Cracks and blisters formed in nanocrystalline tungsten films by helium implantation

Irradiation-enhanced superficial modification and evolution of mechanical behavior in TaTiNbZr refractory high entropy alloy films exposed to low energy helium plasma

Pure W with grain size of 1.77 μm, ultrafine-grained W-10wt.%Cr-2wt.%Ti (W-10C-2 T) alloy with grain size of 161 nm and W-10wt.%Cr-4wt.%Ti (W-10C-4 T) alloy with grain size of 148 nm, were prepared by mechanical alloying followed by hot isostatic pressing (HIP) sintering. Ultrafine-grained structure stability mechanisms of W-10C-2 T and W-10C-4 T can be mainly ascribed to the thermodynamic aspect illustrated by the kinetic calculation of critical maximum W grain size. The average grain size of W-10C-4 T is smaller than that of W-10C-2 T, and the increasing additional amount of Ti can further inhibits grain growth. The second phase particles can interact with free oxygen to purify and strengthen grain boundaries, and the faster thermal diffusion rate of Cr and Ti can improve the density of W-10C-2 T and W-10C-4 T alloys obviously, compared with pure W. The Vickers hardness of W-10C-2 T and W-10C-4 T alloys were tested, and results show that they possess ultrahigh hardness, the value of their Vickers hardness is 1237 ± 74 kgf/mm2 and 1402 ± 46 kgf/mm2, respectively, which is much larger than that of pure W and coarse-grained W-based alloys. The ultrahigh hardness comes from the abundant grain boundaries (GBs) that act as obstacles and potential barriers for dislocation motion, and second phase strengthening. High-temperature annealing treatment results show that W-10C-2 T and W-10C-4 T alloys possess excellent thermal stability at the annealing temperature of 1000 °C and 1100 °C, and the thermal stability mechanisms were explored. 

Ultrafine-grained W-based alloys prepared by HIP with ultrahigh hardness and excellent thermal stability

Research and development of nanocrystalline W/W-based materials: novel preparation approaches, formation mechanisms, and unprecedented excellent properties

Although tungsten is considered as one of the primary candidates for plasma-facing material (PFM) in future fusion reactors, blistering induced by plasma irradiation adversely affects fusion reactors. To overcome blistering, in this study, we proposed an approach to reduce the blistering by releasing hydrogen or helium (H/He) through the grooved surfaces of PFM. In order to verify the feasibility of this approach and the effectiveness of the transverse release of H/He, the deep grooves as the channel simulants on the tungsten surface were fabricated with different spacing using focused ion beam (FIB). The result of helium irradiation shows that the presence of grooved surfaces can reduce blisters and inhibit the rapid growth of He blisters. In addition, the blistering reduced significantly with decreasing groove spacing, especially when the groove spacing is less than 2 µm. In addition, He-induced blistering shows obvious crystal orientation dependence, and the (001) surface shows the most serious radiation damage.

Meng Li

Papers

Decrease of blistering on Helium irradiated tungsten surface via transversal release of helium from the grooved surfaces