Reorientation of hydrides and its effect on the mechanical properties of zircaloy-4 cladding tubes

The reorientation of hydrides and its effect on the fracture of zircaloy-4 cladding tubes with the hydrogen content of 220 wt. ppm were investigated. The reorientation of hydrides along the radial directions was most pronounced if the tube was cooled from 300 .deg. C to 200 .deg. C under circumferential loading. Reorientation occurred much less frequently in either higher (cooled from 400 .deg. C to 300 .deg. C) or lower (cooled from 200 .deg. C to 100 .deg. C) temperature range. The reorientation of hydrides was found to increase with the increase of loading time, suggesting time dependent stress-aided dissolution of circumferential hydrides (hydride platelets in the circumferential-axial plane) and reprecipitation of radial hydrides (hydride platelets lying in the radial-axial plane). The strength and ductility decreased with the reorientation of hydrides. The strength decreased to ∼380 MPa and the ductility decreased to zero in the tube which was reorientation-treated from 300 .deg. C to 200 .deg. C (R43AC). Fracture surface of R32AC sample exhibited flat cleavage fracture along the radial hydride platelet