Heteroepitaxial recrystallization: A new mechanism discovered in a polycrystalline γ-γ′ nickel based superalloy

Abstract : The dynamic recrystallization mechanisms and kinetics of a recently developed γ-γ′ nickel based superalloy are studied at different subsolvus temperatures. Special care is paid to the evolution of γ′ particles and their influence on recrystallization phenomena. An original dynamic recrystallization mechanism is highlighted thanks to the combined use of Energy Dispersive Spectrometry and Electron BackScattered Diffraction mapping techniques. This mechanism leads to the formation of large heteroepitaxial pairs, made of a primary precipitate embedded in a recrystallized grain having the same crystallographic orientation. Recrystallization nuclei arise from inverse precipitation of γ phase at the rim of primary γ′ precipitates, prior to deformation. This heteroepitaxial recrystallization mechanism is reported here for the first time. It controls dynamic microstructure evolution at low strains and is then progressively replaced by the conventional discontinuous necklace recrystallization process at higher strains.