To obtain a synergistic combination of high strength and high ductility in titanium alloys, design and creation of heterogenous precipitate microstructure have attracted increasing attention. Herein, using Ti-3Al-5Mo-4.5V (wt.%, an titanium alloy) as a model alloy, we demonstrated that a highly heterogenous -phase precipitate microstructures with well-controlled length scale of spatial heterogeneity (i.e., micron-sized primary α and nano-scale secondary α precipitates), can be synthesized through activating the ω-assisted α nucleation transformation pathway that operates in metastable titanium alloy alone. A detailed analysis of transformation pathway for phase and the underlying ω-assisted α nucleation mechanisms is carried out using the integrated advanced characterizations, theoretical calculations and simulations based on DFT, and phase-field modeling. Experimental results show unambiguously that the embryonic ω particles (also known as athermal ω) with partially collapsed structure are incapable of refining secondary α (α). In contrast, the isothermal ω particles with a complete structural collapse play an important role in assisting α nucleation, resulting in the formation of the ultrafine α lamellae at nanoscales after two-step aging heat treatments. The contributions from the isothermal ω particles are then quantified using first-principles calculations and phase-field simulations. It is found that, even though the solute partitioning between a growing isothermal ω particle reduces the α nucleation driving force in the surrounding β matrix, the elastic interaction between the ω particles and the α nucleus provides more driving force for α nucleation at specific locations of the ω/β interface. Our work extends the microstructure design strategy based on -assisted nucleation mechanism from metastable to Ti-alloys, thereby significantly widening the application space of the strategy.

中文翻译：

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α/β钛合金中高度异质析出物微观结构的制备


为了获得钛合金高强度和高延展性的协同组合，异质析出物显微组织的设计和创建越来越受到人们的关注。在此，使用 Ti-3Al-5Mo-4.5V（wt.%，一种钛合金）作为模型合金，我们证明了高度异质相沉淀物微观结构，具有良好控制的空间异质性长度尺度（即微米级）初级α和纳米级次级α沉淀物）可以通过激活仅在亚稳态钛合金中运行的ω辅助α成核转变途径来合成。利用集成的先进表征、基于 DFT 的理论计算和模拟以及相场建模，对相的转变路径和潜在的 ω 辅助 α 成核机制进行了详细分析。实验结果明确表明，具有部分塌陷结构的胚胎ω粒子（也称为无热ω）无法细化次级α（α）。相比之下，结构完全塌陷的等温ω粒子在辅助α成核方面发挥着重要作用，从而在两步时效热处理后形成纳米级超细α片层。然后使用第一原理计算和相场模拟来量化等温 ω 粒子的贡献。研究发现，尽管生长的等温 ω 粒子之间的溶质分配降低了周围 β 基体中的 α 成核驱动力，但 ω 粒子与 α 核之间的弹性相互作用为特定位置的 α 成核提供了更多的驱动力。 ω/β 界面。 我们的工作将基于辅助成核机制的微观结构设计策略从亚稳态扩展到钛合金，从而显着拓宽了该策略的应用空间。