Characterization and modeling of the influence of initial microstructure on recrystallization of zircaloy-4 during hot forming

The present article proposes a detailed study of recrystallization of zircaloy-4 under hot forming conditions by means of experimental and numerical tools. Thermomechanical tests and characterization campaigns that have been necessary for this work are described. Then, the different microstructure evolution mechanisms are characterized, from the simplest one to the most complex. Grain growth kinetics is quantified and the influence of second phase particle population is analyzed. Then, a complete study of dynamic and post-dynamic recrystallization is provided. The occurrence of a continuous mechanism is confirmed and the influence of thermomechanical conditions upon recrystallization is assessed. Later, the numerical framework used to simulate grain growth, continuous and post-dynamic recrystallization is presented. After having successfully reproduced the grain coarsening kinetics with and without second phase particles, the model is used to describe continuous dynamic recrystallization and post-dynamic recrystallization from an initial equiaxed and fully recrystallized microstructure. The agreement between experimental and numerical results is assessed in detail. Finally, post-dynamic recrystallization is simulated, starting from two deformed microstructures characterized by electron back-scattered diffraction technique and immersed into simulations. This allows to discuss and reproduce the influence of initial microstructure.