Local plastic deformation in the vicinity of topologically close-packed phases in a Ni-based single crystal superalloy

Abstract

• The local deformation behaviors of the TCP phase containing regions in a single crystal Ni-based superalloy were investigated through micro-scale mechanical tests and atomic-scale microstructural characterizations. • The TCP phase hinders the activations of non-parallel slip systems, resulting in a single slip system being active near the TCP phase. • The TCP phase alters the local chemical distribution in the surrounding γ’ precipitate, raising the antiphase boundary (APB) energy. • Due to increased APB energy and the elastic strain field near the TCP phase, the TCP/γ’ interface is not the weakest spot, leading to slip occurring 50–100 nm away from the interface. • Despite the presence of the TCP phase, the overall yield strength is mainly determined by reductions in the γ’ volume fraction and the solid solution strengthening effect in the γ matrix during the high-temperature exposure. The role of a topologically close-packed (TCP) phase (μ phase) on the plastic deformation of a Ni-based superalloy was investigated employing a combination of in situ scanning electron microscope micropillar compression and atomic-scale characterization using atom probe tomography and transmission electron microscopy. Micropillar tests revealed two distinct slip behaviors: TCP-free pillars deformed via multiple slip systems, whereas TCP-containing pillars deformed by single slip. Notably, while previous studies have reported fracture at the TCP/γ’ interface, our findings revealed that in the TCP-containing pillars, deformation was rarely observed at the interface. Instead, slip predominantly occurred in regions approximately 50–100 nm away from the interface. Chemical analysis near the TCP/γ’ interface via APT showed an excess Ta content near the interface increasing the antiphase boundary energy and enhancing local order strengthening. Moreover, an approximate 8 % lattice misfit at the TCP/γ’ interface, coupled with the elastic mismatch between the two phases, provided additional slip resistance in the vicinity of the interface. This study sheds light on the intricate interplay between TCP phase formation, microstructural evolution, and mechanical properties in Ni-based superalloys offering valuable insights into the role of the TCP phases.

Topics & Concepts