Abstract
To understand the synergistic effect of hydrogen gas and internal hydrides on the mechanical properties of ZIRCALOY-4, plate specimens were gaseously hydrided up to 340 ppm H and then tested in a hydrogen gas environment of various pressures up to 2020 kPa at 25 °C, 100 °C, and 200 °C. Notched tensile specimens were used to better understand the 'ductile-brittle transition.' The results showed that for both uncharged and hydrided specimens, the notch tensile strength decreased with increasing hydrogen pressure as well as increasing temperature. A ductile-brittle transition was found on specimens tested at 25 °C and at hydrogen pressures between 0 and 1010 kPa. Fractographic finding suggest that this transition is closely related to the precipitation and distribution of brittle hydrides. The observed transition disappeared as the temperature increased to 100 °C and above.