Creep damage mechanism and γ′-phase morphology of a V-notched round bar in Ni-based single crystal superalloys

The circumferential V-type notched specimen has been designed to investigate the effect of multiaxial stress state on creep rupture behavior of Ni-based single crystal superalloys at 980 °C. The stress on the minimum net-section is chosen to be 400 MPa. Tests on smooth specimens were also carried out under 400 MPa for comparison. Time to creep fracture was found to be higher in the notched specimens. Scanning Electrical Microscope (SEM) analysis indicated that rupture initiates at the notch root in the notched specimen and at the inner in the smooth specimen. Finite element analysis was carried out to understand the stress distribution and the creep damage evolution under multiaxial stress state. The morphology the evolution of γ′-phase proved that directional coarsening was strongly dependent on the local principal stress field. These findings can be helpful to understand the effect of notch on the creep rupture behavior and mechanism, especially on the γ′-phase morphology evolution.