Enhanced helium ion irradiation tolerance in a Fe-Co-Ni-Cr-Al-Ti high-entropy alloy with L12 nanoparticles

摘要

L12-strengthened high entropy alloys(HEAs)with excellent room and high-temperature mechanical prop-erties have been proposed as promising candidates as structural materials for advanced nuclear systems.However,knowledge about their radiation response is fairly limited.In the present work,a novel HEA with a high density of L12 nanoparticles was irradiated with He ion at 500°C.Transmission electron microscope(TEM)and atom probe tomography(APT)were employed to study the evolution of mi-crostructural stability and radiation-induced segregation.Similar to the single-phase FeCoNiCr HEA,the main microstructural features were numerous large faulted dislocation loops and helium bubbles.While the irradiation resistance of the present L12-strengthened HEA is much improved in terms of reduced bubble size,which could be attributed to the considerable He trapping efficiency of the coherent pre-cipitate/matrix interface and the enhanced capability of the interface for damage elimination when the matrix channel width is narrow.APT analysis revealed that an inverse-Kirkendall-mechanism-dominated radiation-induced segregation(RIS)occurs around bubbles,where a significant Co enrichment and Ni de-pletion can be clearly observed.In addition,the competing dynamics of ballistic mixing and elemental clustering that raised from the irradiation-enhanced diffusion in a highly supersaturated matrix,along with the low precipitation nucleation barrier due to the small lattice misfit,lead to a dynamical pre-cipitation dissolution and re-precipitation appears under irradiation.Such a promising phenomenon is expected to promote a potential self-healing effect and could in turn provide a sustainable irradiation tolerance over the operational lifetime of a reactor.