Online Lecture by prof. Nathalie Bozzolo

Recrystallization phenomena in Nickel based superalloy forgings

Speaker: prof. Nathalie Bozzolo,  Centre de Mise en Forme de Matériaux , CEMEF – MINES ParisTech (France).

Title:
Recrystallization phenomena in Nickel based superalloy forgings

Abstract:
The focus of the presentation will be placed on polycrystalline Nickel based superalloys used for aircraft engine turbine disks, and more precisely on recrystallization phenomena taking place while forging those pieces.

Recrystallization is a crucial issue in this field since the forged components are submitted to strict microstructure requirements to sustain the severe and complex solicitations to which the disks will be submitted all along their in-service life.
The most usual phenomenon controlling the final grain size while forging nickel based superalloys is known to be dynamic recrystallization proceeding discontinuously through necklace nucleation. Post-dynamic evolutions may nevertheless also be of utmost importance in the control of the final microstructure in a large forging after cooling down to room temperature.
In addition, particular attention must be paid to second phase particles which are supposed to limit grain growth by the so-called Smith-Zener interactions.

The design of lab experiments to accurately describe the kinetics of such microstructure evolutions and their dependence to the applied thermomechanical conditions will be discussed and the care to be taken in quantitative microstructure analyses will be emphasized also.
Once the mechanisms are identified and their kinetics described, they both can be simulated, using either mean field models, or advanced full field approaches when intrinsic heterogeneities must be considered.

The presentation will provide a few examples of both experimental and numerical results, which will also emphasize the interest of combining both approaches to better understand the material behavior through a realistic and intrinsically complex thermomechanical path representative for a typical industrial process.

This session was chaired by prof. Leo Kestens (Ghent University).