Effects of Pre-existing Dislocations on the Coupled Evolution of He Bubbles and Dislocation Structures in SIMP Steel under He Irradiation at Different Temperatures
Description
Helium-induced hardening and embrittlement, and their interaction with pre-existing dislocations, are key issues limiting the application of ferritic/martensitic steels in advanced nuclear systems. A low-activation martensitic steel, SIMP, was irradiated with 540 keV He²⁺ ions to 1 × 1017 ions cm⁻² at 300, 450 and 600 °C, comparing as-received specimens with specimens pre-strained to fracture. Transmission electron microscopy showed that, with increasing temperature, the mean helium bubble diameter increased from 1.01 ± 0.57 to 10.15 ± 5.00 nm in the pre-strained specimens and from 1.16 ± 0.53 to 17.85 ± 6.25 nm in the as-received ones, while the number density decreased by two orders of magnitude and the morphology changed from near-spherical to faceted and even needle-like. The unirradiated pre-strained specimens already contained 2.01 × 1022 m-3 of resolvable dislocation loops, which increased to 4.35, 3.04 and 3.58 × 1022 m-3 after irradiation at 300, 450 and 600 °C. Pre-existing dislocations therefore markedly change the evolution paths of the two defect populations. For helium bubbles, they promote nucleation at low temperature, are offset by competitive absorption of point defects at intermediate temperature, and suppress bubble migration and coalescence at high temperature through the larger dislocation structures. For irradiation-induced dislocation loops, they act as local sinks restricting loop growth at low temperature, and reduce the number of retained loops at intermediate temperature by enhancing loop migration and rearrangement, whereas at high temperature the pre-existing loops reorganise and grow rapidly and are therefore less affected.
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Institutions
- Institute of Modern PhysicsGansu, Lanzhou