Observation of interface disruption and Lomer-Cottrell locks in a crept L12-strengthened Ni-based superalloy

High-temperature, creep-resistant Ni-based superalloys used in turbine blades for aviation and power generation offer a potential route toward global energy savings. However, the fundamental mechanisms governing their long-term creep failure remain insufficiently understood. In this study, we propose a compositionally modified Ni-based polycrystalline Inconel 738LC alloy by reducing Co and increasing Al content. This modification enhances the yield strength from 844 to 924 MPa and significantly improves creep resistance at 750 °C under 600 MPa compared to the conventional Inconel 738LC series. We investigated the creep deformation mechanisms by analyzing microstructural evolution—particularly at the γ/γ′ interfaces—using transmission electron microscopy (TEM) and atom probe tomography (APT). The results reveal that creep deformation generates stress concentration at the corners of cuboidal γ′ precipitates, leading to interfacial disruption and the formation of abundant Lomer–Cottrell (LC) locks. These features contribute to both localized softening and overall hardening effects. Further TEM dark-field imaging under two-beam conditions demonstrates that during the later stages of creep, LC dislocations are also formed along solute-segregated planar faults within the γ′ precipitates. These dislocations result from the cross-slip of $\frac{a}{6}\left[1\bar{1}2\right],\frac{a}{6}\left[1\bar{1}0\right],\frac{a}{6}\left[1\overline{12}\right]$ superpartial dislocations along the γ′ planar faults, from octahedral {111} planes to cubic {001} planes. Even though numerous twins and stacking faults (SFs) are additionally seen in the current alloy upon creep, the presence of LC-locking sessile dislocations—formed at both the γ′/γ interfaces and along solute-rich planar faults within the γ′ precipitates—emerged as a key feature contributing to the enhanced creep resistance. Their formation hinders dislocation motion and stabilizes the microstructure under prolonged thermal stress. Consequently, these γ′-LC dislocations and the associated interface-disrupted configurations collectively improve creep strength and extend rupture life. This study offers valuable insights into LC locks-mediated creep mechanisms, highlighting a promising pathway for the design of next-generation Ni-based superalloys.