| Decomposition processes of α phase in Cu-9Ni-6Sn alloy have been investigated by means of side band observation around (200)_α peak, hardness and lattice parameter measurements with aging time and microstructural observations. When the specimens are aged below 400℃ after solution treatment, the supersaturated solid solution α is decomposed by three stages. In the first stage, the modulated structure forms along the <100>_α direction, the side band appears around (200)_α peak and the satellite occurs in the selected area diffraction pattern, these results indicating that the supersaturated solid solution α is decomposed by the spinodal decomposition. And then in the second stage, the matastable phase of γ′ with DO_(22) type superlattice nucleates from the modulated structure. At the final stage of transformation, the y phase decomposes into the unequilibrium cellular structure consisting of α phase and DO_(19) type superlattice. When the specimens are aged above about 450℃ after solution treatment, however, the equilibrium cellular structure consisting of α phase and DO₃, type superlattice forms from the initial stage of transformation without any reactions such as spinodal decomposition and transition of metastable phase. |
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