Abstract In addition to design geometry, surface roughness, and solid-state phase transformation, solidification microstructure plays a crucial role in controlling the performance of additively manufactured components. Crystallographic texture, primary dendrite arm spacing (PDAS), and grain size are directly correlated to local solidification conditions. We have developed a new melt-scan strategy for inducing site specific, on-demand control of solidification microstructure. We were able to induce variations in grain size (30 μm–150 μm) and PDAS (4 μm - 10 μm) in Inconel 718 parts produced by the electron beam additive manufacturing system (Arcam ® ). A conventional raster melt-scan resulted in a grain size of about 600 μm. The observed variations in grain size with different melt-scan strategies are rationalized using a numerical thermal and solidification model which accounts for the transient curvature of the melt pool and associated thermal gradients and liquid-solid interface velocities. The refinement in grain size at high cooling rates (>10 4 K/s) is also attributed to the potential heterogeneous nucleation of grains ahead of the epitaxially growing solidification front. The variation in PDAS is rationalized using a coupled numerical-theoretical model as a function of local solidification conditions (thermal gradient and liquid-solid interface velocity) of the melt pool.

中文翻译：

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用于电子束增材制造中晶粒尺寸和初级枝晶臂间距的现场特定控制的局部熔体扫描策略

摘要 除了设计几何形状、表面粗糙度和固态相变外，凝固微观结构在控制增材制造部件的性能方面起着至关重要的作用。晶体结构、初级枝晶臂间距 (PDAS) 和晶粒尺寸与局部凝固条件直接相关。我们开发了一种新的熔体扫描策略，用于诱导特定位置的凝固微观结构按需控制。我们能够在由电子束增材制造系统 (Arcam ® ) 生产的 Inconel 718 零件中引起晶粒尺寸 (30 μm–150 μm) 和 PDAS (4 μm - 10 μm) 的变化。传统的光栅熔化扫描导致约 600 μm 的晶粒尺寸。使用数值热和凝固模型对不同熔体扫描策略观察到的晶粒尺寸变化进行合理化，该模型解释了熔池的瞬态曲率和相关的热梯度和液固界面速度。在高冷却速率 (>10 4 K/s) 下晶粒尺寸的细化也归因于在外延生长的凝固前沿之前晶粒的潜在异质成核。PDAS 的变化通过使用耦合数值理论模型作为熔池局部凝固条件（热梯度和液固界面速度）的函数来合理化。在高冷却速率 (>10 4 K/s) 下晶粒尺寸的细化也归因于在外延生长的凝固前沿之前晶粒的潜在异质成核。PDAS 的变化通过使用耦合数值理论模型作为熔池局部凝固条件（热梯度和液固界面速度）的函数来合理化。在高冷却速率 (>10 4 K/s) 下晶粒尺寸的细化也归因于在外延生长的凝固前沿之前晶粒的潜在异质成核。PDAS 的变化通过使用耦合数值理论模型作为熔池局部凝固条件（热梯度和液固界面速度）的函数来合理化。