Low plastic deformation: Its impact on the microstructural evolution during heat treatment of nickel-based wrought superalloy GH4698

Abstract

A comprehensive investigation into the effects of low plastic deformation (LPD) at ambient temperature on the microstructural evolution of the nickel-based wrought superalloy GH4698 during solution heat treatment (SHT) was conducted. Applying 2%–10 % LPD to cylindrical specimens did not markedly alter the grain morphology. However, a portion of the initial annealing twin boundaries (TBs) would transform into other types of grain boundaries under the application of the stress field. Deformation microstructures with effective strains ranging from 0.025 to 0.042 (corresponding to the entire region of the 4 % deformed sample and the near-end region of the 6 % deformed sample) exhibited a pronounced increase in twin fraction during SHT, accompanied by the formation of multiple large twin-related domains (TRDs) and several abnormally large grains (ALGs). The occurrence of TRDs and their internal ALGs stems from the constrained nucleation of recrystallization and extensive twinning. The residual strain energy not alleviated through recrystallization, driven by thermal stress, initiates twin nucleation and promotes grain boundary migration. The emergence and disappearance of island-like twins, as well as twins terminating within grains, suggest that the introduced TBs include not only coherent TBs but also potentially highly mobile incoherent TBs during the evolution of TRDs.