Direct Observation of Interstitial Dislocation Loop Coarsening in $\ensuremath{\alpha}$-Iron

Direct Observation of Interstitial Dislocation Loop Coarsening in $α$ -Iron

S. Moll, T. Jourdan, and H. Lefaix-Jeuland

Phys. Rev. Lett. 111, 015503 – Published 3 July 2013

Abstract

Interstitial loop coarsening by Ostwald ripening can provide insight into single point defects but is very difficult to observe in $α$ -iron and many other metals where nanoscale vacancy clusters dissociate and annihilate loops. We show that by implanting helium in the samples at a carefully chosen energy, it is possible to observe Ostwald ripening of loops by transmission electron microscopy during in situ isochronal annealings. This coarsening of loops results in a sharp increase of the mean loop radius at around 850 K. Using cluster dynamics simulations, we demonstrate that loops evolve due to vacancy emission and that such experiments give a robust estimation of the sum of the formation and migration free energies of vacancies. In particular, our results are in good agreement with self-diffusion experiments and confirm that entropic contributions are large for the vacancy in $α$ -iron.