Damage behavior of multi-laser powder bed fusion 316L SS irradiated with He ions at high temperature

ML-PBF (Multi-laser powder bed fusion) is an additive manufacturing solution for large-scale nuclear components, with the irradiation-induced damage behavior of its fabricated materials being critical to their safe service in nuclear reactors. Helium ion irradiation at high temperature (700 °C) was carried out to investigate the differences in high-temperature helium hardening behavior in ML-PBF 316L SS between single laser forming zone and overlap zone. The results showed that both zones exhibited comparable microstructural features, including cellular and columnar substructures. However, the overlap zone displayed a refined average grain size. Additionally, the dislocation density in the overlap zone was smaller due to in-situ annealing during multi-laser processing, along with smaller nano-oxide particles (20.77 nm) and a higher number density (7.8×10²⁰ m⁻³) compared to the single-laser forming zone. The degree of irradiation hardening increased with increasing irradiation dose in both zones. And the overlap zone demonstrated a lower degree of hardening compared to the single-laser forming zone at the same irradiation dose. The average densities of helium bubbles in the single laser forming zone and overlap zone were 3.54×10²³/m³ and 3.16×10²³/m³, while the average sizes were 2.1 and 2.3 nm, respectively. The average densities of Frank's dislocation loops in both zones were 5.13×10²²/m³ and 5.29×10²²/m³, and the average size was 5.7 and 4.9 nm, respectively. Analysis of the contributions of helium bubbles and dislocation loops to irradiation hardening using the DBH model confirmed the disparity in irradiation hardening behavior between the two zones was primarily attributed to the difference in helium bubble characteristics (including number density and size).