Properties and microstructures of M951 alloy after long-term exposure

The amount of M23C6 from decomposed MC during long time ageing at 900 °C is much greater than at 1100 °C. The carbide particle can retard mobile dislocations shearing γ′ precipitates, and secondary γ′ precipitates vary limitedly so that the 900 °C/100 h stress rupture life reaches peak value. With increase of ageing times at 1100 °C, a large amount of fine spheroidal γ′ particles precipitate among secondary γ′ precipitates so that the 1000 °C yield strength of the alloy abnormally increases comparing to that with standard heat treatment. After exposure at 1100 °C, the dislocation networks at the interface of γ′/γ are destroyed gradually and cannot hinder more dislocations cutting into γ′ particles, which results in the decrease of stress rupture life. The room-temperature tensile deformation mechanisms of specimens after long-term exposure at 1100 °C are mainly controlled by dislocation glide and climb. It shows that ageing temperature has an important effect on deformation mechanism.