Generation Behavior of Abnormally Large Grain in Superalloy 718

Abstract

Abstract The behavior of strain-induced abnormal grain growth (AGG) in superalloy 718 has been investigated using compression testing and subsequent heat treatment below the d-phase solvus temperature of 980 °C. The nuclei of AGG grains were slightly newly recrystallized grains by a nucleation because small grains without dislocation was observed in the as- deformed microstructure. AGG was caused by the difference in intragranular misorientation (related to the stored strain energy in a grain) between dynamic recrystallized grains and deformed matrix. The initiation of AGG was retarded with decreasing plastic strain and produced microstructures consisted of larger grains having more complex morphology. It was observed that grain boundary migrated locally in the direction perpendicular to, or mainly in the direction parallel to the S3 {111} twin boundaries along with the formation of high-order twins. As a result of multiple twinning, AGG grains seemed to evolve with the growing directions changed.