难混溶合金粉末中核/壳结构形成过程的可视化模拟与观测研究

Visualized simulation and observational study on core/shell structure in immiscible alloy powders

采用自制热台建立了环形温度梯度场,利用丁二腈-水(SCN-H_(2)O)溶液开展了原位相分离观测实验,“模拟”了微重力条件下难混溶合金粉末中核/壳结构形貌的演化过程。结果表明:第二相(L_(2))微球在向试样中心迁移过程中尺寸不断变化。首先,初始L_(2)相在两相区内因碰撞而尺寸变大,但变化不明显;其次,部分L_(2)相在超过双节点温度位置进入单相区后,尺寸减小;最后,随着试样温度降低,L_(2)相因剧烈碰撞而尺寸急速增大,形成核结构。此外,核是由尺寸较大的L_(2)相微球经多次碰撞后在试样中心凝固而形成的。

An annular temperature gradient field was established by a self-made hot stage,and in-situ observation on the phase separation using SCN-H2O solution was performed to“simulate”the evolutionary procedure of the core/shell structure forming in immiscible alloy powders under microgravity conditions.The results show that the size of the second phase(L_(2))microspheres keeps changing during the migration to the specimen center.Firstly,the initial L_(2)phase becomes larger in the two-phase region due to collisions,but it is not obvious.Secondly,the size decreases after L_(2)phases exceed the binodal-temperature position and enter the single-phase region.Finally,with the decreasing temperature of specimen,the size of L_(2)phase increases rapidly due to fierce collisions and forms a core structure.In addition,the core structure is formed by the L_(2)phase microspheres experiencing multiple collisions in the center of the specimen.