Helium influence on the microstructure and swelling of 9%Cr ferritic steel after neutron irradiation to 16.3Â dpa

Specially fabricated samples of the European reference 9Cr-WTaV steel EUROFER 97 alloyed with 0.081 mass% natural B and 0.081 and 0.114 mass% pure isotope 10B were neutron-irradiated with about 16.3 dpa at temperatures in the range from 523 K to 723 K to study the influence of helium produced by 10B(n,α)7Li transmutation reaction on microstructure, swelling and hardness. The spatial and size distributions of helium bubbles or cavities after irradiation at different temperatures were investigated by transmission electron microscopy. Vickers microhardness HV0.1 tests were performed on the as received specimens and specimens after irradiation. The influence of irradiation temperature and helium concentration on the size and density of the bubbles or cavities was analyzed and correlations with the hardness, tensile properties, and the fracture surface were discussed.