Influence of Y addition on microstructural evolution and irradiation hardening in a V-4Cr-4Ti alloy under He ion irradiation

: The microstructural evolution and irradiation hardening of V-4Cr-4Ti and V-4Cr-4Ti-0.3Y alloys were compared after irradiation with 180 keV He ions at room temperature to a fluence of 1 × 10 17 ions/cm 2 , corresponding to a calculated peak damage level of 2.3 dpa. Y addition refined the grain structure and modified the precipitation state of V-4Cr-4Ti. After irradiation, V-4Cr-4Ti-0.3Y showed a distinct positron trapping behavior and S-W trajectory, indicating a Y-modified local chemical environment. TEM results showed comparable dislocation-loop number densities in both alloys, while V-4Cr-4Ti-0.3Y exhibited slightly smaller loops and no TEM-visible He bubbles in the observed region. In contrast, high-density He bubbles formed in V-4Cr-4Ti. Both alloys exhibited irradiation hardening, with hardness increments of 1.11 and 1.15 GPa for V-4Cr-4Ti and V-4Cr-4Ti-0.3Y, respectively. DBH analysis indicated that dislocation loops and He bubbles largely accounted for the measured hardening in V-4Cr-4Ti, whereas the loop contribution alone underestimated the measured hardening in V-4Cr-4Ti-0.3Y, indicating an additional contribution from unresolved irradiation-induced defects. These results suggest that minor Y addition modifies He-related defect evolution and suppresses TEM-visible He bubble formation under the present irradiation condition.