Abstract Direct energy deposition (DED) is a promising additive manufacturing technology for large-scale fabrications of high-value components. Grain structure control is challenging but meaningful for achieving desirable mechanical properties. A multi-scale three-dimensional (3D) Finite Volume Method-Cellular Automaton (CA-FVM) model is developed. The grain structure evolution in the transition-mode melting is investigated, and the simulated grain structures show fairly good qualitative and quantitative agreement with the experimental results. The influences of laser power and scanning speed on the formed grain structure are examined. A progressive columnar-to-equiaxed transition (CET) is found. The elongated grain is the primary grain morphology, even with the CET. The effects of high temperature gradient on the development of columnar structure are difficult to overcome. Moreover, nanoparticle reinforcement is numerically investigated as a promising technique to realize the site-specific grain structure control by interfering with the columnar growth. We expect this study to provide a deeper understanding of the DED-produced grain structure and improve confidence in the site-specific structure control.

中文翻译：

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直接能量沉积过渡模式熔化中的晶粒结构演变

摘要 直接能量沉积 (DED) 是一种很有前途的增材制造技术，可用于高价值部件的大规模制造。晶粒结构控制具有挑战性，但对于实现理想的机械性能很有意义。开发了多尺度三维 (3D) 有限体积方法 - 元胞自动机 (CA-FVM) 模型。研究了过渡模式熔炼中的晶粒结构演变，模拟的晶粒结构与实验结果在定性和定量上均表现出较好的一致性。研究了激光功率和扫描速度对形成的晶粒结构的影响。发现了渐进的柱状到等轴过渡 (CET)。即使使用 CET，拉长的晶粒也是主要的晶粒形态。高温梯度对柱状结构发展的影响难以克服。此外，纳米颗粒增强作为通过干扰柱状生长来实现位点特定晶粒结构控制的有前途的技术进行了数值研究。我们希望这项研究能够更深入地了解 DED 产生的晶粒结构，并提高对特定位点结构控制的信心。