Effect of high-frequency beam oscillation on the microstructure and mechanical properties of deep-penetration vacuum laser-welded Inconel 718 joints

When a deep-penetration weld was fabricated by high-energy beam welding, the microstructure and mechanical heterogeneities along the depth direction frequently occurred, which had an adverse effect on the serviceability of the deep-penetration welded nickel-based superalloy components. To address this issue, this study introduces a high-frequency beam oscillation strategy to actively homogenize the microstructure and properties of Inconel 718 joints with depth of penetration exceeding 21 mm fabricated by vacuum laser beam welding. Results demonstrated that oscillation significantly refined the Laves phase. With the increase of oscillating frequency, the content of Laves phase decreased from 6.28 % to 4.07 %, the fraction of large Laves particles (>3.0 µm) decreased from 9.82 % to below 6.4 % and the secondary dendrite arm spacing was reduced from 4.71 µm to under 3.85 µm. This refinement is attributed to Nb element homogenization, which hinders Laves phase formation, and the physically limited growth space within refined secondary dendrite arm spacing. The weld joint with high-frequency beam oscillation showed a more uniform tensile strength with a coefficient of variation of 1.15 % and an average strength of approximately 850.8 MPa. This work provides a novel pathway to tailor the microstructure and mechanical performance for single-pass deep-penetration welding of thick 718 components.