microstructure evolution during static recrystallization and grain growth of low alloyed zirconium sheets (Zr7O2)

Low alloyed zirconium sheets (Zr7O2) have been cold-rolled up to 80 % thickness reduction and submitted to various isothermal treatments. The aim was to identify the mechanisms which produce microstructure and texture changes during recrystallization and grain growth. XRD and texture analysis, FEG-SEM with EBSD as well as TEM were used to analyze the various specimens. Three types of substructures were observed in the initial deformed material. Accordingly, the nucleation starts in the most deformed areas and continues in the somewhat less deformed areas, which corresponds to a non oriented nucleation and results in a set of new grains, the size of which is very rapidly stabilized. In the last stage of recrystallization, the grains which have resisted the recrystallization disappear progressively by several mechanisms including in situ recrystallization. Therefore, the texture at the end of the recrystallization resembles the one of the deformed state. Normal grain growth leads to a moderate grain size increase due to the precipitates which slow down the grain boundary motion. This is also the stage where the texture changes due to the size advantage, after recrystallization, of grains in some specific orientations.