Influence of welding speed on mechanical properties and fracture behaviour of friction stir welded Haynes® 282 Ni superalloy

This study investigates the joining of gamma prime (γ′)-strengthened Haynes® 282 (H282) Ni superalloy using Friction Stir Welding (FSW) with a novel hemispherical dome-shaped tool at different welding speeds. After post-welding heat treatment (PWHT), the stir zone (SZ) of the joints, regardless of welding speed, exhibited a tensile strength of approximately 1360 MPa, compared to the base metal strength (subjected to the same PWHT) of about 1144 MPa, resulting in a UTS-based joint efficiency of 100%. The microstructural analysis identified primary Ti- and Mo-rich (MC) carbides, secondary Cr-rich (M 23 C 6 ) carbides, and γ′ precipitates as key constituents within the austenitic γ matrix after PWHT. During FSW, the plastic deformation and material flow significantly altered the dispersion characteristics of brittle intergranular MC carbides, transforming them from an intergranular interconnected network (colonies) in the BM to discrete carbides that are randomly dispersed at the grain boundaries in the SZ. The increased strength of the SZ is attributed to this dispersion transformation, as the primary MC carbides are the preferential sites for the void nucleation during tensile loading. Increased welding speed led to reduced frictional heat input, resulting in finer grain size and increased local elongation while maintaining similar weld strength. Therefore, the microstructure of the H282 alloy is minimally impacted by the frictional heat input across various process parameters during FSW. This finding underscores the advantages of FSW for H282 alloy over other fusion welding techniques, where precise control of process parameters is crucial to prevent elemental segregation in the fusion zone.