• Applied Microscopy
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• v.45 no.2
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• pp.58-62
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• 2015

Formation of an icosahedral phase in the bulk glass forming $Ti_{40}Zr_{29}Be_{14}Cu_9Ni_8$ alloy during crystallization from amorphous phase and solidification from melt is investigated. The icosahedral phase with a size of 10 to 15 nm forms as a thermodynamically stable phase at intermediate temperature during the transformation from amorphous to crystalline phases such as Laves and ${\beta}$-(Ti-Zr) phases, indicating that the existence of the icosahedral cluster in the undercooled liquid. On the other hand, the icosahedral phase forms as a primary solidification phase even though the Laves phase is stable at high temperature, which is can be explained based on the high nucleation rate of icosahedral phase relative to that of competing crystalline Laves phase due to lower interfacial energy between icosahedral and liquid phases.

• Korean Journal of Materials Research
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• v.21 no.3
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• pp.168-173
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• 2011

Precipitation of the ordered icosahedral quasicrystal in Mg-6wt%Zn-1wt%Y alloy has been characterized by transmission electron microscopy observations. The lamellar-type icosahedral qusicrystal phases (I-phase) with the face-centered icosahedral (FCI) structure are observed in alloy after solution treatment at $550^{\circ}C$. In the alloy annealed at $400^{\circ}C$, polygon-shaped I-phases are observed in the ${\alpha}$-Mg matrix. The interfaces of the I-phase with the matrix are facetted and the facets are on five-fold and two- fold plane of the I-phase. The orientation relationship of the I-phase with the matrix is determined to be $[I5]_I//[001]_{Mg}$, $(2f)_I//(2\overline{1}0)_{Mg}$ and $[I2]_I//[311]_{Mg}$, $(5f)_I//(0\overline{1}1)_{Mg}$. The icosahedral grains are occasionally found to be twinned with one of the five-fold axis as the twin axis. The twin boundaries appear to be fairly straight and perpendicular to the fivefold twin axis. The icosahedral twin can be expressed as a rotation of $63.4^{\circ}$ or $116.62^{\circ}$ around two fold zone axis.

• Korean Journal of Crystallography
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• v.1 no.2
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• pp.91-98
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• 1990

A twin model for icosahedral phase of rapidly solidified AB transition metal alloy is suggested. Electron diffraction patterns of our icosahedral twin model are simulated, taking into account of multiple diffraction. The simulated pattern with 5-fold symmetry well agrees with the experimental one. Our twin model is closely relevant to the icosahedral phase.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.6
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• pp.362-368
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• 2005

Formation and thermal stability of a quasicrystalline phases in Al-Fe-Mo alloys were investigated by means of melt-spinning process and subsequent heat treatment test. Thermal decomposition and phase transformation process of the as-spun alloys were studied using X-ray diffraction and electron microscopy. The melt-spun Al-Fe-Mo alloys contained an icosahedral quasicrystalline phase with a quasilattice constant of 0.457 nm. Icosahedral phase formed at a composition of $Al_{82.5}Fe_{14}Mo_{3.5}$ as a metastable phase during rapid solidification was transformed into the stable crystalline phases, cubic 1/0 approximant and monoclinic ${\lambda}$-phase, upon heating. A metastable icosahedral and cubic(a = 0.93 nm) phases in as-spun $Al_{65}Fe_{20}Mo_{15}$ alloy were decomposed into two cubic(a = 0.62, 0.31 nm) phases by heat treatment.

• Bulletin of the Korean Chemical Society
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• v.8 no.2
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• pp.63-68
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• 1987

The photolysis and thermal reaction of hexafluorobenzene solution of icosahedral dicarba-closo-dodecaborane and various carbenes have been shown to lead to the formation of four isomeric insertion products to icosahedral molecules. The results showed the carbene insertion reaction to 1, 2-dicarba-closo-dodecaborane to occur at the positions of 4-, 5-, 7-, and 11-borons, 9-, and 12-borons 3-, and 6-borons and 8-, and 10-borons. The samples of 1, 7-, and 1, 12-dicarba-closo-dodecaborane with carbenes in hexafluorobenzene by photolysis showed no reaction. To find out the reactivities of carbenes to dicarba-closo-dodecaboranes, the total energies have been calculated and have been discussed the tendency for carbene insertion reactions to icosahedral carboranes.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.190-191
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• 2006

• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2774-2780
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• 2014

A dynamics study of relaxation and fragmentation of icosahedral argon cluster with a vibrationally excited $Ar_2^+$ (${\nu}$) is presented. Local translation is shown to be responsible for inducing energy flow from the embedded ion to host atoms and fragmentation of the cluster consisting of various low frequency modes. The total potential energy of $(Ar_2^+)Ar_{12}$ is formulated using a building-up procedure of host-guest and host-host interactions. The time dependence of ion-to-host energy transfer is found to be tri-exponential, with the short-time process of ~100 ps contributing most to the overall relaxation process. Relaxation timescales are weakly dependent on both temperature (50-300 K) and initial vibrational excitation (${\nu}$ = 1-4). Nearly 27% of host atoms in the cluster with $Ar_2^+$ (${\nu}$ = 1) fragment immediately after energy flow, the extent increasing to ~43% for ${\nu}$ = 4. The distribution of fragmentation products of $(Ar_2^+)Ar_{12}{\rightarrow}(Ar_2^+)Ar_n+(12-n)Ar$ are peaked around $(Ar_2^+)Ar_8$. The distribution of dissociation times reveals fragmentation from one hemisphere dominates that from the other. This effect is attributed to the initial fragmentation causing a sequential perturbation of adjacent atoms on the same icosahedral five-atom layer.

• Journal of Powder Materials
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• v.18 no.2
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• pp.149-158
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• 2011

Electro-Discharge Sintering (EDS) employs a high-voltage/high-current-density pulse of electrical energy, discharged from a capacitor bank, to instantaneously consolidate powders. In the present study, a single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical $Ti_{52}Zr_{28}Ni_{20}$ powders in size range of 10~30 and $30\sim50{\mu}m$ consisting of ${\beta}$-(Ti, Zr) and icosahedral phases were applied to examine the structural evolution of icosahedral phase during EDS. Structural investigation reveals that high electrical input energy facilitates complete decomposition of icosahedral phase into C14 laves and ${\beta}$-(Ti, Zr) phases. Moreover, critical input energy inducing decomposition of the icosahedral phase during EDS depends on the size of the powder. Porous Ti and W compacts have been fabricated by EDS using rectangular and spherical powders upon various input energy at a constant capacitance of $450{\mu}F$ in order to verify influence of powder shape on microstructure of porous compacts. Besides, generated heat (${\Delta}H$) during EDS, which is measured by an oscilloscope, is closely correlated with powder size.

• Applied Microscopy
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• v.32 no.1
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• pp.31-37
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• 2002

As-cast microstructure of Mg-rich $Mg_{68}Zn_{28}Y_4$ has been investigated by a detailed transmission electron microscopy. The as-cast $Mg_{68}Zn_{28}Y_4$ alloy consisted of three different types of phases: $10{\sim}20{\mu}m$ size primary solidification phase, dendritic phase grown from the primary phase and a eutectic structure formed at the later stage of solidification. The primary solidification phase has an icosahedral structure with a large degree of phason strain. 1/1 rhombohedral approximant phase with lattice parameters: $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$ is first observed in Mg-Zn-Y system. The rhombohedral structure can be obtained by introducing phason strain in the six dimensional face centered hyper-cubic lattice. The decagonal phase nucleates with orientation relationship with the icosahedral phase, and $Mg_4Zn_7$ nucleates with orientation relationship with the decagonal phase, indicating a close structural similarity between the three phases. Gradual depletion of Y during solidification plays an important role in heterogeneous nucleation of decagonal and $Mg_4Zn_7$ phases from icosahedral and decagonal phases respectively.

• Transactions on Electrical and Electronic Materials
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• v.4 no.1
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• pp.1-6
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• 2003

We have studied the size confinement effect on the properties of melting-like transition of small icosahedral copper clusters using a classical molecular dynamics simulation based on a well fitted empirical potential. We investigated the caloric curves of icosahedron nanoclusters and the significant depression in the melting temperatures of the copper nanoclusters was compared with that of the bulk copper. A structural transitions from decahedral to icosahedral shapes were shown. As the cluster size increased, the melting temperature increased, and the latent heat increased but seem to be saturated. However, the specific heat was unrelated to the cluster size.