Abstract
Helium bubbles have been precipitated in niobium and Nb-1% Zr by room-temperature irradiation with α-particles followed by isothermal annealing at 1050°C. It has been established that the bubbles grow by a migration and coalescence mechanism. After long annealing times all the bubbles are strongly faceted but many are extremely elongated. From the growth rates of the bubble populations it is possible to establish that the rate-controlling mechanism is surface diffusion for small bubbles and facet nucleation for larger bubbles. A model for the growth of elongated bubbles by facet nucleation is developed and from it the energy of an edge on a {100} facet can be estimated as 1.2 × 10 −11 J/m for niobium. In the Nb-1% Zr alloy the edge energy is at least four times greater.
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