Improved Inconel 718 superalloy repaired performance on 304 stainless steel shafts via recrystallization and Laves phase suppression in hybrid additive-subtractive manufacturing

Additive manufacturing (AM) demonstrates promising applications in component repair, yet its continuous processing mode unavoidably induces localized heat accumulation, leading to critical defects such as microstructural heterogeneity, harmful phase formation and residual stress. These issues collectively compromise the structural integrity and functional performance of repaired components. To address these limitations, this study proposes a hybrid additive-subtractive manufacturing (HASM) strategy integrating off-axis fine wire-laser directed energy deposition (OAFW-LDED) with periodic milling operations. By employing a self-developed dual five-axis hybrid machining system, we achieved precise layer-wise repair of Inconel 718 superalloy on 304 stainless steel shafts. The HASM process orchestrates multistage thermo-mechanical control through OAFW-LDED/milling cycles, achieving controlled material deposition and unique microstructural evolution via mitigated thermal accumulation, enhanced solidification rates, and localized remelting-recrystallization. This approach refined the average equivalent grain size from 85.7 ± 3.2 μm to 56.2 ± 1.8 μm (34 % reduction), alleviated thermal stresses, and suppressed Nb segregation at dendritic boundaries. Notably, it transformed continuous long-chained Laves phases into discrete blocky particles. The average peak hardness increased by 26 % (from 271 to 340 HV), and surface flatness increased by 300 % (from 473.5 to 157.7 μm). This work presents a scalable manufacturing framework for high-performance remanufacturing of critical shaft components, demonstrating the synergistic benefits of combining AM's geometric freedom with subtractive manufacturing's precision control.