Friction stir welding of Haynes 282 Ni superalloy by using a novel hemispherical tool

In the present investigation, friction stir welding (FSW) of a gamma prime (γ') strengthened Haynes 282 nickel-base superalloy by using a novel hemispherical tool is documented. A joint efficiency of ~ 96% was achieved in the as-welded condition, which further increased to ~ 100% after two-step post-weld aging heat treatment. An extremely fine (~ 2 μm) grained microstructure was observed in the FSWed region compared with the coarse (~ 48 μm) grain base metal region. The carbides (MC and M₂₃C₆) and γ' precipitates are identified as the important microstructural constituent phases observed in the welded region. The aging heat treatment resulted in the precipitation of the γ' strengthening phase and altered the morphology of the M₂₃C₆ carbide phase in the welded region from a continuous film to discrete particles at the grain boundaries. The preliminary results concerning tool life suggest that no significant tool wear occurs at least up to a welding distance of 200 mm. Therefore, the novel hemispherical tool design allows the successful FSW of high-temperature application materials without any significant tool wear or high heat generation.