Effects of intragranular defects on helium accumulation damage in nanocrystalline nitrides

Nanomaterials with a high density of interfaces, which absorb helium (He) atoms and suppress the expansion of He bubbles, can exhibit a superior neutron radiation tolerance. However, the intragranular defects formed under long-term radiation can interact strongly with the He atoms, which would bring more uncertainties to the reliability of materials served in neutron radiation environment. In this work, He atoms and intragranular defects were introduced uniformly into the nanocrystalline (NC) ZrN and TaN films for investigating the effects of the intragranular defects on the He accumulation damage in nanomaterials. The microstructure, lattice parameter and surface morphology of the NC nitrides were investigated systematically. The results showed that the He accumulation damage was very sensitive to the structure of intragranular defects in the He-implanted materials. The cross-grained stacking faults in the ZrN films may act as diffusion channels for the He atoms, facilitating the He accumulation at the grain boundaries, while the vacancy-type dislocation loops in the TaN films can act as small cracks trapping the He atoms, resulting in the formation and unstable expansion of the He platelets in the interior of the grains.