Microstructure and Texture Evolution During Hot-Pack Rolling of Nickel-Base Superalloys to Thin Sheet and Foil

Microstructure evolution during hot-pack rolling of nickel-base superalloys to ~1-mm-thick sheet and ~200-μm-thick foil was investigated with electron backscatter diffraction. The microstructure was observed at increasing levels of strain, which revealed the progressive formation of an unrecrystallized, banded microstructure at sheet gage. The bands contained large orientation gradients, sometimes spanning multiple texture components considered to be stable with respect to the imposed plane-strain compression. After reaching stable orientations, grain-scale shear bands were observed within individual unrecrystallized bands that resulted in local subgrain rotations that formed new bands of different orientation. This phenomenon, which is known as band splitting in the literature, was shown to be the result of continuous dynamic recrystallization as opposed to discontinuous dynamic recrystallization or classical static recrystallization. The unrecrystallized bands were eliminated by unidirectional rolling to foil but not by cross rolling.