Abstract: Structure evolution and nature of defects in bcc iron by displacement cascade are investigated with molecular dynamics simulation.Under irradiation displacement cascade induces temporarily self-interstitials,vacancies,<100>, <110>, and <111> dumbbell defects,and composite defects as well,such as,composite defect of <110> and <111> dumbbell defects.composite defect of <110> and dumbbell defects,and defect clusters.Numerical results show that a higher PKA energy might induce more SIAs.The region where atoms are displaced by displacement cascade is about 11-15a₀ in size.A smaller PKA energy gives rise to a smaller region of displacement cascade.At initial stage of 0-0-0.75 ps in displacement cascade,recombination of self-interstitial atoms and vacancies is found.

Key words: molecuhr dynamics, displacement cascade, iron