin crystal of the minority phase
(faint-contrast solid-liquid interface) grows and
"invades" the solidification front laterally (from left
to right) on top of a single crystal of the majority
phase (strong-contrast interface). Its lateral
propagation velocity increases while solidification
proceeds. At a certain time, the tip destabilizes and
oscillates, which gives rise to a periodic eutectic
structure.
Horizontal dimension: 430
microns. (Movie provided by Silvere Akamtsu) (1.2 Mb)
Directional solidification parallel to gravity in AlSiCu eutectic alloys. The first movie shows an unmodified irregular eutectic. Imposed temperature gradient of 23.0 K/mm, and sample velocity of 17 microns/s
The second movie shows a Sr-modified irregular eutectic. Imposed temperature gradient of 18.4 K/mm, and sample velocity of 10.5 microns/s
Top view of a three-dimensional phase-field simulation of eutectic solidification. The growth direction is towards the observer. The composition of the liquid far ahead of the growth front is slowly varied in the course of time, such that the volume fractions of alpha (red) and beta (green) phase change with time. The initial condition is an unstable lamellar array, which rapidly splits to form beta rods. As the volume fraction of beta phase increases, the rods become thicker until a transition to lamellae occurs. In the further evolution, the alpha lamellae become thinner and thinner until they break up into alpha rods. For details, see A. Parisi and M. Plapp, Defects and multistability in eutectic solidification patterns, EPL 90, 26010 (2010). (5 Mb) This movie derives from phase-field simulations performed by Mathis Plapp and his collaborators.
This movie shows a phase-field simulation of eutectic colony growth during directional solidification. The growth direction is upward, and the 'camera' follows the isotherms such that a flat front appears immobile in the movie. A binary eutectic (color scale red-blue) front is destabilized by ternary impurities (green) on a scale that is much larger than the lamellar spacing. For details, see M. Plapp and A. Karma, Eutectic colony formation: A phase field study, Phys. Rev. E 66, 061608 (2002). (4.3 Mb) This movie derives from phase-field simulations performed by Mathis Plapp and his collaborators.