Publications
Evolution of mechanical properties in ErT2 films
The mechanical properties of rare earth tritide films evolve as tritium decays into {sup 3}He, which forms bubbles that influence long-term film stability in applications such as neutron generators. Ultralow load nanoindentation, combined with finite-element modeling to separate the mechanical properties of the thin films from their substrates, has been used to follow the mechanical properties of model ErT{sub 2} films as they aged. The size of the growing {sup 3}He bubbles was followed with transmission electron microscopy, while ion beam analysis was used to monitor total T and {sup 3}He content. The observed behavior is divided into two regimes: a substantial increase in layer hardness but elasticity changed little over {approx}18 months, followed by a decrease in elastic stiffness and a modest decease in hardness over the final 24 months. We show that the evolution of properties is explained by a combination of dislocation pinning by the bubbles, elastic softening as the bubbles occupy an increasing fraction of the material, and details of bubble growth modes.