Delayed hydride cracking in zirconium alloys in a temperature gradient

Abstract

Past theoretical models of delayed hydride cracking in zirconium alloys have assumed a uniform temperature distribution in the material. However, in real components, a temperature gradient may be set up, for example, when a through-wall crack leaks hot, pressurized fluid. Since hydrogen is thermodynamically inclined to diffuse to cold regions, its diffusion to the flaw tip in a thermal gradient will be affected. We have modified the steady-state model of delayed hydride cracking to take account of such a temperature gradient. The new model predicts an increase in the crack velocity in a positive temperature gradient (crack-tip cooler than surroundings) and a reduction in a negative temperature gradient. The model also predicts a shift in the temperature at which cracking ceases if the temperature is attained by heating; this critical temperature increasing in a positive gradient and decreasing in a negative gradient. Experiments have confirmed the trends predicted by the modified model of DHC.