Effect of high temperature and irradiation on the near-surface microstructure of YHx

To study the microstructural evolution of Yttrium hydride (YH x ) under operational conditions, the surface phase transformation, morphology, and microstructure of YH x samples fabricated by spark plasma sintering (SPS) were characterized after high-temperature proton irradiation and isochronous annealing. Grazing incidence X-ray diffraction (GIXRD) results showed that yttrium oxide formed in all irradiated and annealed samples. Scanning electron microscope (SEM) observations revealed surface blistering, which is related to the irradiation dose. The near-surface microstructure was further characterized by transmission electron microscopy (TEM), which showed the presence of voids near the surface. Irradiated samples exhibited a higher number density of cavities and a reduction in cavity size compared to the isochronous annealing samples. Temperature and irradiation-induced vacancies were found to contribute to increased hydrogen mobility and hydrogen dissociation, as revealed by density functional theory (DFT). The mechanism underlying the evolution of the near-surface microstructure, including void formation and surface blistering, was thereby elucidated. • Surface blistering behavior of YH x was observed, which was caused by H diffusion. • Near-surface voids distribution Vs depth after irradiation or anneal was analyzed. • H diffusion mechanism in the near surface effect by vacancy was revealed by DFT. • Temperature and irradiation effects on YH x microstructure were studied in detail.