Unique double steady state creep rate and deformation mechanism of a CoNi-based superalloy

Abstract

The creep behavior of CoNi-based superalloys at high temperatures and low stress conditions (960 °C/150 MPa) was investigated. A unique double steady state creep rate is observed as the creep of such superalloy proceeds. The formation of the first steady state creep rate can be attributed to the γ/γ′ interface preventing dislocations from de-shearing the γ′ phase and the formation of <101> superdislocations in the γ′ phase. As a large number of dislocations shear into the γ′ phase, the creep rate increases rapidly. The formation of large size γ′ phase obstructs the other γ′ phase rafting, the superdislocation networks at the interface of large size γ′ phase and a<100> superdislocation in γ′ phase causing a hardening effect, which led the superalloy to second steady state creep rate and improve the creep resistance.