Study of non-linear kinetics of order-disorder transition with compositional modulation

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Kinetics of the order-disorder transition with compositional modulation was studied with the non-linear kinetic equation which had been improved by the present workers. The equation was solved for the instability of an order phase. It was expected from the features of the solutions that in some off.stoichiometric alloys an ordering tends to enhance compositional modulation. In order to confirm the conjecture, the process of ordering and phase separation in Fe-Al alloys was investigated intensively by X-ray diffraction and electron microscopy. It was observed that the behaviors of spinodal decomposition and precipitation in <DO_3> phase depend strongly upon the initial size of antiphase domains in agreement with the theoretical expectation. The heterogeneous ordering process in CuPt was observed in atomic scale with a field-ion microscope, and the growth kinetics of order domains was found to be correlated with the degree of order within the domains and the domain size. The phenomenon was explained successfully with another simple equation. A spinodal decomposition enhanced by electron irradiation was first recognized in an Fe-Mo alloy. This was also explained well in terms of a non-linear effect of point-defects introduced by irradiation. From the theoretical and the experimental results mentioned above, it is concluded that the correlation between elemental processes, which corresponds to a non-linear term in a kinetic equation, plays a quite important role in the order-disorder transition with compositional modulation.