Abstract
Proton irradiation is often used as a proxy for neutron irradiation but the irradiated layer is typically <50 μm deep; this presents a problem when trying to obtain mechanical test data as a function of irradiation level. Two novel methodologies have been developed to record stress-strain curves for thin proton-irradiated surface layers of SA-508-4N ferritic steel. In the first case, in-situ loading experiments are carried out using a combination of X-ray diffraction and digital image correlation on the near surface region in order to measure stress and strain, thereby eliminating the influence of the non-irradiated volume. The second approach is to manufacture small-scale tensile specimens containing only the proton irradiated volume but approaching the smallest representative volume of the material. This is achieved by high-speed focused ion beam (FIB) milling though the application of a Xe+ Plasma-FIB (PFIB). It is demonstrated that both techniques are capable of recording the early stage of uniaxial flow behaviour of the irradiated material with sufficient accuracy providing a measure of irradiation-induced shift of yield strength, strain hardening and tensile strength.
Highlights
In order to increase the power capacity and operational life of modern reactor designs, a better understanding of the performance of materials under high levels of irradiation damage is required
The second method exploits the significantly faster milling rates that can be achieved for plasma Xe+ focussed ion beam (PFIB) technology compared to Ga+ FIBs due to the higher milling currents[39]
The present study aims to apply and compare side by side these novel techniques for the first time in order to record the mechanical response of 3 MeV proton irradiated SA508-4N steel, irradiated to a depth of approximately 30 μm
Summary
In order to increase the power capacity and operational life of modern reactor designs, a better understanding of the performance of materials under high levels of irradiation damage is required. Protons produced by a spallation source typically have energies in the order of 100 s of MeV, inducing displacement damage similar to the effects of neutrons Such high kinetic energy has the advantage of through-thickness irradiation of bulk specimens, so can be analysed using standard mechanical testing methods[6,7,8,9,10,11,12]. This approach suffers from the same limitations as neutron irradiation, in terms of poor displacement efficiency and high residual post irradiation activity. The present study aims to apply and compare side by side these novel techniques for the first time in order to record the mechanical response of 3 MeV proton irradiated SA508-4N steel (a candidate RPV steel), irradiated to a depth of approximately 30 μm
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