Stability of an Ordered phase under Rapid Heating

Down淬火在材料科学和技术领域是一种常用的操作，用于研究手机转变动力学和实现新的结构和功能特性。在本研究中，我们着重于反向操作，即上淬操作，并试图从理论上和实验上阐明低温有序手机的稳定性和相变动力学。特别着重于；(1)低于或高于spinodal无序温度的相变行为；(2)Retro效应的检测与解释。本文首先利用聚类变分法和路径概率法进行了理论计算，提出了一阶跃迁的有序-无序系统中普遍存在的旋量无序现象。基于相场法的进一步理论研究阐明了弛豫过程中反相边界的微观结构演化动力学，并结合FLAPW电子结构计算，对Fe-Pd体系的反相边界的微观结构拓扑进行了更为现实的计算。目前的实验研究可分为两大类。一是对Ni-Mo体系的独立无序温度的检测，二是对Cu-Au体系的Retro效应机理的澄清。前者在升温速率加快时，电阻率和热膨胀系数均出现异常。对于后者，结合激光显微镜，在加热和冷却时仔细观察表面形貌的演变和退化。我们得出的结论是，Retro效应与由于晶界不连续而产生的内应力有关。

Down quenching in a common operation employed in materials science and technology communities both to investigate the kinetics of phone transition and to realize new structural and functional properties. In the present study, we focused on the reverse operation, namely the up-quenching operation, and we attempted to clarify the stability and phase transition kinetics of a low temperature ordered phone both theoretically and experimentally. Particular focuses were placed on ; (1) phase transition behavior below an above the spinodal disordering temperature, and (2) detection and interpretation of Retro effect. We first performed the theoretical calculations based on Cluster Variation Method and Path Probability Method and suggested that the spinodal disordering in a common phenomenon for an order-disorder system of first-order transition. Further theoretical studies based on the Phase Field Method clarified the microstructural evolution kinetics of Anti phase boundary during the relaxation process, and by combining with the FLAPW electronic structure calculations, more realistic calculations for the microstructural topology of Anti Phase boundary was performed for Fe-Pd system. The present experimental investigations are classified into two major categories. One is the detection of spinodal disordering temperature for Ni-Mo system and the other is the clarification of the mechanism of Retro effect for Cu-Au system. For the former, anomaly was detected for both the electrical resistivity and the coefficient of thermal expansion when the heating rate is accelerated. For the latter, combined with Laser Microscopy, the evolution and devolution of the surface morphology is carefully observed upon heating and cooling. We concluded that the Retro effect is associated with internal stresses originated from the constraint due to the discontinuity of grain boundaries.