Abstract A multiscale model is developed to investigate the evolution mechanisms of site-specific grain structures during additive manufacturing (AM) of metallic alloys, using the selective electron beam melting (SEBM) fabrication of Ti-6Al-4V as an example. Specifically, finite-element method is utilized to predict the thermal response at macroscale during SEBM, and the extracted thermal information is then input into a temperature-dependent phase-field model to simulate the grain growth at mesoscale. The grain epitaxial growth, grain selection, grain nucleation and layer-by-layer manufacturing fashion are incorporated, in order to accurately predict grain structure development and relevant physical processes during AM. It is found that, the development of the predominant grain structures in the thick and thin walls, i.e., the large vertical columnar β//Nz grains and slanted columnar grains with various grain orientations, respectively, can be attributed to the competition and collaboration between the thermal gradient and the crystallographically preferred grain growth, as shown from the different growth stages in the simulations. Good agreements in the final grain structures and textures are achieved between the experimental observations and numerical simulations. The present study potentially offers valuable insights and guidance toward designing AM conditions to tailor the grain structures and textures.

中文翻译：

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金属增材制造过程中特定位点晶粒​​结构演化机制研究

摘要 以 Ti-6Al-4V 的选择性电子束熔化 (SEBM) 制造为例，开发了一个多尺度模型来研究金属合金增材制造 (AM) 过程中特定位置晶粒结构的演变机制。具体而言，利用有限元方法预测 SEBM 过程中宏观尺度的热响应，然后将提取的热信息输入到温度相关的相场模型中，以模拟中尺度的晶粒生长。结合晶粒外延生长、晶粒选择、晶粒成核和逐层制造方式，以准确预测增材制造过程中的晶粒结构发展和相关物理过程。发现，在厚壁和薄壁中主要晶粒结构的发展，即，如模拟中的不同生长阶段所示，大的垂直柱状 β//Nz 晶粒和具有各种晶粒取向的倾斜柱状晶粒分别可归因于热梯度和晶体优先晶粒生长之间的竞争和协作。在实验观察和数值模拟之间实现了最终晶粒结构和纹理的良好一致性。本研究可能为设计增材制造条件以定制晶粒结构和纹理提供有价值的见解和指导。如模拟中不同生长阶段所示。在实验观察和数值模拟之间实现了最终晶粒结构和纹理的良好一致性。本研究可能为设计增材制造条件以定制晶粒结构和纹理提供有价值的见解和指导。如模拟中不同生长阶段所示。在实验观察和数值模拟之间实现了最终晶粒结构和纹理的良好一致性。本研究可能为设计增材制造条件以定制晶粒结构和纹理提供有价值的见解和指导。