Verlag des Forschungszentrums Jülich
JUEL-2873
Zell, Volker
Computersimulation und Experimente zur Entwicklung von Heliumblasen in Metallen
92 S., 1994
In this work, the evolution of inert gas bubble microstructures in metals by migration
and coalescence has been studied by a simulation approach for two typical
experimental conditions: (A) Coarsening at constant gas content during annealing
after low temperature implantation and (B) bubble evolution under continuous gas
production at elevated temperatures. For the latter case also experiments in which
Helium was implanted into Nickel were performed with particular emphasis on the
temperature and production rate dependence of bubble size and density.
The simulation shows that the bubble size distributions in case (A) become
asymptotically selfsimilar, whereas under (B) there is no simple scaling behaviour.
The time dependence of the mean bubble radius and the bubble density in case (A)
follow simple power laws. While the bubble densities in (A) are always decreasing
with increasing time, in case (B) the bubble density generally saturates or even
increases, depending on the gas state in the bubbles and the assumption about the
migration mechanism.
The measured bubble densities and mean radii in the experiment show Arrhenius
behaviour in a low temperature regime with a low apparent activation energy
and in a high temperature regime with a high apparent activation energy. The
data indicate that the low temperature regime is controlled by He diffusion via the
self-interstitial/He replacement mechanism and the high temperature regime is He
dissociation controlled according to standard nucleation models. Also the rate dependence
confirm these findings. Effects of bubble migration and coalescence could
not be identified. The bubbles are considered to be in an overpressurized state. The
results are compared with data obtained from Nickel in the case of an experiment
of type (A) and with data from stainless steel.
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