Effect of grain morphology on the mechanical properties of GH4099 superalloy fabricated by laser powder bed fusion

This work systematically investigates the evolution of grain morphology and its effect on the mechanical properties of GH4099 nickel-based superalloy fabricated by laser powder bed fusion (L-PBF) under different heat treatment conditions. By comparing the as-built columnar grains (H1), fully recrystallized equiaxed grains (H2), and their respective precipitation-strengthened states (HA1, HA2), it is revealed that high-temperature homogenization (1160 °C) effectively triggers static recrystallization, significantly improving grain sphericity and structural uniformity, thereby enhancing ductility. Aging treatments promote the precipitation of γ′ phases in large volume fractions, markedly increasing yield strength (HA1: 955 MPa, HA2: 761 MPa), albeit with some reduction in ductility. Cyclic loading–unloading tests demonstrate that highly uniform equiaxed grains with complex grain boundary networks (HA2) substantially improve back-stress uniformity, toughness, and energy dissipation capacity. Through comprehensive microstructural characterization and mechanical analysis, the microstructural control paths for optimizing the strength–ductility balance and service reliability of SLM GH4099 are elucidated, providing theoretical support for process optimization and engineering application of additively manufactured superalloys.