Helium bubbles evolution mechanism of SA508-3/52 joint and its effect on nanoindentation hardness and swelling

After metallographic corrosion of dissimilar metal welded joints, a distinct uncorroded bright band, referred to as the ‘white bright band’ (WBB), is often observed on the austenite side immediately adjacent to the fusion line. To investigate the evolution mechanism of helium bubbles in the WBB of dissimilar metal welded joints and their effect on hardening and expansion, SA508-3/52 joints were subjected to irradiation with He+ at ion fluences of 1, 3, and 5 e16 ions/cm2 at 300°C. Helium bubbles have been identified as the main contributors to the hardening of the WBB, and the degree of hardening increases with increasing ion fluence. At a 3 e16 ions/cm2 ion fluence, helium bubbles exhibit the highest hardness contribution of 82.16%. At a distance of 3 μm from the fusion line in the WBB, where the major elemental composition is Fe65Cr10Ni25, the helium bubble number density peak values under three different ion fluences are 4.14, 13.69, and 17.94 × 1023/m3, with corresponding size peak values of 1.73, 1.72, and 1.36 nm, respectively, consistently showing the lowest values within the WBB. This results in the smallest swelling rates, with peak swelling rates of 0.011%, 0.037%, and 0.024% at this location.