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

Journal article

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 × 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 × 10−3 dpa or less recover close to the pristine value of thermal diffusivity. For doses of 3.2 × 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 1000 K.

Authors: Reza, A; He, G; Dennett, CA; Yu, H; Mizohata, K

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Acta Materialia
• Volume: 232
• Article number: 117926
• Publication date: 2022-04-07
• Acceptance date: 2022-04-05
• DOI: 10.1016/j.actamat.2022.117926
• EISSN: 1873-2453
• ISSN: 1359-6454
• Language: English
• Keywords: transient grating spectroscopy; point defects; fusion materials; annealing; thermal conductivity; defect recovery; FFR