Nanocrystalline–Amorphous Transition in ZrN Nanofilms Induced by Helium Accumulation at Grain Boundaries

Helium (He) accumulation, a byproduct of nuclear transmutation, poses a significant reliability challenge for the materials used in nuclear reactors. Nanomaterials, with their high density of interfaces, offer superior He tolerance by absorbing He atoms and suppressing bubble growth. However, the long-term stability of these materials under continuous He accumulation remains a concern. This study investigated the microstructural and mechanical property responses of ZrN nanofilms to excessive He accumulation. Different doses of He atoms were introduced via magnetron sputtering. The results indicate that increasing the He dose induced a nanocrystalline-to-amorphous transition and instability in the mechanical properties. The structural and mechanical instability, characterized by surface blistering, softening, abnormal lattice shrinkage, and amorphization, was primarily triggered by the degradation of the grain boundaries with He accumulation, and an amorphization model of nanomaterials is proposed.