Stress dependence of the creep behaviors and mechanisms of a third-generation Ni-based single crystal superalloy

Elevated temperature creep behaviors at 1100 °C over a wide stress regime of 120–174 MPa of a third-generation Ni-based single crystal superalloy were studied. With a reduced stress from 174 to 120 MPa, the creep life increased by a factor of 10.5, from 87 h to 907 h, presenting a strong stress dependence. A splitting phenomenon of the close- (about 100 nm) and sparse- (above 120 nm) spaced dislocation networks became more obvious with increasing stress. Simultaneously, a₀<010> superdislocations with low mobilities were frequently observed under a lower stress to pass through γ′ precipitates by a combined slip and climb of two a₀<110> superpartials or pure climb. However, a₀<110> superdislocations with higher mobility were widely found under a higher stress, which directly sheared into γ′ precipitates. Based on the calculated critical resolved shear stresses for various creep mechanisms, the favorable creep mechanism was systematically analyzed. Furthermore, combined with the microstructural evolutions during different creep stages, the dominant creep mechanism changed from the dislocation climbing to Orowan looping and precipitates shearing under a stress regime of 137–174 MPa, while the dislocation climbing mechanism was operative throughout the whole creep stage under a stress of 120 MPa, resulting a superior creep performance.