In-situ measurements of L12 phase formasion by means of SR-SWAXS

本研究旨在建立一种新的实验方法，利用同步辐射小角和中（宽）角散射技术（SR-SWAXS）来研究一阶有序-无序转变过程中相分离的动力学。同步辐射源的时间分辨小角散射技术已成为研究相分离快速动力学的有力工具。本项目的目的是将SR-SAXS方法扩展到更高的散射矢量区域，即100点左右，以研究Al-Li和其他合金中伴随相分离和L12型有序的动力学。目前的研究结果总结如下：1。本研究建立的时间分辨SR-SWAXS方法证明，在有序不稳定的温度区域，有序先于相分离。然而，从淬火开始，总是存在很小的相分离。相分离和有序之间的耦合程度应该不是很强，但是否完全没有耦合仍然是一个悬而未决的问题。在加热时效良好的Al-Li样品过程中，SAS和100的变化表明DSC信号的变化与δ′的体积分数直接相关，DSC曲线的双峰形状简单地来自于动力学条件。

This research aims to establish a new experimental method to inquire into the kinetics of phase esparation accompanying first-order order-disorder transition by utilizing a synchrotron-radiation small-angle and medium (wide) -angle scattering technique (SR-SWAXS) .Time-resolved small-angle scattering technique with synchrotron radiation source has been used as a powerful tool to examine the fast kinetics of phase separation. The purpose of this project is to extend the time-resolved SR-SAXS methods to a higher scattering vector region, namely, around 100 spot, to investigate the kinetics of concomitant phase separation and L12 type ordering in Al-Li and other alloys.The present results are summarized as :1. The time-resolved SR-SWAXS method developed in the present study proved that ordering precedes the phase separation in the temperature region below ordering instability. However, a very small phase separation always exists from the very beginning of quench. The degree of coupling between phase separation and ordering should be not very strong, but whether there is no coupling at all is still an open question.2. During heating a well-aged Al-Li samples, the change in the SAS and 100 shows that the change in the DSC signal is directly related to the volume fraction of delta', and the double-peak shape of DSC curve simply comes from kinetic conditions.