Determining the local mechanical responses of zirconium and hydrides using in situ indentation and crystal plasticity modeling

Zirconium alloys are widely used in the cores of nuclear reactors, but their mechanical properties can deteriorate over time due to hydrogen embrittlement. This study employs in situ nanoindentation in a Scanning Electron Microscope (SEM) to investigate the local mechanical responses of zirconium and its hydrides. The indentation tests were conducted at different locations within the hydrides and their surrounding α-grains to study their orientation-dependent responses. High-spatial resolution Electron Backscatter Diffraction (EBSD) was used to measure the orientations of grains and hydrides, and to map the pre-indentation values into a Crystal Plasticity Finite Element (CPFE) model. The combination of numerical modeling and in situ experimentation enabled the study of how hydrides interact with one another and with the surrounding α-grains. It is shown that the presence of hydrides leads to different hardening mechanisms. The first mechanism occurs due to dislocations generated in the surrounding α-grains during hydride precipitation, prior to indentation, leading to a weaker hardening response. No apparent indentation-induced slip-hydride interaction was observed for the first hardening mechanism. The second mechanism is due to the interaction of indentation-induced slip bands of α-grains with hydride precipitates, which leads to a more noticeable hardening response. In addition, it was observed that the indentation of hydrides induces slip bands within them.