Integrity of Chamfered Edges in Inconel Superalloy Joints with Circular Pins through Friction Welding

Abstract

This study thoroughly examines friction welding methods for joining stainless steel (SS), Inconel 718 and Inconel 825, with a focus on the microstructure, mechanical properties and overall quality of the welded joints. Through a series of controlled experiments, it analyses the influence of key welding parameters like rotational rpm, axial force and welding time on joint strength and performance. The welding was carried out using optimised parameters as rotational speed of 2450 rpm, soft load of 700 Nm, friction load of 1400 Nm, forge load of 3000 Nm and a cooling time of 6 seconds. A chamfered joint design is implemented to enhance the heat concentration and material flow at the weld interface. In this configuration, the rotating male shaft incorporates a chamfer on the Inconel side, while the stationary female shaft features a complementary chamfer. This promotes focused heat generation at the edge and stronger bonding with reduced welding time. The optimised configuration resulted in impressive mechanical performance for the Inconel 825-SS316 shaft joint as maximum force of 147.67 kN, ultimate tensile strength (UTS) of 650.58 MPa and yield stress of 455.41 MPa. For different shaft geometries, a pin-type chamfer is used for hollow shafts, while a taper chamfer is adopted for solid shafts to ensure optimal contact and bonding during friction welding. Failures were typically observed at the weld zone, primarily due to excessive contact area, which limited effective heat generation and bonding. However, the chamfered configuration reduces the contact area, enabling more localised heat and pressure application, resulting in a stronger and more reliable weld.