The Collapse of Defect Cascades to Dislocation Loops During Self-Ion Irradiations of Iron, Nickel, and Copper at 30, 300, and 600 K

The formation of dislocation loops by self-ion irradiations of iron, nickel, and copper has been studied in situ in the Argonne National Laboratory (ANL) high-voltage electron microscope (HVEM) as functions of ion dose and irradiation temperature. At low doses {≤10¹² ions/cm²) at room temperature individual cascades were observed to collapse to vacancy dislocation loops in copper with high probability, in nickel with lower probability, and in iron with zero probability. Cascade collapse was observed at low doses at 30 K in copper and nickel, but at rates less than their respective rates at room temperature. A loop formation rate for nickel at 600 K is also reported. At higher doses (>10¹³ ions/cm²) where overlap of cascades becomes significant, loops were first observed in iron and with a supra-linear buildup with dose. Also at higher doses a decrease in loop production rate in copper and nickel was observed because of loop coalescence. The material and temperature dependence of cascade collapse probabilities is suggested to be related to thermal spike mechanisms during the cascade formation lifetime.