Nanocrystalline tungsten at high radiation exposure

Evolution of nanocrystalline (NC) tungsten under radiation exposure is investigated by atomic scale simulations in the low temperature high dose limit. Statistical analysis of samples containing at least a million atoms, with grain size varying from 5 nm to 20 nm, shows that the pattern of microstructural evolution of a NC material differs significantly from that of a single crystal. The high resistance to swelling in the low grain size limit stems from a combined effect of the initial excess volume of atomic configurations at grain boundaries and high integral volume of grain boundary defect-denuded zones. Grain boundaries annihilate defects through the rearrangement of their local atomic configurations acting as fluctuating dynamic sinks for defects. Grain size distribution slowly broadens as a function of dose, delaying the onset of an asymptotic radiation-driven steady state in comparison with a single crystalline material. Spatial limitations imposed by the size and topology of grains prevent the formation of a percolating dislocation network, resulting in only isolated dislocation loops being retained in the microstructure even at high radiation exposure.