This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.

中文翻译：

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γ-强化镍基高温合金激光粉末床熔覆技术的综述

本文回顾了γ'镍基高温合金的激光粉末床熔融（L-PBF）制造技术。L-PBF类似于焊接；因此，在L-PBF的制造过程中可能会发生焊接裂纹机制，例如凝固，液化，应变时效和延性浸裂。球形孔和缺乏熔合空隙是在用L-PBF制造的γ'强化镍基高温合金中可能发生的其他缺陷。缺陷形成与L-PBF工艺中使用的工艺参数之间存在相关性。凝固裂纹的先决条件包括由于偏析元素引起的非平衡凝固，单元之间存在液膜，临界温度范围宽以及存在热应力或残余应力。这些先决条件存在于L-PBF流程中。L-PBF制造的经γ'强化的高温合金中发现的相与等效铸造材料的相非常相似，其中γ，γ'和γ/γ'的共晶和碳化物通常存在于显微组织中。另外，由于高冷却速率，在制成的L-PBF材料中，γ'颗粒的尺寸较小。此外，由于L-PBF材料中存在缺陷并且晶粒尺寸小，因此其蠕变性能不如铸造材料。但是，某些垂直构造的L-PBF材料具有与铸造材料相近的蠕变性能。由于冷却速度高，在制成的L-PBF材料中γ'颗粒的尺寸较小。此外，由于L-PBF材料中存在缺陷并且晶粒尺寸小，因此其蠕变性能不如铸造材料。但是，某些垂直构造的L-PBF材料具有与铸造材料相近的蠕变性能。由于冷却速度高，在制成的L-PBF材料中γ'颗粒的尺寸较小。此外，由于L-PBF材料中存在缺陷并且晶粒尺寸小，因此其蠕变性能不如铸造材料。但是，某些垂直构造的L-PBF材料具有与铸造材料相近的蠕变性能。