Sun Hui, Jian Zengyun, Jiang Bingqing, Xu Junfeng, Zhang Tiantian
School of Materials Science and Chemical Engineering, Xi'an Technological University Xi'an Shaanxi 710021 China
School of Mechatronic Engineering, Xi'an Technological University Xi'an Shaanxi 710021 China.
RSC Adv. 2019 Feb 18;9(10):5815-5824. doi: 10.1039/c8ra10189b. eCollection 2019 Feb 11.
Research into the conditions for forming uniform melt-free crystal sites and the effect of the melt state on solidification behaviors is theoretically significant and has valuable applications. However, there are no quantitative data on these aspects due to rigorous experimental requirements. In this study, the variation of the melt structure at different superheating temperatures and the cooling rate during the deep solidification of cold niobium melt was investigated by a large-scale molecular dynamics simulation method. The solid/liquid coexistence method, the radial distribution function, an energy-temperature analysis, the average energy, an atomic cluster analysis, and a visualization analysis were adopted to analyze the variations in microstructure transitions. The temperature undercooling plots of Nb melt at different superheating temperatures suggested that the metal melt structure should be classified into three regions (regions 1 and 2, each with different melt structures that vary with temperature, and region 3, whose melt structure does not change with temperature); the critical cooling rate of the crystal-amorphous transition was 1.0 × 10 K s and the solidification undercooling increased with increasing superheating temperature until maximal undercooling was obtained. Simultaneously, it was found that the maximal undercooling occurred at ∼0.432 ( is the melting point) and the maximal superheating occurred at ∼1.216 .
研究均匀无熔体晶体位点的形成条件以及熔体状态对凝固行为的影响具有重要的理论意义和应用价值。然而，由于实验要求严格，目前尚无关于这些方面的定量数据。在本研究中，采用大规模分子动力学模拟方法，研究了冷铌熔体深度凝固过程中不同过热度下熔体结构的变化以及冷却速率。采用固/液共存法、径向分布函数、能量-温度分析、平均能量、原子团簇分析和可视化分析等方法，分析了微观结构转变的变化。不同过热度下铌熔体的温度过冷曲线表明，金属熔体结构可分为三个区域（区域1和区域2，每个区域具有随温度变化的不同熔体结构，区域3的熔体结构不随温度变化）；晶体-非晶转变的临界冷却速率为1.0×10 K s，凝固过冷度随过热度的增加而增大，直至获得最大过冷度。同时发现，最大过冷度出现在约0.432（为熔点）处，最大过热度出现在约1.216处。
