Mechanisms of dynamic recrystallization and coarse-grained band formation in GH2787 superalloy during thermomechanical treatment

The control of grain size in superalloys through thermomechanical treatment (TMT) proves crucial, as it directly impacts their mechanical properties and service life. Exploring the mechanisms governing abnormal grain growth (AGG) remains vital to maintaining the microstructural stability and performance of superalloys. A combination of thermomechanical simulation, finite element analysis (FEA), and quasi-in-situ EBSD was employed to examine the microstructural evolution of the GH2787 superalloy during TMT. The mechanisms of dynamic recrystallization (DRX) under hot deformation were analyzed. At 10% strain, the sample exhibited three DRX mechanisms: discontinuous, continuous, and twinning-induced recrystallization (TIDX). Particular attention was paid to abnormal grain coarsening during subsequent solution heat treatment. FEA revealed an arc-shaped gradient in effective strain across the cross-section of the deformed specimen, extending from the edge toward the center. During post-deformation heat treatment, coarse-grained bands, enriched with twin boundaries (TBs), formed at the interface between low-energy (GOS<0.5°) and high-energy (0.5°<GOS<1°) layers. Grain coarsening initiated from newly formed, undistorted recrystallized (RX) grains. Driven by the local energy landscape, RX grains initially exhibited a tendency to expand by merging with similarly oriented high-energy grains and subsequently consumed adjacent grains, thereby promoting further coarsening.