Microstructure evolution in tungsten during low-energy helium ion irradiation

In situ transmission electron microscopy (TEM) study was performed to investigate the microstructural changes in tungsten during low-energy He+ ion irradiations in an electron microscope linked with an ion accelerator. The irradiations were carried out with 8 and 0.25 keV He+ ions at 293, 873 and 1073 K. In the case of the 8 keV irradiation, irradiation-induced vacancies act as nucleation sites for dislocation loops and helium (He) bubbles. Accordingly, such defects were formed even at the higher temperatures. With increasing irradiation temperature, the growth rates of dislocation loops and He bubbles rise remarkably. Although no vacancies are produced during 0.25 keV irradiation, He platelets, interstitial loops and He bubbles were formed. Impurity atoms may act as trapping centers for He atoms, which form bubbles by ejecting W atoms from their lattice site.