Shear deformation behavior of Zircaloy-4 alloy plate

Zircaloy-4 alloy is widely used in light water reactors. During cold rolling, this alloy is prone to cracking under shear stress. The microstructural characteristics after shear deformation have been investigated in this study in order to provide technical support for avoiding failure of this alloy. Shear tests for recrystallized Zircaloy-4 alloy plate were performed at room temperature using a designed shear testing device. Shear fracture surface and microstructure were carefully characterized by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) techniques, respectively. Results showed that grains in the initial plate are strongly oriented with their c-axis close to the transverse direction (TD). Shear fracture surface can be simply divided into two typical zones based on the morphology features: (I) smooth zone and (II) rough zone. The plate exhibited anisotropy of shear yield strength in the order given as: Normal direction (ND)<Rolling direction (RD)<TD < 45 degrees away from TD (TD45 degrees), which was associated to the initial texture based on the Schmid factor theory. The fracture shear strain increased with the increase area of zone (I). Prismatic < a > slip and {10<(1)over bar>2} ((1) over bar 011 > tensile twinning were the predominant deformation modes during the shear deformation. In addition, {10 (1) over bar2} ((1) over bar 011 > tensile twinning activity was high in grains oriented with their c-axis perpendicular to the shear stress direction (SSD). Furthermore, work hardening occurred due to slip and twinning in the shear deformation region (SDR), which substantially increased the microhardness of the SDR (198 HV) as compared to that of matrix (157 HV). Shear failure tended to occur on the RD-TD45 degrees plane with external load.