Main Supervisor: Magnus Hörnqvist Colliander
Abstract: Thermomechanical processes are a crucial manufacturing step because they can “reset” the microstructure, and set the starting point for all following steps. In turn, the microstructure can be used to tailor the mechanical properties of the material. It is therefore of great importance to understand how deformation parameters affect the resulting microstructure. The mechanism responsible for this “reset” of microstructures is recrystallization, where the thermal energy and internal stored energy drive the creation of new, deformation-free, grains at the expense of the deformed ones. However, recrystallization is a complex phenomenon affected by alloy composition, temperature, strain, strain rate etc.
In the work presented here, the dynamic, and meta-dynamic recrystallization mechanisms occurring in Ni-base superalloy Haynes 282 are investigated, both below and above the secondary carbide solvus temperature (1100 \C) at various strains, strain rates and post-deformation holding times. Discontinuous dynamic recrystallization, with a clear nucleation of grains at grain boundaries, was observed to be the dominating recrystallization mechanism. For strains up to 0.8 the increase in recrystallized fractions stemmed from nucleation of new grains, whereas for larger strains continued increase in recrystallized fractions was caused by grain growth. Particle stimulated nucleation, where MC carbides acted as nucleation sites, was also observed. Carbides located at grain boundaries did not affect the recrystallization progression significantly. During deformation, the strain rate was seen as the governing factor on the final microstructure, while temperature, strain and holding times were the dominating parameters affecting the meta-dynamic recrystallization. Larger strains led to shorter times to reach a fully recrystallized microstructure during a post-deformation hold. The average grain size also decreased with higher strains applied prior to a static hold.
Examiner: Mats Halvarsson
Opponent: Soran Birosca
PJ, seminar room, Fysik Origo, Campus Johanneberg
28 October, 2022, 09:00
28 October, 2022, 11:00