Regulating the coarsening of the γ′ phase in superalloys

Abstract

The properties of superalloys are typically deteriorated by the coarsening of the nano-sized γ′ phase, which is the primary strengthening component at high temperatures. Stabilizing the γ′ phase represents one of the key challenges in developing next-generation superalloys. Herein, we fabricate a cobalt-nickel-based superalloy with a nanoscale coherent γ′ phase, (Ni,Co)3(Al,Ti,Nb), which is isolated by stacking-fault ribbons in the alloy matrix as a result of the Suzuki segregation of alloying atoms. Additionally, we demonstrate that this new nanostructure can slow down the coarsening of the γ′ phase at high temperatures. As a result, the cobalt-nickel-based superalloy displays considerably high tensile yield points, exceeding 1650 MPa at room temperature and 1250 MPa at 973 K, which are markedly higher than those of the commonly used nickel- and cobalt-based superalloys. This study thereby paves a new path for developing superalloys with exceptional mechanical performance and thermal stability. By using a novel nanostructure, a team has made a cobalt-based superalloy with a high tensile yield point whose γ' phase resists coarsening. Coarsening of the nanoscale γ' phase of superalloys — the process by which large particles grow at the expense of smaller ones — tends to degrade the properties of superalloys since the γ' phase is the main strengthening component at high temperatures. By isolating the γ' phase through forming stacking-fault ribbons in the alloy matrix via Suzuki segregation of the alloying atoms, Yunping Li of Central South University in China and collaborators at Tohoku University in Japan realized a cobalt-nickel-based superalloy with a tensile yield point of 1,650 megapascals at room temperature (1,250 megapascals at 973 kelvin). They consider this method to be promising for realizing superalloys with superior mechanical properties and thermal stability. A large number of multilayered stacking faults are detected along {111} planes during aging (arrows in a) of present superalloy. Every γ′ phase particle is isolated by multilayered stacking-fault ribbons and grows slightly. The coarsening rate of the γ′ phase decreases significantly after plastic deformation, implying that the formation of multilayered stacking-fault ribbons as a consequence of Suzuki segregation can obviously retard the coarsening of γ′ phase in this novel alloy.