EFFECT OF HYDROGEN CONTENTS ON THE MECHANICAL-PROPERTIES OF ZIRCALOY-4

Zircaloy-4 plate specimens were gaseously hydrided up to 340 ppm H and then tested at 25, 100, 200 and 300-degrees-C. Notched tensile specimens were chosen to better understand the ductile-brittle transition associated with hydrogen content. The results showed that, at 25-degrees-C, a ductile-brittle transition occurred on the notched specimens of zircaloy-4 with hydrogen contents between 30 ppm and 140 ppm. The ductile-brittle transition became less distinct as temperature increased to 100-degrees-C and above. This was attributed to the improved ductility of the zirconium matrix by examining the temperature dependence of fracture surface and hydride morphology. Load serrations were observed on the hydrided, notched specimens tested at 200-degrees-C and above, which was related to dynamic strain aging. The stress-strain curves exhibited yield points on the specimens without hydriding. The yield points were suppressed on the hydrided specimens, which was explained by the mechanism that twinning-assisted slip may be hindered by hydrides.