The behavior and roles of antiphase boundaries in order-disorder transformation processes

研究的目的是阐明有序-无序转变过程中反相界的行为和影响。为了模拟反相边界结构的变化，通过发展自由能的Ginzburg-Landau型展开式来制定动力学方程。从模拟中得出以下结果。(1)当T> T_c（有序化的临界温度）时，无序化是通过反相界面上形成的无序区的扩展而实现的。(2)当T <T_c时，反相界面在表面上会出现不平整，形成一对发夹结构。从L1_（长周期反相超结构）到L1_2的转变是通过发夹的后退进行的。<2-s>(3)在低温区域，反相边界的表面能相对高，使得反相边界趋于变得平坦。利用透射电子显微镜（TEM）和X射线衍射实验研究了周期性反相界对有序-无序转变的影响。<2-s>在L_1_尺寸变化较小的Cu_3Pt样品中，周期性反相界通过发夹机制减少，使L_1_转变为L_1_2。<2-s><2-s>另一方面，在具有大的变体尺寸的样品中，L1_相保持亚稳态。<2-s>高分辨透射电镜观察表明，在Fe-Si合金中，反相界的“润湿”厚度随退火时间的延长而增加。模拟和实验结果证实了反相界对合金有序-无序转变过程的重要影响。

The objective of the research is to clarify the behavior and the effects of antiphase boundaries on the order-disorder transformation process. The kinetic equation was formulated by developing a Ginzburg-Landau type expansion of the free energy in order to carry out simulation of the changes in antiphase boundary structures. From the simulations, the following results were drawn. (1) At T>T_c ( the critical temperature of ordering ), disordering undergoes by expansion of a disorder region which has formed on antiphase boundaries. (2) At T<T_c, antiphase boundaries can have unevenness on the surface where a pair of hairpins are formed. The transformation from L1_<2-s> ( long period antiphase superstructure ) to L1_2 proceeds by receding of the hairpins. (3) At a low temperature region, the surface energy of antiphase boundaries is relatively high so that antiphase boundaries tend to become flat. Therefore, periodic antiphase boundaries cannot move and then the L1_<2-s> becomes metastable.Transmission electron microscopy (TEM) and X-ray diffraction experiments were performed to examine the effects of antiphase boundaries on the order-disorder transformation. In the specimen of Cu_3Pt with a small variant size of L1_<2-s>, periodic antiphase boundaries are reduced by the hairpin mechanism to transform L1_<2-s> to L1_2. In the specimen with a large variant size, on the other hand, the L1_<2-s> phase remains metastable. High resolution TEM observation showed that in an alloy of Fe-Si the thickness of "wetting" on antiphase boundaries increases with annealing time. The results of the simulations and experiments confirmed that antiphase boundaries give significantly important effects on the process of order-disorder transformation in alloys.