Microstructure and Texture Evolution of Ni-based Superalloy During Deformation and Thermomechanical Treatments

Abstract:

The microstructure evolution, grain boundary character distribution, strain distribution, and texture evolution of Ni-based superalloy during cold rolling and subsequent recrystallization annealing treatments were studied by electron back-scattered diffraction technique. Results show that when the cold deformation degree is small (ε≤45%), the grains are elongated along the rolling direction into a flat shape and distributed evenly in the matrix. The strain is mainly concentrated near the grain boundary and the twin boundary (TB), and the high-angle grain boundaries (HAGBs) and TBs are gradually transformed into sub-grain boundaries (Sub-GBs) and low-angle grain boundaries (LAGBs). Meanwhile, the Goss texture {110}<001>, Brass-R texture {111}<112>, Twinned-Copper texture {552}<115>, and Copper texture {112}<111> appear. When the rolling reduction exceeds 70%, the grain shape gradually changes from flat to fibrous, the deformation uniformity of the grains gradually becomes better, the strain distribution becomes uniform, and LAGBs begin to dominate. In addition, the texture types do not change, but the texture intensity increases. After the annealing at 1120 °C for 15 min, the length fraction of annealing twins is increased with increasing the rolling reduction. Besides, the deformation textures are transformed into the recrystallization textures, the texture types are increased, but the texture intensity weakens. Furthermore, the Copper texture {112}<111> is continuously transformed into the Twinned-Copper texture {552}<115> when the proportion of annealing twins increases. Additionally, the {124}<211> texture is generated in the as-annealed alloy after rolling reduction of 30%–80%.

Key words:Ni-based superalloy;cold rolling;annealing twins;grain boundary character distribution;texture evolution