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Dynamics of Ordering with Phase Separation in Iron-Silicon Alloys
Abstract In the phase diagrams of some alloys which undergo order-disorder transition of higher-order, there are sometimes two-phase fields where an ordered phase with lower-symmetry coexists with a higher-symmetry phase. In such a mixed-phase field, the ordering is expected to proceed at the same time as phase separation. Iron-aluminum alloys with Al content near 25 at% are a typical alloy-system in which we can observe such type of ordering reaction 1–4. The corresponding phase diagram5 has a triangular mixed-phase field of disordered A2(bcc) and B2(Pm3m), and also a phase field of (A2+D03 (Fm3m)) in the lower temperature region. The transitions from A2 to B2 and from B2 to D03 are of higher-order at their critical temperatures, and eliminate the symmetry elements of translation along a/4 and <100>a/2, respectively, where a is twice the lattice dimension of basic bcc lattice. The ordering reactions occuring in the alloys quenched into the two-phase fields were extensively observed using an electron microscope by Allen et al. 2,3 and the present authors 1,4. The observation revealed complicated processes strongly depending on alloy-composition, temperature and initial state of order. Prior to the experiment, Allen and Cahn2 predicted sequence of mechanisms during the processes, through discussion on the form of the equilibrium phase diagram of Fe-Al using Landau’s mean field model for higher-order transitions.
Dynamics of Ordering with Phase Separation in Iron-Silicon Alloys
Abstract In the phase diagrams of some alloys which undergo order-disorder transition of higher-order, there are sometimes two-phase fields where an ordered phase with lower-symmetry coexists with a higher-symmetry phase. In such a mixed-phase field, the ordering is expected to proceed at the same time as phase separation. Iron-aluminum alloys with Al content near 25 at% are a typical alloy-system in which we can observe such type of ordering reaction 1–4. The corresponding phase diagram5 has a triangular mixed-phase field of disordered A2(bcc) and B2(Pm3m), and also a phase field of (A2+D03 (Fm3m)) in the lower temperature region. The transitions from A2 to B2 and from B2 to D03 are of higher-order at their critical temperatures, and eliminate the symmetry elements of translation along a/4 and <100>a/2, respectively, where a is twice the lattice dimension of basic bcc lattice. The ordering reactions occuring in the alloys quenched into the two-phase fields were extensively observed using an electron microscope by Allen et al. 2,3 and the present authors 1,4. The observation revealed complicated processes strongly depending on alloy-composition, temperature and initial state of order. Prior to the experiment, Allen and Cahn2 predicted sequence of mechanisms during the processes, through discussion on the form of the equilibrium phase diagram of Fe-Al using Landau’s mean field model for higher-order transitions.
Dynamics of Ordering with Phase Separation in Iron-Silicon Alloys
Matsumura, Syo (author) / Oyama, Hitoshi (author) / Oki, Kensuke (author)
1988-01-01
6 pages
Article/Chapter (Book)
Electronic Resource
English
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