Effects of electron irradiation on precipitation phenomena in a high voltage electron microscope

Precipitation phenomena in thin foils of aluminium alloys have been investigated in a 500 kV electron microscope. During heating of a thin foil of an aluminium-1.4 wt% silicon alloy, a large number of dislocation loops were formed in the area exposed to electron irradiation. These dislocation loops were grown during heating and irradiation and finally the dislocation density in the exposed area was extremely increased. The nucleation of silicon precipitates was also remarkably affected with irradiation. That is, fine distribution of precipitates was observed in the exposed area. The width of precipitation free zones near grain boundaries was decreased with increasing electron irradiation. The growth rate of γ′-precipitates in an aluminium-5.5 wt% silver alloy was almost unaffected by electron irradiation. The formation of misfit dislocations at the coherent interface of θ′-precipitates in an aluminium-4 wt% copper alloy was promoted by electron irradiation. The roles of interstitials and vacancies produced by electron irradiation on the above-mentioned phenomena are discussed.