Achieving and stabilizing fine near-equiaxed grains in additively manufactured Ni-superalloys

Site-specific grain-structure control is desirable for turbine blades with region-specific performance requirements. Here, we demonstrate that a columnar-to-equiaxed transition can be initiated in electron-beam additive manufacturing within individual melt pools and retained through controlled overlap ratio and melt pool geometry. A high overlap ratio with shallow melt pools increases grain density and suppresses competitive dendritic growth, yielding near-equiaxed grains with an average size of ∼30 μm on single-crystalline substrates. A tailored heat-treatment protocol incorporating optimized recovery annealing relieves stresses while preventing recrystallization, thereby stabilizing the refined microstructure. This strategy enables grain structure design without altering established alloy compositions.