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

研究了含一级相变的铜基合金的退火行为，特别考虑了相分离和有序无序的竞争过程。取得了以下研究成果：1.L1有序Cu-39at%Pt合金的退火过程因退火温度是否高于某一特定温度而有很大不同。这一现象表明，在平衡相图的(L1_1+Al)区存在一条有序-无序的亚稳转变线。在Cu-25at%Pt合金中，L1&lt；2-S&gt；向L1&lt；22&gt；的转变是通过湮没发夹状的周期性反相界来进行的。发夹状反相界(APB)是通过接触相邻的周期APB或借助热APB而形成的。将含时Landau-Gintzburg展开应用于动力学方程，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没过程。在镍含量较高的铜镍锡合金中，调幅分解进行得更快。从实验X射线边带出发，考察了合金中成分波的波长、幅度和分布，以阐明分解过程。淬态合金的衍射图没有显示有序晶格衍射点，但经过短暂的退火热处理后，D0&lt；22&gt；出现了弥散散射。经连续退火后，Ni含量较低的合金中的散射增强，而Ni含量较高的合金中的L1_2则相反。

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.