Electron microscopy characterization of the weld line zones of an inertia friction welded superalloy

Microstructure in the weld line (WL) zone produced by inertial friction welding has been studied for a series of RR1000–RR1000 welds using transmission electron and scanning electron microscopy. A fully recrystallised fine grain structure was found to form throughout the WL zone, characterized by straight and smooth grain boundaries, high energy status and modified grain boundary chemistry due to very fast cooling after welding. Very fine γ′ particles with unimodal size distribution were reprecipitated in the WL zone. The fine γ′ particles are spherical in shape, high in number density and characterized by an imbalanced chemistry, containing less Al, Ti, Ni, Ta γ′-forming elements but more Cr, Co, Mo γ-forming elements than all types of parent γ′ particles. As a result, a hard and strong WL zone was produced by the inertial friction welding.

• Microstructural investigation of the weld line for varied inertia friction welds of RR1000 has found that the morphology, energy status and chemistry of grain boundaries; the size, shape and composition of strengthening precipitates; the morphology and distribution of carbides and borides in the weld line zone are changed fundamentally. All these changes are compared to the parent alloy.