Necking contributions to σ-phase formation in a hot-corrosion-resistant superalloy during creep exposure

Stress has been shown to accelerate the formation of the σ phase in the experimental Ni-based superalloys during the high-temperature exposure. However, with the necking phenomenon occurring in strained-to-fractured specimens after the creep exposure at 1073 K/365 MPa for 1700 h, the stress decreases, while the amount of the σ phase increases from the fracture face to the end of the fractured gauge section. Nucleation mechanisms of the σ phase are discussed. The energy dynamics analysis indicates that the decrease of the σ-phase density by necking is mainly due to the increased matrix strain energy, while the shape, size, and composition of the σ phase are not affected by necking.