Effect of Silicide and α2 Phase on the Creep Behavior of TC25G Alloy at High Temperature

Abstract

TC25G alloy was heat treated at 950 °C/3 h, AC + 580 °C/6 h, AC and the bimodal structure with primary α phase + β transition structure was obtained. The creep properties of the alloy were tested in 550–600 °C/150–250 MPa. The results show that the precipitations of silicide and α₂ phase is accompanied by the creep process. α₂ phase plays a dispersion strengthening role in both the primary and steady-state creep stages. However, in the accelerated creep stage, the mechanism of α₂ phase and dislocation changes from cutting mechanism to bypassing mechanism, and the strengthening effect is weakened. Silicide inhibits grain boundary slip mainly in the primary creep stage, and inhibits dislocation slip in the steady-state and accelerated creep stages. At 550 °C, n = 1.6 and Q = 280–371 kJ/mol (150–250 MPa) indicate that the creep of the alloy is a self-diffusion process, and the creep deformation is mainly controlled by dislocation slip. At 570–600 °C, n = 3.2 indicates that the dislocation climb controls the creep deformation. Meanwhile, compared with Q = 274 kJ/mol at low stress (150 MPa), Q = 365 kJ/mol at the high stress (200–250 MPa) indicates that the second phase precipitation enhancement is enhanced.

Graphical Abstract