The effect of reheat treatment on microstructure and stress rupture property of a directionally solidified nickel-based superalloy after long-term thermal exposure

The recovery of microstructure and creep properties of a directionally solidified superalloy after long-term thermal exposure was investigated. After reheat treatment, successful restoration of γ′ microstructure is achieved including morphology, size and chemical composition. However, carbides degradations within interior grains and at grain boundaries are irreversible through the reheat treatment. Short and long-term creep rupture properties are effectively improved by the reheat treatment, but cannot be fully recovered compared to that of the original material. During prolonged thermal and creep exposure, grain boundary carbides degradation occurred rapidly in comparison with that in the original material, which is regarded as the main reason leading to the reduction of stress rupture lifetime.