Laser Powder Bed Fusion (LPBF) process, is becoming more and more widespread in industry. The possibilities of microstructural control offered by this process are an opportunity to study the contribution of the different length scales of microstructure to the fatigue behavior. This paper is devoted to the understanding of this fatigue behavior resulting from the interactions between the process induced defects and the different polycrystal length scales. Two distinct defect − microstructure competition regimes have been identified. The first concerns microstructures containing large Lack of Fusion (LoF) defects. These LoFs drastically reduce the fatigue life, while microstructure has no influence on the fatigue strength. The second regime concerns microstructures containing small defects. A limited effect of the polycrystalline microstructure was revealed. Furthermore, this paper demonstrates that the ratio between damage initiation defect size and grain size, used in literature to describe the defect and microstructure sensitivity of fatigue strength, is not applicable over a wide range of defects and microstructures, such as obtained by additive manufacturing processes. Finally, the comparison between the fatigue behavior of different microstructure and defect features shows that producing a finer microstructure improves fatigue strength despite the presence of a significant defect population.

中文翻译：

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增材制造的 316L 不锈钢的疲劳行为：缺陷和微观结构影响之间的竞争


激光粉末床熔融 （LPBF） 工艺在工业中越来越广泛。这个过程提供的微观结构控制的可能性是研究不同长度尺度的微观结构对疲劳行为的贡献的机会。本文致力于理解这种疲劳行为是由工艺诱导缺陷和不同多晶长度尺度之间的相互作用引起的。已经确定了两种不同的缺陷 - 微观结构竞争机制。第一个涉及包含大熔合缺失 （LoF） 缺陷的微观结构。这些 LoF 会大大缩短疲劳寿命，而微观结构对疲劳强度没有影响。第二种情况涉及包含小缺陷的微观结构。揭示了多晶微观结构的有限影响。此外，本文还表明，文献中用于描述疲劳强度的缺陷和微观结构敏感性的损伤起始缺陷大小与晶粒尺寸之间的比率不适用于广泛的缺陷和微观结构，例如通过增材制造工艺获得的缺陷和微观结构。最后，不同微观结构和缺陷特征的疲劳行为之间的比较表明，尽管存在大量缺陷，但产生更精细的微观结构可以提高疲劳强度。