Evolution of microstructure and twin density during thermomechanical processing in a γ-γ' nickel-based superalloy
Microstructure evolution has been studied in the nickel-based superalloy PER®72 subjected to hot torsion, to annealing below the primary γ' solvus temperature and to annealing at a supersolvus temperature, with a special emphasis on grain size and twin content. Dynamic abnormal grain growth occurs before the onset of dynamic recrystallization. The resulting bimodal grain size distribution affects the grain-coarsening kinetics at the supersolvus temperature, so that the final microstructures depend on the former straining stages. As a consequence, the twin content does not follow a univocal relationship with the average grain size. The grain boundary velocity history before reaching the final grain size is a contributing factor, and this is notably related to the initial grain size distribution width. Dynamically recrystallized microstructures are by nature more homogeneous and thus give rise to lower rates in supersolvus grain coarsening, and accordingly lead to relatively lower twin densities. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: Abnormal grain growth ; Average grain size ; Bimodal grain-size distribution ; Boundary velocity ; Contributing factor ; Dynamic recrystallization ; Grain boundaries ; Grain boundary engineering ; Grain coarsening ; Grain growth ; Grain size ; Grain size and shape ; Hot torsion ; Initial grain size ; Microstructural evolution ; Microstructure ; Microstructure evolutions ; Ni-based superalloys ; Nickel- based superalloys ; Plastic flow ; Recrystallized microstructures ; Solvus temperature ; Superalloys ; Supersolvus temperatures ; Thermo-mechanical processing ; Thermomechanical processing ; Twin boundaries ; Twin boundary
Record created on 2014-11-14, modified on 2016-08-09