Alrasheedi Nashmi, Stefan-Kharicha Mihaela, Sari Ibrahim, Ahmadein Mahmoud, Kharicha Abdellah
Mechanical Engineering Department, Imam Mohammad Ibn Saud Islamic University, Riyadh 11564, Saudi Arabia.
Metallurgy Department, Montanuniversitaet of Leoben, Franz-Josef-Str. 18, A-8700 Leoben, Austria.
Materials (Basel). 2024 Jun 6;17(11):2768. doi: 10.3390/ma17112768.
Ammonium chloride (NHCl) has been extensively studied as a transparent analogue for investigating the solidification of metals due to its distinctive properties and the simplicity of the experimentation. Furthermore, NHCl exhibits a striking resemblance in solidification behavior to the majority of binary eutectic alloy systems, rendering it a valuable model for studying phase transition phenomena. Experiments conducted on ammonium chloride are frequently employed to validate numerical models for predicting grain structures, macrosegregation, and the columnar-to-equiaxed transition (CET). This latter phenomenon arises due to differences in the velocities of columnar dendrite tips and the liquidus isosurface. However, the kinetics of dendrite tip growth, as a function of supersaturation, remains poorly understood for this commonly used alloy. The objective of this study was to utilize the available experimental data in conjunction with Ivantsov correlations to shed light on the ambiguous kinetics. The results indicate that when considering the crystal-melt density ratio, the Ivantsov solution offers a good correlation. Furthermore, incorporating a moderate interfacial kinetic coefficient enhances the correlations further. This correlation can be implemented in numerical models, which will aid in the determination of the columnar front, the columnar-to-equiaxed transition, and the equiaxed growth velocities.
氯化铵（NH₄Cl）因其独特的性质和实验的简易性，作为研究金属凝固的透明类似物已得到广泛研究。此外，氯化铵在凝固行为上与大多数二元共晶合金体系有显著相似之处，使其成为研究相变现象的有价值模型。对氯化铵进行的实验经常用于验证预测晶粒结构、宏观偏析和柱状晶向等轴晶转变（CET）的数值模型。后一种现象是由于柱状枝晶尖端速度与液相线等温面的差异而产生的。然而，对于这种常用合金，枝晶尖端生长动力学作为过饱和度的函数仍知之甚少。本研究的目的是利用现有的实验数据结合伊万佐夫相关性来阐明这一模糊的动力学。结果表明，考虑晶体 - 熔体密度比时，伊万佐夫解具有良好的相关性。此外，纳入适度的界面动力学系数可进一步增强相关性。这种相关性可应用于数值模型，这将有助于确定柱状前沿、柱状晶向等轴晶转变以及等轴晶生长速度。
