Temperature dependence of threshold stress intensity factor, KIH in Zr-2.5Nb alloy and its effect on temperature limit for delayed hydride cracking

Threshold stress intensity factor or Kill required to initiate a delayed hydride crack in the axial direction of a Zr-2.5Nb tube was determined at temperatures of 160 degrees C to 280 degrees C. K-III remained constant at temperatures from 160 to 250 degrees C, increased with an increasing temperature in excess of 280 degrees C using a load decreasing method. To correlate K-III and dislocation twins, tensile tests were conducted on the Zr-2.5Nb tube and textural changes during tensile tests were investigated using an X-ray diffiractometer. The extent of the twins increased from 150 to 300 degrees C and then decreased at temperatures in excess of 300 degrees C with no twins occurring at 350 T. Temperature dependencies of Kill and a temperature limit for delayed hydride cracking were discussed with cracking of hydrides by the twins. This study provides supportive evidence to the feasibility of Kim's DHC model.