Ultrahigh strength-ductility synergy via heterogeneous grain structure and multi-scale L12-γ′ precipitates in a cobalt-based superalloy GH159

Abstract

Achieving excellent strength-ductility synergy through convenient techniques is highly desirable for modern engineering applications. In this study, we constructed a heterogeneous grain structure consisting of large residual deformed grains and fine recrystallized grains, along with multi-scale L12-γ′ precipitates, in a commercial cobalt-based superalloy GH159. This was achieved via short-term annealing followed by subsequent aging. The mechanical properties were significantly enhanced, demonstrating an exceptional ultimate tensile strength of 1611 MPa, and outstanding uniform and total elongations of 23.5 % and 34.7 %, respectively. We investigated the evolution of the dual heterogeneous structures and the corresponding strengthening mechanisms during deformation. Hetero-deformation induced (HDI) strengthening, L12-γ′ precipitation strengthening, along with nanotwins, L-C locks, and 9R phases contribute significantly to the excellent strength-ductility synergy in GH159. These findings offer a strategy for developing GH159 as a structural material for various engineering applications, providing accessible and cost-effective processing methods that pave the way for large-scale industrial production. Furthermore, this study provides design insights for enhancing the mechanical properties of cobalt-based precipitation-strengthened superalloys.