Atomistic simulation of structural damage during ion irradiation of iron single crystals

Abstract

Abstract. The evolution of atomic displacement cascades initiated near free surfaces with different crystallographic orientations in bcc iron specimens was studied on the base of the molecular dynamics approach. The craters surrounded by adatom mounds were formed in the case of the (111) surface irradiation. The dislocation loops consisted of vacancies were generated after the (110) surface irradiation. The dislocation Burgers vector was a/2 <111> or a <100>. It was shown that the type of structural damage is determined by the anisotropy of propagation of shock waves generated by atomic displacement cascades. For energies of the atomic displacement cascade lower than 20 keV the number of adatoms and survived point defects was higher for specimen with the (110) free surface due to the different character of surface damage. The increase in the cascade energy up to 20 keV results in formation of almost the equal number of survived point defects for the (110) and (111) free surfaces as displacement cascades were developed on larger distance from the irradiated surfaces.

Molecular Dynamics Simulations of Displacement Cascades in BCC-Fe: Effects of Dislocation, Dislocation Loop and Grain Boundary

“…Before the displacement cascade simulation, the accurate models of edge dislocation, screw dislocation, the dislocation loop and the grain boundary should be introduced, respectively. 1/2 [1][2][3][4][5][6][7][8][9][10][11] edge dislocation with the x slip direction and screw dislocation with the y slip direction were established using Atomsk software (version beta-0.12.1) [25]. The BCC crystal containing dislocation was oriented along the x [112], y and z [−110] directions.…”

“…For example, irradiation results in increased hardness, yield stress and ductile-brittle transition temperature. Molecular dynamics (MD) simulation has been extensively used to study defect production from displacement cascades in bulk body-centered cubic (BCC), face-centered cubic (FCC) and close-packed hexagonal (HCP) metals [4][5][6][7][8][9][10]. For example, Sahi et al [7] conducted molecular dynamics simulations to investigate the effect of applied strain and temperature on a displacement cascade in Zr.…”

“…Moreover, a portion of these defects enter into the dislocation, dislocation loop and grain boundary. During the interaction, 1/2 [1][2][3][4][5][6][7][8][9][10][11] edge dislocation climb occurs while screw dislocation may cross-slip. Compared with edge dislocations, screw dislocations are more likely to absorb point defects.…”

“…Figures4 and 5show the atomic structures of the edge and screw dislocations before and after the displacement cascade for BCC-Fe, using the CNA and DXA analysis. The Burgers vector of both the edge and screw dislocations is set as 1/2[1][2][3][4][5][6][7][8][9][10][11].…”