TEM investigation of helium bubble evolution in tungsten and ZrC-strengthened tungsten at 800 and 1000°C under 40keV He+ irradiation

Abstract

Helium-induced defect nucleation and accumulation in polycrystalline W and W0.5 wt%ZrC (W0.5ZrC) were studied in-situ using the transmission electron microscopy (TEM) combined with 40 keV He+ irradiation at 800 and 1000°С at the maximum damage level of 1 dpa. Radiation-induced dislocation loops were not observed in the current study. W0.5ZrC was found to be less susceptible to irradiation damage in terms of helium bubble formation and growth, especially at lower temperature (800 °C) when vacancies were less mobile. The ZrC particles present in the W matrix pin the forming helium bubbles via interaction between C atom and neighbouring W atom at vacancies. This reduces the capability of helium to trap a vacancy which is required to form the bubble core and, as a consequence, delays, the bubble nucleation.At 1000 °C, significant bubble growth occurred in both materials and all the present bubbles transitioned from spherical to faceted shape, whereas at 800 °C, the faceted helium bubble population was dominated in W.

Keywords

• Tungsten
• Zirconium carbide
• Plasma-facing materials
• In-situ helium exposure
• Faceted helium bubbles
• Transmission electron microscopy