Columnar-to-equiaxed grain transition in powder bed fusion via mimicking casting solidification and promoting in situ recrystallization

• DOI: 10.1016/j.addma.2021.102086
• Publication Date: 2021-06-02T13:49:38Z
• Authors: Paria Karimi; Esmaeil Sadeghi; Joakim Ålgårdh; Ali Keshavarzkermani; Reza Esmaeilizadeh; Ehsan Toyserkani; Joel Andersson
• Keywords: 660; Additive manufacturing; Grain structure; Surface and Joining Technology; Bearbetnings-; Electron beam-powder bed fusion; In situ recrystallization; 02 engineering and technology; 620; 12. Responsible consumption; Manufacturing; Additive manufacturing; Electron beam-powder bed fusion; Alloy 718; In situ recrystallization; Grain structure; Alloy 718; Metallurgy and Metallic Materials; Manufacturing, Surface and Joining Technology; Metallurgi och metalliska material; Bearbetnings-, yt- och fogningsteknik; 0210 nano-technology; yt- och fogningsteknik

Abstract Columnar grain structure typically formed along the build direction in the electron beam-powder bed fusion (EB-PBF) technique leads to anisotropic physical and mechanical properties. In this study, casting solidification condition was mimicked, and in situ recrystallization was promoted in EB-PBF to facilitate columnar-to-equiaxed grain structure transition in Alloy 718. This is achieved via a unique linear melting strategy coupled with a specific selection of process parameters in EB-PBF. It was found that site-specific melting using line order number (LON) function affected the cooling rate and temperature gradient, which controlled grain morphology and texture. A high LON resulted in a large equiaxed grain zone with a random texture, whereas a fixed LON with a high areal energy density led to a strong texture. The main driving force in the formation of cracks and shrinkage defects during the transition was investigated. A high LON at a fixed areal energy density reduced the average total shrinkage defects and crack length. The hardness was decreased through the transition, which was linked to the reduction in the size of the γʺ precipitates.