The effect of stacking faults networks and Lommer-Cotterell lock on the creep resistance of Ni–Co based superalloys in dynamic environments

This study examined the creep behavior of a novel Ni-Co based superalloy under dynamic loading conditions, with the test condition shifting from 650°C/930 MPa to 750°C/630 MPa. Quantitative analysis showed that the creep life after the two-stage tests was longer than that predicted by the traditional linear damage accumulation rule. Multi-scale characterization indicated that the grain size and γ' phase remained highly stable throughout the tests, whereas the deformation substructure underwent pronounced topological reorganization. Following the change in creep conditions, the initially isolated parallel stacking faults (SFs) evolved into a dense and interconnected SF network anchored by highly stable Lomer-Cottrell (LC) locks. This reconfigured structure generated a strong synergistic effect of network constraint and node fixation, thereby reducing the average dislocation free path, introducing back stress, and consequently lowering the effective driving force for subsequent creep deformation. In addition, twin boundaries acted as distinct preferential energy barriers, preserving unidirectional slip within the twin regions while promoting the formation of a multidirectional network in the surrounding γ matrix. These results indicate that specific changes in the creep environment can transform micro-damage into a highly damage-resistant state, thereby providing a robust physical basis for nonlinear life prediction and microstructural optimization of superalloys.