Dissipation of MeV ion energy in solids, structure formation and phase changes

Instabilities arise out of dynamic events and can lead to nonequilibrium (s elf-organization) processes. Ion irradiation is by nature a nonequilibrium process and hence formation of structures, metastable or otherwise is to be expected. Recently, it has been theoretically predicted that metals under ion irradiation can lead to dissipative structure formation arising out of radiation damage and their subsequent annealing. The possibility of direct observation of such structures in metals under irradiation is however reduc ed due to nonavailability of a large concentration of defects (mainly point defects) at any point of time. In this experimental presentation we show t hat this can be overcome through the involvement of microstructural imperfe ctions which rearrange during irradiation. Employing microstructurally impu re specimens of Fe and Ni, it is shown that heavy ions dissipate their elec tronic energy to modify atomic arrangements at the microstructure. The incr eased concentration of defects (atomic rearrangements), amenable to statist ical decay is shown to produce effects in the 4-probe resistivity measureme nts which we assign to dissipative structure formation. (C) 1998 Published by Elsevier Science B.V. All rights reserved.