Effect of helium bubbles on irradiation hardening of additive manufacturing 316L stainless steel under high temperature He ions irradiation

Abstract

To evaluate the effects of irradiation on additive manufacturing materials which are expected to be applied in advanced nuclear energy systems, selective laser melting 316L stainless steel (SLM 316L SS) and traditionally manufactured 316L stainless steel (TM 316L SS), were irradiated with 500 keV He ions at 700°C, respectively. SEM, TEM and nanoindentation measurements were performed to survey the effects of helium (He) bubbles on the irradiation hardening. It was found that the degree of irradiation hardening of the two materials increased with an increase of ions fluences. The hardening range of SLM 316L SS was 6-47% while that of TM 316L SS was 32-75%. Moreover, the hardening saturation phenomenon was more pronounced in TM 316L SS than in SLM 316L SS. These results suggested that SLM 316L SS owned higher resistance to irradiation hardening than TM 316L SS. TEM observations showed that the density of He bubbles in TM 316L SS was 7.06 × 1023/m3 while that in SLM 316L SS was 3.33 × 1023/m3. Further, the average sizes of bubbles were 2.2 and 2.4 nm, respectively. The differences of the number density might be why SLM 316L SS had a slighter irradiation hardening than TM 316L SS, which was consistent with Orowan model. It was suggested that the numerous intrinsic microstructures such as entangled dislocation network walls and subgrain boundaries in SLM 316L SS could greatly reduce the density of He bubbles.