The effect of tempering temperatures on the surface swelling of helium-ion-implanted Ti/Ta-added reduced-activation ferritic/martensitic steel

Abstract

The swelling of a newly developed Ti/Ta-added reduced-activation ferritic/martensitic (RAFM) steel is evaluated using helium ion implantation. He ions are injected into sample surfaces covered with a transmission electron microscopy (TEM) grid; subsequent post-implantation annealing (PIA) causes surface mounds to form where He ions are injected. The heights of surface mounds on Ti/Ta-RAFM steels tempered at three different temperatures are found to increase with increasing tempering temperature. TEM observation reveals that helium bubbles formed along lath/block boundaries, dislocations, and precipitate-matrix interfaces. The increased step height of the Ti/Ta-RAFM steel tempered at higher temperature can be attributed to increases in the block and precipitate sizes and a decrease in dislocation density. The mechanism of helium bubble evolution in RAFM steel after helium implantation at room temperature and subsequent PIA is illustrated schematically. The swelling of Ti/Ta-RAFM steel is compared to that of a reference steel with a composition similar to that of Eurofer97.