Enhancing transverse creep resistance of LPBF-fabricated IN718 via time-controlled solution treatment and Σ3 twin boundary engineering

This study systematically investigated the effect of solution treatment time on the microstructure and mechanical properties of IN718 superalloy fabricated by laser powder bed fusion (LPBF), with a focus on its transverse creep behavior. Specimens were solution-treated at 1050 °C for 1-4 h followed by standard two-step aging, to examine the dissolution of Laves phase, recrystallization kinetics, and evolution of Σ3 annealing twin boundaries. Results reveal that 3 h hold at 1050 °C (ST-3h) provides an optimal kinetic balance, achieving complete Laves phase dissolution and producing a fully recrystallized, fine equiaxed grain structure containing approximately 60% Σ3 twin boundaries. This refined microstructure effectively eliminated mechanical anisotropy, enabling transverse tensile properties to achieve parity with longitudinal performance. Notable, the ST-3h specimens exhibited a transverse terminated creep duration exceeding 330 h at 650 °C under 620 MPa, substantially outperforming most reported non-HIPed LPBF IN718 counterparts in the transverse orientation. Post-creep microstructural analysis indicates that the enhanced performance originates from a dual strengthening mechanism: the γ'/γ" co-precipitates promote localized plastic slip and deformation twinning to accommodate strain, while the high density of Σ3 twin boundaries forms a stabilized grain boundary network that effectively suppresses cavity nucleation and crack propagation. This work establishes a clear heat treatment window and provides a theoretical foundation for overcoming the limited transverse creep resistance LPBF-processed superalloys.