Effect of thermal cycles on delayed hydride cracking in Zr-2.5Nb alloy

Delayed Hydride Cracking, DHC, is a mechanism that affects Zr and its alloys. Among other factors, thermal cycles may influence the occurrence of DHC process due to the difference between the hydrogen dissolution and precipitation solvus curves. In this work, DHC propagation rate (VP) was measured in Zr-2.5Nb alloy, after different thermal cycles: 1) by cooling to the Test temperature (Ttest); 2) by heating to Ttest; 3) after cooling to different temperatures (Tcool) and subsequent heating to Ttest = 253 °C and 154 °C. VP measured after cooling followed Arrhenius behavior, and a change in the activation energy was detected around 170 °C. It was confirmed that, under the conditions tested in this report, DHC is not possible at temperatures higher than TA = 210 °C when Ttest is approached by heating. An undercooling of 25 °C was enough to avoid DHC at Ttest = 253 °C. If Ttest = 154 °C DHC could not be stopped by any undercooling. Experimental results of VP and critical temperatures presented good agreement with values calculated with theoretical models reported in literature.