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

研究了含有一级相变的铜基合金的退火行为，特别是相分离和有序-无序的竞争过程。得到以下结果. L1_1有序Cu-39at%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的不同。这一现象表明在平衡相的（L1_1+Al）区域存在有序-无序的亚稳转变线。在Cu-25 at%Pt合金中，L1_<2-S>到L1_<22>的转变是通过周期性的发卡状反相界的湮灭进行的。发夹形反相边界（APB）是通过相邻的周期性APB的接触或通过热APB的辅助而形成的。将含时Landau-Gintzburg展开应用于动力学方程，对周期性APB的湮灭过程进行了计算机模拟。采用合适的能量参数进行模拟，成功地再现了实验观察到的湮没过程. Ni含量较高的Cu-Ni-Sn合金中，调幅分解进行得更快。从实验的X射线边带，成分波的波长，振幅和轮廓的合金已被检查，以澄清的分解过程。淬火态合金的衍射图中没有出现有序点阵衍射点，但经过短时间退火后，出现了D 0的漫散射<22>。通过连续退火，低Ni含量的合金的散射增强，而高Ni含量的合金的散射变为L1_2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.