Microstructure and mechanical property evolution of He-implanted nanochannel W film under post-annealing

Tungsten (W) has been selected as the most promising Plasma Facing materials (PMFs) due to its excellent properties. One of the most challenged problems for W is the He retention. Nowaday, a nanochannel structure film was presented to improve the He irradiation resistance of W. In this work, the microstructure and mechanical property evolution of He-implanted nanochannel W film under post-annealing from 573 to 1273 K were studied. A significant growth of He bubbles and the formation of large size holes at grain boundaries (GBs) were observed after post-annealing at 1273 K. In addition, a formation model of pores structure on surface caused by high energy He implantation was proposed. Moreover, a mitigated lattice swelling was observed at 1273 K due to the He-V clusters and He bubbles migration and coarsening. The shape of the He bubbles at 1273 K was also investigated in detail. The nanochannel film has a better resistance to the degradation of Young's modulus under the He implantation than compact film, due to the loose nanochannel. Hardness increment induced by the implantation of He was analyzed. The hardening effect of the He-implanted film annealing at 1073 K, resulting from the transition of He-V clusters or He bubbles distributions from dislocations to distributed vacancies, should be notice. Finally, the holes at GBs led to the decrease of both Young's modulus and hardness.