The effect of scanning strategy on grain development of MAR-M247 in electron beam powder bed fusion

This study explores the influence of scanning strategies on microstructure evolution using electron beam powder bed fusion (EB-PBF) of MAR-M247, a Ni-based superalloy. An energy density that produces minimum cracking was established by raster melting, and subsequently applied to spot melting to investigate how the spot melting strategy changes the grain growth under localized energy input. Elemental segregation was observed in samples melted with both raster and spot melting strategies. Through controlled variations in point-jump spots in both the X and Y directions (skipped melting spots), spot melting produced diverse grain morphologies and crystallographic textures not observed using raster scanning. Smaller jumps favor columnar structures, while larger jumps induce a transition to equiaxed grains accompanied by the disordered grain distribution. Spot melting exhibited more randomized grain growth, and a columnar-to-equiaxed transition (CET) process was identified within a single sample. Although the study maintained fixed parameters such as coupon size, beam size, and hatch spacing, the results provide insight into how spot melting strategies can be leveraged for microstructure control for the purpose of manipulating and mitigating the cracking behavior for the non-weldable M247 superalloy in additive manufacturing.