Inverse creep and temperature-dependent creep mechanism transition in SPRON 510: Suzuki-segregation-assisted stabilization of planar faults and deformation twins

The creep behavior of the Co–Ni-based alloy SPRON 510 was investigated at 943 K and 1073 K to clarify the appearance of the established Suzuki segregation regime in the bulk creep response of a supersaturated face centered cubic solid-solution alloy. Creep tests were conducted in air under applied stresses of 120, 180, and 330 MPa at 943 K, and 60 and 200 MPa at 1073 K. At 943 K, inverse creep was observed at 120 and 180 MPa. At 330 MPa, a transient stage was followed by an almost steady-state regime because the applied stress exceeded the yield stress. Transmission electron microscopy revealed several stacking faults at 120 MPa and deformation twins at 180 MPa. At 330 MPa, the microstructure evolved from a dense dislocation structure into a fine lamellar defect structure dominated by deformation twins and/or stacking-faulted regions. At 1073 K, the creep rate decreased continuously without a clear steady-state regime, along with sub-boundaries formed during creep. Combined with previous studies on SPRON 510 and related Co–Ni-based alloys, these results indicate that the characteristic behavior at 943 K is attributed to the Suzuki segregation-assisted stabilization of dissociated dislocations, stacking faults, and deformation twins. This stabilization suppresses dynamic recovery and produces creep strengthening and inverse creep. The apparent stress exponents (∼2.3 at 943 K and 4.4 at 1073 K) suggest a transition from planar fault/twin-controlled alloy-type creep to a more recovery-assisted metal-type regime. The inverse-creep response was non-monotonic, showing a post-minimum rate increase followed by leveling-off or slight re-decrease.