Microstructure transformation during warm working of β-treated lamellar Zircaloy-4 within the upper α-range

Torsion and compression tests were used to simulate simple deformation paths within the upper α-range of β-treated Zircaloy-4 (i.e. 500−750 °C). The mechanical behaviour exhibits two different domains: at low temperatures and large strain rates strain hardening takes place before flow softening, whereas this first stage disappears at lower flow stress levels. Deformation microstructures were investigated using the electron backscattering diffraction (EBSD) technique. Continuous dynamic recrystallization (CDRX), based on the increasing misorientation of subgrain boundaries and their progressive transformation into large angle boundaries, mainly occurs during straining. Geometric dynamic recrystallization (GDRX), that involves the transformation of the initial high angle boundaries, also contributes to the “fragmentation” of the initial lamellar microstructure. This mechanism is favoured by higher temperatures and lower strain rates.