Hydride Related Failure under Hoop Stress in Zircaloy-4 Cladding

Abstract

Zircaloy-4 cladding was hydrided in a high-pressure hydrogen gas furnace at a temperature and pressure of 350°C and 20 MPa, respectively. Various hoop stresses were applied to the cladding tube using a copper rod during the hydriding process. The effect of different hoop stresses on the orientation of hydride platelets was studied using optical microscopy (OM) and electron backscattered diffraction (EBSD) techniques. Optical micrographs showed increased hydrides oriented along the radial direction with the applied hoop stress. In addition to radial hydrides, hydrides inclined at an angle between the circumferential and radial directions were also observed. The hydrides formed without applied hoop stress were found to follow (0001)α-Zr//{111}δ-ZrH_1.5 orientation relationship, whereas the hydrides formed under applied hoop stress were oriented perpendicular to the circumferential direction, following the {10 1̅ 1}α-Zr//{111}δ-ZrH_1.5 relationship. Habit planes of {10 1̅ 1}, {10 1̅ 7}, {10 1̅ 3}, and {10 1̅ 0} were observed for the hydrides inclined at an angle to the circumferential direction. These findings provide valuable insights into the behavior of hydrides and their selection of habit planes under applied stress conditions.