The collapse of defect cascades to dislocation loops

Abstract

We review a number of experiments that we have recently performed to investigate the collapse of defect cascades to dislocation loops. This important ion and neutron irradiation phenomenon has been studied with in situ ion bombardment in the Argonne National Laboratory High Voltage Electron Microscope -Ion Accelerator Facility at temperatures of 30 and 300 K in CugAu, Cu, and Fe, and 30, 300 and 600 K in Ni. These experiments have demonstrated that individual defect cascades collapse to dislocation loops athermally at 30 K in some materials (Ni, Cu and CU3AU), while in another material (Fe) only overlapped cascades produced dislocation loops. A slight sensitivity to the irradiation temperature is demonstrated in Cu-jAu and Fe, and a strong dependence on the irradiation temperature is seen in Ni. This phenomenon of cascade collapse to dislocation loops in metals at 30 K provides an understanding for previous neutron irradiation data. The more detailed dependencies of the collapse probability on material, temperature, bombarding ion dose, ion energy and ion mass contribute much information to a thermal spike model of the collision cascade which we will describe.

Primary Radiation Damage Formation

“…[98][99][100][101][102][103][104][105][106] In most cases, the experimental observations are carried out in situ by TEM and the results of MD simulations are in general agreement with the data from these experiments. For example, some material-to-material differences observed in the MD simulations, such as differences in in-cascade clustering between bcc iron and fcc copper, also appear in the experimental data.…”

“…The eighth interstitial is a [110] dumbbell that lies perpendicular to the others and on the left side in Figure 17(a). Figure 16(b-d) are [101] projections through the three center (101) planes in Figure 17(a).…”

Heavy-ion irradiations of Fe and Fe–Cr model alloys Part 2: Damage evolution in thin-foils at higher doses

“…Cascade collapse is therefore possible in Fe, but probably only in cascades which result in higher vacancy concentrations and energy densities than those produced by self-ions. It has been argued that the collapse of cascades initiated by self-ions can occur if the cascade occurs in a region populated with sub-microscopic clusters remaining from earlier cascades, so-called cascade debris, see Part 1 and refs [3,4]. Our observations are again not inconsistent with this picture.…”

“…In many materials the vacancy-rich cores may collapse to form dislocation loops visible in the TEM. This does not seem to happen in Fe in cascades initiated by Fe + ions or Fe primary knock-on atoms [3,4]. Instead the vacancies may aggregate to form microvoids or loose vacancy sponges, not visible in the TEM but detectable by positron annihilation experiments, see e.g.…”

The temperature dependence of heavy-ion damage in iron: A microstructural transition at elevated temperatures

“…In these and other experiments there does seem a clear pattern for <100> loops to predominate in pure Fe at irradiation temperatures T irr ≥ 400 o C. In contrast, in Fe irradiated at 60 o C with neutrons, only ½<111> loops were identified, again of interstitial nature [16]. The only examples we know of <100> loops in low-temperature irradiations are found in Fe irradiated with W + ions at room temperature [17] and with high doses of self-ions [18], and in these cases loops were considered to have formed by a process of cascade collapse and the loop nature was vacancy.…”