The Study Of Irradiation Damage Effect Of Additive Manufacturing 316L Stainless Steel

The additive manufacturing（AM）technology fits the trend of intelligent manufacturing of equipment for advanced nuclear energy system because of its unique advantages such as short cycle,flexibility with respect to structure design and high precision manufacturing.However,due to the significant differences in microstructure between AM and traditional manufacturing（TM）materials,especially the anti-irradiation performance will directly affect the safety of nuclear energy systems’operation,so it is essential to hold the researches about the irradiation damage mechanism of the special intrinsic structures of AM materials.In this study,316L stainless steel（SS）fabricated by selective laser melting（SLM）technology was used as the carrier to study the irradiation damage behavior and properties of AM materials.The irradiation effects such as high temperature helium-induced hardening and embrittlement,irradiation hardening and irradiation swelling were explored,and the effect influence of special intrinsic structures in SLM 316L SS on the evolution of irradiation defects was also investigated.The above researches could help to confirm the applicability of this technology for the production of nuclear energy components.In the study of high temperature helium-induced hardening and embrittlement under constant dose of helium ion irradiation experiments at 700℃,it was found that both the irradiation hardening of TM and SLM 316L SS was increased with the increase of ions dose.However,SLM 316L SS showed the excellent resistance to high temperature helium-induced hardening ability than 316L SS:The hardening degree of TM 316LSS was 32%-75%,but only 6%-47%in SLM 316L SS,and there was a hardening saturation phenomenon in TM 316L SS at dose of 5×10¹⁶ ions/cm²,while SLM 316L SS showed no obvious saturation even 1×10¹⁷ ions/cm² ions dose.The observation of the irradiation defects of the two types 316L SS showed that there were obviously higher density helium bubbles in TM 316L SS(7.06×10²³/m³),which is much higher than that in SLM 316L SS(3.33×10²³/m³).By measuring the contribution of irradiation defects to hardening through dispersed barrie hardening（DBH）model,it could be confirmed that numerous special intrinsic structures such as entangled dislocation network walls and grain boundaries in SLM 316L SS inhibited helium and significantly reducedthe density of helium bubbles,which was the micro explanation of why SLM 316L SS owned the higher resistance to irradiation hardening.In the temperature range of 350-900℃,further studies on the evolution mechanism of helium bubbles in SLM 316L SS had found that the evolution of helium bubbles might be controlled by the vacancy diffusion mechanism of helium atoms in the low temperature regime（350-550℃）.At the high temperature regime（700-900℃）,the activation of the migration and coalescence（MC）mechanism of helium bubbles will affect the diffusion behavior of helium atoms controlled by the displacement mechanism.The difference influence of the special intrinsic structures on the evolution of helium bubbles was directly confirmed in the process of temperature rise.At 700-900℃,the heterogeneous nucleation phenomenon of helium bubbles was obvious near the dislocation structures.Only at 900℃,the aggregation behavior of helium bubbles was found at the oxide-matrix interface.The effect of grain boundaries on helium bubbles could be observed in the separate twin-jet electropolishing samples experiments at much lower temperatures（150-450℃）.In addition,the analysis of helium-induced swelling in SLM 316L SS at the temperature range of 350-900℃ showed that the swelling degree in SLM 316L SS was significantly lower than that in TM 316L SS.These above results indicated that the special intrinsic structures of SLM 316L SS had a significant influence on the evolution of irradiation defects and could effectively reduce the impact of helium bubbles on materials properties.Under studies on the displacement damage induced heavy ions（Xe and Fe ions）with continuous doses at different temperatures,it was found that the irradiation hardening curves of two types of 316L SS reached saturation rapidly with the increase of the dose both at room temperature（RT）and high temperature（700℃）.The irradiation hardening at RT reached maximum value when the dose was lower than 1dpa,while saturation was achieved between 1-3 dpa under 700℃,and the degree of hardening at high temperature was significantly lower than that under RT irradiation.In addition,regardless of RT or 700℃ irradiation,the hardening curves of SLM 316L SS was generally below TM 316L SS.The critical effective volume parameters of defects calculated by Makin-Minter formula could be inferred to lower density irradiation defects in SLM 316L SS.The microscopic observation of the irradiation defects revealed defects characteristics consistent with the irradiation hardening behavior:there were dislocation loops defects in two types of 316L SS after irradiation,but the density of dislocation loops at 700℃ was much lower than that under RT irradiation.This was because the improvement of migration ability of point defects at high temperature promoted the recovery of defects in materials,which made the both 316L SS showed lower irradiation hardening at high temperature.Under the same irradiation conditions,there were lower density of dislocation loops in SLM316L SS than TM 316L SS,which was caused by the presence of complex dislocations,fine grain boundaries,oxide particles and other special intrinsic structures in SLM 316L SS acting as sinks of irradiation defects.As a result,the defect production rate and the density of defects with final equilibrium state were lower,which made SLM 316L SS had better resistance to irradiation hardening than TM 316L SS.