Recrystallization and the Development of Abnormally Large Grains After Small Strain Deformation in a Polycrystalline Nickel-Based Superalloy

The formation of abnormally large grains has been investigated in the polycrystalline nickel-based superalloy Ren, 88DT. Cylindrical specimens with a 15 mu m grain size were compressed to plastic strains up to 11.0 pct and subsequently rapidly heated to above the gamma' solvus at 1423 K (1150 C) and held for 60 seconds. All deformed samples partially recrystallized during the heat treatment, with the recrystallized grain size varying with the degree of deformation. The largest final grain size occurred in samples deformed to approximately 2 pct strain, with isolated grains as large as 700 mu m in diameter observed. It is proposed that abnormally large grains appear due to nucleation-limited recrystallization, not abnormal grain growth, based on the high boundary velocities measured and the observed reduction in grain orientation spread.