Effects of texture and microstructure on the propagation of iodine stress corrosion cracks in zircaloy

Abstract

An investigation of stress corrosion crack propagation in Zircaloy is performed at 300 °C in four Pa flowing iodine environment. By varying the orientation of fracture mechanics specimens, the effect of crystallographic texture, heat treatment, and microstructure onK ISCC is studied. Texture is found to have a strong effect on bothK ISCC and the fracture path. As the resolved fraction of basal poles parallel to the direction of crack opening decreases,K ISCC in stress-relieved material increases from 4 MPa√m atf = 0.70 to 17 MPa√m atf = 0.19. The same trend is observed in recrystallized material. However, theK ISCC values are somewhat greater. Transgranular cleavage is the preferred mode of crack propagation. Several ductile modes of separation complement the cleavage process. At high crack velocity, tearing between facets is promoted. At lowK, nearK ISCC, very little tearing is observed and cleavage zones larger than the grain size are common. Fluting is preferred in the low regime. In recrystallized material a transition to completely intergranular failure is observed nearK ISCC.