Melting and Solidification Behavior of 316L Steel Induced by Electron-Beam Irradiation for Additive Manufacturing

Abstract

Additive manufacturing AM technologies have attracted much attention because it enables us to build 3D parts with complicated geometry easily and control material properties significantly via the control of microstructures. In the powderbed fusion PBF type AM process, 3D parts are fabricated by repeating a process of melting and solidifying metal powders by laser or electron beams. In general, the solidification microstructures can be predicted from solidification conditions defined by the combination of temperature gradient G and solidification rate R on the basis of columnar-equiaxed transition CET theory proposed by Hunt [Mater. Sci. Eng. 65, 75 1984 ]. However, it is unclear whether the CET theory can be applied to the PBF type AM process because of the high G and R, even for general 316L stainless steel. In this study, to reveal relationships between microstructures and solidification conditions, we have analyzed solidification microstructures of 316L steel induced by electronbeam irradiation and evaluated solidification conditions at the solid/liquid interface using a computational thermal-fluid dynamics CtFD method. It was found that equiaxed grains were often formed under high G conditions contrary to the CET theory. CtFD simulation revealed that there is a fluid flow up to a velocity of about 400 mm s -1 , and suggested that equiaxed grains are formed owing to the effect of fragmentations and migrations of dendrites.

Digital Twin Science of Metal Powder Bed Fusion Additive Manufacturing: A Selective Review of Simulations for Integrated Computational Materials Engineering and Science

“…These include simulations for (i) part design (38)(39)(40)(41)(42) , (ii) determining the placement of multiple parts in the building space (i.e., build envelope), and (iii) the design of supports (43) . There are also simulations for (iv) the analysis of residual strain caused by thermal stress (44) , (v) the feeding of raw materials such as wire and powder, (vi) the process of melting and fusing the powder using LBs (45) , and electron beams (EBs) (46)(47)(48) , and (vii) microstructure formation through crystal growth and phase transformation during solidification and subsequent cooling processes (28,(48)(49)(50)(51) (52) . Many process parameters must be used appropriately to produce sound build-parts, and computer simulations play significant roles.…”