Helium effects on recovery and recrystallization of powder metallurgically processed tungsten

To study the effects of helium (He) produced by the nuclear transmutation of 14 MeV neutron irradiation on the stability of grain microstructure of tungsten (W)-fabricated through a powder metallurgically (PM) process-high energy He and post implantation experiments were conducted. The recovery of worked structure and recrystallization behavior were examined using hardness measurement and microstructural observation. He with a concentration of 20 appm was implanted homogeneously though the specimen thickness below 100 degrees C. Post-implantation annealing was then conducted from 1100 degrees C to 1500 degrees C in vacuum. The hardness of the PM-W specimen increased after the He implantation, and the decrease of the hardening through the annealing was suppressed in the He-implanted specimens. Metallographic observations demonstrated that the dislocation cell structure in the grain of He-implanted PM-W was retained even after the 10 h annealing at 1500 degrees C. In conclusion, the 20 appm He suppressed the recovery of cell structure and recrystallization of the PM-W up to 1500 degrees C.