1996 Fiscal Year Final Research Report Summary
Analysis of Ordering Dynamics in Ll_2-Alloys with a Vectorized Order-Parameter
| Project/Area Number |
07805060
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical properties of metals
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
KUWANO Noriyuki Associate Professor Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 大学院・総合理工学研究科, 助教授 (50038022)
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| Co-Investigator(Kenkyū-buntansha) |
HATA Satoshi Research Associate Interdisciplinary Graduate School of Engineering Sciences, Ky, 大学院・総合理工学研究科, 助手 (60264107)
ITAKURA Masaru Research Associate Interdisciplinary Graduate School of Engineering Sciences, Ky, 大学院・総合理工学研究科, 助手 (20203078)
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| Project Period (FY) |
1995 – 1996
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| Keywords | kinetic equation / degree of order / antiphase boundary / Potts-model / wetting phenomenon / computer-simulation / Ginzburg-Landau model / free energy |
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| Research Abstract |
A kinetic equation has been formulated with the Ginzburg-Landau expansion in order to analyze the ordering processes and the associated changes of microstructures in Cu_3Au-type (Ll_2)alloys. The Ll_2 unit-cell has four lattice points which are divided into alpha-and beta-sublattice sites. Since the numbers of alpha-and beta-sublattice sites are different from each other (1 and 3), Ll_2 has four phases depending on which lattice point is beta-site. A single order-parameter cannot describe the state of order including the phase, as far as it has a real number. In the present study, a vectorized order-parameter S=S (eta1, eta2, eta3, eta4) is introduced, following a Potts model. Each parameter, eta1, eta2, eta3, eta4, has a non-negative value. First, the energy coefficients in the kinetic equation were determined so that the equilibrium phase diagram for Cu-Pt was reproduced. The changes in microstructures associated with ordering were analyzed by performing compuersimulation using the kinetic equation. Following results were obtained : (i) Around an antiphase boundary, the phase changes smoothly in the way that eta1 decreases and eta2 increases compensationally. (ii) At an antiphase boundary, there forms a narrow region of a zero-degree of order and of high concentration of Pt, which corresponds to a "wetting phenomenon." (iii) The profiles of order-parameters obatined by the present simulation agree well with those calculated by a cluster-variation method. (iv) The hairpin mechanism in the annihilation process of periodic antiphase boundaries was successfully reproduced by the simulation. (v) Other important behaviors of antiphase boundaries and changes in microstructure were analyzed with the present kinetic equation.
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