Nucleation Mechanism of Discontinuous Dynamic Recrystallization with Restrained Grain Boundary Sliding

The discontinuous dynamic recrystallization (DDRX) nucleation process was investigated during the TMP of a nickel-based superalloy with a coarse columnar-grain structure. Special attention was focused on the formation mechanism of the ‘newborn boundary’ which separates the free-strain volume from deformed grain. The special grain morphology and large grain size restrained the grain boundary sliding of the studied alloy, and hence made it difficult to form a subboundary through strain induction or twining to separate the free-strain volumes from the deformed grains. This is very different with the classical DDRX theory, where the grain boundary sliding has less restraint and hence leads to grain boundary shearing and the following strain induced boundary or twin boundary. However, the experiment results showed that DDRX took place and developed well during the studied deformation process with restrained grain boundary sliding. It was found that the ‘newborn boundary’, which separates the free-strain volume from deformed grain to close this area, was formed through dislocation piling-up and rearrangement instead of strain induction or twinning caused grain boundary shearing. Hence, a potential nucleation theory was then proposed and discussed, which is expected to enrich the discontinuous dynamic recrystallization theory. Graphic Abstract