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 oC 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 unirradiated W at 1200 oC. In the as fabricated material dislocations and small vacancy clusters of 1 to 3 vacancies are present. After annealing at 1200 oC, the small vacancy clusters disappear and only the dislocations with almost un-changed density remain. Also, hardness is reduced by 4% and creep increases by 13%. Neutron irradiation at 1200 ◦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 ◦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.