On joining additive manufactured metals via friction welding technology: a comprehensive mechanical and microstructural study on 316 L stainless steel components

Abstract

Rotational Friction Welding (RFW) is a solid-state joining technique that enables the assembly of metallic components below their melting temperature, while also avoiding harmful gas emissions commonly associated with fusion-based methods. Despite their high mechanical strength, parts manufactured by RFW often struggle to meet the industrial demand for complex geometries beyond their typical cylindrical and disc shapes. Laser Powder Bed Fusion (PBF-LB/M) allows fabrication of geometrically intricate parts with high precision and mechanical reliability. However, it faces challenges such as high production costs and dimensional limitations. Combining PBF-LB/M with RFW enables the production of larger and complex metal parts. The purpose of this study is to demonstrate the feasibility and benefits of this hybrid approach for 316 L stainless steel (SS). To accomplish this, 316 L SS parts were initially fabricated using PBF-LB/M and then joined by RFW. The joints were analyzed to evaluate weld integrity, microstructural evolution, phase stability, and mechanical performance. The analysis reveals three distinct microstructural zones: the weld zone, the thermo-mechanically affected zone, and the base metal zone. Grain refinement is observed in the weld zone, whereas coarser grains appear toward the base metal zone. Phase analysis exhibits a fully austenitic structure without any detrimental secondary phases. Mechanical testing shows increased hardness in the weld zone associated with grain refinement. Tensile tests reveal that the fracture occurred outside the welding region, specifically in the base metal zone. These findings highlight a finer, defect-free weld zone without secondary phases in RFW joined PBF-LB/M 316 L SS components.