Abstract
Zircaloy-4 plate specimens were gaseously hydrided up to 180 ppm H. The specimens were tested under sustained load in a hydrogen gas environment of various pressures up to 505 kPa at 100, 150 and 200°C. The crack velocity vs. stress intensity curves had a typical 3-stage characteristics for subcritical crack growth (SCG). The stage II crack growth velocity, (da/dt) II , was generally increased with temperature. The threshold stress intensity, K th , decreased with temperature but was not sensitive to the hydrogen pressure up to 505 kPa. The hydrided specimens showed lower values of K th than those of uncharged specimens. The fractographic findings showed different features for the uncharged specimens and the hydrided specimens cracking in hydrogen gas. The fracture surface of hydrided specimens had two portions. On the portion of stage I and stage II crack growth, the fracture surface was similar to those tested in Ar; while on the portion of later stage II and stage III, the fracture surface became quasicleavage, which was similar to that for the uncharged specimen tested at 200°C in 505 kPa H 2 . From the SCG curves and the fractographic findings, for the hydrided specimen cracking in hydrogen gas, internal hydride-induced crack growth controlled the early stage of SCG; while the later stage was controlled by the gaseous hydrogen embrittlement. The transition of fracture mode may be due to the change of stress state.