Transformative thermal processes: Enhancing microstructure and Mechanics in Rotary Friction Welded IN718 and SS304L Alloys

The investigation of dissimilar metal welds, especially between austenitic stainless steel (SS304L) and Inconel 718 (IN718), is essential for use in challenging environments that demand superior mechanical performance. Current research often overlooks the influence of different heat treatment processes on microstructural and mechanical characteristics, presenting a gap in understanding their implications on joint performance. This investigation employed friction welding to create joints between SS304L and IN718 subjected to two heat treatments before welding: solution treatment (ST) and solutiontreated aging (STA). The materials were characterized through optical and scanning electron microscopy, highlighting the presence of distinct microstructural zones, including fine-grain deformation, thermomechanical affected, and heat-affected zones. Microhardness testing revealed that ST-treated joints exhibited higher hardness values compared to STA, attributed to grain refinement and increased strain hardening. Tensile testing indicated that STAtreated welds, while demonstrating lower yield strength (500 ± 3 MPa) and ultimate tensile strength (665 ± 4 MPa), exhibited greater ductility (15 ± 1%). In contrast, ST joints showed superior mechanical performance, with yield strength at 570 ± 4 MPa and ultimate tensile strength at 710 ± 2 MPa. The failure modes predominantly occurred in the SS304L HAZ (heat-affected zone), underscoring the influence of thermal treatment on joint integrity. This research provides appreciated visions into the impact of thermal and mechanical treatments on microstructural evolution and mechanical properties in dissimilar metal joints, establishing the reliability of friction welding as an effective joining technique for applications in aerospace and high-temperature environments.