In this study, the effects of laser volumetric energy density (η) on the metallurgical defect behavior and microstructure evolution of H13 die steel fabricated by selective laser melting (SLM) additive manufacturing are systematically studied, and underlying thermal mechanisms are revealed. The results indicate that the metallurgical defect behavior is significantly affected by the applied η, which is controlled by laser power P and scanning speed v. With increasing P or decreasing v, η increases, the metallurgical defects such as pores and poor fusion initially decrease and then increase, and the density initially increases and then decreases. The typical microstructures induced by SLM are columnar dendrites and equiaxed dendrites. Their growth direction, distribution, and size at different positions in the molten pool are quite different. The size of the columnar crystals with directional full growth is highly correlated with the applied η. As the applied η increases, the length and diameter of the columnar crystals increase, but grains with nonuniform distribution are obtained under a higher η of 122.22 J mm−3. Under the optimized η of 111.11 J mm−3 (P = 200 W, v = 1000 mm/s), the H13 die steel samples fabricated by SLM are near-fully dense and have almost no metallurgical defects (the density reaches 99.13%), and the dense columnar crystals with uniform distribution are obtained. This study may provide a theoretical and experimental basis for the design and optimization of SLM processing parameters and the reliable fabrication of SLM-processed parts with controlled defects and microstructures.

中文翻译：

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选择性激光熔化增材制造金属零件的冶金缺陷行为、微观结构演变和潜在热机制

本研究系统地研究了激光体积能量密度 (η) 对选择性激光熔化 (SLM) 增材制造制造的 H13 模具钢的冶金缺陷行为和微观结构演变的影响，并揭示了潜在的热机制。结果表明，冶金缺陷行为受施加的 η 显着影响，受激光功率 P 和扫描速度 v 的控制。随着 P 的增加或 v 的减小，η 增加，气孔和熔合不良等冶金缺陷最初减少，然后增加，密度先增加然后减少。SLM 诱导的典型微观结构是柱状枝晶和等轴枝晶。它们在熔池中不同位置的生长方向、分布和大小都有很大的不同。具有定向完全生长的柱状晶体的尺寸与应用的 η 高度相关。随着施加的 η 增加，柱状晶体的长度和直径增加，但在 122.22 J mm-3 的较高 η 下获得分布不均匀的晶粒。在优化的 η 为 111.11 J mm−3 (P = 200 W, v = 1000 mm/s) 下，SLM 制造的 H13 模具钢样品几乎完全致密，几乎没有冶金缺陷（密度达到 99.13%） ，得到分布均匀的致密柱状晶体。该研究可为 SLM 加工参数的设计和优化以及具有受控缺陷和微观结构的 SLM 加工零件的可靠制造提供理论和实验基础。