Effect of heat treatment on microstructure and microhardness of FGH96 inertia friction welding

Using the inertial friction welding method, FGH96 high-temperature alloy was welded. The microstructure and properties of the welded and heat-treated FGH96 joint were studied by means of optical microscope, scanning electron microscope and microhardness tester. The results show that complete dynamic recrystallization occurs in the central area of the weld, the recrystallized grains are fine, the grain size is 4.6 μm ± 0.3 μm, and the secondary γ′ phase is completely dissolved, resulting in a lower hardness than the parent material organization. With the distance from the weld, the secondary γ′ phase content gradually increased, and the volume fraction of γ′ phase remained basically unchanged after 1.5 mm from the weld, but the γ′ phase morphology gradually changed from spherical to cubic, leading to a gradual increase in hardness. After heat treatment, the content and morphology of the secondary γ′ phase in the weld area changed similarly to the weld state, but the grain size of the base material increased from 11.4 μm ± 0.3 μm to 13.5 μm ± 1.0 μm after heat treatment, which is the reason for the lower hardness of the base material after heat treatment compared with the weld state. In addition, the precipitation of three γ′ phases after heat treatment is the reason for the higher hardness of the weld in the heat-treated state than in the welded state.