Microstructure evolution and Young's modulus of He-implanted nanocrystalline tungsten film

Abstract

Nanocrystalline tungsten has been widely investigated due to its excellent irradiation resistance. In this study, the microstructure and related Young's modulus of nanocrystalline tungsten film prepared by dual ion beam sputtering deposition and subsequently irradiated by 30 keV He+ of varying fluences at room temperature have been studied by experimental and simulation methods. The mean He bubble size is about 0.7 nm, and the implanted He is preferred to be trapped by the grain boundaries. Few He bubbles are formed nearby the high density defect regions due to more trapping sites for He atoms. The lattice swelling increases with the increase of He fluence. The Young's modulus of the films was measured by LAwave, which indicates the Young's modulus decreases with the increase of He fulence. Molecular dynamics simulations are performed to explore the dependence of Young's modulus on the swelling and the properties of He bubbles. The results indicate that the lattice swelling has a limited influence on Young's modulus. The concentration of He is confirmed to seriously affect the Young's modulus after He implantation. With the same concentration of He atoms, the distribution of He bubbles is a key factor on tensile strength. The He bubbles at grain boundary have a stronger influence on the tensile strength than that in grain interior. He bubbles with higher He/V ratios affect more significantly on the mechanical properties. All these results provide new understandings for radiation damages of nano-materials used in reactors.