Manipulating He diffusion in RAFM steels through preintroduced defect engineering under low-energy plasma irradiation

Abstract This study investigates the impact of preintroduced defects on helium (He) diffusion in reduction-activated ferrite/martensitic steel under He plasma irradiation of 100 eV at room temperature. Defects are introduced via cold deformation before irradiation. Microstructural evolution is characterized using transmission electron microscopy, Doppler broadening spectroscopy, and synchrotron x-ray diffraction. Compared to the undeformed specimen, the 30% deformation@annealed specimen exhibited increased dislocation density and almost no vacancies, showing larger He bubbles and broader affected zones. Dislocations enhance He diffusion toward defect traps, facilitating localized accumulation that enables He self-trapping and bubble nucleation and growth. In contrast, 30% deformation specimens without annealing exhibited high dislocation density and abundant vacancies, demonstrating medium-sized bubbles within narrower zones. The high vacancy concentration effectively traps He atoms, strongly inhibiting their mobility. Concurrently, the dispersion of He among numerous vacancy sites reduces local concentration, suppressing bubble growth. Furthermore, under simultaneous dislocation-enhanced and vacancy-inhibited diffusion conditions, the retarding effect of vacancies dominates the microstructure in only 30% deformation specimens.