Abstract
Zircaloy-4 plate specimens were gaseously hydrided up to 220 ppm H and then tested in a hydrogen gas environment of various pressures up to 2020 kPa at 25, 100 and 200 °C. Notched tensile specimens were chosen to better understand the ductile-brittle transition associated with hydrogen content and hydrogen pressure. The purpose of the present investigation is to understand the synergistic effect of hydrogen gas and internal hydrides on the mechanical properties of zirconium alloys. The results showed that for the specimen with 90 ppm H, the notch tensile strength decreased with increasing hydrogen pressure as well as increasing temperature. Compared with uncharged specimens, the hydrides in the specimen further lowered the notch tensile strength of the specimens. A ductile-brittle transition was found on specimens tested at 25 °C and at hydrogen pressures between 0 and 1010 kPa. For the specimen containing 220 ppm H, the reduction of area at 25 °C and at hydrogen pressures of 1010 kPa and above was drastically reduced, almost completely brittle. From the fractographic finding, the ductile-brittle transition was closely related to the precipitation of brittle hydrides. The ductile-brittle transition disappeared as temperature increased to 100 °C and above. This can be attributed to the improved ductility of the zirconium matrix with increasing temperature.