| Shrnutí: | <p>Tungsten is a leading candidate for plasma-facing components (PFCs) in fusion reactors owing to its excellent thermomechanical properties. During operation, PFCs are subjected to neutron irradiation, high temperatures and high strain rates, causing changes to material performance. This study investigated the effect of strain rate (SR) and radiation damage through micromechanical testing of [001]-orientated unirradiated single crystal W and single crystal W irradiated to 1.67 dpa at 900 °C.</p>
<p>Constant strain rate spherical nanoindentation experiments using 5 μm and 10 μm radius tips were executed at 3.2x10-3 s-1, 3.2x10-4 s-1 and 3.2x10-5 s-1 to produce indentation stress-strain curves. The unirradiated sample showed an absence of work hardening and large pop-ins due to the lack of defects present. An increase in hardening and yield stress was seen after irradiation; the irradiated sample also exhibited significant work hardening behaviour, which can be attributed to radiation-induced microstructural barriers to dislocation motion such as Re-Os precipitates, dislocations and voids. Work hardening behaviour remained consistent across the strain rates.</p>
<p>Characterisation of the pile-up, strain localisation and density of geometrically necessary dislocations around the nanoindents revealed an increase in pile-up height after irradiation and indicated the presence of a constrained plastic zone due to radiation-induced defects, causing increased material flow towards the surface. Due to challenges in the rate-controlled nanoindentation method, total indenter displacement, and thus total strain, unintentionally increased with SR. Pile-up height normalised by residual indentation depth was found to increase with SR, but further refinement of the method would allow a more reliable method of characterising deformation behaviour.</p>
<p>Crystal plasticity finite element modelling using a set of parameters fitted to the experimental results successfully captured the radiation-induced increase in pile-up height and constraint of the plastic zone with remarkable agreement, and provided clarity on the subtle rate effects exhibited.</p>
<p>This work reinforces the ability to study material performance in a fusion environment through micromechanical testing methods. Furthermore, consistency in the radiation-induced hardening and deformation behaviour observed in this study and self-ion irradiated W gives credence to ion irradiation in emulating neutron-irradiation effects, despite producing different damage mechanisms.</p>
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