Competing processes of phase separation and disordering during first order transitions in Cu-based alloys

研究了含一阶相变的Cu基合金的退火行为，并特别参考了相分离和有序-无序竞争过程。得到了以下结果：L1_1，有序Cu-39 at%Pt合金的退火过程因退火温度是否高于某一温度而有很大不同。这一现象说明在平衡相图的（L1_1+Al）区域存在有序-无序亚稳过渡线。在Cu-25 at%Pt合金中，从L1_<2-S>到L1_<22>的转变是通过发夹形周期性反相边界的湮灭进行的。发夹状反相边界（APB）是通过相邻周期性反相边界的接触或通过热反相边界的辅助形成的。利用随时间变化的Landau-Gintzburg展开动力学方程，对周期APB的湮灭过程进行了计算机模拟。在适当的能量参数下，模拟成功地再现了实验观察到的湮灭过程。在Ni浓度较高的Cu-Ni-Sn合金中，独立分解速度更快。为了弄清合金的分解过程，从实验的x射线边带上，研究了合金中成分波的波长、振幅和分布。淬火态合金的衍射图中没有出现有序点阵衍射斑点，但经过短时间退火后，出现了d0 <22>的弥漫性散射。在连续退火过程中，低镍合金的散射增强，而高镍合金的散射则转变为l12合金的散射。

Annealing behaviors of Cu based alloys which includes first order transitions have been investigated with special reference of competing processes of phase separation and order-disordering. The following results were obtained.1. The annealing processes in an L1_1, ordered Cu-39 at%Pt alloy are quite different from each other, depending upon whether the annealing temperature is higher than a certain temperature or not. This phenomenon exhibits that there is a metastable transition line of order-disorder in the area of(L1_1+Al)of the equilibrium phase diagram.2. In a Cu-25 at%Pt alloy, the transition from L1_<2-S> to L1_<22> proceeds by annihilation of periodic antiphase boundaries of hairpin shape. The hairpin shaped antiphase boundaries(APB)are formed by touching of adjacent perodic APB, or through an aid of thermal APB.3. Applying the time-dependent Landau-Gintzburg expansion to the kinetic equation, we performed computer-simulation for the annihilation process of periodic APB. The simulation with proper energy-parameters reproduced successfully the annihilation process observed experimentally.4. In Cu-Ni-Sn alloys with higher concentration of Ni, spinodal decomposition proceeds faster. From the experimental X-ray side bands, the wave-length, amplitude and profile of the composition waves in the alloys have been examined in order to clarify the decomposition processes. The as-quenched alloys show no order-lattice diffraction spots in their diffraction patterns, but after a short annealing, diffuse scatterings for D0_<22> appear. By successive annealing, the scatterings are intensified in alloys with a lower Ni concentration, but they alter to those for L1_2 in higher Ni alloys.