Effect of grain boundary character on intergranular hydrides precipitation in zirconium

Grain boundary characteristics play a crucial role in the formation of intergranular hydrides, which may cause brittle fracture in zirconium alloys. However, the impact of grain boundary character on microscopic hydride precipitation remains unclear. Here, we investigate the nucleation and precipitation of intergranular hydrides in zirconium by using In-situ transmission electron microscopy observations and post-precipitation electron backscattered diffraction analysis. The nucleation of intergranular hydrides is highly dependent on the interacting angle (α_GB-BP) between the grain boundary plane and the basal plane. For low-angle grain boundaries, hydrides prefer to grow into the grain interior when the α_GB-BP is less than 60°, otherwise, no hydride precipitation occurs. For high-angle grain boundaries, hydrides nucleate along the grain boundary when the α_GB-BP is less than 39°. As the α_GB-BP increases, hydrides grow into the grain interior. A thermodynamic model is developed to analyze the nucleation of needle-shaped hydrides. The variation of the intergranular hydride as a function of the grain boundary energy and the α_GB-BP is predicted. This finding provides new insight into utilizing grain boundary engineering to modulate intergranular hydride precipitation and offers a pathway to control hydrogen embrittlement in zirconium alloys.