金属凝固过程同步辐射X射线成像用多功能凝固装置

Synchrotron X-ray radiography has been an important means to in-situ observe the solidification of metallic alloys. However, there are many drawbacks with the solidification apparatuses in use, such as limited heating temperature, low and unstable temperature gradient in directional solidification, uncontrolled atmosphere, and the incapability to select the observation field. As a result, the experimental error is too large; the alloy choice is severely confined, and the experiment often fails as the solidification interface does to get into the observation field. The aim of this project is, based on the Shanghai Synchrotron Radiation Facility (SSRF), to construct a novel solidification apparatus for real-time observation of the solidification of metallic alloys. The apparatus possesses the following functions: (1) directional solidifications at vertical and horizontal direction can be carried out, respectively; (2) it can afford high-purity inert atmospheres for the sample and heater; (3) the long-time heating temperature reaches 1873K; (4) the temperature gradient is up to 200 K/mm, and keeps stable during experiment; (5) the observation object can be selected anytime during experiment. With this apparatus, investigations will be performed on (1) the natural convection in liquid and solidification structure formation when single phase alloys solidify along horizontal direction, (2) the dynamic process of the directional solidification interface evolution with a third element addition of Co-Sn eutectic alloy whose eutectic interface branches in seaweed mode in the undercooled melt, and (3) the crystallization behavior of the primary Al3Fe in the Al-Fe hypereutectic alloy melt that is superheated to different degrees above the liquidus temperature and its dependence on the modification agent.

同步辐射X射线实时成像已成为研究金属凝固过程的重要手段。然而，现有凝固装置不具备视场实时选择功能，加热温度低，温度梯度小且不稳定，凝固环境气氛无法有效控制，导致实验数据误差大，实验金属选择范围小，实验成效低。本项目基于上海同步辐射光源，对金属凝固过程X射线实时成像用凝固装置进行全新设计，研制出可实现下述功能、具有国际领先水平的实验系统：（1）能进行垂直、水平方向定向凝固；（2）能为试样提供高纯气体保护；（3）可在1873K温度长期使用；（4）温度梯度可达200K/mm，并在凝固过程中保持稳定；（5）观察过程中可对目标进行选择、跟踪。使用该装置，研究下述问题：（1）单相合金水平定向凝固时液相自然对流规律与组织形成机制;（2）自由凝固时呈海藻状生长的Co-Sn共晶在第三组元作用下定向凝固界面失稳演化的微观动力学；（3）熔体过热和变质处理对Al-Fe过共晶合金中初生Al3Fe相结晶行为的影响。

同步辐射X射线实时成像已成为研究金属凝固过程的重要手段。在本项目的资助下，研制出了在上海同步辐射光源使用的多功能金属凝固装置，主要设备包括一台高精度运动台、一台高性能金属定向凝固炉和一台金属深过冷凝固炉，有效解决了先前凝固实时观察装置不具备视场随动功能，加热温度低，温度梯度小且不稳定，凝固环境气氛无法有效控制，实验金属局限大等问题，为高质量开展金属凝固过程X射线实时成像研究创造了条件。进行了Al-Cu、Co-Sn和Mg-Gd合金的定向凝固，在建立起凝固组织形貌及参数与温度梯度和生长速度关系的同时，借助X射线实时成像结果，揭示了熔体过热温度和冷却速度对晶体形核和生长过程的影响机制。进行了Co-B合金的深过冷凝固，获得了块体Co23B6亚稳相，表征了该亚稳相分解的动力学。提出了共晶合金深过冷快速凝固过程中初生共晶重熔分数的计算方法，揭示了合金性质对初生共晶重熔的影响规律。项目发表论文24篇，申请国家发明专利5项，国际学术会议大会报告或邀请报告8人次，培养博士生6人，硕士生4人。