Microstructure and texture evolution of β-air cooled commercial-purity zirconium during rolling

To explore the microstructure and texture evolution of β-air cooled (β-AC) commercial-purity zirconium during rolling, a β-AC zirconium sheet was rolled at room temperature to various reductions (5–50 %) and then subjected to detailed characterizations utilizing electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) techniques. The results reveal that the initial β-AC sheet exhibits a typical Widmanstätten structure with scattered orientations, which undergoes significant microstructure and texture changes during subsequent rolling. At reduction <20 %, the density of deformation twin increases with higher strains, leading to continuous refinement of the initial coarse lath structures. Meanwhile, texture components with grain c-axes inclined ±30–40° from normal direction (ND) toward transverse direction (TD) or parallel to TD (c//TD) are gradually developed. At reduction >20 %, new twins are no longer formed and dislocation slip becomes the predominant deformation mode, allowing a strong basal texture with most c-axes parallel to ND (c//ND) to be eventually developed. After the rolling reduction reaches 50 %, the average grain size decreases from 20.5 ± 17.5 μm to 3.3 ± 4.0 μm, along with specimen hardness enhanced from 172.3 ± 6.8 HV to 278.5 ± 5.3 HV. Detailed analyses reveal that the hardness enhancement in the rolled specimens is primarily attributed to grain-refinement and dislocation strengthening. The rolling texture could also make a significant contribution to hardening, particularly when the deformation amount is relatively high.