In-situ TEM/heavy ion irradiation on ultrafine-and nanocrystalline-grained tungsten: Effect of 3 MeV Si, Cu and W ions

Plasma facing components for future fusion applications will experience helium- and neutron-induced structural damage. Direct observation of the in-situ dynamic response of such components during particle beam exposure assists in fundamental understanding of the physical phenomena that give rise to their irradiation resistance. We investigated the response of ultrafine and nanocrystalline-grained tungsten to 3 MeV heavy ion irradiations (Si2 +, Cu3 + and W4 +) for the simulation of neutron-induced damage through transmutation reactions via in-situ ion irradiation–transmission electron microscopy experiments. Defect densities as a function of irradiation dose (displacement per atom) and fluence were studied. Four stages of defect densities evolution were observed, as a function of irradiation dose: 1) increase in defect density at lower doses, 2) higher defect production rate at the intermediate doses (before saturation), 3) reaching the maximum value, and 4) drop of the defect density in the case of W4 +, possibly due to defect coalescence and grain boundary absorption of small defect clusters. The effect of grain size on defect densities was investigated and found that defect densities were independent of grain size in the ultrafine and nanocrystalline region (60–400 nm). These results were compared to other heavy ion irradiation studies of structural materials.