Heavy-ion damage in α Fe

Abstract

WE summarise here some preliminary observations of damage in α Fe irradiated with low doses of heavy ions at room temperature. Although the damage produced by such irradiation has been studied in a number of pure metals and alloys using transmission electron microscopy¹, there have been comparatively few studies of materials of technological interest. Iron is of particular interest since it is a major constituent in many practically important alloys including ferritic steels. The use of heavy-ion irradiation (typically to doses ≲ 10¹³ ions cm⁻² and energy ≲ 200 keV) provides a convenient method of simulating the displacement cascades generated in metals undergoing fast neutron irradiation. In a majority of the metals and alloys studied the damage consists of a population of vacancy loops produced heterogeneously at the cascade sites by a collapse of the vacancy-rich cascade centres. Interstitial loops are not normally observed at the low doses commonly used, and this is thought to result from the close proximity of the damage region to the foil surface (the mean range of ions is typically ∼ 100 Å) which acts as a dominant sink for the mobile interstitial point defects. There have been no previous reports of low-dose heavy-ion damage in α Fe and in other damage experiments² the vacancy component of the damage was not observed.