Porosity significantly impacts the fatigue performance and stability of dual laser additively manufactured metallic materials. This study presents a comparative analysis of the fatigue behavior of samples fabricated by single-laser powder bed fusion (SL-PBF) and dual-laser PBF (DL-PBF). It shows that porosity defects in the overlap region reduced the fatigue strength of DL-PBF samples by nearly 20 %. Micro-CT analysis revealed that micro-pores in the SL-PBF samples were predominantly located in the contour regions. Machining with a removal depth of 0.5 mm has effectively eliminated over 90 % of internal porosity defects. For monolithic specimens, increasing the sample size and reducing the layer-wise slice area can improve the sphericity of the internal defects (0.71 to 0.85) and reduce the porosity density (0.19 % to 0.011 %). Molecular dynamics simulations further examined the influence of pore size, spacing, and quantity on fatigue behavior. Larger pore sizes promote the formation of {11 2¯ 1} <1¯1¯26> twin variants, as the pore diameter increased from 20 Å to 80 Å, the proportion of variants structure increased from 3.6 % to 11.5 %. Fatigue failure initiated from a single pore, with stress propagating towards a distant pore, forming crack paths. Stress was relieved along these crack trajectories, leading to secondary crack branches that spread into low-stress zones around other defects, which resulted in fatigue cracks with vein-like morphologies. This work provides systematic insights into the fatigue degradation mechanisms induced by porosity and offers actionable strategies for improving the fatigue resistance of multi-laser PBF components through process control.

中文翻译：

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微孔形成机理和孔隙率对 Ti6Al4V 双激光-粉末床熔融疲劳性能的影响

孔隙率会显著影响双激光增材制造金属材料的疲劳性能和稳定性。本研究对单激光粉末床熔融 （SL-PBF） 和双激光 PBF （DL-PBF） 制备的样品的疲劳行为进行了比较分析。它表明，重叠区域的孔隙缺陷使 DL-PBF 样品的疲劳强度降低了近 20%。显微 CT 分析显示，SL-PBF 样品中的微孔主要位于轮廓区域。去除深度为 0.5 mm 的加工有效地消除了 90% 以上的内部孔隙缺陷。对于整体试样，增加样品尺寸并减少分层切片面积可以提高内部缺陷的球形度（0.71 至 0.85）并降低孔隙率密度（0.19 % 至 0.011%）。分子动力学模拟进一步研究了孔径、间距和数量对疲劳行为的影响。较大的孔径促进了 {11 2 ̄ 1} <1 ̄1 ̄26> 孪晶变体的形成，随着孔径从 20 Å 增加到 80 Å，变体结构的比例从 3.6 % 增加到 11.5 %。疲劳失效始于单个孔隙，应力向远处的孔隙传播，形成裂纹路径。沿这些裂纹轨迹的应力得到缓解，导致次生裂纹分支扩散到其他缺陷周围的低应力区，从而导致具有脉状形态的疲劳裂纹。这项工作为孔隙率引起的疲劳降解机制提供了系统性的见解，并为通过过程控制提高多激光器 PBF 组件的抗疲劳性提供了可行的策略。