Stability of High Energy Faults in Ni-Based Superalloys

High energy faults generated by lattice dislocations entering the strengthening precipitates of Ni-based superalloys are at the core of unique mechanical properties of these structural materials. Since the energies of the anti-phase boundary (APB) and complex stacking fault (CSF) can be increased by appropriate alloying additions, multiple research studies investigated this topic (e.g., such elements, as Ta, Nb and Ti were shown to increase the APB energy most effectively). However, the question about the stability of these defects has not received the attention it deserves. If they can transform spontaneously into lower energy structures, then the strengthening effect of the precipitates will be compromised. Using atomistic simulations, we found that the APB can spontaneously transform into super intrinsic stacking fault (SISF) and the CSF can spontaneously transform into L12 lattice structure. We demonstrate that Nb solutes produce very different effects in two considered transformation cases: addition of Nb increases the temperature of spontaneous APB → SISF transformation, and decreases the temperature of spontaneous CSF → L12 transformation. These results provide a different perspective on the processes vital to fascinating mechanical properties of Ni-based superalloys.