Morphology and microstructure evolution of surface hydride in zirconium alloys during hydrogen desorption process

Abstract In the research, we firstly reported the morphology and microstructure evolution of surface hydride in Zircaloy-4-500 ppmH during hydrogen desorption process. The morphological evolution of surface hydride in hydrogen desorption process was investigated with BSE-TOPO and AFM, revealing that the spot-like or string convex features along surface hydride were present at 573 K and disappeared at 1073 K. The microstructure observation with TEM (prepared with cryo-FIB) indicates that the surface region of convex feature actually consists of two layers of fine α-Zr grains, which were the hydrogen-depletion region created by hydrogen release. The formation mechanism of surface hydride convex was the diffusion of hydrogen from the internal to the surface, leading to the generation of multiple δ-hydrides in sub-surface. Therefore, the hydrogen desorption mechanism was also proposed. As the channeling of hydrogen release, surface hydride actually plays a crucial part in hydrogen desorption process.