Zerong Yang

The conventional process development for powder bed fusion (PBF) processes targets the manufacturing of defect-free parts, e.g., with low porosity, no layer binding faults and cracks, or high dimensional accuracy. These topics are addressed for laser powder bed fusion (PBF-LB/M) in Chap. 8 and electron beam powder bed fusion (PBF-EB) in Chap. 7 for different alloys. However, although a part is defect-free, the microstructure and consequently the mechanical properties vary locally in complex geometries manufactured with standard process strategies. The microstructure is mainly influenced by the local solidification conditions during manufacturing. Epitaxial crystal growth occurs in combination with a natural grain selection along the whole part due to different crystal growth rates depending on the local transient temperature field and the crystal orientation. Depending on the PBF process and the manufacturing conditions, nucleation plays an important role during microstructure formation regarding the grain size and orientation and there are two different strategies to circumvent or benefit from these effects. In the first strategy, the processing conditions are modified in such a way that the solidification conditions are almost equal regardless of the part geometry (see Chap. 7). The second strategy is to tailor the local solidification conditions to achieve a beneficial local microstructure, e.g., to exploit a material anisotropy to ensure the orientation with the highest stiffness in the part-loading direction. Both strategies are costly and time-consuming regarding pure experimental development.

Electron beam powder bed fusion (PBF‐EB) is a promising technology for fabricating complex parts with near‐net‐shape precision. Moreover, PBF‐EB offers a unique opportunity to tailor the microstructure, thereby tuning local mechanical properties. Numerical simulation has emerged as a powerful tool for predicting the evolution of texture and grain structure during PBF‐EB. Herein, the in‐house developed and experimentally validated simulation software, , is employed to investigate the impact of scanning strategy on the texture and grain structure of CMSX‐4 in PBF‐EB‐processed thin tilted lattice struts, commonly found in cellular structures. The core of consists of a finite difference solver for temperature field computation and a cellular automaton model for simulating grain structure evolution. Nine distinct scanning strategies are systematically explored. The resulting texture and grain structures are meticulously compared and comprehensively discussed. Notably, the contour scanning strategy yields distinctive texture and grain structures compared to other explored scanning strategies. This study highlights the capability of in assisting microstructure customization in the PBF‐EB process, and advances the understanding of the relationship between PBF‐EB scanning strategy and resulting microstructure in tilted lattice struts.

Powder Bed Fusion (PBF) not only enables the fabrication of metal parts with complex geometries in near-net-shape, but also offers the potential to tailor the microstructure and, consequently, the mechanical properties of the final product. In this contribution, we present our in-house developed simulation software SAMPLE3D (Simulation of Additive Manufacturing on the Powder scale using a Laser or Electron beam in 3D), which is designed specifically for simulating grain structure evolution during PBF processes. The core of SAMPLE3D is composed of a finite difference model and a cellular automaton model. The finite difference model is used to obtain the temperature field caused by an electron or laser beam. This temperature field is further used in the cellular automaton model to simulate grain structure development where grain selection as well as nucleation is considered. A range of information can be extracted from the simulation results, such as texture, grain morphology, and grain boundary arrangement. SAMPLE3D provides a way to get insight into the relationship between PBF process strategies and microstructures. SAMPLE3D has been employed to investigate the texture and grain structure evolution of various materials in different research projects.