NONUNIFORM RECRYSTALLIZATION IN A MECHANICALLY ALLOYED NICKEL-BASE SUPERALLOY

The recrystallization behavior of mechanically alloyed and extruded MA 6000 oxide dispersion strengthened (ODS) nickel-base superalloy has be en studied as a function of the position of the sample in the extruded bar. It was found that there are profound differences across the cros s section of the bar, the edge regions recrystallizing more easily rel ative to the core. Furthermore, the recrystallized grains tend to be m uch more anisotropic at the edges. It appears that these differences a re caused by inhomogeneous deformation. The oxide particles are more a ligned along the extrusion direction at the regions near the surface, presumably because of the more extensive deformation in those regions. This explains the greater anisotropy in the recrystallized grains and the relative case of recrystallization (since the boundary mobility a long the extrusion direction is high for aligned particles). Stored en ergy measurements confirm that the observed effects cannot be explaine d by differences in the driving force for recrystallization.