Effect of native carbon vacancies on evolution of defects in ZrC_(1-x)under He ion irradiation and annealing

The dynamic study of radiation-induced defects with annealing is critical for the material design for nextgeneration nuclear energy systems.The native vacancy could affect the development of defects,which lacks study.In the present work,the as-hot pressed ZrC_(1-x)(x=0,0.15,0.3)ceramics which comprised crystallites of a few microns in size with different amounts of carbon vacancies were irradiated by 540 ke V He^(2+)ions at room temperature with a fluence of 1×10^(17)/cm^(2).The radiation-induced lattice expansion was found to be a common phenomenon in a sequence of ZrC_(0.85)≥ZrC_(1.0)>ZrC_(0.7).Both X-ray and electron diffractions confirmed maintenance of structural integrity without amorphization after irradiation.Inside the irradiated region,only“black-dot”type defects,i.e.,clusters of point defects were observed while no helium-induced cavities,cracks,or extended dislocations were detected.The as-irradiated ZrC_(1-x)were then annealed at different high temperatures.Upon annealing at 800℃,very tiny helium-induced cavities were found to be generated and the crystal lattice recovered to a great extent,especially for the sub-stoichiometric samples.While annealed at 1500℃,all the samples almost fully recovered the crystal lattices close to those of as-hot pressed ones.Meanwhile,large cavities and extended dislocations were generated.With increasing amount of native carbon vacancies,the size of cavities increased while the length and density of extended dislocations decreased.Inverse changes of lattice parameters during irradiation and annealing processes have been interpreted by the kinetics of defects.Finally,the correlation between native vacancies and damage behavior is discussed.