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 sigma 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 sigma phase increases from the fracture face to the end of the fractured gauge section. Nucleation mechanisms of the a phase are discussed. The energy dynamics analysis indicates that the decrease of the sigma-phase density by necking is mainly due to the increased matrix strain energy, while the shape, size, and composition of the a phase are not affected by necking. (C) 2013 Elsevier Inc. All rights reserved.