Skalon Mateusz, Meier Benjamin, Leitner Thomas, Arneitz Siegfried, Amancio-Filho Sergio T, Sommitsch Christof
IMAT Institute of Materials Science, Joining and Forming, Graz University of Technology, Kopernikusgasse 24, 8010 Graz, Austria.
Joanneum Research, Materials-Institute for Laser and Plasma Technology, Leobner Straße 94, 8712 Niklasdorf, Austria.
Materials (Basel). 2021 Mar 6;14(5):1251. doi: 10.3390/ma14051251.
The quality and characteristics of a powder in powder bed fusion processes play a vital role in the quality of additively manufactured components. Its characteristics may influence the process in various ways. This paper presents an investigation highlighting the influence of powder deterioration on the stability of a molten pool in a laser beam powder bed fusion (LB-PBF, selective laser melting) process and its consequences to the physical properties of the alloy, porosity of 3D-printed components and their mechanical properties. The intention in this was to understand powder reuse as a factor playing a role in the formation of porosity in 3D-printed components. Ti6Al4V (15 μm-45 μm) was used as a base material in the form of a fresh powder and a degraded one (reused 12 times). Alloy degradation is described by possible changes in the shape of particles, particle size distribution, chemical composition, surface tension, density and viscosity of the melt. An approach of 3D printing singular lines was applied in order to study the behavior of a molten pool at varying powder bed depths. Single-track cross-sections (STCSs) were described with shape parameters and compared. Furthermore, the influence of the molten pool stability on the final density and mechanical properties of a material was discussed. Electromagnetic levitation (EML) was used to measure surface tension and the density of the melt using pieces of printed samples. It was found that the powder degradation influences the mechanical properties of a printed material by destabilizing the pool of molten metal during printing operation by facilitating the axial flow on the melt along the melt track axis. Additionally, the observed axial flow was found to facilitate a localized lack of fusion between concurrent layers. It was also found that the surface tension and density of the melt are only impacted marginally or not at all by increased oxygen content, yet a difference in the temperature dependence of the surface tension was observed.
粉末床熔融工艺中粉末的质量和特性对增材制造部件的质量起着至关重要的作用。其特性可能会以多种方式影响该工艺。本文进行了一项研究，重点突出了粉末劣化对激光粉末床熔融（LB-PBF，选择性激光熔化）工艺中熔池稳定性的影响及其对合金物理性能、3D打印部件孔隙率及其机械性能的影响。目的是了解粉末再利用作为3D打印部件孔隙形成中一个起作用的因素。Ti6Al4V（15μm - 45μm）以新鲜粉末和劣化粉末（重复使用12次）的形式用作基础材料。合金劣化通过颗粒形状、粒度分布、化学成分、熔体表面张力、密度和粘度的可能变化来描述。为了研究不同粉末床深度下熔池的行为，采用了3D打印单线的方法。用形状参数描述并比较了单道横截面（STCS）。此外，还讨论了熔池稳定性对材料最终密度和机械性能的影响。利用电磁悬浮（EML）通过打印样品片来测量熔体的表面张力和密度。研究发现，粉末劣化会在打印操作过程中使熔融金属池不稳定，促进熔体沿熔道轴的轴向流动，从而影响打印材料的机械性能。此外，观察到的轴向流动会促进同时存在的层之间局部未熔合。还发现，熔体的表面张力和密度仅受到氧含量增加的轻微影响或根本不受影响，但观察到表面张力的温度依赖性存在差异。
