Morphological and nanomechanical changes in tungsten in high heat flux conditions

Abstract

Morphological and nanomechanical alteration of tungsten in extreme environments, like those in edge localized modes in nuclear fusion environments, up to 46.3 GWm−2 heat fluxes were experimentally simulated using electrothermal plasma. Surface and subsurface damage to the tungsten is seen mainly in the form of pore formation, cracks, and resolidified melt instabilities. Mirco voids, rosette-type microfeatures, core-shell structure, particle enrichment, and submicron channels all manifest in the damaged subsurface. The formation of voids in the subsurface was determined to originate from the ductile fracture of hot tungsten by plastic flow but not developed to cracking. The voids were preferentially settled in grain boundaries, interfaces. The directionality of elongated voids and grains is biased to the heat flow vector or plasma pathway, which is the likely consequence of the thermally driven grain growth and sliding in the high-temperature conditions. The presence of a border between the transient layer and heat-affected zone is observed and attributed to plasma shock and thermal spallation of fractural tungsten at high temperature. Plasma peening-like hardening effects in tungsten were observed in the range of 22.7–46.3 GWm−2 but least in the case of the lowest heat flux, 12.5 GWm−2.

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

“…In our previous studies, we identified stress-driven surface diffusion as the primary driving force for nanotendril growth at the early stage of plasma exposure, where the stress is developed in the nearsurface layer of plasma-facing component (PFC) tungsten due to over-pressurized nanometer-size bubbles formed by the implanted helium ions in the PFC material. These nanotendrils are the precursor to the surface nanostructure that eventually grows to form the fuzz-like structure on the PFC surface [5,8,[23][24][25]. Additionally, subsurface bubble dynamics [26][27][28][29][30], dislocation loop punching [17,31,32], bubble bursting, and surface crater formation [17,[33][34][35] play important roles in the early stages of the nanotendril growth process.…”

Estimation of irradiation damage of alpha particles and D-T ions on structural materials

“…Regarding to the ions for the experiments, we chose hydrogen and helium ions. For the hydrogen ions, we chose deuterium and tritium ions, while for the helium ion, we chose 4-He, sincesd these three ions are the three most important ions in the fusion reaction [8][9][10]. For our experimental data, we chose two microns as our material thickness.…”