The competing effects of temperature and neutron irradiation on the microstructure and mechanical properties of ITER grade tungsten

In the current work, ITER grade W irradiated at 1200 degrees C to a dose of 0.18 dpa has been investigated by Transmission Electron Microscopy (TEM), Positron Annihilation Spectroscopy (PAS), X-ray diffraction, impulse excitation and depth-sensing micro-indentation. The results are compared with those of annealed un-irradiated W at 1200 degrees C. In the as fabricated material dislocations and small vacancy clusters of 1 to 3 vacancies are present. After annealing at 1200 degrees C, the small vacancy clusters disappear and only the dislocations with almost unchanged density remain. Also, hardness is reduced by 4% and creep increases by 13%. Neutron irradiation at 1200 degrees C results in the increase of the dislocation line density by 3.7 times and in the formation of dislocation loops and voids. The irradiation also causes a hardness increase of about 20% and a creep decrease of 15%. Both the elastic and shear moduli decrease by 4% after irradiation at 1200 degrees C contrary to the effect of only annealing at this temperature which causes an increase in their values by 4%. Texture changes are observed only after neutron irradiation.

Automated summary

The study found that neutron irradiation of ITER grade W resulted in an increase in dislocation line density, formation of dislocation loops and voids, increase in hardness, and decrease in creep. However, annealing treatment only eliminated small vacancy clusters in the material, leaving behind dislocations with slightly reduced hardness and increased creep.