Origin of dislocation structures in an additively manufactured austenitic stainless steel 316L
Origin of dislocation structures in an additively manufactured austenitic stainless steel 316L
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DOI：
10.1016/j.actamat.2020.07.063
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发表时间：
2020-10-15
期刊：
影响因子：
9.4
通讯作者：
Thoma, D. J.
中科院分区：
文献类型：
--
作者：
Bertsch, K. M.;de Bellefon, G. Meric;Thoma, D. J.
在本实验中，首次通过几何约束控制热应力的影响，系统地研究了增材制造不锈钢中位错结构的起源。不锈钢 316L 零件以“1D”棒、“2D”壁和“3D”矩形棱柱的形式生产，以评估热膨胀/收缩约束对缺陷微观结构发展的影响，并阐明增材制造 (AM) 位错微观结构的起源。使用定向能量沉积 (DED) 和粉末床选择性激光熔化 (SLM) 构建的 1D、2D 和 3D 组件中，位错密度、组织、化学微偏析、沉淀结构和取向错误随着凝固材料周围不断增加的约束进行了分析。在DED零件中，位错密度不依赖于局部错误取向或微偏析模式，而是从1D零件中的大约rho（垂直于）约10（12）m（-）（2）演变为3D零件中的rho（垂直于）约10（14）m（-2），这表明产生AM位错结构的主要是热变形。在DED 3D零件和SLM零件中，位错密度最高（rho（垂直于）约10（14）m（-2））并且对应于直径约300-450 nm的位错单元的形成。在某些情况下，但并非所有情况下，位错单元与枝晶微偏析重叠。结果表明，枝晶微观偏析、沉淀物或局部定向错误会影响加工过程中位错的组织方式，但并不负责产生组织化的细胞结构。这项工作表明增材制造位错结构源于打印过程中的热变形，这主要是由熔池和热循环周围的约束决定的。 (C) 2020 Acta Materialia Inc. 由 Elsevier Ltd 出版。保留所有权利。
In this experiment, the origin of dislocation structures in AM stainless steels was systematically investigated by controlling the effect of thermal stress through geometric constraints for the first time. Stainless steel 316L parts were produced in the form of "1D" rods, "2D" walls, and "3D" rectangular prisms to evaluate the effect of constraints to thermal expansion/shrinkage on the development of defect microstructures and to elucidate the origin of additively manufactured (AM) dislocation microstructures. Dislocation density, organization, chemical micro-segregation, precipitate structures, and misorientations were analyzed as a function of increasing constraints around solidifying material in 1D, 2D, and 3D components built using both directed energy deposition (DED) and powder-bed selective laser melting (SLM). In DED parts, the dislocation density was not dependent on local misorientations or micro-segregation patterns, but evolved from approximately rho(perpendicular to)approximate to 10(12) m(-)(2) in 1D parts to rho(perpendicular to) approximate to 10(14) m(-2) in 3D parts, indicating that it is primarily thermal distortions that produce AM dislocation structures. In DED 3D parts and SLM parts, dislocation densities were highest (rho(perpendicular to) approximate to 10(14) m(-2)) and corresponded to the formation of dislocation cells approximately 300-450 nm in diameter. Dislocation cells overlapped with dendrite micro-segregation in some but not all cases. The results illustrate that dendritic micro-segregation, precipitates, or local misorientations influence how the dislocations organize during processing, but are not responsible for producing the organized cell structures. This work shows that AM dislocation structures originate due to thermal distortions during printing, which are primarily dictated by constraints surrounding the melt pool and thermal cycling. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.