Radial-constraint additive friction stir deposition of Inconel 625 alloy

Solid-state additive manufacturing avoids the elemental segregation and dendritic defects inherent in fusion-based processes; however, challenges remain in terms of material utilization and process stability. To address these issues, the present study proposes a novel radial-constraint friction stir additive manufacturing strategy for Inconel 625, employing a custom-designed constraint ring to mitigate radial flash and enhance deposition efficiency by introducing an auxiliary in-situ forging effect. The intense thermomechanical coupling triggers comprehensive dynamic recrystallization, resulting in a significantly refined, equiaxed grain structure (avg.2.5 μm) and the formation of a unique Z-axis heterogeneous architecture characterized by alternating grain-size bands. This hierarchical microstructure, coupled with high-density dislocation networks and fragmented second-phase precipitates, enables a remarkable yield strength of 960 ± 45 MPa, a nearly 80% improvement over the base material, while maintaining robust ductility. Quantitative modeling reveals that the mechanical superiority is a synergistic outcome of multi-scale strengthening mechanisms, including Hall-Petch grain boundary, dislocation, and heterodeformation-induced effects. Moreover, the microstructural homogenization significantly enhances the alloy's electrochemical stability in saline environments.