液固相变形核率转变的物理模拟

Simulation Study of Nucleation Rate Transition during Solid-liquid Phase Change

以NH4Cl-70wt%H2O溶液为模型合金,考察了型壁冷却条件对液固相变形核及晶粒生长过程的影响。实验发现:在相同的充型温度下,降低型壁的温度,溶液过冷度增大,形核率增大,出现了"爆炸形核"现象;但当进一步降低型壁温度时,反而出现了形核率随过冷度变化趋势逆转的现象,分析其原因是原子扩散动力学,以及相变热力学耦合作用的结果,这与金属体系不同冷却速度条件下的形核过程呈现出同样的规律,说明NH4Cl-70wt%H2O溶液与金属体系在形核特性上具有相似性,可用于金属形核过程的良好模拟。

The effects of mould temperature on the nucleation rate of NtLC1-70wt%H2O system were investigated. The results show that nucleation rate increases and a ＂big-bang＂ nucleation occurs with the decrease of mould temperature; however, with further decrease of the mould temperature, the change trend of nucleation rate reverses due to the coupling effect of diffusion dynamics and transformation thermodynamics. These phenomenon are in good resemblance both in trends and quantity with that of metal solidification process, which demonstrates the similarity of nucleation characteristics between the NH4C1-70wt%H2O system and metals, and indicates that NI-LCI-70wt% H2O system can be reasonably adapted for the physical simulation of nucleation in solidification of metals.