Effect of heat treatment on delayed hydride cracking in Zr-2.5 Wt Pct Nb

Delayed Hydride Cracking: Theory and Experiment

“…Since there would still be a significant volume fraction of un-reoriented hydrides in the specimens containing 110 wppm H that were cooled from 300°C (573 K), T DAT obtained in these specimens would also be subject to some lowering of its stress amplification by the delamination process as a result of the presence of residual, un-reoriented hydrides. This would explain why T DAT in the specimens having an H content of 50 wppm tested by Amouzouvi and Clegg [2] and others was at least as high as 200°C (572 K), which is *20°C higher than the highest T DAT of 182°C (542 K) obtained in Ambler's [1] experiments.…”

“…This growth rate is approximately what is predicted by Ambler [1] from his test data when the test temperature is approached from a higher temperature of at least 50°C and with K I values ranging from 16.5 to 18.5 MPaHm. The results by Amouzouvi and Clegg [2] imply that T DAT , and hence, the arrest temperature, T A , could be higher than 180°C in their specimens. The K IH value that can be extrapolated from these authors' DHC growth rate versus K I plot for furnace cooled specimens is *10 MPaHm, which is on the high side of what one would expect for this material.…”

“…Amouzouvi and Clegg [2] determined DHC growth rates as a function of K I at 200°C with the test temperature approached from room temperature in samples having a total hydrogen content of 50 wppm. These samples had received a homogenization treatment at 310°C and were initially cooled to room temperature or lower using different cooling rates.…”

“…Referring to the cylindrical geometry used to model the diffusion process shown in Fig. 10.15 and ignoring any h-dependence of the stress field at the crack, the diffusion equation is given by 2 :…”

“…Simpson and Puls [83] and Ambler [1] had made initial attempts to explain these results theoretically based on early versions of the Dutton-Puls DHC growth rate model, while Amouzouvi and Clegg [2] attempted an explanation based on a dislocation sweeping model in their first attempt to explain their results and a critical hydride fracture criterion model derived from an energy balancing criterion in their second attempt [3]. Neither modeling attempts, however, resulted in good agreement between the predictions of the models and the experimental results.…”