Thermal diffusivity recovery and defect annealing kinetics of self-ion implanted tungsten prob e d by insitu transient grating spectroscopy

Tungsten is a promising candidate material for plasma-facing armour components in future fusion reactors. A key concern is irradiation-induced degradation of its normally excellent thermal transport properties. In this comprehensive study, thermal diffusivity degradation in ion-implanted tungsten and its evolution from room temperature (RT) to 1073 K is considered. Five samples were exposed to 20 MeV self-ions at RT to achieve damage levels ranging from 3.2 x 10(-4) to 3.2 displacements per atom (dpa). Transient grating spectroscopy with insitu heating was then used to study thermal diffusivity evolution as a function of temperature. Using a kinetic theory model, an equivalent point defect density is estimated from the measured thermal diffusivity. The results showed a prominent recovery of thermal diffusivity between 450 K and 650 K, which coincides with the onset of mono-vacancy mobility. After 1073 K annealing samples with initial damage of 3.2 x 10(-3) dpa or less recover close to the pristine value of thermal diffusivity. For doses of 3.2 x 10(-2) dpa or higher, on the other hand, a residual reduction in thermal diffusivity remains even after 1073 K annealing. Transmission electron microscopy reveals that this is associated with extended, irradiation-induced dislocation structures that are retained after annealing. A sensitivity analysis shows that thermal diffusivity provides an efficient tool for assessing total defect content in tungsten up to 10 0 0 K. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

Tungsten is a promising candidate material for plasma-facing armour components in future fusion reactors. However, its normally excellent thermal transport properties can be degraded by irradiation. The study shows that thermal diffusivity in tungsten can recover between 450 K and 650 K, but remains reduced after annealing at higher doses. Thermal diffusivity provides an efficient tool for assessing total defect content in tungsten.