The role of the high-energy cascade thermal stage in local ordering of an amorphous metal

The molecular dynamics method with the approximations of the thermal spike model was uo study the role of the thermal spike of a high-energy cascade in formation of a local order in amorphous iron. The simulation of the behaviour of depleted zones (DZs) indicates systematic variations of the local order in the DZ. The analysis of the distributions of Voronoi polyhedra revealed the increase in the number and size of microclusters of the (0446) and (0603) polyhedra by the end of the cascade thermal stage, which agrees with the tendency to “nucleation” and growth of the centres of cubic symmetry. The spectrum of the bond angles defined by the Steinhardt parameter distribution responds weakly to changes in the DZ local structure, indicating the structure stability of the amorphous matrix under conditions of thermal spike development. The growth rate of the crystalline “nuclei” seemed to depend weakly on the concentration of knock-on atoms produced in the DZ by the end of the cascade dynamic stage. Apparently the local heating of short duration in the thermal spike is the basic factor determining the local structure of amorphous iron in the region of the cascade developed.