TiAl alloys with the (α₂ + γ) lamellar structure are highly valued for their excellent high-temperature strength and creep resistance. Understanding the formation mechanism of the lamellar structure is crucial for tuning the microstructure and properties. This work investigates the formation of lamellar structure in Ti-48Al-7Nb-2.5V-1Cr alloy, revealing the presence of hcp-based long-period superstructure (hcp-LPS) as a metastable phase during lamellar formation. The identification of hcp-LPS demonstrates that the necessary solute enrichment for the formation of γ lamellae occurs on the hexagonal α matrix, implying that phase separation of α → Al-rich α lamellae + Al-depleted α lamellae is the first step of lamellar formation. Once phase separation is completed, all subsequent phase transitions occur within the Al-rich α lamellae. Additionally, the formation of twin lamellae is further discussed. The formation of the twin lamellae occurs sequentially. Pre-existing lamella promotes the formation of later lamella by inducing solute enrichment in its surrounding region, and then the successive slip of Shockley partial dislocations with opposite Burgers vectors ensures special stacking of later lamellae. These findings not only contribute to the fundamental understanding of spinodal mechanisms in hexagonal crystals, but also provide novel insights into the formation of twin lamellae.

中文翻译：

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TiAl 合金层状形成过程中六方α相分离及其对后续相变的影响


具有 （α₂ + γ） 层状结构的 TiAl 合金因其优异的高温强度和抗蠕变性而受到高度评价。了解层状结构的形成机制对于调整微观结构和特性至关重要。这项工作研究了 Ti-48Al-7Nb-2.5V-1Cr 合金中层状结构的形成，揭示了在层状形成过程中基于 HCP 的长周期超层结构 （hcp-LPS） 作为亚稳相的存在。hcp-LPS 的鉴定表明，形成γ片所需的溶质富集发生在六边形α基体上，这意味着富α → Al α 层 + 贫铝α片的相分离是层状形成的第一步。相分离完成后，所有后续相变都发生在富铝α薄片内。此外，进一步讨论了双薄片的形成。双薄片的形成是按顺序发生的。预先存在的薄片通过诱导其周围区域的溶质富集来促进后期薄片的形成，然后 Shockley 部分位错与相反的 Burgers 向量的连续滑动确保了后期薄片的特殊堆叠。这些发现不仅有助于从根本上理解六方晶体中的旋状机制，而且为孪晶片的形成提供了新的见解。