Fivefold twin (FFT) and lamellar (LAM) structures are the primary configurations during the crystallization of alloys. However, the co-existence of these two structures in one system and the conversion mechanism are barely explored. In this study, we investigated the rapid solidification process of a Ti₃Al alloy by using molecular dynamics simulation and discussed the evolution of the microstructure under two first-order phase transitions in detail. The first phase transition followed Ostwald's step rule, and the nucleation pathway in the system was supercooled liquid → BCC → FCC/HCP. A new phase transition pattern of FFTs transformed into a LAM structure leading to a second phase transition was found. The FFT atoms first transformed into other atoms as the partition interface, and then the LAM structure consumed Other atoms and grew further. The interconversions between different clusters were unstable and required complex intermediate states to reach stability. These findings provide a new understanding of the relationship between the FFT and LAM structures, especially for the metal that underwent two-phase transitions.

中文翻译：

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Ti3Al合金中五重孪晶转变为层状结构的新相变模式

五重孪晶 (FFT) 和层状 (LAM) 结构是合金结晶过程中的主要结构。然而，几乎没有探索这两种结构在一个系统中的共存和转换机制。在这项研究中，我们研究了 Ti ₃的快速凝固过程铝合金通过分子动力学模拟，详细讨论了两种一级相变下的显微组织演变。第一个相变遵循奥斯特瓦尔德阶跃规则，系统中的成核路径为过冷液体→BCC→FCC/HCP。发现了转换为 LAM 结构的 FFT 的新相变模式，导致第二个相变。FFT 原子首先转化为其他原子作为分区界面，然后 LAM 结构消耗其他原子并进一步增长。不同簇之间的相互转换是不稳定的，需要复杂的中间状态才能达到稳定。这些发现提供了对 FFT 和 LAM 结构之间关系的新理解，特别是对于经历两相转变的金属。