Microstructural evolution during hot compression of a Ni-base superalloy: Dynamic and post-dynamic recrystallization below the secondary carbide solvus temperature

Licentiatavhandling, 2021

With an increased demand to lower emissions, the eciency of aircraft engines have to be improved. One way to achieve this is to increase the operation temperature. However, due to the extremely challenging environments in the hot sections of these engines, the current alloys are at their limits. 

Today, Ni-base superalloys are the materials used for these sections, given their outstanding ability to maintain their strength at temperatures up to 0.8 of their melting temperature, as well as showing excellent corrosion and oxidation resistances. New Ni-base superalloys are developed for these challenges and one of them, Haynes 282, is the alloy investigated in this thesis. In order to tailor an alloys mechanical properties to best suit the needs, the microstructure has be to be processed. The initial working steps for wrought superalloys is forging, which sets the base of the microstructure of all subsequent processing steps. An understanding of how the forging parameters will aect the microstructure is therefore crucial.

The dynamic recrystallization mechanisms of the Ni-base superalloy Haynes 282 during hot deformation in a Gleeble were rst investigated. Temperatures both below and above the carbide solvus temperature were studied in order to determine how these parameters aect the resulting microstructure. The microstructures were investigated using electron backscattered diraction and electron channelling contrast imaging in scanning electron microscopes. In order to simulate industrial conditions, samples were held at temperature after deformation in order to evaluate the post dynamic recrystallization phenomena occurring in the Ni-base superalloy for each temperature and strain rate investigated. The microstructures from samples with and without post-deformation hold were compared. An investigation regarding the role of secondary carbides present at grain boundaries during deformation below carbide solvus was also performed, showing that secondary carbides do not aect the recrystallization signicantly. Parameters like temperature and strain rate have a larger impact.