Simultaneously Reducing Porosity and Strengthening the Additively Manufactured 18Ni300 Steel Through Cyclic Electropulsing Treatment

This study investigates the effect of cyclic electropulsing treatment (EPT) on rapid pore healing and the enhancement of mechanical strength in 18Ni300 maraging steel fabricated using laser powder bed fusion (LPBF) technique. During EPT, high-density electric pulses with an electric current density of 103 A/mm² and a short duration of 500 ms are circularly applied to the LPBF 18Ni300 samples. In-situ computed tomography scan and mechanical testing demonstrate that EPT significantly increases the maximum tensile strength of LPBF 18Ni300 from 1200 to 1600 MPa after 10 cycle applications of EPT, while porosity decreases from an initial value of 0.087‰ to 0.023‰. Multi-physics simulation indicates that the width-to-length (WL) ratio of pores dramatically influences healing efficiency by modulating the distribution of electric current flow. Pores with a smaller WL ratio exhibit more pronounced electric current concentration at the pore edge, resulting in an inhomogeneous distribution of electric current density. This inhomogeneity initiates the development of a temperature gradient and causes the formation of significant thermal stress and plastic deformation, which facilitate the closure process for pores with a smaller WL ratio. Microstructural analysis reveal that the enhancement of tensile strength after a single EPT is attributed to increased dislocation density (dislocation-induced strengthening), while the strengthening observed after 10 EPT cycles is primarily governed by the rapid formation of Ni₃ (Ti, Al) precipitates (precipitation hardening). These findings provide valuable insights into the application of EPT for rapid pore healing and mechanical properties enhancement in LPBF-fabricated precipitation hardening metallic materials.