Microstructural evolution and mechanical properties in Zr705 during the rolling process

Though the deformation behaviour of Zr–Nb alloys has been widely investigated, the studies about the deformation behaviour of the α phase, and the contribution of the α phase, β phase and rotation process to the deformation during rolling have not reached an agreement. When increasing the deformation from zero to 94%, the average thickness of α and β plates monotonously decreased from 701 to 42 nm and from 116 to 14 nm, respectively, whilst the plates were gradually rotated to an orientation parallel to the rolling direction. When increasing the rolling reduction from 42% to 94%, the contribution to the rolling deformation changed from 74.6% to 93.8% for α plates in thickness reduction, from 4.7% to 6.2% for β plates in thickness reduction, but from 20.7% to approximately zero for plate rotation. The refinement of α and β plates and the increment of dislocation density in α plates resulted in a significant increase in the hardness and tensile strength. The rolled Zr705 showed a strain softening at low plastic strains, which may be attributed to the dynamic recovery. This resulted in an early appearance of necking and fracture.

► The α and β plates decreased from 701 to 42 nm and 116 to 14 nm, respectively. ► The contribution to the rolling reduction increased from 74.6% to 93.8% for Rα. ► The contribution to the rolling reduction increased from 4.7% to 6.2% for Rβ. ► The contribution to the rolling reduction reduced from 20.7% to 0% for plate rotation. ► Rolled Zr705 showed a strain softening due to the dynamic recovery.