Effects of hydrogen contents on the mechanical properties of Zircaloy-4 sheets

The purpose of this study was to investigate the effects of hydrogen contents on the mechanical properties of Zircaloy-4 sheets. Zircaloy-4 specimens were gaseously hydrided up to 832 ppm H and then tested at 25, 100, 200, 300 and 400 °C. Tensile specimens were chosen to understand the ductile-to-brittle transition associated with hydrogen content. Scanning electron microscopy was used to examine the fracture surface. The results showed that, at 25 °C, a ductile-brittle transition occurred on the Zircaloy-4 specimen with hydrogen contents between 538 and 832 ppm H. The behavior was not observed as the temperatures were above 100 °C. In the temperature range of 100-300 °C, the specimens charged with 712 ppm H and below exhibited good ductility. The early occurrence of the strain localization for the specimens with hydrogen content larger than 456 ppm H was found at temperatures higher than 200 °C. Fractographic examinations indicated that quasi-cleavages features were observed as the hydrogen content was 712 ppm H and above at the temperatures below 100 °C, whereas ductile fracture occurred for all the hydrided specimens tested at temperatures higher than 200 °C. Stress-strain curves suggested that yield points were observed on the unhydrided specimens while the phenomenon was suppressed on the hydrided ones.