Preparation of ultrafine-grained GH4169 superalloy by high-pressure torsion and analysis of grain refinement mechanism

A grain refinement process for a GH4169 superalloy sheet was proposed with the following parameters: solid solution (1050 degrees C x 0.5 h), cold rolling (50% reduction rate), delta phase precipitation treatment (890 degrees C x 10 h), high-pressure torsion (HPT) (3, 4, and 5 GPa), and recrystallization annealing (950 degrees C x 3 h). An ultrafine-grained sheet with an average grain size of 0.8 mu m was prepared. The microstructure transformation, recrystallization process, and grain refinement mechanism of the materials in each stage were examined. Results revealed that large amounts of subgrain structures and irregularly shaped delta phases existed in the GH4169 superalloy exposed to HPT. During the recrystallization annealing at 950 degrees C, the dispersed and uniformly distributed delta phase blocked the migration of the recrystallized grain boundaries. The distorted microstructure after HPT was replaced with the newly formed fine grain without distortion, eventually forming an ultrafine grain structure with high-angle grain boundaries. After HPT processing was performed at 5 GPa x 2 turns, a cubic texture in the {100} <001> direction was produced in the GH4169 superalloy. (C) 2018 Elsevier B.V. All rights reserved.